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MSFC-STD-xxxx

National Aeronautics and REVISION: DRAFT 1

Space Administration EFFECTIVE DATE: Not Released

George C. Marshall Space Flight Center Marshall Space Flight Center, Alabama 35812

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MSFC TECHNICAL STANDARD

Engineering and Quality Standard

for Additively Manufactured

Spaceflight Hardware

DRAFT 1 – JULY 7, 2015

This official draft has not been approved and is subject to modification.

DO NOT USE PRIOR TO APPROVAL

MSFC Technical Standard

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Title: Engineering and Quality

Standard for Additively Manufactured


Document No.: MSFC-STD-xxxx Revision: Draft 1

Effective Date: Not Released of 77

This draft standard has not been approved and is currently in revision-DO NOT USE PRIOR TO APPROVAL

This document has been reviewed and approved for public release.

DOCUMENT HISTORY LOG

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Draft

N/A Draft 1


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TABLE OF CONTENTS

1. SCOPE 8

1.1 Introduction ---------------------------------------------------------------------------------------- 8

1.2 Applicability --------------------------------------------------------------------------------------- 9

1.3 Certification ---------------------------------------------------------------------------------------- 9

1.4 Risk ------------------------------------------------------------------------------------------------- 10

1.5 Tailoring ------------------------------------------------------------------------------------------- 10

1.6 Summary of Methodology ---------------------------------------------------------------------- 10

2. APPLICABLE DOCUMENTS 16

2.1 General --------------------------------------------------------------------------------------------- 16

2.2 Government Documents------------------------------------------------------------------------- 16

2.3 Non-Government Documents ------------------------------------------------------------------ 16

2.4 Governing NASA Standards -------------------------------------------------------------------- 17

3. ACRONYMS AND DEFINITIONS 18

3.1 Acronyms ------------------------------------------------------------------------------------------ 18

3.2 Definitions ----------------------------------------------------------------------------------------- 19

4. ADDITIVE MANUFACTURING DESIGN 21

4.1 Concepts for AM design ------------------------------------------------------------------------ 21

4.2 Part Classification -------------------------------------------------------------------------------- 21

4.2.1 Consequence of failure ----------------------------------------------------------------------- 22

4.2.2 Non-service parts: Class C ------------------------------------------------------------------- 23

4.2.3 Classes A and B ------------------------------------------------------------------------------- 23

4.2.3.1 Structural Margin ---------------------------------------------------------------------- 24

4.2.3.2 AM Risk --------------------------------------------------------------------------------- 26

4.3 Structural Assessment --------------------------------------------------------------------------- 26

4.4 Fracture Control ---------------------------------------------------------------------------------- 27

4.5 Qualification Testing ---------------------------------------------------------------------------- 27

4.6 Material Property Requirements --------------------------------------------------------------- 28

4.6.1 Material Property Development ------------------------------------------------------------- 29


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4.6.2 Lot Requirements and DVS Maturity ------------------------------------------------------ 30

4.6.2.1 Recycled Powder Lot Representation ----------------------------------------------- 31

4.6.3 Anisotropy -------------------------------------------------------------------------------------- 31

4.6.4 Influence Factors ------------------------------------------------------------------------------ 32

4.6.4.1 Pauses in PBF Machine Operation -------------------------------------------------- 32

4.6.4.2 Specimen Geometry Effects ---------------------------------------------------------- 33

4.6.5 Physical and Constitutive Properties ------------------------------------------------------- 33

4.6.6 Tensile Properties ----------------------------------------------------------------------------- 34

4.6.6.1 Ratio Derived Properties -------------------------------------------------------------- 34

4.6.7 Fatigue ------------------------------------------------------------------------------------------ 35

4.6.8 Fracture Mechanics --------------------------------------------------------------------------- 36

4.6.9 Stress Rupture and Creep Deformation ---------------------------------------------------- 36

4.6.10 Temperature and Environmental Effects ------------------------------------------------- 37

4.6.11 Welds ------------------------------------------------------------------------------------------ 37

4.6.12 Characterization Build Process Control -------------------------------------------------- 38

5. PROCESS CONTROL 38

5.1 Metallurgical Process Control ------------------------------------------------------------------ 38

5.1.1 Qualification of the Metallurgical Process ------------------------------------------------ 38

5.1.1.1 Definition of Metallurgical Process ------------------------------------------------- 38

5.1.1.2 Evaluation Criteria for the Metallurgical Process --------------------------------- 39

5.1.2 Powder ------------------------------------------------------------------------------------------ 39

5.1.2.1 Specification and Control of Powder ------------------------------------------------ 39

5.1.2.2 Recycled Powder Reqirements ------------------------------------------------------- 40

5.1.3 Fusion Process Controls ---------------------------------------------------------------------- 41

5.1.3.1 Pattern Plates ---------------------------------------------------------------------------- 42

5.1.4 Microstructure --------------------------------------------------------------------------------- 43

5.1.5 Thermal Processing --------------------------------------------------------------------------- 43

5.1.5.1 Stress relief ------------------------------------------------------------------------------ 44

5.1.5.2 Hot Isostatic Pressing ------------------------------------------------------------------ 44

5.1.5.3 Heat treatment -------------------------------------------------------------------------- 45

5.1.6 Mechanical Properties for the QMP -------------------------------------------------------- 45

5.1.7 Surface Texture and Detail Resolution Metrics (Reference Parts) --------------------- 46


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5.1.7.1 Reference Parts ------------------------------------------------------------------------- 46

5.1.8 Customized QMP ----------------------------------------------------------------------------- 47

5.1.9 Qualified Metallurgical Process Record --------------------------------------------------- 48

5.1.10 PCRD ------------------------------------------------------------------------------------------ 49

5.1.10.1 Acceptance Testing with PCRDs ---------------------------------------------------- 50

5.1.10.2 PCRD Maintenance -------------------------------------------------------------------- 52

5.1.11 Registration of QMP to a DVS ------------------------------------------------------------ 52

5.2 Part Process Control ----------------------------------------------------------------------------- 53

5.2.1 Part Development Plan ----------------------------------------------------------------------- 53

5.2.2 PDP Design Information --------------------------------------------------------------------- 54

5.2.2.1 First Article Requirements ------------------------------------------------------------ 55

5.2.2.2 Witness Specimen Requirements ---------------------------------------------------- 55

5.2.3 Part Models, Build Assemblies, and Associated Electronic Data ---------------------- 58

5.2.3.1 Model Integrity ------------------------------------------------------------------------- 60

5.2.4 Build Execution, General Policies ---------------------------------------------------------- 60

5.2.5 Production Planning Record ----------------------------------------------------------------- 61

5.2.6 Post-build Operations ------------------------------------------------------------------------- 61

5.2.6.1 Green Part Inspections----------------------------------------------------------------- 61

5.2.6.2 Powder Removal ----------------------------------------------------------------------- 62

5.2.6.3 Platform Removal ---------------------------------------------------------------------- 62

5.2.6.4 Repair allowances and procedures --------------------------------------------------- 62

5.2.6.5 Machining ------------------------------------------------------------------------------- 62

5.2.6.6 Welding ---------------------------------------------------------------------------------- 63

5.2.6.7 Surface treatments --------------------------------------------------------------------- 63

5.2.6.8 Cleaning --------------------------------------------------------------------------------- 63

5.2.6.9 Part Marking and Serialization ------------------------------------------------------- 64

5.2.6.10 Packaging shipping handling --------------------------------------------------------- 64

5.2.7 Part Inspection/Acceptance ------------------------------------------------------------------ 64

5.2.7.1 Part Integrity ---------------------------------------------------------------------------- 64

5.2.7.1.1 Non-Destructive Evaluation ------------------------------------------------------- 65

5.2.7.1.2 Proof testing ------------------------------------------------------------------------- 66

5.2.7.2 Dimensional Inspections -------------------------------------------------------------- 67

5.2.7.3 Certification of Compliance Records ----------------------------------------------- 67


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5.2.8 Manufacturing Readiness Review ---------------------------------------------------------- 68

5.2.9 Qualified Part Process, Modifications ------------------------------------------------------ 68

5.2.10 Non-Conformance Tracking --------------------------------------------------------------- 69

5.3 Equipment Process Control --------------------------------------------------------------------- 69

5.3.1 Equipment Control Plans --------------------------------------------------------------------- 69

5.3.1.1 Maintenance ---------------------------------------------------------------------------- 70

5.3.1.1.1 Computer Security ------------------------------------------------------------------ 70

5.3.1.2 Calibration ------------------------------------------------------------------------------ 70

5.3.1.3 Qualification ---------------------------------------------------------------------------- 71

5.3.2 PBF Machine Operations -------------------------------------------------------------------- 72

5.3.2.1 Checklists ------------------------------------------------------------------------------- 72

5.3.2.2 Contamination/Foreign Object Debris Control ------------------------------------ 72

5.4 Vendor Process Control ------------------------------------------------------------------------- 73

5.4.1 Design Vendor --------------------------------------------------------------------------------- 73

5.4.2 PBF Build Vendor ---------------------------------------------------------------------------- 73

5.4.2.1 Sub-vendors ----------------------------------------------------------------------------- 74

5.4.2.2 Operator Qualification ----------------------------------------------------------------- 74

5.4.3 PBF Build Vendor Qualification Process -------------------------------------------------- 76

5.4.4 Qualified Vendor List ------------------------------------------------------------------------ 76


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LIST OF FIGURES

Figure 1. Overview of AM part development process ................................................................. 12 Figure 2. Overview of AM metallurgical process development .................................................. 13 Figure 3. Part Classification ......................................................................................................... 22 Figure 4. PCRD acceptance testing and DVS compatibility ....................................................... 50

LIST OF TABLES

Table 1. Abbreviated list of AM Requirements ........................................................................... 14

Table 2. Structural Assessment Criteria to Determine High Structural Margin AM Parts .......... 24 Table 3. Criteria to Evaluate Additive Manufacturing Risk ........................................................ 26

Table 3a. Minimum quantities of witness specimen types by part class ..................................... 58 Table 3b. Basis for acceptance of witness specimen results ........................................................ 58


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1. SCOPE

1.1 Introduction

Additive Manufacturing (AM) stands ready to revolutionize much of the aerospace design and

manufacturing paradigm. The process of building parts incrementally, layer by layer, enables

new designs, reduces costs, and challenges the very order of the typical aerospace hardware

development cycle. The ability to iterate prototype hardware designs with minimal cost and

schedule impact provides flexibility previously impossible in the development cycle of complex

systems. The high cost and lead time associated with complex development hardware have

moved the industry to near-complete reliance on meticulous analysis to preclude the loss of

expensive, painstakingly manufactured hardware in test. AM may rebalance the engineering

equation to restore the role of systematic, incremental development testing in the reliability of

aerospace systems. In more routine circumstances, AM offers a unique ability to reduce the cost

of manufacturing existing complex hardware designs that are currently extremely costly to

produce, particularly in limited quantities common to spaceflight applications.

The unique strengths of the AM process have motivated the spaceflight industry to take the lead

in the incorporation of AM parts in safety-critical structural applications. The greatest

responsibility associated with the implementation of AM in aerospace systems lies not in the

revolution of paradigms, but in the safe implementation of a new and rapidly changing

technology. Compared to most structural material processes, the timeline from invention to

commercialization to critical application has been unprecedented for AM. These requirements

are intended to embrace AM technology and its benefits while respecting it as an evolving and

detail-oriented process.

Many developing AM processes are capable of producing metallic aerospace-quality hardware.

The current leader in these technologies is Powder Bed Fusion (PBF). In the PBF process,

metallic powder is fused layer-by-layer into the shape of the part by a high-energy source, such

as a laser or electron beam. After one layer of the part has fused, a fine layer of additional

powder is spread across the part to create the next layer. As the part building process continues,

the part rests within this bed of metallic powder, thus giving the PBF process its name. Multiple

factors can influence the quality of the resulting PBF part such as powder particle shape, laser

power, thermal conditions in the powder bed, residual stress development, and build chamber

atmosphere. The requirements identified in this standard establish a disciplined methodology

intended to control these variables and manage risks associated with the process. This standard

pertains only to the metallic PBF AM processes with laser or electron beam systems as the power

source.

In this standard, metallic PBF parts are considered to be a unique metallurgical product form.

Users of the technology tend to identify with the AM process based on broad analogies to other

processes with which they are most familiar: casting experts identify with the process from the


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casting perspective; welding experts treat PBF as a highly complex weld; and, powder

metallurgists see PBF as another form of powder metallurgy. Although the casting and welding

analogies provide a philosophical basis for much of the process control methodology presented

in this standard, the AM product is produced in a fashion that has no true precedent and is

therefore considered a unique product form under these requirements.

1.2 Applicability

This document is intended to govern all powder bed fusion AM hardware developed under the

auspices of a sanctioned NASA project. The requirements are specifically designed to

accommodate hardware at all levels of development and criticality, from development prototype

hardware to human-rated, fracture critical spaceflight hardware. Development hardware is

included in the requirement scope to create awareness among AM part designers and developers

to the discipline demanded by the AM process, while providing information on future

requirements that development parts will encounter in maturity.

1.3 Certification

The development of this standard is motivated by the need to establish a basis for certification of

additively manufactured spaceflight hardware. The following working definition for certification

is adopted for the purposes of this standard:

Certification is the affirmation by the program, project, or other reviewing

authority that the verification process is complete and has adequately assured both

the design and as-built hardware meet the established requirements to safely and

reliably complete the intended mission.

The certification process has two fundamental steps. First, upon completing the design, the

design definition is verified to be complete and satisfactory, meeting all levied performance and

safety requirements. With this affirmation, it becomes the certified design state and must include

all information used to evaluate the part against the levied performance and safety requirements

as well as all criteria needed to verify each part produced is compliant to the certified design

state (such as geometry and tolerances, witness specimens and acceptance criteria, non-

destructive evaluations, etc.) The second step in the certification process is the on-going

verification that each part produced is fully compliant with the certified design state based on the

defined criteria.

This standard provides the supplementary requirements unique to AM that are needed to

establish a complete and verifiable part design that can be certified with confidence. The greatest

challenge to the user of this standard is ensuring that the part production process contains all the

necessary process controls (process qualifications, witness sampling, NDE, etc.) to provide

sufficient credible evidence that the produced part complies with the certified design state. This

evidence, once collected and verified compliant, renders a certified AM part. This challenge,

coupled with minimal existing standards for design, material, and process, prompts this standard


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to include a mixture of content that would typically be treated individually in requirements

documents and specifications.

1.4 Risk

Additive manufacturing is in its infancy relative to the production of certified aerospace

hardware. Until production experience matures, the AM process faces added risk associated with

unknown or insufficiently mitigated failure modes. This standard aims to illuminate potential

AM risks, while precluding all known failure modes with the best available mitigation strategies.

These requirements cannot ensure a risk-free AM process; however, carefully executed, AM

parts may not necessarily carry sizable increases in risk.

At the time of this writing, certain failure modes are difficult to mitigate, primarily due to the

“open loop” AM process that operates without active feedback. Available process controls, such

as witness sampling, are useful in uncovering systemic lapses in the AM process, but do not

provide direct evidence of part integrity. In-situ monitoring technologies for active feedback

control or post-build “play-back” verification are emerging and may be informative, yet they

remain in development and their own path to certification lies ahead. Beyond assurances of

process stability, mitigation against local process discontinuities relies mainly on nondestructive

evaluation methods and structural acceptance proof testing. Such mitigations are emphasized

herein, but can be significantly challenged by the design freedom of the AM process.

1.5 Tailoring

These requirements may be tailored to meet the unique needs of a specific program or project.

Each tailored requirement shall meet the intent of this standard and shall be substantiated as risk-

neutral per the applicable program’s risk assessment process so that tailored approaches manage

risk to a level judged equivalent to the controls in this standard. All tailoring shall be approved

by the governing technical authority and documented to become a formal part of the program or

project requirements. Changes to these requirements not substantiated as risk-neutral are not

considered tailoring and shall have proper waiver rationale processed through appropriate

technical authority and programmatic channels.

Commentary: The tailoring process is intended to allow for other approaches that will

meet the intent of these requirements without meaningfully altering the level of risk.

Commentary is provided throughout the standard to assist in interpretation of intent for

each requirement.

1.6 Summary of Methodology

This standard presents methodology for the design and production of additively manufactured

hardware. It provides requirements to establish a certified design state and to accommodate

requirements from NASA’s governing design and safety standards. It does not dictate structural

design criteria.


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The standard uses a classification system to assess risk associated with AM parts and to set

commensurate levels of control. AM parts are classified on their consequence of failure,

structural robustness, and AM risk, where AM risk accounts for part inspection feasibility and

AM build sensitivities. The standard provides development methods for material properties that

emphasize the process-control-sensitive nature of AM while accommodating a continuously

evolving technology. A modest statistical process control methodology that relies upon

continuous monitoring of process performance is used in lieu of the traditional design allowable

approaches that attempt to capture all process variability in a single evaluation of a collection of

material lots and specimens. Material design values are set and maintained relative to these

statistical process control limits.

Methodical development and documentation of process controls at all levels is fundamental to

the approach of this standard. An overview of the AM part development process is illustrated in

Figure 1. The standard requires controls on the AM metallurgical process, the AM part build

process, AM equipment controls, and AM vendors for part design and production. All controls

must fall under engaged quality management systems at the responsible vendor(s).

The standard defines the AM metallurgical process to include powder controls, fusion

parameters, and thermal processing steps. An AM metallurgical process is developed and

assessed on the quality of the material, microstructure, mechanical property capability, surface

texture, and detail rendering. An acceptable AM metallurgical process is documented as a

Qualified Metallurgical Process (QMP) and is specific to the PBF machine on which it was

developed. The development of an AM metallurgical process is illustrated in Figure 2.

The standard presents a part process control methodology that uses one or more Qualified

Metallurgical Processes to build parts. The part process is a sequence of controlled steps that

guide the part from computer model to completed part. The details of this process are

configuration-controlled by the part drawing, a part development plan, and associated

production-planning records. The certification of any given part is anchored by the part integrity

acceptance testing that includes non-destructive evaluation and/or acceptance proof testing. Once

defined and proven through a deliberate first article process, a candidate part process undergoes a

manufacturing readiness review, and, when successful, is documented as a Qualified Part

Process (QPP).


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Figure 1. Overview of AM part development process


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Figure 2. Overview of AM metallurgical process development

A methodical approach to AM equipment maintenance is essential to maintaining the integrity of

the metallurgical and part process controls. Build vendors are responsible for defining,

documenting, and executing a comprehensive AM equipment control plan. In addition to

equipment controls, a systematic operator training and certification program must be defined and

maintained. The AM design vendor, defined as the entity responsible for producing the certified

hardware, must ensure that all steps in the process, from metallurgical process to final part

inspections and shipping, are implemented appropriately under a proper quality management

system.


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Table 1. Abbreviated list of AM Requirements

Category Requirement ID Abbreviated Requirement Description Section

AM

Des

ign

AMR-1 Parts Classification 4.2

AMR-2 Structural design requirements 4.3

AMR-3 Fracture Control 4.4

AMR-4 Qualification testing 4.5

AM

Mate

rial

Pro

pert

ies

AMR-5 Design Value Suite 4.6

AMR-5A Lot variability and recycling 4.6.2

AMR-5B Anisotropy 4.6.3

AMR-5C Material Properties Influence Factors 4.6.4

AMR-5D Physical and constitutive properties 4.6.5

AMR-5E Tensile properties 4.6.6

AMR-5F Fatigue properties 4.6.7

AMR-5G Environmental effects 4.6.10

AMR-5H Weld properties 4.6.11

AMR-5I Characterization build witness requirements 4.6.12

Met

all

urg

ical

Pro

cess

Con

trol

AMR-6 Qualified Metallurgical Process 5.1.1

AMR-6A Powder feedstock controls 5.1.2.1

AMR-6B Powder recycle limits 5.1.2.2

AMR-6C Fusion Process specification 5.1.3

AMR-6D Pattern Plates 5.1.3.1

AMR-6E Microstructural evolution 5.1.4

AMR-6F Thermal processing 5.1.5

AMR-6G Hot isostatic pressing 5.1.5.2

AMR-6H QMP mechanical property capability 5.1.6

AMR-6I Reference Parts 5.1.7

AMR-6J Customized QMP 5.1.8

AMR-6K QMP review, approval, and record 5.1.9

AMR-6L Process Control Reference Distributions 5.1.10

AMR-6M DVS registration 5.1.11

Part

Pro

cess

Co

ntr

ol

AMR-7 Part Development Plan 5.2.1

AMR-7A First article requirements 5.2.2.1

AMR-7B Witness specimens 5.2.2.2

AMR-8 Electronic data records 5.2.3

AMR-8A Model integrity control 5.2.3.1

AMR-9 PBF builds, general policies 5.2.4

AMR-10 Production Planning record 5.2.5


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AMR-10A Sequencing of post-build part processes 5.2.6

AMR-10B As-built part inspection 5.2.6.1

AMR-10C Powder removal process 5.2.6.2

AMR-10D Weld qualification 5.2.6.6

AMR-10E Surface treatment controls 5.2.6.7

AMR-10F Part cleaning 5.2.6.8

AMR-10G Part marking 5.2.6.9

AMR-10H Part handling, packaging, shipping 5.2.6.10

Part

In

spec

tion

/

Acc

epta

nce

AMR-11 Part integrity rational/NDE 5.2.7.1

AMR-11A Proof testing 5.2.7.1.2

AMR-12 Part acceptance, physical measures 5.2.7.2

AMR-13 QPP required list of CoC documentation 5.2.7.3

AMR-14 Manufacturing Readiness Review 5.2.8

AMR-15 QPP locked process/modifications 5.2.9

AMR-16 Non-conformance tracking 5.2.10

Eq

uip

men

t P

roce

ss

Con

trol

AMR-17 Equipment control requirements 5.3

AMR-17A Equipment Control Plan 5.3.1

AMR-17B Maintenance schedules 5.3.1.1

AMR-17C Calibration requirements 5.3.1.2

AMR-18 Machine qualification 5.3.1.3

AMR-19 Operational checklists 5.3.2.1

AMR-19A Contamination control 5.3.2.2

Ven

dor

Pro

cess

Con

trol

AMR-20 Vendor Quality Management Systems 5.4.2

AMR-20A Operator training 5.4.2.2

AMR-20B Build vendor qualification 5.4.3

AMR-20C Qualified Vendor List 5.4.4

AMR-20D Required use of qualified vendors 5.4.4


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2. APPLICABLE DOCUMENTS

2.1 General

Documents listed in this section are referenced within this standard, primarily for information,

reference, or background to the development or intention of the requirements. Governing NASA

standards are expected to have been levied at the project or program level.

2.2 Government Documents

FIPS PUB 180-4 Secure Hash Standard (SHS), Federal Information Processing

Standards Publication, National Institutes of Standards and

Technology, 2012

NASA-STD-5001 Structural Design and Test Factors of Safety for Spaceflight Hardware

NASA-STD-5009 Nondestructive Evaluation Requirements for Fracture-Critical Metallic

Components

NASA-STD-5012 Strength and Life Assessment. Requirements For Liquid Fueled Space

Propulsion System Engines

NASA-STD-5017 Design and Development Requirements for Mechanisms

NASA-STD-5019 Fracture Control Requirements for Spaceflight Hardware

NASA-STD-6016 Standard Materials and Processes Requirements for Spacecraft

JSC-65828 Structural Design Requirements and Factors of Safety for Spaceflight

Hardware

MSFC-SPEC-164 Cleanliness of Components for Use in Oxygen, Fuel, and Pneumatic.

Systems, Specification for

2.3 Non-Government Documents

CMH-17 Composite Materials Handbook - 17

DOT/FAA/AR-03/19 Material Qualification and Equivalency for Polymer Matrix

Composite Material Systems: Updated Procedure (2003)

IEST-STD-CC1246E Product Cleanliness Levels - Applications, Requirements, and

Determination

ASTM B214 Standard Test Method for Sieve Analysis of Metal Powders

ASTM B215 Standard Practices for Sampling Metal Powders


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ASTM B311 Standard Test Method for Density of Powder Metallurgy (PM)

Materials Containing Less Than Two Percent Porosity

ASTM B822 Standard Test Method for Particle Size Distribution of Metal

Powders and Related Compounds by Light Scattering

ASTM E8 Standard Test Methods for Tension Testing of Metallic Materials

ASTM E466 Standard Practice for Conducting Force Controlled Constant

Amplitude Axial Fatigue Tests of Metallic Materials

ASTM E606 Standard Practice for Strain-Controlled Fatigue Testing

ASTM E1820 Standard Test Method for Measurement of Fracture Toughness

ASTM F2792 Standard Terminology for Additive Manufacturing Technologies

ASTM F3055 Standard Specification for Additive Manufacturing Nickel Alloy

(UNS N07718) with Powder Bed Fusion

ISO/ASTM 52921 Standard Terminology for Additive Manufacturing-Coordinate

Systems and Test Methodologies

ISO 13322 Particle size analysis -- Image analysis methods -- Part 1: Static

image analysis methods

MMPDS Metallic Materials Properties Development and Standardization

SAE AMS 2750 Pyrometry

SAE AMS 2774 Heat Treatment Wrought Nickel Alloy and Cobalt Alloy Parts

SAE AMS 2801 Heat Treatment of Titanium Alloy Parts

SAE ARP 1962 Training and Approval of Heat-Treating Personnel. Standard:

SAE AS9100 Quality Management Systems – Requirements for Aviation, Space

and Defense Organizations

SAE AS9102 Aerospace First Article Inspection Requirement

SAE J1739 SAE Surface Vehicle Standard, Potential Failure Mode and Effects

Analysis in Design (Design FMEA), Potential Failure Mode and

Effects Analysis in Manufacturing and Assembly Processes (Process

FMEA)

2.4 Governing NASA Standards

Additively manufactured parts shall comply with the intent of all governing standards levied

upon the project. The novelty and uniqueness of AM parts and the AM process provide no


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exemption from these requirements. The requirements of this standard are employed in addition

to these broader requirements to control aspects that are specific to AM parts and the AM

process where the governing standards are silent. The requirements of this standard, where

differing from those of higher governing standards may be used to meet the intent of those

requirements.

Commentary: Examples of broader governing standards mentioned above include NASA-

STD-6016, NASA-STD-5012, or JSC 65828. This standard is intended to compliment these

broader requirements. To demonstrate the intended governance and intersection of these

requirements, consider the scenario for AM parts of alloy Ti-6Al-4V. These parts would

be subject to the section of NASA-STD-6016 on titanium, with requirements on subjects

such as contamination (e.g. cadmium solid metal embrittlement), prohibition of welding

with commercially pure titanium weld wire, or precluding the use of the part in oxygen

systems. However, the intent of the section of NASA-STD-6016 on material property

requirements (MMPDS A-basis) would be met through the material property requirements

of this standard on AM.

3. ACRONYMS AND DEFINITIONS

3.1 Acronyms

AM Additive Manufacturing (and variants)

ASL Approved Supplier List

A2LA American Association for Laboratory Accreditation

CoC Certificate of Conformance

DVS Design Value Suite

MMPDS Metallic Materials Properties Development and Standardization

FMEA Failure Modes and Effects Analysis

HIP Hot Isostatic Pressing

MRR Manufacturing Readiness Review

NDE Non-destructive Evaluation

PBF Powder Bed Fusion

PCRD Process Control Reference Distribution

PDP Part Development Plan

CQMP Custom Qualified Metallurgical Process

PSD Particle Size Distribution


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PFMEA Process Failure Modes and Effects Analysis

QMP Qualified Metallurgical Process

QMS Quality Management System

QPP Qualified Part Process

QVL Qualified Vendor List

RFCB Responsible Fracture Control Board

3.2 Definitions

Additive Manufacturing: process of creating objects from three-dimensional computer models

incrementally, typically layer by layer, from material stock. This is contrasted with

subtractive manufacturing technologies that remove material to create the object, such as

machining. Adj., additively manufactured

Build: a single, complete operation of the powder bed fusion process to create objects in the

powder bed. Multiple objects are commonly created during a build.

Build area: the area in the build plane where the fusion process is adequately controlled. The

build area may be defined smaller than the full reach of the energy beam if needed to

maintain the quality level of the fusion process.

Build box/build volume: the volume in which parts may be reliably produced in the powder bed.

The volume is defined the build area and maximum Z-position.

Build lot: all objects created during a single build operation.

Build plane: plane in which fusion takes place during powder bed fusion. Commonly, the build

plane is fixed and the build platform is incrementally lowered to create the powder bed.

Build platform: flat, solid material base upon which powder bed fusion objects are built. A full

build platform is the largest standard platform intended for a powder bed fusion machine.

Build run: a sequence of consecutive builds utilizing the same qualified part process

Build vendor: the entity responsible for production of powder bed fusion parts to meet the

requirements of the certified design state. The build vendor may be synonymous with the

design vendor or a sub-vendor to the design vendor.

Catastrophic Hazard: the presence of a risk situation that could directly result in loss of life,

disabling injury, or loss of a major national asset.

Certified design state: a complete, stable design state that has been reviewed and verified as

meeting all levied requirements to safely and reliably complete the intended mission.


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Design state: collection of all information required to define a part design, produce parts

compliant with the design, verify parts are compliant with the design, and information and

evidence needed to confirm the design is compliant with all operational and safety

requirements.

Design vendor: the entity responsible for establishing and managing the certified design state to

which parts are evaluated and certified.

Fatigue Limit: a cyclic stress or strain range below which fatigue initiation failures are

considered unlikely based on fatigue characterization testing. The fatigue limit is

commonly defined at a pragmatic cycle count appropriate for the hardware, often 107 or

108 cycles.

Heat Treat Lot: all objects subjected to a complete heat treatment sequence at the same time in

the same equipment.

Nadcap: formerly NADCAP (National Aerospace and Defense Contractors Accreditation

Program), a global cooperative accreditation program for aerospace engineering, defense

and related industries.

Part: fundamental unit or object defined by the design state. A qualified part process may include

multiple parts in a build.

Pattern Plate: a piece of solid sheet or plate material the size of the full build platform upon

which a standard pattern is drawn with the energy beam using a defined set of control

parameters. The pattern plate is used to document and monitor the quality and control of

the fusion energy source.

Powder Bed Fusion: an additive manufacturing process that uses a high-energy source to

selectively fuse, layer-by-layer, portions of a powder bed.

Powder Lot: (also powder blend lot) a quantity of powder supplied by a certified powder

producer that was manufactured by the same process and equipment, and blended

simultaneously. The blended powder lot may contain multiple heats of powder when all

heats independently meet the powder specification.

Reference Part: a standardized part used to confirm the performance of a powder bed fusion

machine for a given metallurgical process. The reference part is primarily used to

document and monitor the surface texture and detail resolution capability of the process.

Self-supporting structure: (unsupported limit) part features that may be built in an overhanging

condition without the need for support structure below it. The maximum angle at which

overhanging part features may be reliably build without supporting structure is the

unsupported limit.


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Support Structure: supplementary, sacrificial material built along with a part used to anchor

overhanging geometry, provide dimensional stability, and promote proper thermal

management within the powder bed during a build.

Unique build/heat treat lots: (material property lot requirements) material that does not have

either build or heat treat lot commonality.

Witness line: a visual demarcation along build layer planes indicating a change in steady-state

operation of the powder bed fusion process. The demarcation may be a geometry shift,

change in surface texture, change in coloration, or any other distinct non-uniformity.

Z-position: The location, or position, of the build platform along the axis of motion used to

create the incremental layered build.

Commentary: To the extent possible, this standard uses terminology as established by, or

consistent with, international standards organizations.

4. ADDITIVE MANUFACTURING DESIGN

This section provides requirements governing the design, development, assessment, testing and

acceptance of AM hardware. Topics include part classification, structural assessment, fracture

control, and material property requirements.

4.1 Concepts for AM design

Design for additive manufacturing is a newly developing discipline. AM designers must consider

process factors beyond those common to traditional metallic design for subtractive

manufacturing (machining). For example, reliability and performance of AM designs can be

greatly influenced by subtle factors such as the surface finish in self-supporting structures.

Beyond the motivations for design innovation, weight savings, and cost savings, AM designer

objectives must include part reliability through minimizing support structures through self-

supporting design, ease and verification of powder removal, design for inspection, design for

adequacy of proof test, accommodating the AM build volume for parts and required witness

specimens, allowance for finishing operations, and controlling surface texture or providing for

access for surface texture improvement. The quality of an AM design is not judged based on its

cost-savings, weight-savings, or geometric complexity alone, but on all of the above elements

that influence the practicality of reliable AM implementation.

4.2 Part Classification

[AMR-1] All AM parts shall be assigned a classification in accordance with section 4.2.

The ten categories within the AM classification system accommodate all parts, from fracture

critical, human-rated flight parts to proof-of-concept builds. The classification system is used


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throughout this standard to levy appropriate levels of process control, qualification, and

inspection. Figure 3 illustrates the classification system.

The part classification system uses a two-tier system to designate AM parts based on relative

risk. The alphabetical class is determined by consequence of failure, Class A being high, and

Classes B and C being low, with Class C parts considered as non-service. The numerical

subclasses of Classes A and B are determined by a combination of structural margin assessments

and the risk associated with the AM implementation. Each of these metrics is assessed based on

evaluations described in this section.

Commentary: These class designations are not to be confused with those used in the

ASTM International standards for AM parts, such as F3055. The ASTM classes are used

to represent part processing only and are unrelated.

Figure 3. Part Classification

4.2.1 Consequence of failure


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The first division among AM parts is based upon the consequence of failure for the part: if

failure of the part creates a catastrophic hazard, then consequence of failure is assigned high

(Class A); otherwise, consequence of failure is assigned low (Class B or C).

Commentary: The consequence of failure for any human-rated hardware should be

determined from the Failure Modes and Effects Analysis (FMEA) or may follow from

assessments done for fracture control classification. Parts that are non-fracture critical

(e.g. fail safe parts) may be assigned low consequence of failure. The low risk category of

non-fracture critical parts is not applicable to AM due to lack of maturity. The

consequence of failure for parts in non-flight development hardware should be based on

collateral damage assessments and is chosen at the discretion of the project.

Considerations for high consequence of failure may also include the loss of a “National

Asset” or similar high-cost hardware or facility that warrants the added controls for Class

A parts. Range safety requirements may also govern consequence of failure evaluations. A

higher class designation may be chosen for a part to enforce greater controls.

4.2.2 Non-service parts: Class C

Parts assigned low consequence of failure are to be further categorized based on whether the

parts are intended for service: all low consequence parts intended for service are assigned to

Class B, while non-service parts are assigned to Class C. Class C parts are divided into two

categories based on their purpose: parts to be used for functional evaluation are assigned to Class

C1, all others are assigned to Class C2.

Commentary: The bar dividing high and low consequence of failure is set high

(catastrophic), mirroring the fracture control approach. Class B parts are not

synonymous with benign failures - Class B parts are to be aerospace quality parts of high

reliability. Many failures falling short of catastrophic remain extremely costly, e.g. the loss

of a robotic interplanetary mission. For a part to be considered “not for service,” it is not

to be used for any other purpose than an isolated, functional evaluation. The intent is to

limit Class C1 parts to those that may be evaluated on a stand-alone basis, away from

high-value facilities or hardware where failure presents non-consequential collateral

damage. An example of a Class C1 part undergoing functional evaluation would be a

valve housing undergoing burst test evaluation in a properly controlled burst test facility.

AM parts used for testing while integrated with high-value hardware or advanced facilities

are intended to be assigned into Class B at a minimum. Class C2 is intended for all non-

functional builds, such as parts used to investigate AM build feasibility.

4.2.3 Classes A and B

All parts intended for service are placed into Class A or Class B: parts with a high consequence

of failure are assigned to Class A; parts with low consequence of failure intended for service are


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assigned to Class B. Classes A and B are subdivided into four sub-classes based on risk

presented by structural demands and the inherent risks posed by the AM design, build, and

inspection process.

4.2.3.1 Structural Margin

Structural margin is the first evaluation for determining subclass within Class A and Class B.

Each structural assessment criterion applicable to the part shall be compared against the

minimum requirements shown in Table 2. If all structural assessment requirements meet or

exceed those of Table 2, then the part is considered to have high structural margin and is

assigned either sub-class 3 or 4. If any of the structural margin requirements of Table 2 are not

met, then the part is assigned either sub-class 1 or 2 based on higher structural demand. An AM

Risk assessment arbitrates the final sub-classification.

Table 2. Structural Assessment Criteria to Determine High Structural Margin AM Parts

Material Property Criteria for High Structural Margin

Loads Environment Well defined or bounded loads environment

Environmental Degradation Only due to temperature

Ultimate Strength 30% margin over factor of safety

Yield Strength 20% margin over factor of safety

Point Strain Local plastic strain < 0.005

High Cycle Fatigue, Improved Surfaces 4x additional life factor or 20% below required

fatigue limit cyclic stress range

High Cycle Fatigue, As-built Surfaces 10x additional life factor or 40% below required

fatigue limit cyclic stress range

Low Cycle Fatigue No predicted cyclic plastic strain

Fracture Mechanics Life 10x additional life factor

Creep Strain No predicted creep strain

Commentary: The purpose of the structural margin assessment is to identify the relative

structural performance demands on the part. Parts with high structural margin are less

sensitive to variations and uncertainty in material performance. The use of structural

margin in classification of parts is not uncommon (see the classification system in SAE

AMS 2175 Classification and Inspection of Castings); however, past use of such structural

criteria has typically been simplistic and non-specific. The criteria herein are intended to

be sufficiently comprehensive of common structural failure modes to allow the margin

required in each to be specific to its property. For example, the strength margin

requirements are set to cover potential variability in strengths, not to bound fatigue or


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fracture behavior, as these properties are addressed directly. The following notes are

provided for each aspect of the structural assessment to be considered:

Loads Environment - The loads environment for spaceflight systems and structures is

rarely comprehensively understood. Examples of loads that are not well understood or

bounded include parts passing through or operating near resonance, or parts requiring

forced-response, coupled dynamic loads analysis to predict fluid-structure interaction.

Commonplace uncertainties such as the precise magnitude of a random vibration or loads

due to quasi-static pressure or thrust loads are considered sufficiently defined and do not

violate the intent of this criterion.

Environmental Degradation - To meet the high structural margin criteria, temperature is

the only allowed source of environmental material degradation. Exposure to hydrogen

embrittling environment would be an example failing this criteria.

Ultimate and Yield strength - These assessments are performed as defined by the

governing structural requirements. Methodologies for yield and ultimate evaluations often

differ by analysis organization. The requirements for high structural margin are expressed

in percent strength capability in excess of the required factor of safety.

Point Strain - This evaluation is required for all parts and is intended to limit the

dependence on ductility for high structural margin parts. Linear elastic evaluation where

peak, local von Mises stress remains below yield is sufficient. Proper modeling practice

for converged mesh discretization dependence within stress models is assumed. For cases

where peak, local von Mises stress is greater than yield, any approved method of

calculating plastic strain is acceptable, such as elastic-plastic finite element analysis or

Neuber notch analysis.

High cycle fatigue - For cyclic stress above the defined fatigue limit cyclic stress, margin

is judged by demonstrating additional cyclic life factor. For cyclic stress below the

defined fatigue limit cyclic stress, margin is judged based on the percentage that the

applied cyclic stresses are below the fatigue limit. Fatigue initiation life evaluation

includes the influence of the surface condition. The factors provided for “improved

surfaces” intend that such surfaces have been altered through machining, or other

chemical or mechanical processes, to eradicate or mitigate the effects of the as-built AM

surface on fatigue life as substantiated experimentally. Part surfaces that remain in the

as-built condition are to be evaluated against fatigue data developed with a representative

as-built surface.

Low cycle fatigue - Plastic point strains are not intended to occur cyclically for high

structural margin parts.

Fracture Mechanics Life - This evaluation is only intended for parts subject to damage

tolerance analysis.


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Creep - Confirmation of no creep deformation is intended only in cases where creep

inducing environments are present.

4.2.3.2 AM Risk

The final sub-classification of all Class A and Class B parts is based on Additive Manufacturing

Risk. AM Risk is scored on criteria presented in Table 3: if the summed AM Risk scores >=5,

then the part is assigned high AM Risk and placed in sub-class 1 or 3; parts with low AM risk are

placed in sub-class 2 or 4.

Table 3. Criteria to Evaluate Additive Manufacturing Risk

Additive Manufacturing Risk Yes No Score

All critical surface and volumes can be reliably inspected, or the

design permits adequate proof testing based on stress state?

0 5

As-built surface can be fully removed on all fatigue-critical surfaces? 0 3

Surfaces interfacing with sacrificial supports are fully accessible and

improved?

0 3

Structural walls or protrusions are ≥ 1mm in cross-section? 0 2

Critical regions of the part do not require sacrificial supports? 0 2

Total

Commentary: New opportunities presented by the AM process, such as previously

impossible geometries, also present new risks in the use of the parts. Limitations to

accessibility and inspection are prominent among these risks. The AM Risk criteria

questionnaire is phrased such that a positive answer corresponds to a zero score, not

contributing to AM Risk.

4.3 Structural Assessment

[AMR-2] All projects involving AM parts shall have clearly defined structural design

requirements and factors of safety.

AM parts shall follow all required structural requirements governing the project with the

exception of material properties. Handling of AM material properties shall be in accordance

with section 4.6 of this standard.

Commentary: Examples of commonly used structural standards include NASA-STD-5001,

NASA-STD-5012, or JSC-65828. These standards generally require the use of material

design allowables developed in accordance with MMPDS or CMH-17. As a new, process-

sensitive product form, procedures for handling AM material properties have not yet been

codified, thus policies and procedures described in section 4.6 of this standard are to be

used.


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4.4 Fracture Control

[AMR-3] All AM parts used in hardware subject to NASA-STD-5019 shall have fracture

control rationale documented expressly in the fracture control plan applicable to that part.

Fracture control classification and rationale for all AM hardware is to be approved by the

responsible fracture control board (RFCB). The low risk non-fracture critical category of

NASA-STD-5019 does not apply to AM parts. Comparable rationale may be approved by the

RFCB as an alternative approach. Fracture critical AM parts accepted as damage tolerant require

sufficient flaw screening rationale through inspection or proof test and damage tolerance analysis

based on applicable material properties developed for the AM product form. Damage tolerance

tests performed on the AM part (or a representative analog part) may be used for fracture control

rationale at the discretion of the RFCB. Material properties used in fracture control related

analysis are to be submitted to the RFCB for review.

Commentary: The part development plan should be submitted to the RFCB to provide full

context of the AM part, including its AM classification, and associated process controls

and inspections. This standard provides significant latitude to the RFCB to determine the

adequacy of the overall fracture control rationale for AM hardware. It is expected that

this will frequently result in achieving fracture control through an RFCB-approved

alternative approach that relies on a combination of process control, inspections, proof

and other acceptance tests, analysis, and/or damage tolerance testing. Under typical

program governance models, the RFCB provides recommendations to either program

management or the technical authority regarding approval or disapproval of fracture

control rationale.

4.5 Qualification Testing

[AMR-4] All AM parts shall be subject to a qualification test program to demonstrate the

performance and functionality of the part to meet the design mission requirements, life

factors, and life cycle capability.

Qualification testing requires parts produced to a Qualified Part Process (QPP). See section 5.2.

Any AM part that functions as part of a mechanism requires qualification, design life

verification, and acceptance testing defined by NASA-STD-5017. The protoflight approach to

qualification of hardware as defined in NASA-STD-5001, which does not include a dedicated

test article, is not considered applicable to AM hardware of Classes A1 through B2, nor is the

“no-test” option for verification by analysis only. Parts may be qualified individually (if

applicable), as part of a sub-system qualification, or as part of an overall system qualification

Commentary: The importance of test verification for the design and functionality of AM

parts is heightened as new design capabilities and concepts are enabled by the technology.

Many aspects of AM design may need to be verified including the dynamic response of


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unique geometry, flow efficiency through passages with as-built surface finish, or

traditional structural margin under realistic, life-cycle environments.

One of the goals of developing the AM process for critical aerospace needs is to diminish

the dependence on costly, long-lead development items that limit the degree of

experimental validation in the design and verification process. Depending on the

complexity of the system, the reduced fabrication time and cost of AM parts enables

incremental test and development, reducing the design and development risk of flight

articles. Use of the protoflight concept may be an indicator that the AM process is not

being properly employed. The qualification test series is important with AM hardware to

uncover life-cycle failure modes that may not be revealed in a less comprehensive

protoflight test. For the current maturity of the AM process, there is need for experimental

certification evidence for the design performance of the part through the qualification test

series and for the integrity of each individual part through acceptance testing with proof

test, NDE, and other AM build-related controls.

4.6 Material Property Requirements

The AM Design Value Suite (DVS) is a collection of material properties developed for a specific

AM alloy and condition for use in the structural assessment of the part. The material properties

in the DVS are determined to an appropriate statistical significance to meet the intent of the

material property reliability requirements and structural analysis requirements. The end use of

the DVS for an AM alloy is directly analogous to the use of an entry in the MMPDS for a given

alloy and condition.

[AMR-5] A Design Value Suite of material properties shall be developed and maintained

by the responsible part design vendor for each applicable AM alloy and condition.

Documentation substantiating the development of the DVS shall be submitted for review

and approval through the Material Usage Agreement (MUA) process of NASA-STD-6016.

Actual values within the DVS must be made available for NASA review as requested. The

DVS shall only be applied to parts produced to an appropriate QPP.

Commentary: The material property policy for AM currently differs from traditional

methods as prescribed by NASA-STD-6016 for metallic materials, i.e. the use of the

MMPDS framework for the development of design allowables for a given material, product

form, and product thickness. The MMPDS philosophy has important underpinnings that

are significantly challenged by any material production process that is highly

individualized and sensitive to process control. The traditional design allowables

approach assumes the material production process is under careful control of an

aerospace-quality specification. The assumed corollary to this is that aerospace quality

materials are produced by a fairly select group of companies that are highly vested in their

craft and understand the intricacies of process control required to produce materials

meeting the specifications. Given these assumptions on process control in the MMPDS


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framework, design allowables are generated once on a statistically significant quantity of

specimens (100-300) on a selection of material lots (typically 10) and are considered to

encompass the expected variability of material produced under the control of the

governing specification. Processes such as welding, which are individualized (under end-

user control and unique to end-user needs) and potentially sensitive to process control,

have always challenged this design allowable philosophy; therefore, allowables for such

processes have not yet been included in the MMPDS. The AM process currently

challenges the concept of once-and-done design allowables in many significant ways: 1)

the process is new and evolving, 2) the process runs without control feedback (mostly), 3)

the process requires minimal investment for material producers compared to traditional

aerospace materials thus providers are increasingly ubiquitous and lacking in experience

and standards of performance, and 4) the process has numerous control parameters and

potential failure modes that remain poorly understood.

To integrate AM in its current state of maturity into critical flight structures requires an

on-going, process control intensive approach to developing and maintaining material

design values. (The terminology “material design values” is used to differentiate the

approach from the traditional material design allowable methods discussed previously.)

Rather than a one-time development of comprehensive allowables, the method required

herein employs an increased level of scrutiny on the build-to-build material quality

accompanied by periodic review and acceptance of the material design values. This is

unique because it requires sustained engagement and interaction of the engineering and

production communities to monitor the process and confirm controls are adequate for

produced parts to meet the design value assumptions.

Development and maintenance of the suite of design value properties requires the use of

Process Control Reference Distributions (PCRD) of properties (tensile and fatigue) to

monitor the build-to-build quality of the AM process. The PCRDs provide a more

insightful assessment of process quality than the common simplistic comparison against a

specification minimum property. The DVS must remain compatible with the PCRDs.

PCRDs are defined and their use described in section 5.1.10

The continuous process control approach holds advantages for accommodating the AM

philosophy. The burden of diversity in the original data pool for developing design values

is lessened by reducing its responsibility for encompassing risks of process control drift in

a single data pool. Having sufficient quantities of ongoing process control data shifts a

degree of material property risk away from flight risk toward a more tolerable

programmatic risk of rejecting production hardware. This approach also allows the AM

process and associated suites of design values to remain more nimble in the light of

changing technology.

4.6.1 Material Property Development


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A prerequisite to the development of AM material properties is to have a controlled AM process.

The process control requirements and prerequisites for producing AM materials for

characterization are similar to those required for parts. See section 4.6.12, Characterization Build

Process Control.

4.6.2 Lot Requirements and DVS Maturity

[AMR-5A] The DVS shall account for the effects of lot variability and powder recycling.

Commentary: Traditionally, when design properties are developed, sufficient lot

variability is incorporated into the original data set to enable the assumption that the

design values will adequately encompass the lot variability of future materials procured to

the governing specification. The common 10-lot requirement of the MMPDS or 5-lot

requirement of CMH-17 serves this purpose. Because the powder material form is

universal to all products of the PBF process and powders are often custom ordered, there

are significant advantages to investment in large powder lots. To accommodate a flexible

paradigm for initial development of design value suites for the AM process, this standard

allows the use of a DVS with limited lot diversity in cases where parts are produced from

powder lots that represent a substantial part of the DVS.

For a DVS to be used in structural assessment of Class A and Class B parts, the lot

representation in the DVS must either be at a Provisional level, which allows for parts built from

lots substantially represented within the DVS, or at a Mature level, which allows the use of the

DVS with other compatible material lots. A Mature DVS requires a minimum of five powder

lots and ten unique build/heat treat lots with nominally balanced distribution across all design

values. A Provisional DVS requires a minimum of two powder lots and five unique build/heat

treat lots with nominally balanced distribution across all design values. The Provisional DVS

remains so until accruing the required lot quantities for the Mature DVS. For use of the

Provisional DVS for part assessment, substantial lot representation is defined as a minimum of

15% of the Provisional DVS population. Though limited lots may be represented, the

Provisional DVS is to meet the minimum specimen quantities for calculating design values as

specified in the following sections.

Incorporation of a new powder lot for building parts with a Provisional DVS requires sufficient

characterization builds and testing to integrate the powder lot with substantial representation

(>15%). Once the Mature DVS lot criteria have been met, the DSV is assumed to sufficiently

encompass the expected process variability and no longer requires further incremental lot

accrual. It is recognized that in this lot accrual paradigm, earlier lots may have a

disproportionately large representation. Data reduction must acknowledge this and any

weighting effects minimized to the degree feasible.

Commentary: While logistically intensive, the accrual method to incorporate lot variability

into the DSV provides needed flexibility through incremental development. This paradigm


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introduces programmatic risk associated with the development and use of a less than fully

mature DVS in the hardware design process. Though the risk to flight safety is sufficiently

mitigated through DVS/Part lot commonality requirement of the Provisional DVS, there is

substantial programmatic design-related risk if the DVS is optimized to minimally

bounding values (e.g. right up to the 99/95 minimums) based on limited lot representation.

The risk is that when additional lot variability is incorporated into the DVS, revised

assessment of the DSV data may no longer support the prior values, causing significant

impact to design and production schedules. The values in a Provisional DVS (and even a

Mature DVS) should maintain reserve margin against the design values derived from data

with minimal lot variability. The magnitude of this reserve margin is a matter of

engineering judgment and programmatic risk tolerance.

4.6.2.1 Recycled Powder Lot Representation

The representation of recycled powder feedstock within the DVS, up to the maximum recycle

limits in section 5.1.2.2, determines the limits for recycled powder use in Class A and Class B

parts. The recycle status of powder in the DVS is to be monitored.

Representation of recycled powder feedstock in the DVS is to be sufficient to demonstrate that

the material performance following the recycling operations is fully accounted for in the DVS.

This will generally require a minimum 20% data representation for powder at the limiting

recycle metrics. The material properties of primary concern for powder reuse are fatigue and

fracture performance, where the accumulation of oxides or other debris are expected to impact

the material resistance to initiation and evolution of damage.

The substantiation of the DVS (AMR-5) is to directly address and define the powder recycle

limits incorporated in the DVS.

4.6.3 Anisotropy

[AMR-5B] The build orientation shall be identified and maintained for all material

property development activities. Material properties in the DVS are not required to be

orientation specific if bounding values are used and anisotropy is demonstrated as

negligible.

Commentary: The nature of the AM process lends itself to creating texture in

microstructure that can be a source of anisotropy in the elastic and elasto-plastic

deformation response of the material. Requiring the AM metallurgical process to include

recrystallization of the as-built microstructure and hot isostatic pressing to reduce internal

defect quantities and patterns are intended to minimize the AM-related anisotropy in

material properties. Under proper control of a QMP, the measured anisotropy in the AM

product form should be equivalent to, or less than, that demonstrated in rolled product

forms such as plate or bar. The development of the DVS may use a bounding approach to


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accommodate anisotropy following reasonable confirmation that the anisotropy is

negligible for proper design analysis and part performance purposes. The orientation

designations for parts and specimens should be consistent with ISO/ASTM 52921.

Surface texture effects that arise from build orientation may be significant in material and

part performance, but are not considered anisotropy in this context.

4.6.4 Influence Factors

[AMR-5C] The Design Value Suite shall be developed and actively maintained to include

data that evaluates AM-related factors that influence the mechanical performance of the

AM product form.

The AM material product form is capable of producing part geometry that is near-net or final

form. This introduces a variety of potential factors that may influence the mechanical

performance of the part. The design value suite must clearly acknowledge and accommodate

these factors to ensure design values are properly applied in part assessment. As appropriate,

these factors may be generated through ratio methods as described in section 4.6.6.1 or

properties may be developed independently to accommodate these influence factors.

Commentary: The most common influence factor associated with AM material properties

is the surface texture effect on fatigue performance as discussed in detail in section 4.6.7.

This may not, however, be the only scenario with influence. Powder bed thermal

conditions affect local microstructural evolution. Thermal conditions are influenced by

AM part geometry and mechanical properties of material within a part may vary compared

to properties generated from separately built coupons. The limit on wall thickness or

structural detail size relative to mechanical capability requires attention. In the case of

thin-wall structures, the AM surface texture or surface-connected porosity may represent a

meaningful fraction of the structural wall thickness and thereby influence strengths,

ductility, and fatigue initiation capability. Due to effects of beam incident angle, the

location on build platform can also be an influence factor, particularly regarding surface

texture.

4.6.4.1 Pauses in PBF Machine Operation

The DVS is to document the acceptable time limit for pauses in standard machine operation

associated with steady-state build operations. The maximum allowable pause in standard

operation is to be experimentally verified as non-consequential to material properties by

including such pauses in characterization builds for evaluation mechanical properties. This

maximum allowable pause is to be specified in the production planning records associated with

AM part process controls. Any pause exceeding this limit is to be documented as a non-

conformance.


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Commentary: Various PBF machine designs and operational states include the possibility

or even likelihood of pauses in operation, such as pauses in machine operation to handle

powder movement or refilling. This allowance for pause is intended only to include pauses

inherent to the operation of the PBF machine. It does not include stoppage due to machine

faults or build errors. Any pause due to machine fault or error is a non-conformance. The

verified allowable pause limit may be useful in the disposition of these non-conformances.

4.6.4.2 Specimen Geometry Effects

Commentary: In the development of data to understand AM related influence factors in

scenarios such as thin-wall structures, test specimen geometries are often a challenge. It

is recommended that geometries corresponding to ASTM testing standards be used

whenever possible, but the geometric capabilities of AM will challenge the ability to

consistently utilize standardized specimens, especially when studying influence factors or

performing a mechanical evaluation on a first article. This limitation is not to be used as a

rationale to not perform such tests. Properly understanding AM material performance

requires investment, particularly at this early stage of AM implementation. Consider

tensile testing for example. Even within the bounds of approved specimens of ASTM E8, a

tensile test always provides a value reflecting some influence of the specimen geometry - a

large round specimen will provide a somewhat different answer than a small flat specimen.

The design value suite should be anchored with standardized specimens compliant with a

governing test standard, such as the appropriate ASTM standard or equivalent. When

different, or non-standard specimens are used to evaluate an AM influence factor to be

applied to standard test data in the design value suite, the influence of specimen design

needs to be separated from the effects of the AM process in determining these factors. The

most common and appropriate way to accomplish this is to test the specimen geometry

independently by machining it from a wrought product form along with adjacent

specimens of standard ASTM geometry. This comparison will allow isolating specimen

geometry effects from AM-specific influence factors.

4.6.5 Physical and Constitutive Properties

[AMR-5D] The DVS shall document the physical and constitutive properties appropriate

for design assessment.

Physical and constitutive properties are presented as typical basis (mean value) and are defined

as a function of temperature. These values are to be generated as described by the MMPDS.

Because they are typical basis, these values may be considered sufficiently mature at the

Provisional DVS lot sampling level of section 4.6.2.


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If all AM materials registered to the DVS (see section 5.1.11) result in a material with

appropriate chemical and microstructural consistency to a wrought product form with physical

and constitutive properties codified in an approved source such as the MMPDS, these values

may be used. The source of physical and constitutive properties, and rationale if using codified

wrought values, is to be documented within the DVS.

Commentary: Physical properties commonly used in design assessment of metallic

materials include density, specific heat, thermal conductivity, and thermal expansion.

Other properties, such as magnetic permeability, may occasionally be required.

Constitutive properties commonly used in design assessment of metallic materials include

the modulus of elasticity, Poisson’s ratio, and quasi-static or cyclic flow behavior. While

values of elastic modulus and Poisson’s ratio are presented on typical basis, flow

properties (quasi-static or cyclic stress-strain curves) used for design assessment should

reflect the design values for tensile properties. Considerations for the development of

quasi-static material flow curves based on design values can be found in the MMPDS.

4.6.6 Tensile Properties

[AMR-5E] Tensile strength design values shall be maintained at or below the 99%

probability at 95% confidence tail of the applicable Process Control Reference

Distributions (PCRDs).

The intent of the A-basis static strength property requirements of NASA-STD-6016 are satisfied

when all material characterizations and process controls of this standard are fully implemented.

The submittal of an MUA describing the development and status of the DVS satisfies the NASA-

STD-6016 material property control requirements. This DVS documentation also satisfies

material property requirements levied by other structural requirements documents, such as

NASA-STD-5012 or JSC-65828.

No minimum tensile specimen quantity is specified for the DVS. The process of establishing

Process Control Reference Distributions (section 5.1.10) and the subsequent continuing

acceptance testing of witness specimens provides sufficient rigor. The tensile design values in

the DVS are subject to the lot requirements of section 4.6.2; however, the use of tensile test

witness specimens in process control implies that tensile data will continue to accrue even after

the Mature DVS lot requirement is met.

4.6.6.1 Ratio Derived Properties

The paired ratio method may be used to populate the DVS with other flow-dominated material

properties, as required. In this context, flow-dominated properties are those that are governed by

the onset of plastic flow and subsequent ductile failure mechanisms. It is reasonably assumed

that these properties will follow the trends of tensile properties in magnitude and variability. The

most common are compression yield, shear ultimate, and bearing strength. When developed


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with the ratio method, these properties are often referred to as “derived properties.” The method

to derive properties with matched pair ratios using tensile strengths is described in the MMPDS.

Matched pairs are to be built in the same build. A matched pair ratio for a derived property

requires a minimum of ten tests to establish the ratio to be applied to the tensile design values.

Properties developed with this methodology are subject to the lot requirements in section 4.6.2.

4.6.7 Fatigue

[AMR-5F] The Design Value Suite for a given AM product shall include fatigue properties.

Fatigue initiation life is a key concern with the AM process. Fatigue initiation life properties are

to be developed in the form of stress-life or strain-life curves. All fatigue curves, shall be

explicitly labeled with their basis, e.g. typical or bounding. The fatigue curve basis shall be

consistent with the analytical methodology prescribed by governing structural requirements. The

process for developing the design fatigue curve from the test data is to be included in

documentation associated with AMR-5.

Fatigue properties are subject to the lot requirements of section 4.6.2. Ten tests are required to

define a fatigue curve for a given condition. For high cycle fatigue, a minimum of four tests is

required as run-outs at the defined fatigue limit or as failures within 20% of the fatigue limit. A

fatigue limit may not be defined lower than 10e7 cycles. AM products are not considered to

have an endurance limit. For applications with exceptionally high cycle counts (e.g. >10e8), a

methodology to acquire anchoring test data is required for Class A parts. Methodology for

predicting such fatigue limits may be employed for Class B parts when properly documented.

Effects of surface texture and surface improvement treatments must be included in the fatigue

design curves of the DVS. A minimum of three surface conditions is required for

characterization: 1) a bounding as-built surface, 2) vertical Z-direction fatigue for PCRDs, and 3)

a neutral surface finish condition. The bounding as-built surface will generally require the use of

unsupported fatigue specimens inclined to the Z-axis at the unsupported limit, horizontal fatigue

specimens with a hollow core of unsupported ceiling, or fatigue specimens inclined with support

interface along the gage. The bounding fatigue surface is also to address dependence upon

location on the build plate due to the angle of beam incidence. The vertical, Z-direction fatigue

specimens represent a moderate as-built surface for process control and design purposes. The

neutral surface finish condition is intended as a measure of the fatigue performance of the bulk

AM material rendered by the applicable QMPs and is prepared in accordance with fatigue test

standards (e.g., ASTM E466 or ASTM E606), typically low stress ground or carefully machined

and polished. Fatigue curves for other as-built configurations may be developed and utilized in

assessment when the surface characteristics of the test specimens are documented and

comparable surface characteristics have been confirmed in the first article and/or witness article

assessments. Fatigue life of fully machined surfaces may use standard surface finish factors

applied to the neutral-surface fatigue curves. Other surface improvement methods, such as

honing or polishing, that do not ensure complete, uniform removal of all as-built surface remnant


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or at least 0.005 inches (0.13mm) from all treated surfaces are to be evaluated through testing.

Surface treatments, such as peening that improve fatigue life by altering the near-surface stress

state without actually removing the surface, must be fully characterized through fatigue testing.

Furthermore, such methods require a documented methodology to ensure repeatable part

coverage of the surface treatment and verification of coverage in the first article evaluation.

Commentary: Frequently hardware presents particular challenges with respect to fatigue

assessment due to compounding complexities of geometry, stress prediction, stress

“shakedown” behavior, surface finish effects, and so forth. Additive manufacturing

presents a unique opportunity for analog test coupon evaluation of complex geometries.

The development of fatigue analog specimens requires structural analysis investment to

ensure specimens properly reflect predicted hardware cyclic stress distributions.

Properly implemented, fatigue analog specimens may be used to confirm or anchor

complex fatigue analysis scenarios. Fatigue analogs may also serve as build witness

specimens to confirm fatigue performance for parts with fatigue-critical areas that are

difficult to inspect for confirmation of geometry and surface texture.

4.6.8 Fracture Mechanics

If the part design assessment includes evaluation of crack-like defects by fracture mechanics,

properties in the form of fracture toughness and fatigue crack growth rate are required in the

DVS. Fracture mechanics properties are most commonly presented and utilized at a typical basis

(mean value) when used for fracture control assessment of hypothetical defects. Depending

upon policies for structural assessment and fracture control, the evaluation of known defects or

analytical assessments of proof test efficacy may require lower bounding toughness and upper

bounding fatigue crack growth rate in the assessment. The development of these bounding

properties is not commonly subject to the full lot maturity rules. Generally, fracture mechanics

properties are sufficiently satisfied by meeting the minimum for Provisional DVS lot maturity

level of section 4.6.2.

Commentary: It is recommended that all DVS include some level of fracture mechanics

characterization, even if the parts produced are not intended for fracture critical

applications. For practical purposes, these properties define the material capability in the

most likely form of failure in hardware applications. It is important to understand the

performance of AM alloys in fracture mechanics dominated failure modes. Many common

AM alloys are sufficiently tough to require elastic-plastic test methods to get meaningful

toughness results. The use of ASTM E1820 for toughness testing is highly encouraged.

4.6.9 Stress Rupture and Creep Deformation

When required for part assessment, material properties for stress rupture or creep mechanisms

are to be included in the DVS. The MMPDS provides guidance for performing these tests as


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well as for data reduction and presentation. Designs requiring dependable stress rupture or creep

performance should include a stress rupture witness test in the QPP. This is consistent with

common practice for lot release control for many high temperature alloy products.

4.6.10 Temperature and Environmental Effects

[AMR-5G] Environmental effects on material properties shall be properly represented in

the DVS.

When required for part assessment, the DVS shall include the effect of temperature on material

properties based on testing of the AM product form. Design curves in the DVS cannot be

extrapolated beyond tested temperatures. The determination of temperature effects on properties

shall follow the fundamental methods shown in the MMPDS, which allows for flexibility in

determining temperature effects working curves. The effect of temperature is to be evaluated at

a sufficient number of temperatures to produce a smooth, continuous curve of temperature

effects over the design temperature range. Sharp gradients in temperature effects shall be

defined through adequate temperature sampling to fully capture trends. In general, the effects of

temperature on material properties may be considered sufficiently characterized with the

minimum Provisional DVS lot maturity level of section 4.6.2. Material properties that reveal

increased scatter due to the effects of temperature may require further lot sampling. To

determine a temperature effects working curve for tensile properties, a minimum of three tests

are required at each sampled temperature. The effects of temperature on fatigue and fracture

properties may occur at broader temperature intervals to reduce the test burden; however, in such

cases, the temperature effects on these properties are not to be interpolated, but are to use the

bounding values of adjacent data.

With proper documentation, existing temperature effect curves may be used to inform the testing

of the AM alloy and reduce test burden by confirming AM alloy performance at essential

temperatures, such as high gradient regions and the bounding values. The existing temperature

effect curves are to come from an approved design source. The alloy and product form used as

the reference must be consistent with the microstructure and room temperature tensile properties

of the QMPs registered to the DVS.

Environmental effects other than temperature must also be represented in the DVS if relevant to

the design. The development of these properties is to be consistent with established practice. In

regard to hydrogen embrittlement behavior, no assumptions or correlations to other product

forms are made. The effect of hydrogen exposure is to be verified directly on the AM product

form. The hydrogen embrittlement effects are strongly dependent upon temperature.

4.6.11 Welds

[AMR-5H] Material properties for welds in AM products shall be developed directly on

the AM product form. Weld properties are to be incorporated into the applicable DSV.


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Lot maturity requirements to substantiate the statistical basis of weld material properties are to be

negotiated with and approved by NASA.

4.6.12 Characterization Build Process Control

[AMR-5I] Characterization builds shall have, at a minimum, witness specimen and

acceptance criteria equivalent to a Class B2 part.

An AM characterization build is defined as any build used to produce material for

characterization purposes in the development of process control baseline data (See PCRD,

section 5.1.10) or to support the population of the DVS for a given AM process.

5. PROCESS CONTROL

PBF process control is divided into four broad areas, each of which requires a qualification

procedure: 1) metallurgical process control, which includes feedstock control, the fusion process,

and subsequent microstructural evolution through heat treatment; 2) part process control, which

includes the first article evaluation, digital model control, witness specimens, and build lot

execution; 3) equipment process control, which includes machine maintenance, calibration, and

operational procedures, and 4) vendor process control, which includes the foundational quality

infrastructure at the vendor, the vendor qualification process, and operator qualifications.

5.1 Metallurgical Process Control

Metallurgical process control for AM is intended to control the fundamental aspects of the

powder fusion process and subsequent processing that renders the final desired microstructure.

This includes controlling the powder feedstock, the fusion process parameters, and the post-build

thermal treatment process.

5.1.1 Qualification of the Metallurgical Process

[AMR-6] All Class A or B parts shall be built using a Qualified Metallurgical Process

(QMP).

Commentary: Note that the development of a qualified metallurgical process requires

PBF equipment with active qualification status as described in section 5.3.1.3.

5.1.1.1 Definition of Metallurgical Process

A qualified metallurgical process (QMP) is foundational to AM process control. For purposes of

this standard, a AM metallurgical process is defined by the following information:

a. Powder feedstock controls that ensure consistency in the metallurgical process,

b. Machine-specific parameters controlling all aspects of the fusion process, and

c. Thermal processes used to affect microstructural evolution.


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5.1.1.2 Evaluation Criteria for the Metallurgical Process

The following information shall be evaluated to qualify a candidate metallurgical process as a

QMP:

a. A powder control specification

b. Consolidation quality / as-built density

c. Micrographs of evolving microstructure through each phase of thermal treatment

d. Evidence of basic mechanical performance through tensile properties (ultimate strength,

yield strength, elongation) and high cycle fatigue performance

e. Metrics describing the surface texture and rendered detail characteristics of the process

Criteria to evaluate these aspects of a candidate metallurgical process are provided in the

following sections.

5.1.2 Powder

Control of the powder feedstock is essential to consistent performance of the metallurgical

process. Controls are required for chemistry, particle size and shape, contamination control, and

storage and handling

Commentary: The chemistry requirements for powder feedstock need to be controlled to

render the proper chemistry in the final metallurgical state. Control and specification of

powder chemistry for an AM alloy generally will not be unique relative to available

standardized powder chemistries. Unique controls of chemistry may be more common

with a Purpose-Defined QMP. The influence of particle shape and size distribution is of

considerable importance. Unfortunately, there currently are no open industry standards

that govern this for the PBF AM process. The shape and statistical distribution of particle

sizes in the powder bed are influential in the handling characteristics of the powder during

the AM layering process. The powder must have handling characteristics that allow it to

consistently spread uniformly across the powder bed with proper density to support a

quality fusion process. Controls on particle size distribution will dictate these handling

characteristics while also influencing the process layer thickness and quality of rendered

detail. Controlling the tails of the particle distribution are important. For obvious

reasons, the quantity of particles much larger than the layer thickness must be limited.

For the PBF processes applicable to this standard, large particle control and verification

is typically feasible with a sieve process. The quantity of the smallest particles will

influence the powder handling and should also be limited. Verification of particle size

distribution below 45 micron will require methods such as light scattering, sedimentation,

or image analysis.

5.1.2.1 Specification and Control of Powder


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[AMR-6A] Powder control shall be enforced through a material specification developed

under the auspices of the responsible engineering organization or with content specified in

the PDP.

The procurement of virgin powder is to have the following minimum controls:

a. Powder producers and suppliers are to operate under a Quality Management System

(QMS) compatible with aerospace suppliers and are maintained on the approved supplier

list within the QMS of the build vendor,

b. Method of manufacturing is to be specified,

c. Chemistry requirements, including acceptable methods of measurement and tolerance,

d. Particle shape and particle size distribution (PSD) requirements, including specific limits

on large and small particles. Acceptable methods of powder sampling and determining

PSD shall be specified. Examples include ASTM B215 (sampling), ASTM B214

(sieving), ASTM B822 (light scattering), and ISO 13322 (image analysis),

e. Prohibition on post-production additions to the powder lot for control of PSD or

chemistry,

f. Cleanliness and contamination controls,

g. Packaging methods and environment controls.

To meet large orders, powder heats may be blended into a single lot at the powder vendor if

every lot blended independently meets the specification. Lot blending shall not occur other than

at the original powder supplier when used in the production of Class A and Class B parts.

The powder provider Certificate of Compliance (CoC) shall contain confirmation of each

requirement in addition to a lot identification number and the date and location of production.

5.1.2.2 Recycled Powder Requirements

[AMR-6B] The use of recycled powder is permitted for parts of all classes provided the

practices of this section are enforced.

For builds of Class A and B parts, only one powder lot is to be present in the machine at a time.

Recycle limits are to be addressed by the following metrics: machine operation hours, days

powder is present in the PBF machine, and number of build operations. Other metrics for

monitoring powder recycle limits may be proposed.

The maximum allowable recycle metric is determined by the limits of recycled powder

characterization in the DVS (section 4.6.2.1) or the following maximums.

For Class A and Class B part builds in non-reactive powders, every 1000 hours of machine

operation, 60 days, or 30 build operations, whichever is first, the recycled powder lot shall be

completely removed from the machine. For powders that readily oxidize, such as titanium

alloys, the recycle interval limits are 500 hours of machine operation, 30 days, or 10 build

operations. The removed powder may be utilized Class C1 and C2 parts are not subject to the


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recycled powder limits and may utilize powders that have exceeded the Class A and Class B

recycle limits.

Class C1 parts may be built from an in-house blend of powder lots if each lot in the blend

independently meets the powder specification. Class C2 has no powder blending restrictions.

After every cycle through the powder bed, used powder is to be sieved to remove any

conglomerates. At reuse or with the addition of virgin powder, the used powder is to be blended

to randomize the PSD by removing any segregation present from powder addition, sieving, or

handling in the AM process. If the above blending requirement is not practical in the machine

operation scheme, powder is to be properly sampled from the operational system to confirm that

detrimental segregation is not present within the recycle limits.

5.1.3 Fusion Process Controls

[AMR-6C] Factors governing the fusion process shall be specified to achieve an as-built

material density greater than 99.7% of the reference density of the alloy while producing a

suitable microstructure and surface texture.

In the context of this requirement, factors governing the fusion process are all those parameters

that can be specified for control of the PBF machine during the part build process, such as laser

power, scan speeds, layer thickness, fill patterns, contour/outline parameters, etc., in addition to

other salient factors such as chamber atmosphere, recoater blade material/configuration, and

build plate alloy. All such parameters must be specified as part of the QMP, and once qualified,

the fusion process parameters cannot change without re-qualification of the QMP. In defining

the fusion process, the make, model, and serial number of the PBF machine is specified along

with the version numbers of the controlling firmware and software used to develop the QMP.

For qualification of the fusion parameters, the density shall be determined from as-built material

using ASTM B311 or an approved equivalent. The fusion parameters control the development of

the as-built microstructure and can influence the evolved microstructure; therefore, fusion

parameters may also be influenced by the microstructural requirements that follow in section

5.1.4. The fusion parameters are to provide for an appropriate level of control over geometric

detail, surface finish, and other fusion-related characteristics of the as-built structure. Such

characteristics of the fusion process are to be suitable to the intended use of the part.

For PBF machines that do not allow direct access to (or control of) each of the fusion parameters,

control of the fusion process shall be specified at the most fundamental level allowed by the

machine platform, that is, all available inputs are explicitly specified. Any software or firmware

updates to the machine platform that affect the fusion process are cause for re-qualification of the

metallurgical process for that machine.

For purposes of the QMP record, the fusion parameters may be included explicitly or in the form

of identifying a computer file containing the parameter set that must be used when building to


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the QMP. If a parameter file is specified in lieu of explicit parameters, the filename and

cryptographic hash for the file (section 5.2.3) are to be specified in the QMP record.

Commentary: The fundamental goal of fusion process control is to achieve consolidation

of the powder to the greatest extent possible without the presence of fusion-related defects.

Fusion parameters effect on surface finish, particularly those parameters used in

contouring or outlining each layer may have significant influence on the fatigue and

durability aspects of the final part if such features cannot be fully removed. While density

is the first metric for determining the adequacy of the fusion process, the quality of the

resulting surface texture and microstructure may be equally important.

5.1.3.1 Pattern Plates

[AMR-6D] The fusion process controls for a QMP shall be physically documented using an

AM Pattern Plate.

For this standard, an AM Pattern Plate is a piece of wrought sheet or plate material the size of the

full build platform upon which a standard pattern is drawn with the beam using the parameter set

defined by a QMP. When fusion process parameters are finalized for the QMP, the Pattern Plate

documents the performance of the energy source and associated control systems as governed by

that QMP. The Pattern Plate then becomes a reference standard to help monitor the future the

health of these systems. The material, metallurgical condition, thickness, and surface condition

(peened, brushed, polished, etc.) of the Pattern Plate are to be specified fully in the QMP

documentation. The Pattern Plate should be an appropriate match to the material for which the

QMP is developed. The Pattern Plate is to be designed to evaluate all regions of the build area:

center, edges, and corners. The pattern is to include lines, shapes, and other markings that can be

precisely measured to confirm consistent beam quality and the dimensional accuracy and

precision of the control system. A standard set of metrics associated with the Pattern Plate are to

be evaluated and documented each time a Pattern Plate is produced. When used for re-

qualification of a metallurgical process or a qualification of a PBF machine, Pattern Plate metrics

defined by the QMP process may be used as acceptance criteria once typical variability has been

established and allowable tolerances assigned.

Commentary: Examples of expected metrics include dimensional accuracy, bead width

under QMP parameters in center, edges and corners, laser timings at the intersection fill

and contour passes, consistency across zones (for Category 3 machines), etc. As with the

development of any custom metric, developing the measurement technique, the expected

measurement error, and the expected process variability is important for the use of the

metric as an acceptance criteria. For Pattern Plates, multiple specimens from the PBF

machine in known calibrated state will be needed to establish the expected variability.

Pattern Plate variability should be small. Proper measurements require resolution of

approximately 5 microns.


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5.1.4 Microstructure

[AMR-6E] The QMP shall demonstrate and document the controlled evolution of

microstructure from the as-built state to the final state and establish microstructural

acceptance criteria for use with any part requiring microstructural witness sampling.

The QMP is to document the microstructure at each step of the thermal process, including the as-

built state, intermediate stages revealing recrystallization, and final microstructure. The as-built

microstructure is to be free from defects. For example, the following would be cause for

rejection of the microstructure quality: excessive porosity, linear porosity at contours or layer

boundaries, micro-cracking, keyhole defects, or the development of significant columnar grains

based on the crystallographic texture of prior layers. The recrystallized grain structure is to be

predominantly uniform and non-directional—free of remnants of the as-built structure, though

subtle texture effects reflecting the build orientation are acceptable. The final microstructure

shall reflect proper homogenization, grain boundary quality, and strengthening mechanisms

appropriate to the alloy. Microstructural acceptance criteria defined through the QMP are to be

sufficiently complete to provide reliable process control. Examples of appropriate

microstructural acceptance criteria include average grain size, grain shape, grain boundary

appearance, presence of (or lack of) certain phases, precipitates, carbides, etc.

Commentary: AM parts subject to a QMP require post-build thermal processing to render

a metallurgical condition characterized by a homogenous, largely equiaxed grain

structure. In the as-built state, directly from the powder bed, the AM microstructure is

extremely complex. While this microstructure may present metallurgical opportunities for

improved performance, it clearly introduces risks for unpredicted behavior. To maximize

the reliability of AM parts, the variability of the as-built AM microstructure must be

removed. This standard requires that all qualified metallurgical processes provide a

controlled evolution in microstructure from a good quality, as-built structure of high

density, and free of excess porosity and micro-cracking, to a final microstructure, fully

recrystallized with uniform grain size reflecting none of the as-built structure. This is

generally achieved through a thermal treatment (commonly, a hot isostatic pressing

operation) at temperatures sufficiently high to achieve homogenization and

recrystallization of the alloy. The goal of this microstructural evolution process is to

optimize the final microstructure by limiting the size of the recrystalized grains and

providing optimal conditions for the alloy’s strengthening mechanisms to take place.

5.1.5 Thermal Processing

[AMR-6F] All QMPs shall include thermal processing operations to evolve the as-built

PBF microstructure into a final form providing proper and predictable material

performance.


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Appropriate aerospace quality specifications are to control all thermal processes. The part is to

be confirmed free of residual powder prior to thermal processing. Prior to thermal treatment, the

part is to be cleaned to remove any contaminants such as dirt, grease, or oils.

Vendors used for thermal processing are to be Nadcap accredited. See section 5.4.2.1.

Commentary: Specifications such as the following or their equivalents are suitable to

control AM thermal processes: SAE AMS 2801 Heat Treatment of Ti Alloy Parts, SAE

AMS 2774 Heat Treatment of Ni and Co Alloy Parts. Thermal processing conditions may

be adapted as required for the AM process and are not required to conform to the time and

temperature profiles in the heat treating specifications. The intent is for the heat treating

process to be properly controlled through the procedures of such documents, mainly as

enforced by their second tier requirements such as SAE ARP1962 Training and Approval

of Heat Treating Personnel and SAE AMS 2750 Pyrometry. Consistent heat treatment is

critical to reliable quality of AM parts. Knowledgeable heat treatment providers, who are

properly equipped and trained, are essential.

5.1.5.1 Stress relief

Stress relief thermal cycles are not mandatory for a QMP. If utilized, the hold time, temperature,

heating and cooling rates, and atmosphere of the stress relief thermal cycle shall each be

specified with compatible tolerances.

Commentary: There are two primary reasons to include a stress relief cycle in the overall

thermal process of AM parts. The stress relief cycle is most commonly employed prior to

removal of parts from the build platform as a means to reduce residual stresses in the as-

built part while the part is dimensionally constrained by the platform and its built support

structure. This aids in geometric stability of the parts during platform and support

structure removal. A second benefit is that the stress relief cycle serves to moderate

macro-scale residual stresses while temperatures remain below that for easy grain growth

kinetics. The as-built residual stress state provides the necessary energy to drive the

required recrystallization; however, without some measure of stress relief, non-uniform

grain growth may occur within parts when exposed to the thermal cycle used to affect

recrystallization. Achieving a proper balance between stress relief and the hot isostatic

pressing cycle should result in a uniformly recrystallized microstructure while avoiding

non-uniformities in grain growth caused by macro-scale stored elastic energy in the part.

5.1.5.2 Hot Isostatic Pressing

[AMR-6G] Hot Isostatic Pressing (HIP) is mandatory for all QMPs.

HIP conditions shall be chosen to provide a time and temperature appropriate to properly

homogenize and recrystallize the as-built microstructure as well as to close the majority of

microporosity present from the building process. The pressure, atmosphere, hold time,


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temperature, and the heating and cooling rates, of the HIP cycle shall each be specified with

compatible tolerances.

Commentary: It is common to utilize established HIP processes that have been defined for

classes of alloys within the industry. Due to the mass of HIP equipment, fast cooling rates

can be difficult to achieve for alloys sensitive to quenching conditions from such

temperatures. Though slow, the uniformity of part cooling from HIP may be influenced by

the thermal mass of the build platform, if still attached. If influential, removal of the

platform prior to HIP is recommended.

5.1.5.3 Heat treatment

Further heat treatment following HIP shall be performed if required to achieve the proper final

microstructure for the alloy. The atmosphere, hold time, temperature, and the heating and

cooling rates, for each of the heat treating steps shall each be specified with compatible

tolerances.

Commentary: Most alloys will require further heat treatment following the HIP process to

control the final stages of microstructural evolution. The cooling rates obtainable from

most HIP equipment will be relatively slow. Often the slow cooling rate from HIP is not

be compatible with the quench rates needed to freeze a solutionized state of a

microstructure for further response, such as precipitation hardening.

5.1.6 Mechanical Properties for the QMP

[AMR-6H] The documentation of a QMP shall include mechanical property capability

demonstration test results for tensile and fatigue properties.

The results of the mechanical property demonstration tests are not a rejectable criteria for

purposes of qualifying a metallurgical process. These values will be evaluated for use in Process

Control Reference Distributions and for registration of the QMP to a DVS, as described in

sections 5.1.10 and 5.1.11. See commentary.

A minimum of 30 tensile tests from 3 independent build/heat treatment lots is required from one

or more powder lots. The QMP record is to include the tensile test data and the calculated mean

and standard deviation of the capability demonstration test set.

A minimum of ten high cycle fatigue tests shall be run at a single cyclic stress condition. These

fatigue tests will be used to generate an initial fatigue PCRD for the QMP. See section 5.1.10 on

PCRD development for recommendations. The QMP record is to include a description of the

fatigue test including specimen geometry and cyclic stress conditions as well as the cycles to

failure for each of the specimens.

Commentary: Strength and microstructure are common witness criteria for routine

confirmation of the quality of the metallurgical process. Combined, these two


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characteristics are considerably more informative than either is alone. The deferral of

applying acceptance criteria to the mechanical properties at the QMP level is motivated by

the desire to maintain the systematic approach to qualifying AM processes, parts, and

design values. The future acceptance criteria for mechanical properties will flow from an

assessment of compatibility of the QMP mechanical performance with the design value

suite. In the development of a unique AM alloy or alloy condition, which is currently very

common, the QMP needs to exist in a rigorous form before the design value suite and

associated process control reference distributions can be developed. Deferring

acceptance criteria on mechanical properties supports the sequence of establishing a QMP

as a prerequisite to the development of characterization data for the process, ensuring

rigor and consistency in the mechanical evaluations. For most common cases of

establishing a QMP (such as when a new machine is brought on line to broaden capability

but will be running a QMP intended as identical to existing QMPs), the process of

approving the metallurgical process will be nearly concurrent with the task of establishing

the process control reference distribution for the QMP and registering the QMP with an

existing DVS. In such cases, the mechanical property testing developed for the QMP does

serve as an acceptance criterion, but it is tracked as part of the DVS registration process.

5.1.7 Surface Texture and Detail Resolution Metrics (Reference Parts)

[AMR-6I] Surface texture and detail resolution capability of a QMP shall be documented

and quantified using Reference Part(s).

The surface texture and detail rendering metrics are to be established at the center of the build

plate and at the furthest location for beam reach of the build plate area. The Reference Part shall

be designed with quantitative metrics to establish QMP surface texture and detail resolution

performance and to aid in future monitoring and qualification of PBF machine performance.

This standard does not apply minimum quality metrics for surface texture and detail resolution

for purposes of qualifying a metallurgical process. The QMP should be refined regarding these

metrics to meet part performance goals or to satisfy material property performance goals, such as

fatigue life. A Reference Part is to document and quantify QMP performance regarding the PBF

part building process. In contrast, the Pattern Plate, section 5.1.3.1, is used to document the

performance of only the energy source and control system in the absence of the PBF process

itself. Like the Pattern Plate, the Reference Part is intended to provide quantitative criteria to

judge process performance and repeatability in future use of the QMP in part builds or in PBF

machine qualification. When used for such purposes, Reference Part metrics defined by the

QMP process may be used as acceptance criteria.

5.1.7.1 Reference Parts


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A Reference Part is to be developed along with standardized metrics to inspect the as-built

Reference Part to quantify surface textures and detail resolution. The nature of the test article is

not specified and may vary with the design needs and priorities of the part, project, or

organization.

For this standard, an AM Reference Part is any standardized part, or parts, used to confirm

performance of the PBF machine. A Reference Part is to be designed with clear features that

serve as metrics of build quality, dimensional accuracy, and process stability. A Reference Part

need not be large and must be such that it can be produced in the furthest locations on the build

plate. Like the Pattern Plate, the Reference Part shall have a defined set of verifiable and easily

measured or quantified features including dimensions, surface texture, and detail rendering. The

Reference Part is used in establishing a QMP, and is the basis by which the QMP documents the

build quality in terms of detail rendering and surface texture. NASA may review the Reference

Part and associated metrics for adequacy.

Commentary: While process control inspections of parts provide considerable reoccurring

evidence of build quality, a standardized article optimized to that intent will more readily

provide evidence, both qualitative and quantitative, to the quality of the geometric

rendering of the process. This information may be used to compare the build quality of

various powder lots, or as an indication of developing optical or mechanical issues in the

PBF machine. The test article does not need to be large. NASA, NIST, and other

organizations have proposed such articles. The primary intent is to have surface texture

(or roughness) measurements on indicative surfaces such as horizontal surfaces, vertical

surfaces, 45-degree overhanging surfaces, and open-passage free ceilings. For

quantifying detail resolution capability, this may be as simple as a series of holes,

protrusions, or radii of decreasing size, such that the smallest size maintaining its form

may be used as the metric. There may be many more useful or informative options for

measuring detail resolution appropriate to the intended purpose of the QMP. Once

established, the Reference Part and inspection method along with the resulting metrics are

documented as part of the QMP.

5.1.8 Customized QMP

[AMR-6J] QMPs that have been customized for specific performance characteristics shall

be identified and shall include appropriate process control witness evaluations that may be

employed to confirm the performance characteristic is achieved.

Customized QMPs are distinguished from typical QMPs by having specific controls on the

metallurgical process to achieve a particular performance characteristic important to successful

use in design. If these unique process controls are required to achieve a performance

characteristic that is reflected in the design value suite and assumed present by the structural

design assessment, then the QMP is to be identified as a Customized QMP (CQMP). QMPs


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representing typical optimization of the metallurgical process for an alloy to achieve expected

performance under conditions common for the alloy class are not considered Customized QMPs.

Commentary: The following is an example of a Customized QMP. Components for a

critical, high-performance liquid helium transfer pump are to be designed and

manufactured with the AM process. A metallurgical process which targets optimal

ductility and toughness in an AM version of the Ti-6Al-4V alloy at -269C is desired. Such

a process could entail unique controls on the oxygen and other interstitial content of the

feedstock powder and final product as well as uniquely controlled thermal processing. If

these unique process controls are required to achieve performance (cryogenic fracture

toughness) that is reflected in the design value suite and assumed present by the structural

design assessment, then the QMP is to be identified as a Customized QMP (CQMP). The

CQMP needs to identify a quantifiable metric to confirm the unique process controls have

been properly implemented. In this example, the CQMP may find it sufficient to specify a

minimum notched-tensile ratio requirement using smooth and notched-tensile tests at

cryogenic temperature in addition to the standard witness specimens.

5.1.9 Qualified Metallurgical Process Record

[AMR-6K] The responsible materials and processes organization(s) shall evaluate

candidate metallurgical processes for approval as QMPs. Once approved, a QMP shall be

documented in a configuration-controlled record that can be referenced explicitly by a

QPP.

The development of candidate QMPs is the responsibility of the build vendor. The approval of a

QMP is the responsibility of the design vendor. The QMP is the fundamental connection

between material design assumptions and actual build execution. A partnership between design

and build vendors, if not the same entity, is required for successful implementation of these

requirements.

The format of the QMP record is not specified, but four distinct sections are expected:

a. definition of the QMP (powder controls, fusion process, and thermal processes),

b. metallurgical acceptance criteria for build acceptance when required by a QPP,

c. Process Control Reference Distributions and acceptance criteria for tensile and fatigue

witness performance, and

d. documentation of acceptance, including test results, micrographs, surface texture/detail

rendering metrics, QMP Pattern Plate with metrics, and other criteria used to qualify the

metallurgical process.

Once approved, a QMP shall be considered locked such that no changes are allowed without

formal re-evaluation and approval. A QMP may be treated as proprietary information. NASA

may review a QMP and its supporting data at any time.


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5.1.10 PCRD

[AMR-6L] Each QMP shall have associated Process Control Reference Distributions

(PCRDs) for tensile and fatigue properties. Witness specimen test acceptance criteria

associated with the PCRD are documented within the QMP.

Four PCRDs are required for each QMP: ultimate tensile strength, yield strength, elongation, and

fatigue life at a fixed cyclic stress condition. The PCRDs and their associated acceptance criteria

are documented as part of the QMP record. The role of the PCRD is to provide a measure of

statistical process monitoring in the AM process of producing Class A and Class B parts.

Because QMPs are PBF machine-specific, each PBF machine has PCRDs to monitor tensile and

fatigue performance of material produced to the QMP. The PCRDs will monitor both the

performance of the specific machine (e.g., beam quality) as well as systemic performance

metrics such as powder lot quality. Initially, the PCRDs are to be based upon the mechanical

property capability tests reported with the qualification of the metallurgical process. When the

QMP is placed into service, the quantity of data available to define the PCRD will grow rapidly

from the witness sampling process.

The type of distribution used for the PCRD is not dictated by this standard and should be set

based on observation of the data and standard distribution checks, such as Anderson-Darling.

(The MMPDS and CMH-17 have considerable information for the task.) Any appropriate

distribution and associated characteristic parameters may be used to define the PCRD. It is

recommended the PCRD utilize the simplest distribution that sufficiently models the data to

provide process monitoring. In the case of tensile data, the expectation is that a normal

distribution will be found sufficient for this purpose. In such case, the PCRD is simply defined

by two numbers: the estimated distribution mean and standard distribution. For the fatigue

PCRD, a distribution is fit to the cycles-to-failure data. These data may be transformed by fitting

the PCRD to the logarithm of the cycles-to-failure data. The choice of fatigue specimen and

testing conditions must be compatible with the demands that accompany the continuous nature of

witness specimen testing.

Commentary: The fatigue witness specimen and test conditions are not specified to allow

for user flexibility. To provide guidance, the following recommendations are provided for

the fatigue witness specimen and test procedure. The vertical, as-built surface is an

acceptable test condition. It has the advantage of reduced specimen preparation cost and

provides a good measure of process control for parts dependent upon unimproved surfaces

in fatigue-critical areas without higher debits and variability that accompanies fatigue of

overhanging build surfaces. For parts not dependent on as-built surface quality, a fatigue

specimen surface representative of the part may be a better choice. The test may be run at

a positive load ratio to eliminate the need for reversing load conditions. The cyclic stress

level is best chosen to provide failure in 250,000 to 1,000,000 cycles, which maintains a

predominantly high cycle fatigue initiation mechanism but test times of only a few hours.


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Special considerations may be needed for materials with low yield strength, high

hardening, and good fatigue strength, such as the 18-8 stainless steel family, where

stresses needed to fail witness specimens in the target cycle life may initially be above the

monotonic yield. Low cycle fatigue testing may also be used for the PCRD if considered

more appropriate to application. If cyclic stresses exceed the cyclic proportional limit,

strain-controlled test methods (e.g., ASTM E606) are to be utilized.

Figure 4. PCRD acceptance testing and DVS compatibility

Commentary: Figure 4 represents the interaction of PCRD testing and the DVS. The

PCRD is used to accept process control witness specimen (PCWS) results in tensile and

fatigue taken from part builds and characterization builds. The DVS must maintain

compatibility with the tail of the PCRDs. The DVS is also informed by, and needs to be

compatible with, testing from characterization builds, which will include conditions far

broader than PCRD tests, as well as tests from first article mechanical evaluations and

other such sources.

5.1.10.1 Acceptance Testing with PCRDs

The witness sampling criteria of section 5.2.2.2 are set to minimum quantities that allow a

reasonable engineering assessment to be made, on a part-by-part basis, that the AM process did


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not experience systemic deviations in process control during the build of any given part. A

stronger case for process control is possible for build runs of multiple parts or where a PBF

machine is in steady state operation on a day-to-day basis for a given QMP. It is strongly

recommended that witness specimen results be continuously plotted on a control chart for each

QMP (specific to process and PBF machine). Trending will enable earlier detection of process

drift and the potential to take corrective action prior to impacting part production. Successful

demonstration of process monitoring and implementation of statistical process controls through

witness specimens may be used to petition for reduction in witness specimen quantities for cases

where steady-state production or long build runs of parts are in place.

The minimum number of tensile witness specimens for use with the PCRDs is six, a bare

minimum to allow an evaluation of mean and an estimate of variability. The results from the

tests are to be compared to the ultimate strength, yield strength, and elongation PCRDs utilizing

criteria that will identify when a meaningful change in the process may have occurred. There are

an abundance of statistical methods available for such purposes. For ultimate and yield

strengths, this standard allows for any method that identifies both changes in mean and changes

in variability. Due to expected variation and the limited size of the data set, acceptable criteria

for elongation need not directly assess variability, but are to evaluate for a decrease in the mean

with a limit on the lowest individual tested value. The chosen methods and associated rationale

shall be documented. The methods chosen to evaluate the witness specimen acceptance criteria

should be implemented in the simplest possible form in the QPP.

Commentary: The required assessment of witness specimen results relative to the PCRD

does not need to be sophisticated. Very simple spreadsheet tools are more than adequate

to perform the checks. There are also many options available. It is recommended to use

simple statistical modeling with random number generation and iteration (Monte Carlo

method) to predict the effects of acceptance criteria choices prior to implementation. A

very effective choice is the Anderson-Darling test that determines if sampled data likely

belong to a specified distribution. Other simple choices would be the t-test for difference

in means and the F-test for differences in variability. The significance level (commonly

designated Alpha) for hypothesis tests needs to be chosen to balance likelihood of rejection

with sensitivity to process drift. A value of Alpha = 0.05 is recommended. Simply defined

bounds on the allowable difference in means and standard deviation between the witness

set and the PCRD values are also feasible, but rationale for the choice of bounds needs to

be documented. Considerable discussion on this topic is available in DOT-FAA-AR-03-19

and CMH-17 under the topic of “determining equivalency between an existing database

and a new dataset for the same material.”

Judging acceptance against the PCRD for fatigue is not as rigorous because only two specimens

are required for pragmatic reasons. The acceptance requirement for fatigue witness specimens is

the average fatigue life of the two tests exceed the lower 95% probability bound of the fatigue

PCRD. This provides a very simple acceptance evaluation at the QPP level.


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Commentary: Though less rigorous in statistical significance, the fatigue acceptance tests

are no less important. There are many failure modes in the AM process that are largely

benign to monotonic mechanical tests that readily influence the fatigue capability of the

material with respect to initiation and propagation of damage.

5.1.10.2 PCRD Maintenance

The PCRDs are to be reviewed or updated on a regular basis to incorporate witness data. Update

interval should not exceed 30 builds or whenever a witness set fails to meet the PCRD. Initially,

lot variability may be lacking in the PCRD data set and adjustments may be expected. Careful

review is required whenever a PCRD is adjusted. NASA is to be made aware when PCRDs are

adjusted to broaden variability or lower the mean value.

Witness specimen data that fail to meet the PCRD acceptance criteria require particular attention.

As part of the review and disposition of the non-discrepancy associated with the witness test

failure, the failing witness data are to be marked for inclusion or exclusion from the PRCD

update process. Failing data associated with known, non-relevant process escapes, such as

mechanical testing errors, may be excluded. Failing data associated with unique process escapes,

such as heat treating errors, may be excluded if corrective actions are taken. Failing data that

cannot be associated with an identified and corrected process escape is to be included in the

PCRD update unless specific rationale can be presented for exclusion.

Compatibility between the PCRD and any registered DVS is to be confirmed at each review or

update.

5.1.11 Registration of QMP to a DVS

[AMR-6M] Prior to use in Class A or Class B parts, the QMP shall be registered to a DVS.

Commentary: The DVS for an AM product has a “parent” QMP or CQMP associated with

it. This is the original QMP used to form the first data sets and define the fundamental

metallurgical requirements reflected in the DVS for the material. It is considered

registered by default. Given that QMPs are machine-specific, a methodology to associate

other compatible QMPs with a DVS is required. This methodology is intended to

adequately manage the risk of using the DVS specific to an AM alloy and condition with

compatible QMPs. Without the QMP fully represented in the DVS, there remains risk that

the AM product may not comply. Given the registration requirements and required

process control monitoring, the likelihood of this occurring is considered acceptably

mitigated.

A candidate QMP is considered registered to a DVS after the following are confirmed and

documented:

a. Metallurgical and powder chemistry controls are consistent with the parent QMP

b. PCRD for strength is compatible with the DVS at the 99/95 tails,


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c. Candidate QMP strength data should be statistically combineable with that used in

developing the DVS, e.g. Anderson-Darling tests. If not, document how DVS

accommodates the difference.

d. PCRD for fatigue is consistent with DVS fatigue design values

e. The results of the following tests of material from the QMP must be consistent other data

supporting the DVS

i. Tensile tests at temperature: High and low bounding temperatures and key

locations of strength gradients with temperature, 3 tests at each temperature

ii. High cycle fatigue tests at the bounding as-built surface condition (section 4.6.7)

tested at cyclic conditions where DVS predicts failure at 500,000 cycles using

typical basis for ambient laboratory air. Average of five tests is to lie within the

scatter of existing data.

iii. Low cycle fatigue tests using a surface condition present in the DVS data tested at

a strain range of user’s choice that facilitates comparison. The average of five

tests is to lie within the scatter of existing data.

iv. Fracture toughness tests at ambient conditions. The average of three tests is to

fall within the statistical range of existing DVS data.

For a CQMP or to enable part use in damaging environments, the candidate QMP registration is

to also include evaluations that demonstrate the adequacy of the material’s performance under

those conditions.

5.2 Part Process Control

Part process control encompasses all part production processes beginning with the PBF machine,

through final part acceptance. Part process control is defined by the content of the part drawing

and part development plan. Part process control is implemented through a comprehensive part

traveler system ensuring orderly and documented execution of all drawing and PDP

requirements. The authority to proceed with part production follows a successful manufacturing

readiness review, where the part process is “locked” and documented as a Qualified Part Process

(QPP). The QPP specifies the QMP, drawing, PDP, traveler, acceptance of first article

evaluation, and all electronic files used in the part production process.

5.2.1 Part Development Plan

[AMR-7] A Part Development Plan (PDP) is required for all parts of Class A1 through

Class C1.

In conjunction with the drawing, the PDP documents all necessary information about the

production of AM parts as required by this standard. The combined content of drawing and PDP

shall be sufficient to develop a proper build traveler controlling the execution of the part build.

Control of the part production process shall ensure that all requirements of the PDP are met. The

PDP is to be under configuration control. The form and format of the PDP is not specified, It


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should be customized to suit the prevailing engineering and quality control documentation

system. The PDP may refer to other available, configuration-controlled documentation as

desired to streamline the document. The minimum required content of the PDP and part drawing

is contained in this section and summarized as a list in Annex 1. The PDP for Class C1 parts is

only required to convey necessary information for part process control not readily placed on the

drawing. Class C2 parts do not require a PDP.

Commentary: The purpose of the PDP is to consolidate all the requirements of AM part

production into a drawing companion document that governs the design, development, and

production of an AM part. This level of planning is required due to the complex, process-

sensitive nature of building parts with AM. The AM process currently has minimal

standardization; yet, the process presents numerous opportunities for deviations capable

of influencing part quality. Due to this complexity and lack of standardization, it is

recommended that the PDP be the controlling process referenced by the drawing to

control the production of the part. The PDP may be divided into individual sections or

volumes to control dissemination of information. For example, because the PDP

documents design-related information such as rationale for part classification, first article

evaluation requirements, or rationale for witness sampling, this content may be separated

from content required for actual part production and processing.

5.2.2 PDP Design Information

To serve its function, the PDP is to include a brief summary documenting key outcomes of the

design and assessment process. The following content is expected: material, operating

environment(s), model views of the part highlighting critical features, the part classification,

summary rationale and content used for each classification determination (consequence of

failure, structural margin, and AM risk), definition and rationale for witness sampling, and first

article evaluation requirements. For parts with low structural margin, a brief list of key

governing margins is to be documented for considerations in witness sampling. For parts with

high AM risk, the location and nature of risk areas on the part are to be identified. As

appropriate, this section of the PDP may be separate from content defining the build process and

part processing requirements.

Commentary: The PDP will be the primary means to understand the status of an AM part

in the context of its design and intended use for those responsible for defining and

assessing its overall rationale for service. This includes members of diverse communities,

such as the manufacturing readiness review team and the fracture control community, who

are asked to evaluate the part in its overall context to determine if witness controls,

planned inspections, acceptance tests, etc., are sufficient to adequately mitigate the risks

associated with the part. An accurate, thorough, but concise summary of design

information in the PDP is important to achieving consensus for control of AM parts.


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5.2.2.1 First Article Requirements

[AMR-7A] The PDP for all Class A and B parts shall include a first article assessment plan

addressing the requirements in the section.

The first article evaluation is based upon the finalized build configuration including all parts,

supports, and witness specimens, and is to include all part processes beginning with PBF through

final part inspection, acceptance, and marking. If multiple parts are built simultaneously during

a build, a representative subset of the parts may be used for the first article evaluation. The first

article evaluation plan is to include a complete description of each stage of the evaluation, with

emphasis on evaluations needed as the part proceeds through processing. Some first article

evaluations may require more than one part to adequately capture all objectives. The first article

evaluation plan, process, and report should follow the intent of SAE AS9102, Aerospace First

Article Inspection Requirement. At a minimum, the first article evaluation plan should address

the following topics, though relevance and importance is expected to vary by part:

• Powder removal and confirmation techniques

• Platform removal procedures

• Thermal processing procedures

• Dimensional inspections, accessible and post-sectioning

• Surface improvement procedures, sufficiency and coverage

• Surface texture measurements, accessible and post-sectioning

• Part sectioning cut plans

• Testing within part: metallography, chemistry, mechanical (QMP to be confirmed)

• AM risk area evaluations - sectioning and tests shall target any high AM risk areas of the

part

• Witness specimen evaluation - All defined witness specimens for the build shall be tested

and reported

• Part post-processing - Evaluation of part post-process machining or surface treatments

• Part cleaning requirements

Commentary: It is expected that a number of preliminary “first article-type” evaluations

may occur during the part development process. The formal first article should only be

implemented after all part development processes are finalized. Changes following the

formal first article evaluation and approval of the QPP may require re-qualification. It is

recommended that the first article plans be submitted for review by the MRR team prior to

execution to ensure adequacy of the plans and a successful MRR.

5.2.2.2 Witness Specimen Requirements

[AMR-7B] All AM builds of Classes A1 through C1 shall contain witness specimens for

process control in accordance with this section.


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The witness specimen requirements are given in Tables 3a and 3b. Table 3a specifies minimum

specimen quantities and Table 3b provides a summary of the basis for acceptance of witness test

results. A description of each test type, its intended use, and methods of acceptance follow. All

witness specimen testing and acceptance criteria are to be clearly documented in the PDP. If a

witness test fails to meet the defined acceptance criteria, a non-conformance against the part is to

be documented in the QMS per section 5.2.10.

Commentary: These witness specimens are intended primarily to identify systemic losses

or drifts in process control. By their nature, build witness specimens represent a small

sample of the spatial (location in build volume) and time aspects of the build; therefore,

they cannot necessarily insure against local, transient, or intermittent loss of process

control during a build.

Tensile testing is required for evidence of fundamental process control on a part-by-part basis

and for continuous monitoring of the AM process. Tensile witness specimens are to be oriented

in the vertical (Z) direction and utilize the same geometry of the specimens used to establish the

PCRD for the QMP specified by the QPP. Tensile test specimens shall be represented in the full

Z-height of the build and, to the degree possible, be positioned behind the part relative to the

travel direction of the recoater. For Class A and Class B parts, tensile test witness results are

compared against the appropriate PCRDs as described in section 5.1.10.1. Tensile test results for

Class C parts are assessed according to specified engineering requirements or are provided for

engineering information only.

Commentary: Tensile specimens are commonly stacked atop each other to cover the Z-

height of the build. Depending on the part height and tensile specimen design, more than

one stack is generally needed. The best policy is to allow for alternating tensile specimen

gage locations in the stacks to provide the best possible test coverage of the Z-height.

Metallographic witness specimens are to be prepared and evaluated against the criteria defined

by the QMP. In Class A1 and A2 part builds, the second metallographic specimen shall be

placed to evaluate a second point in the build with respect to location and time. If a witness sub-

article(s) is being produced and evaluated metallurgically, this will account for one of the

metallurgical specimens.

Chemistry of the final build product shall be confirmed for Class A1 and A2 parts. Methods

capable of confirming the full chemistry shall be specified in the QPP. With documented

rationale in the QPP and approved at the MRR, chemistry may be omitted for alloys considered

insensitive to subtle chemistry variations.

Commentary: An example of a “chemistry insensitive” material for these purposes would

be the common Cobalt Chrome alloy used frequently used in AM processes. An example of

alloys considered chemistry sensitive would be those with a complex chemistry reliant

upon small quantitates of constituents to drive precipitation kinetics for proper


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performance, such as UNS N07718. A CQMP with custom chemistry controls would also

be considered “chemistry sensitive” and require confirmation in these classes.

High cycle fatigue testing of a minimum of two specimens is required for Class A and B parts.

These tests are to be performed using the identical specimen design, preparation, and cyclic

stress conditions used for the high cycle fatigue PCRD. Acceptance is evaluated against the

PCRD as described in section 5.1.10.1.

Low Margin Point testing is required for Class A1 and A2 parts, which have catastrophic failure

consequence and low structural margin. The tests are mandatory, but the type and quantity will

be specified based on the structural conditions present in the part. Each build in these Classes is

to be evaluated by testing the material directly at these conditions. A single test point or an

average of test results must exceed the value specified for that material property in the DVS.

Commentary: In the PDP, the structural analysis summary is to include a review of the

governing structural margins for the part, that is, the lowest margin(s) for structural

criteria other than ultimate strength, yield strength, or local point strain. Strength and

ductility related performance is covered by the required tensile tests. The low margin

criteria include conditions such as high or low cycle fatigue, fracture life, creep, etc.

Usually, a part will be challenged with only one such condition; however if multiple

critical conditions are present, each should be evaluated. For example, if a part design is

governed primarily by thermally driven low cycle fatigue, then at least one low cycle

fatigue test specimen from each build shall be tested in a method consistent with that used

to develop the low cycle fatigue properties in the DVS directly at the part’s design point

for temperature and cyclic strain range. If the same part also had a governing high cycle

fatigue condition superimposed, a point design test for high cycle fatigue would also be

run at the temperature, stress ratio, and cyclic stress range defined at that location in the

part. The test approach needs to match that in the DVS such that the result can be

compared equitably against the value for that condition in the DVS. Though only one test

data point is required for process control witness of Low Margin Point testing, it is

recommended that duplicates or more be allowed for during build planning to

accommodate potential specimen losses during testing.

Witness Sub-article testing is specified for builds with high AM Risk. The use of witness sub-

articles is not mandatory for every part. They are intended to witness critical areas of a build

with high risk as a sub-article, or local feature of a part—a concept enabled by the AM process.

Witness sub-articles may be required to provide sufficient process control evidence for part

features that cannot otherwise be inspected or verified in the part directly. Witness sub-articles

may be utilized for any appropriate evaluation: mechanical, metallurgical, dimensional, surface

texture, calibration of non-destructive inspection tools, etc.

Class A1 parts require one Witness Article be evaluated for every six flight parts produced. The

Witness Article shall be evaluated according to the First Article plans and criteria.


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Customized QMPs that maintain special controls on the metallurgical process to provide specific

performance characteristics require witness testing to verify that characteristic. CQMP

verification testing is required for Class A parts and recommended for Class B parts. CQMP test

requirements will generally be unique to the QMP.

Table 3a. Minimum quantities of witness specimen types by part class

Class

A1 A2 A3 A4 B1 B2 B3 B4 C1 C2

Tensile 6 6 6 6 6 6 6 6 2 -

Metallography 2 2 1 1 1 1 - - - -

Chemistry 1 1 - - - - - - - -

HCF 2 2 2 2 2 2 2 2 - -

Low Margin Point A/R A/R - - - - - - - -

Witness sub-article A/R - A/R - A/R - - - - -

Witness article 1 for 6 - - - - - - - - -

CQMP A/R A/R A/R A/R A/R A/R - - - -

Notes:

A/R = As required when specifed in the QPP

Table 3b. Basis for acceptance of witness specimen results

Class

A1 A2 A3 A4 B1 B2 B3 B4 C1 C2

Tensile (UTS and YS) PCRD PCRD PCRD PCRD PCRD PCRD PCRD PCRD Min -

Tensile Elongation PCRD* PCRD* PRCD* PRCD* PCRD* PCRD* PRCD* PRCD* Min -

Metallography Comp Comp Comp Comp Comp Comp - - - -

Chemistry Comp Comp - - - - - - - -

HCF PCRD PCRD PCRD PCRD PCRD PCRD PCRD PCRD - -

Low Margin Point DVS Min DVS Min - - - - - - - -

Witness sub-article Comp - Comp - Comp - - - - -

Witness article Comp - - - - - - - - -

CQMP A/S A/S A/S A/S A/S A/S - - - -

Notes:

PCRD = Process Control Reference Distribution

PCRD* = Process Control Reference Distribution, mean and lowest value criteria.

A/S = Acceptance as-specifed in the QPP

Comp = Comparative assessment based on defined criteria in the QMP or QPP.

DVS Min = Results shall exceed the value in the design value suite for that point condition

Commentary: There are significant programmatic risks associated with the timing of

witness specimen evaluation relative to part production rates and monitoring of process

stability. It is highly advantageous to optimize the return rate on witness specimen

acceptance to reveal potential systemic process control issues as quickly as possible.

5.2.3 Part Models, Build Assemblies, and Associated Electronic Data


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[AMR-8] All electronic data files used to define the AM process for a part shall be

documented in the QPP, properly verified prior to use, archived, and maintained fully

traceable.

This requirement includes any electronic data source or record that would be needed to fully

reproduce the build process from the original design state. When the part process control is fully

mature and ready to be locked, each critical file associated with creating the build is to be

identified by filename and its cryptographic hash in either the PDP, build traveler, or

summarized in the QPP. Each of the files shall be properly archived with necessary safeguards

against loss.

Electronic data that contains information considered proprietary or controlled under regulations

such as the International Traffic in Arms Regulations shall be marked. Appropriate access

control to data marked with restrictions must be maintained at all times in the process of

producing AM parts.

Commentary: The variety of files required to execute the AM process can be large. This

includes, but is likely not limited to, part CAD files, neutral geometry definition files,

witness specimen geometry files, the assembled part build file (parts, witness specimens,

and support structures), STL files, slice files, parameter files, log files, and execution

scripts. These electronic records must be considered in the same context of material

traceability. It is required to know the source of each file and any parent-child

relationships between files. In some cases, file operations are transient such as the export

of an STL or slice file. In these cases, log files must document all parameters controlling

the operation.

Any logical location may be used to document these files. Files related primarily to the

design process such as native CAD geometry and exported geometry neutral files may be

best documented in the PDP. Files necessary in the execution of the actual build may be

better documented in the process traveler or in the summary QPP.

The method chosen to enable continued verification of the integrity of the electronic files is

to identify them by their cryptographic hash. Information on cryptographic (secure) hash

can be found in NIST publication FIPS 180-4 Secure Hash Standard. (For clarity, FIPS

180-4 is not levied as a requirement, only information.) A file’s cryptographic hash is

generated with an algorithm designed to detect the slightest change in the content of a file.

The intent is to prevent accidental changes to file content, loss of revision identification,

data loss in file transfer, and other such cases that may endanger the integrity of the

certified design content. The MD5 or SHA-1 cryptographic hash function is recommended

for these purposes. Though MD5 and SHA-1 have vulnerabilities for security-sensitive

applications, each is sufficient for monitoring data integrity in this scenario. Tools to

generate and compare the MD5 or SHA-1 hash are common and commercially available.

In considering where to document the files and hashes, consider that verification of a file’s


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MD5 or SHA-1 hash is most easily accomplished with access to the copy-and-paste

operation.

The following example demonstrates the intent of the hash requirement and intended use.

After transferring a large build file to the PBF machine, the operator will generate the

hash of the transferred file. The newly generated hash is compared against the reference

hash documented in the QPP, ideally by a simple copy and paste into the hash generation

software. If identical, this verifies the identity and integrity of the transferred file to be

exactly as specified by the QPP, independent of filenames or other identifiers.

5.2.3.1 Model Integrity

[AMR-8A] Methodologies used to ensure model design integrity is maintained throughout

the AM process are to be documented in the applicable quality management system.

The integrity of the certified design must be maintained in the process of producing the AM part.

Just as standard processes exist to confirm part drawings properly specify final part configuration

prior to release, a similar process is required to check the integrity of the actual solid models and

any associated information containing design intent, such as reduced dimension drawings.

Design integrity must also be maintained throughout the AM-related manipulations of the post-

design electronic data, including error-free creation of stereolithography (STL) files with proper

resolution, and generation of AM platform-specific slice files. This methodology is to be

enforced through the applicable quality management system.

5.2.4 Build Execution, General Policies

[AMR-9] For Class A and Class B parts, the following general policies shall govern the

build process.

a. The QPP shall specify the applicable powder recycle state limits based on the DVS or

section 5.1.2.2. The powder recycle state of the PBF machine is to be known and

documented as compatible with the QPP specification.

b. The build is to run to completion without unplanned intervention. Any intervention shall

be documented as a non-conformance (section 5.2.10).

c. Any build interruption resulting in unintended Z-position motion may not be restarted,

except if converted to a Class C part.

d. Any build that pauses with no loss of Z-position or atmosphere control may be restarted

within a time limit explicitly defined in the QPP. The restart criteria shall be supported

by comprehensive test data and represented in the development of the DVS.


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e. The content of the build plate may not be altered relative to that used in the first article

qualification process. There shall be no parts added, subtracted, or rearranged in the

build.

f. Available process monitoring and data logging shall be maximized.

5.2.5 Production Planning Record

[AMR-10] The QPP shall include a comprehensive production planning record to

sequence and document the execution of all actions needed to produce the AM part.

The core of the QPP is the production planning record, or traveler, that controls all aspects of the

AM production process. The methodology for developing and implementing production

planning records shall be controlled through the quality management system. As a quality

record, the planning record may also be used as the documentation source of process control

information and, depending upon its implementation, a record of verifications made during the

process.

The production planning record shall be comprehensive and adapted to the specific operational

environment of the AM facility. All steps with bearing on the outcome of the part are to be

represented in the planning record. The planning record may reference other checklists or

operating instructions that are actively maintained as part of the quality management system.

The process planning shall ensure the recording of part-specific information required by the

QMP or other parts of the overall QPP. For example, if the QPP allows multiple QMPs

(machines) to produce the part, there will be specific information required to document the

implementation of the QPP, such as which QMP is in use, the powder lot number in use, the

powder lot recycle status in hours or builds, the build-plate dimensions required by the QPP, etc.

NASA may review production planning records as its discretion.

Commentary: Operations will always differ at every facility, particularly in a new and

unstandardized field such as AM. It is highly recommended that the AM facility conduct a

Process Failure Modes and Effects Analysis (pFMEA) to facilitate thorough

implementation of controls in the production planning record and that all steps with

influence on the AM part be represented in the planning record. Guidance on the pFMEA

approach can be found in SAE J1739.

5.2.6 Post-build Operations

[AMR-10A] Through the PDP, drawing, or production planning documents, the QPP shall

specify explicit controls and sequencing for all post-build operations for all Class A and

Class B parts.

5.2.6.1 Green Part Inspections


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[AMR-10B] Prior to post-build processes that may alter the as-built state of the part, all

parts shall receive, at a minimum, full visual inspection to record any indications of build

anomalies.

Build anomalies include, but are not limited to, witness lines on the part surface, unusual

discoloration, laminar defects such as cracks or tears, separation of part from support structures,

and geometric distortion.

5.2.6.2 Powder Removal

[AMR-10C] The QPP is to provide specific procedures for removing powder post-build for

any part with geometry precluding line-of-sight confirmation of powder removal. Methods

to confirm powder removal prior to further part processing shall also be specified.

Commentary: Removing residual powder following the HIP process may not be feasible,

therefore it is important that all passages are verified clear of powder prior to this step.

Proper cleanliness may be impossible to achieve later in post processing, particularly for

debris-sensitive hardware.

5.2.6.3 Platform Removal

The production planning record (and PDP, if warranted) must unambiguously specify the

sequence of part removal from the build platform relative to other post-build operations as well

as control the method of platform removal.

Commentary: Considerations in sequencing platform removal include dimensional control

of the part and stress relief operations, powder removal considerations, effect of the mass

of the build platform in heat treating operations, etc.

5.2.6.4 Repair allowances and procedures

The QPP shall include explicit provisions controlling any operation used to repair or improve the

condition of the part due to defect.

For Class A and Class B parts, repair operations are not allowed without prior written

authorization from the design vendor. All repair operations are to be fully documented as part of

a non-conformance record in the quality management system (section 5.2.10) and delivered with

the certificate of compliance for the part. Repair polices for Class C parts shall be as stated. Part

operations that constitute a repair include, but are not limited to, blending, sanding, grinding,

machining, welding, or brazing for the purposes of defect removal.

5.2.6.5 Machining

All machining operations to achieve the final part geometry are to be controlled and sequenced

by the production planning documentation to comply with the PDP and drawing requirements.


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Commentary: Machining operations need to be properly staged relative to joining

operations, inspections, and thermal processing.

5.2.6.6 Welding

[AMR-10D] All welds on Class A or Class B parts shall be developed and qualified to an

appropriate aerospace welding specification. Similar controls are recommended for welds

in Class C parts. Weld lands shall be prepared to remove all remnants of as-built PBF

surface.

This standard does not levy inspection requirements for welds in AM hardware. Inspections are

dictated by standard practice based on the class of weld or the fracture control classification of

the weld.

Welding operations are to be properly sequenced in the post-build operations, particularly with

respect to heat treatment, to optimize weld performance and to minimize weld residual stress.

Commentary: Available experience in welding of AM materials indicate weldability

similar to wrought product forms of the AM alloy. Welding standards will typically be

levied by the overall program or project. Examples of potentially appropriate welding

standards include AWS D17.1, NASA-STD-5006, or MSFC-SPEC-3679.

5.2.6.7 Surface Treatments

[AMR-10E] Any surface treatment operation applied to the part that is influential in the

performance of the part, structural or otherwise, shall be under specific process control.

Surface treatment methods are to be fully developed, demonstrated, clearly specified, and

qualified. The qualified and locked process is to be part of, or referenced by, the production

planning documentation.

Commentary: Surface improvements may be linked to part performance, particularly for

fatigue life and fluid flow characteristics. When a surface condition is specified as part of

the certified design state, it may be associated with specific performance criteria in the

DVS or otherwise. Control and verification of the surface improvement process becomes a

process-sensitive aspect of the post-build operations. Process controls are needed to

ensure consistent processing of parts. The first article process will certify the operations.

Following certification, no changes to the process can occur without proper review and

approval.

5.2.6.8 Cleaning

[AMR-10F] Part cleanliness requirements compatible with the contamination control plan

for the hardware shall be specified on the drawing or in the PDP. Cleanliness levels and

methods of verification are to comply with appropriate governing standards such as IEST-


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STD-CC1246 or MSFC-STD-164. The QPP shall specify all cleaning operations needed to

meet and verify the specified part cleanliness requirements. AM parts used in oxygen

service shall have specific rationale in the PDP addressing required particulate cleanliness.

Commentary: Cleanliness in AM hardware is a significant concern, primarily for two

reasons: first, the as-built surface finish contains partially fused powder particles that are

difficult to remove without abrasion, but that may be liberated under strain, vibration,

fluid flow, or other actions; second, the AM process allows for design details, such as

small, convoluted passages, that are particularly difficult to get clean of particulate debris.

It is important that cleanliness levels for both nonvolatile residue and particulate

contamination are specified. For AM parts in oxygen service, the rigor of the particulate

cleaning operations requires careful review. The compatibility of the system having AM

parts act as a source of particulate debris in the oxygen flammability assessment will

influence the required cleanliness level and the effort required to achieve it.

5.2.6.9 Part Marking and Serialization

[AMR-10G] All Class A and Class B parts shall be marked with part identifiers and serial

numbers. Though recommended, Class C parts do not require marking and serialization.

Incorporation of a static part identifier directly to the build geometry is acceptable as long as it is

protected during post-build operations. The use of the build process to include serialization is

not compatible with a locked, unchanging electronic definition of the part and is not to be used.

The location and method for all marking is to be indicated on the drawing.

5.2.6.10 Packaging shipping handling

[AMR-10H] The QPP shall include controls and instructions for proper handling,

packaging, and shipping of the part.

5.2.7 Part Inspection/Acceptance

5.2.7.1 Part Integrity

[AMR-11] All parts in Class A and Class B shall have rationale documented in the PDP

assuring part integrity commensurate with its consequences of failure and associated

requirements.

Commentary: As discussed in the Scope section 1 of this standard, the largest latent risk in

the utilization of AM parts in critical spaceflight applications lies in the limitations to

verify individual part integrity. At this time, where process control methods are not

sufficiently developed and qualified to independently verify part integrity, the best AM

designs are not necessarily those that optimally reduce part or weld counts or provide the


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most innovative structural packaging. The best AM designs are those that achieve these

goals tempered by design aspects that allow full verification of part integrity through

inspection or testing.

Because of the extreme diversity of AM parts and use scenarios applicable to this

standard, specific requirements are not levied on the degree of inspection or acceptance

proof testing required for each part. These polices are dictated by the governing

structural safety requirements for the part, such as fracture control. As stated in section

2.2 on governing documents, AM parts are not exempt from the overarching requirements

levied on the system as a whole. AM designs are going to challenge inspection and

acceptance proof testing procedures significantly. It must be recognized that not all AM

parts will have a viable path to flight certification at this time due to limitations in our

ability to verify part integrity. For critical flight applications, the responsibility to

evaluate part integrity rationale will generally rest with the fracture control community,

where the disciplines of material and processes, structural assessment, NDE, and safety

and mission assurance intersect.

5.2.7.1.1 Non-Destructive Evaluation

All Class A and Class B parts are expected to receive comprehensive NDE for surface and

volumetric defects within the limitations of technique and part geometry.

Commentary: Class A parts that are fracture critical and utilize a damage tolerant

rationale require careful attention. At this time, it is not clear that defect sizes from NASA-

STD-5009 are applicable to AM hardware, particularly when as-built AM part surface is

involved. To quantify the risks associated with parts that must demonstrate damage

tolerance, it is incumbent upon the structural assessment community to define critical

initial flaw sizes (CIFS) for the part to define the objectives of the NDE. A demonstration

of adequate life starting from the NASA-STD-5009 flaw sizes is generally inappropriate for

fracture critical, damage tolerant AM parts. Knowledge of the CIFS will allow the NDE

and fracture control community to evaluate risks and communicate meaningful

recommendations regarding the acceptability of the risk. It is recognized that parts in

subclasses 1 and 3 with high AM Risk may have regions inaccessible to NDE. For

understanding these risks, it is important that inaccessible regions are identified along

with the corresponding CIFS. Parts in subclasses 2 and 4 should exhibit much greater

coverage for reliable NDE. The PDP, fracture control report, or NDE plan are

appropriate places to document NDE coverage and corresponding CIFS information.

Many AM parts will require the use of multiple NDE techniques to achieve full coverage.

A combination of radiography, penetrant, eddy current, or ultrasonic techniques may be

common and should be considered. Surface inspection techniques may require the as-built

surface be improved to render a successful inspection, depending upon the defect sizes of

interest and the signal to noise ratio. Surfaces improved by methods such as machining or


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abrasion require etching prior to penetrant inspection to remove smeared metal. Note that

removal of the as-built AM surface merely to a level of visually smooth may be insufficient

to reduce the NDE noise floor due to the propensity for AM near-surface porosity and

boundary artifacts.

The AM process offers a unique opportunity to build hardware for demonstration of defect

detection directly in the part. A demonstration part with simulated CIFS defects, surface

connected and volumetric, can be built with modest development investment. Part-specific

demonstrations of detection capability will be expected while accepted probability of

detection defect sizes are established applicable to AM parts and materials.

In the application of NDE, the types of defects that are relevant to the AM process must be

considered. The physics of the layered AM process tend to prohibit volumetric defects with

significant height in the build (Z) direction. The concern instead is for planar defects, such

as aligned or chained porosity or even laminar cracks, to form along the build plane. This

mechanism has a number of implications: planar defects are particularly well suited for

growth; the primary defect orientation of concern is defined, which may be meaningful in

analysis or with detection methods dependent upon alignment with volumetric defects; AM

planar defects will generally exhibit very low contained volume; the limited Z-height of

planar defects can be demanding on incremental step inspection processes such as

computed tomography. There are longstanding NDE standard defect classes for welds and

castings. The defects characteristic to these processes will generally not be applicable to

the AM process. It is not recommended that welding or casting defect quality standards be

applied to AM hardware. This implies that until an accepted AM defect catalog and

associated NDE detection limits for AM defects is established, the NDE techniques and

acceptance criteria remain part-specific point designs.

5.2.7.1.2 Proof testing

[AMR-11A] All Class A1/A2 and Class B1/B2 parts shall require a proof test as part of

acceptance testing.

It is highly recommended that all AM parts are proof tested as effectively as their design will

accommodate.

In the context of this standard, a proof test is a structural acceptance test procedure applied to

each part either as a process control check (workmanship proof) or to establish the structural

integrity of the part (integrity proof). A workmanship proof test has an important, but secondary

role in ensuring part integrity, typically because reliable and quantitative NDE is in place to

provide sufficient evidence of part integrity. An integrity proof test has a primary role in

assuring part integrity. An integrity proof test may be specified in addition to NDE to add

reliability for critical parts or to mitigate limitations in NDE coverage. The type of proof test,

workmanship or integrity, is to be specified in the PDP to make clear the role of the proof test in


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mitigating risk. The difference between the two proof test types is the degree of part coverage

and quantification of the proof state. A workmanship proof test requires only structural

assessment to determine it is not detrimental to the part. An integrity proof test requires more

involved assessment of proof test conditions relative to flight conditions, including all loads and

environments. The integrity proof test assessment compares local stress states throughout the

part at proof and flight conditions based on directional component stresses, identifying regions of

the part where the proof test is effective. A coverage map of the part illustrating the efficacy of

the integrity proof test is to be documented to help quantify risk mitigation by the proof test. To

optimize part coverage of integrity proof testing, the proof test operations may require combined

load states of pressure, applied external forces, and temperature. Integrity proof tests for

complex parts may need a sequence of operations or load steps. Commonly, unique fixtures are

required to achieve a proper proof test to close volumes for pressurization, properly represent

external or inertial forces, or to spin rotating hardware.

For fracture critical/damage tolerant parts, the integrity proof test assessment may also require an

evaluation of the flaw size screened in proof and the estimated life assured by proof testing.

Proof test cyclic life evaluations may occur analytically or experimentally.

The following recommendations will aid in the successful use of proof testing as a contributor to

AM part certification:

a. Proof test methods should be an integral to the AM design to optimize coverage against

all load cases.

b. The proof test should maintain a minimum proof factor of 1.2 to be considered effective.

c. Considerations of material defect response (fracture toughness behavior) need to be

understood for proof and flight conditions.

d. Multi-cycle proof test methods are highly recommended where the proof conditions are

repeatedly applied to the part between three and five times. This is of particular interest

for certain types of AM laminar defects that may coalesce or sharpen after the initial

proof cycle. Multi-cycle proof test methodology improves reliability under such

conditions.

5.2.7.2 Dimensional Inspections

[AMR-12] The QPP shall be explicit regarding all physical measurements and associated

acceptance criteria required for part acceptance, including dimensional inspections and

surface texture measurements.

Internal measurements may be confirmed utilizing computed tomography provided a part analog

reference is used to confirm accuracy and precision of the measurements and calibration of the

tool and data post processing.

5.2.7.3 Certification of Compliance Records


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[AMR-13] The QPP shall contain a list of all records needed to establish part compliance

with the requirements of the QPP. All such records shall be maintained within the QMS.

All records associated with the part must remain fully traceable, including those provided by

external vendors for operations such as heat treating, machining, or inspection. All non-

conformance documentation is to be included. All witness specimen test results and records are

to be included. When complete, it is recommended that a final certification of conformance

record be generated demonstrating all requirements have been met, all non-conformances

resolved, and that the part is fit for service.

5.2.8 Manufacturing Readiness Review

[AMR-14] Class A and Class B parts shall be subject to a Manufacturing Readiness Review

(MRR) to confirm that the planned production process will achieve an AM part meeting

the requirements of the certified design.

All constituents of a candidate part process are to be assembled for review, including the

drawing, PDP, production planning, successful first article report, and any additional

documentation used to control the part production process. At a minimum, the MRR team shall

include individuals cognizant of the part from the disciplines of design, structural assessment,

materials and processes, additive manufacturing production, and safety and mission assurance.

The MRR team is to review the assembled manufacturing controls for the AM part and confirm

that all necessary process controls and production planning are in place to meet the certified

design intent. If the MRR team is not satisfied with the candidate part process, the MRR team

shall clearly identify all deficiencies. Once deficiencies are corrected, the candidate part process

is subject to another MRR.

At the successful conclusion of the MRR, the approved candidate part process is established as a

Qualified Part Process (QPP).

5.2.9 Qualified Part Process, Modifications

[AMR-15] Following a successful MRR and establishment of the QPP, no changes to the

build configuration and its electronic files or post-build processes is permitted without the

written approval of NASA.

The need for, and degree of, re-qualification of the process following proposed changes is at the

discretion of NASA.

Additional QMPs may be added to a QPP under the following scenario:

a. The addition of the new QMP is the only change to the QPP;

b. The new QMP is to be used by the same build vendor and facility for which the QPP was

established;

c. The new QMP is nominally similar to the baseline QMP;


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d. The new QMP is properly registered to the DVS for the part;

e. The new QMP has documentation of a successful first article evaluation of the part.

Commentary: The primary intention of this process for adding a QMP to an existing QPP

is to facilitate allowing additional PBF machines of identical make and model at the same

build vendor to participate in building parts to the QPP. The notion of “nominally

similar” QMPs means that while fusion parameters may be slightly different due to

machine variability, there are no fundamental differences in the QMPs such as layer

thickness, and that they produce nominally identical metallurgical products including

microstructure, mechanical properties, surface finish, and detail rendering. Expansion

beyond this concept will likely require a new QPP be established.

5.2.10 Non-Conformance Tracking

[AMR-16] All Class A and B parts shall have a non-conformance tracking system defined

and enforced through the applicable quality management systems.

AM parts are subject to the rules governing non-conformance as applied by the project. All

vendors are to be aware of and compliant with the non-conformance tracking system. Any

repairs, indications of cracks, crack-like defects, or NDE indications of undetermined source are

to be elevated to senior review and disposition. Any indication of such defects in occurring

under a QPP is cause for review even if the part is to be scrapped.

Commentary: Each project will generally have its own rules for resolution of non-

conformance items, including which are elevated for higher-level review and risk visibility.

Senior review of crack-like defects is important not only for the integrity of the non-

conforming part, but also regarding the process discontinuity that created the condition.

The common forum for senior non-conformance review in the NASA system is the Material

Review Board (MRB). For fracture critical AM parts, the responsible fracture control

board should be made aware of non-conformances in flight hardware involving defects.

5.3 Equipment Process Control

[AMR-17] The equipment control requirements of this section shall be in place and

verifiable through the Build Vendor QMS prior to production of any Class A or Class B

parts. These controls are not required, but highly recommended for Class C parts.

5.3.1 Equipment Control Plans

[AMR-17A] The PBF Build Vender shall maintain within the QMS an Equipment Control

Plan (ECP) for all PBF machines and associated equipment addressing calibration,

qualification, and maintenance.


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The Build Vendor shall maintain a master ECP. Multiple sub-tier ECP documents may be

maintained in the QMS to cover various machine types and facility situations. All PBF machines

under control of the build vendor are to be addressed by the ECP.

As of this baseline revision of this standard, PBF machines fall into three broad categories that

are useful when considering equipment controls:

Category 1. Single, fixed electron beam, vacuum/low pressure inert atmosphere

Category 2. Single, fixed laser, purged inert atmosphere

Category 3. Moving laser or multiple laser, purged inert atmosphere

5.3.1.1 Maintenance

[AMR-17B] The ECP shall include comprehensive preventive maintenance schedules for

all PBF machines and critical associated equipment as appropriate.

The preventive maintenance schedule is to meet, at minimum, all recommended maintenance

items identified by the PBF machine manufacturer. Additional items unique to the installation or

facility are also to be addressed.

Maintenance records are to be kept within the QMS for every PBF machine and critical

associated equipment.

Commentary: Critical associated equipment may include sieve equipment, measuring or

calibration instruments, etc., that are influential to the successful operation of the PBF

process.

5.3.1.1.1 Computer Security

Maintenance operations are to include continuous, active computer security (cybersecurity or

information technology security) on all computer systems and associated devices, including

storage devices used to transfer files that are associated with any aspect of the PBF part design

and build process.

5.3.1.2 Calibration

[AMR-17C] The ECP shall prescribe calibration requirements and intervals for all PBF

machines and associated equipment as appropriate.

PBF machine calibration and verification shall address all aspects of the PBF system:

mechanical, optical, electrical, software, and firmware. Specification values and allowable

tolerances for all calibration metrics are to be documented in the ECP for each PBF machine.

All aspects of the PBF that are controlled, commanded, or monitored during execution of the

PBF process shall be included in the calibration and verification process. Unless otherwise


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documented in the ECP, all calibration measurements are to be made using NIST traceable

calibration standards.

The list of calibration metrics is to include, at minimum, those identified by the PBF machine

manufacturer used to declare the PBF machine fit for service. Additional verification/calibration

items are likely to occur specific to PBF machine installations. All mechanical movements and

alignments influential to the PBF process, such as platform and recoater arm motion and

alignment, are to be verified within specification or calibrated as required. The laser system and

associated electronic or optical control system, electron beam source and control systems,

atmosphere controls, ventilation, and all sensors are to be part of the specification verification

and calibration process. Software and firmware versions are to be verified.

Calibration interval is not to exceed 180 days.

Upon calibration, if any calibration metric is not within specification, all parts produced since the

last calibration shall be given non-conformance status. This may influence the choice of

calibration intervals to mitigate programmatic risk, particularly for PBF machines whose

calibration stability is not well characterized.

Commentary: This standard cannot prescribe all calibration items that may be required

for any given machine or operational scenario. The build vendor is responsible for

developing a comprehensive calibration routine documented in the ECP. For all

categories of PBF machines, the mechanical movements and alignments of platform,

powder feeds, recoater arm, etc., are to be included as well as sensors or controls that

governor these operations. Atmosphere controls and monitoring sensors (vacuum quality

in Category 1, or purge gas quality and pressure/oxygen level in Category 2 and 3

machines) are to be thoroughly calibrated. In all machine categories, the beam quality is

of obvious concern. For example, in the laser based category 2 and 3 machines, the

following minimum metrics would be expected:

• Laser power

• Beam profile

• Laser spot size and shape, center, edges and corners

• Laser focus length

• Laser on and off rise and fall times

• Laser position controls

• Laser zone alignment and interaction for Category 3 machines.

5.3.1.3 Qualification

[AMR-18] Each PBF machine shall have an active qualification status in order to establish

a QMP or to produce parts in Class A or Class B.

Active qualification status for a PBF machine must be established at installation and renewed

within every 12 months. Active qualification status is nullified by any of the following: changes


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to the machine beyond predefined preventative maintenance, moving the machine, changing the

machine set-up or essential components, any update to software or firmware.

To establish or re-establish active qualification status, each PBF machine is to satisfy all of the

following requirements:

a. Preventive maintenance occurring as scheduled and documented.

b. All defined calibration metrics verified as scheduled and documented.

c. Pattern Plate produced to an appropriate QMP with beam performance metrics

confirmed.

d. Reference Part produced to an appropriate QMP with build quality metrics confirmed.

e. Reference Part Qualification Witness Specimen testing, equivalent to those required for a

material characterization build (section 4.6.12, Class B2), is complete with results

accepted to the applicable QMP.

The qualification status, active or inactive, is to be posted clearly on every PBF machine.

The QMS is to document the qualification status for all PBF machines along with all records

supporting the qualification status.

5.3.2 PBF Machine Operations

5.3.2.1 Checklists

[AMR-19] Each PBF machine shall have detailed operational procedures and

accompanying checklist(s) for all standard operations.

All steps needed to prepare and execute a part build in the PBF machine are to be detailed in

checklists. Production planning records of a QPP are to either include or reference these

checklists. As specified by the QPP, completion of steps may require QMS documentation and

independent verification by the quality assurance organization.

5.3.2.2 Contamination/Foreign Object Debris Control

[AMR-19A] Equipment Process Control Plan shall address the control of contamination

and foreign object debris during all operations of PBF machines and associated equipment.

These controls are to address the specifics of all operations within the PBF machine environment

to mitigate the risk of process contamination. These policies are to be specifically addressed in

the training for all personnel with unsupervised access to the PBF machine environment.

Commentary: The contamination control policy needs to address all potential sources of

powder contamination during handling, storage, processing (e.g., blending/sieving),

machine loading or any other operation. All forms of contaminant such as dirt, dust,

clothing debris, lubricants, solvents, cross-contamination of powder types and lots, are to

be considered and mitigated at an appropriate level. Known contaminants, such as certain


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spray lubricants, are to be controlled or banned from the immediate PBF machine

environment. All tools, fixtures, or other materials that enter the PBF machine chamber

are to be clean and fully compliant with the contamination control plans.

5.4 Vendor Process Control

This standard differentiates two types of vendors for AM parts: a design vendor and a build

vendor. In practice, these may or may not be the same organization and the division of

responsibilities may not lie precisely as stated here; however, all responsibilities are to be

accounted for. The formalities controlling the design and build vendor process apply to Class A

and Class B parts intended for service.

5.4.1 Design Vendor

The design vendor holds the responsibility for establishing and managing the certified design

state to which parts are evaluated and eventually certified. The following responsibilities define

the role of the design vendor:

• Maintain the controlling QMS for managing part quality

• Define part performance and safety requirements

• Design of part — part geometry, post-processing requirements, inspections, witness

specimens

• Select materials and processes and manage the associated DVSs

• Perform structural assessment

• Establish part design certification

• Interface with build vendor(s)

• Manage non-conformances

• Maintain all records with certification of compliance

• Certify the part

Control of the design vendor is beyond the scope of this standard. It is assumed that the contract

through the NASA program or project to produce the hardware will levy appropriate

requirements to assure the design vendor is capable.

5.4.2 PBF Build Vendor

The PBF build vendor holds the responsibility to build the AM part to meet the requirements of

the certified design state. For the purposes of this standard, the PBF build vendor is the

organization responsible for the execution of the PBF process. There may be numerous

additional vendors required to execute the post-build operations required to complete the part.

These sub-vendors may be under the control of the PBF build vendor or the design vendor.

[AMR-20] All vendors and sub-vendors engaged in the production of AM parts are to

operate with certification to AS9100 or an approved alternative QMS.


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The following responsibilities define the role of the PBF build vendor:

• Maintain a certified QMS for managing PBF production operations

• Interface with design vendor and understand requirements of the certified design state

• Maintain PBF machines, associated equipment, and facilities

• PBF machine operator training

• Work with design vendor to develop and register QMPs

• Execute PBF builds

• Document all non-conformances

• Maintain all records with certification of compliance

Commentary: To successfully implement the requirements of this standard, the design and

build vendors, if not the same entity, need to operate as a partnership rather than simply

service providers. The interactions needed to develop QMPs, register QMPs with a

Design Value Suite, understand machine performance through the PCRD and witness

testing all requires close interaction and open communication.

5.4.2.1 Sub-vendors

Ensuring the quality of sub-vendors for AM part processing is the responsibility of either the

design vendor or build vendor, based on the contracting source. The responsible vendor is to

maintain an active program to ensure all sub-vendors operate under an appropriate QMS and to

maintain an Approved Supplier List (ASL). Sub-vendors providing processing or testing (such as

heat treating, mechanical testing, or chemical analysis) are to be accredited through Nadcap, the

American Association of Laboratory Accreditation (A2LA), or other nationally accepted

accreditation body.

5.4.2.2 Operator Qualification

[AMR-20A] PBF build vendors shall define and maintain an active operator training

program with operator certifications.

Commentary: There is currently no defined system for operator certifications in AM

technologies. The intent of this requirement is to ensure appropriate depth in the knowledge and

skills and of the AM workforce involved in the production of aerospace parts. Programs are

developing within the industry and if suitable may be used in lieu of an internally structured

program.

The following guidelines are provided to establish expectations of the build vendor workforce

credentials and the associated training program. The following hierarchy of certification levels is

not mandatory, but an equivalent recognition of abilities and responsibilities needs to be present

to achieve vendor qualification. Operators of PBF equipment involved in the production of

Class A or Class B hardware are expected to have credentials equivalent to, or exceeding, those

described representing an AM Level II Certified Operator.


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Trainee

Prerequisites:

No prior experience needed

Typical Duties:

Trainee may participate in the day-to-day operations of PBF machines and associated

equipment. A trainee is not to operate PBF equipment unsupervised.

AM Level I Certified Operator

Prerequisites:

Minimum of three months experience under direct supervision of a Level II or III.

Must pass written and practical test administered by a Level III

Completed all basic training offered by the PBF machine manufacturer

Full understanding of applicable QMS and associated responsibilities

Typical Duties:

Machine cleaning, operational checks

Basic machine operations,

Execution of established builds

Operates under supervision of Level II or III

AM Level II Certified Operator

Prerequisites:

All Level I requirements

One year minimum experience under direct supervision of a Level II or III.

Must pass written and practical test administered by a Level III

Completed all advanced training offered by the PBF machine manufacturer

Comprehensive knowledge of all machine functions

Full understanding of applicable QMS and associated responsibilities

Typical Duties:

Set-up and trouble-shooting of PBF equipment

Execution and analysis of Pattern Plates and Reference Parts

Trouble-shoots and iterates build schemes to optimize build performance

Build file generation in accordance with QPP requirements

Develops machine operation checklists

Operates under supervision of Level III

AM Level III Certified Operator

Prerequisites:


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All Level II requirements

Minimum three years of experience

Bachelor’s degree or higher in applicable science or engineering field

Comprehensive knowledge of all machine functions

Understanding of the physics and metallurgy of the PBF process

Typical Duties:

Developing QMPs

Establishing proper QMS oversight for all PBF activities

Development, implementation, and approval of production planning records

Sets machine calibration metrics and intervals

Develops training and administers certification written and practical tests

5.4.3 PBF Build Vendor Qualification Process

[AMR-20B] NASA shall conduct the PBF build vendor qualification process in accordance

with section 5.4.3.

The Office of Safety and Mission Assurance (OSMA) at the NASA Center responsible for the

hardware is responsible for qualification of PBF build vendors. NASA Centers may accept an

existing vendor qualification from other Centers. The build vendor qualification process requires

on-sight verification audit of the vendor’s ability to meet all the requirements of this standard

that are within the vendor’s responsibility. NASA is to conduct the site audit with a minimum of

one OSMA representative knowledgeable in AM and one PBF subject matter expert. Approval

of a PBF build vendor is at the sole discretion of NASA. Following the audit, NASA is to

provide the vendor with a written record of the audit result and qualification status of approved

or disapproved. NASA is to provide any disapproved vendor with written rationale for the

disapproval and identify corrective actions that may resolve issues preventing qualification. The

production and inspection of test parts, QMP development records and other such evidence are

expected to be involved in the vendor qualification process. All topics are open to the audit

process and may be wide-ranging, including QMS certification, PBF machine operations, ITAR

information handling, IT security controls, and metallurgical expertise.

5.4.4 Qualified Vendor List

[AMR-20C] NASA shall maintain a Qualified Vendor List (QVL) of all PBF build vendors

with approved qualification status per Section 5.4.3.

[AMR-20D] All Class A and Class B parts shall be produced by a vendor on the QVL.


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Annex 1. Part Development Plan Content

The part drawing and the AM Part Development Plan are to address the following minimum

content together. If the design and build vendors are separate entities, then the PDP may be

separated into design and build documents for control of proprietary design information. The

combination of drawing and AM Part Development Plan is to be sufficient to produce the

production planning records.

Drawing number, part name, part description

CAD model views to illustrate the part and key features

System of units used in the part definition and CAD files

Material

o Identification of the qualified metallurgical process(es) (QMPs) to be used

Part classification with summary rationale for consequence of failure, structural margin,

and AM risk

First article requirements, or reference to a separate plan

List of required witness tests, witness articles, and associated acceptance requirements

Illustration of the compete build with part orientation, location, and witness specimens

Build platform material, dimensions, and tolerances

Method and sequence for build platform removal

Critical dimensions and associated tolerances to be verified for part acceptance and

process control

Specific controls for post-build part processing operations:

Support removal, locations and methods for surface improvement, final machining,

welding, etc.

Part inspection requirements, including methods and acceptance criteria

Part marking requirements

Packaging, handling, and shipping requirements

Complete list of all required part acceptance certificate of compliance information.

o Dimensional inspection report, NDE reports, powder lot, build logs, etc,

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