ENGINEERING TRIPOS, PART IIA MANUFACTURING … · 2012-09-26 · physical coupling between...

1

ENGINEERING TRIPOS, PART IIAMANUFACTURING ENGINEERING TRIPOS, PART I

MODULE 3C1: MATERIALS PROCESSING AND DESIGN

MODULE 3P1: MATERIALS INTO PRODUCTS

HANDOUT 1: COURSE INTRODUCTION

Materials Processing and Design: What did you learn in Part I?O i f d lOverview of ModuleCoupling: Material-Process compatibilityCoupled design problemsFailure analysisStructure of Module 3C1/ 3P1References

© 2012 H.R. Shercliff

H.R. ShercliffOctober 2012

Hugh

Text Box

1

Materials, Processing and Design: What did you learn in Part I?

Material Selection

• Material classes selected for a given design specification, using property charts. • Optimization of the design meant maximum performance (e.g. minimum mass, maximum stored energy per unit volume), or minimum material cost, or minimum environmental impact

Analysis can identify an appropriate combination of material properties to maximise• Analysis can identify an appropriate combination of material properties to maximise (“performance indices”)

Bending, Compression Torsion

Rider weight

Bending from braking

hi

Bending, Compression Torsion

Rider weight

Bending from braking

hi

e.g. light, stiff bike frame E1/3/ E1/2/ E/


Pedalling torque

Load from road

or crashing

Pedalling torque

Load from road

or crashing

Performance indices, E/, E1/2/etc., depending on assumed geometric constraints

For complete case study: see www.alumatter.org

Manufacturing Process: a method of shaping, joining, surface-treating (finishing) a material

ng g


Sand casting

Sh

apin

Blow moulding

Sh

apin

at


Fusion welding

Join

ing

Thermal-spray coating

Su

rfac

e tr

ea

2

Shaping Add shape to a raw material

Manufacturing processes are classified by function – i.e. what the process does:

Operations on materials


Surfacetreatment

Heattreatment

Machining Add features + shape details

Change a bulk property

Change a surface property

Operations on components


Joining Combine components


Process Selection

Processes screened for compatibility between design requirements and process attributes (presented as attribute charts)

• Technical limits: material compatibility, shape and size limits• Quality limits: tolerance and roughness

E i li it i b t h i f t i t t• Economic limits: economic batch size, manufacturing cost per part

e.g. steel connecting rod

Screen for:- material- shape

mass


- mass- minimum section thickness- tolerance- roughness- economic batch size

Rank on cost per part.

3


Material-process compatibility matrix Roughness chart


NB These charts are more refined versions of those in the Materials Databook, from:

Ashby M.F., Shercliff H.R. and Cebon D.

Materials: Engineering, Science, Processing & Design, Butterworth–Heinemann, 2007/2009

For complete case study: see Chapter 18

Shaping processes are generally suited for making particular shapes.



Wire drawing, extrusion, rolling, shape rolling: prismatic shapes Stamping, folding, spinning, deep drawing: sheet shapes Casting, moulding, powder methods: 3-D shapes

Shape-process compatibility is therefore discriminating in screening.

4


Cost model for batch processing

n

C

n

CCC Lc

m

Material cost

Overhead cost

Tooling cost

material, including “consumables”

dedicated tooling (dies, moulds etc)

mC

cC


hourly overhead (labour, energy, share of capital)LC

batch size

production rate per hour

n

n

Extensions to process selection methodology

Screening on primary constraints extends to all process classes:

• Shaping: material and shape• Joining: material(s), joint geometry and mode of loading• Surface treatment: material, and function of treatment

Further screening may be conducted for each class on secondary constraints:

Summary: limits to selection methodology

• CES software may be used to conduct process selection at this level: screening on attributes and ranking by cost

Further screening may be conducted for each class on secondary constraints:

• Shaping: mass, section thickness, tolerance, roughness• Joining: ease of disassembly, equipment portability,

ability of joint to provide a seal, conduct heat or electricity• Surface treatment: acceptability/compatibility of coatings, dimensional change


attributes, and ranking by cost.

• These techniques get you a significant way into the problem – designers should obviously do the simple things first!

• However, these techniques are essentially decoupled – design considering either material or process requirements (except for material-process compatibility).

• The complexity in design and manufacture stems from material-process interactions: exploring these is the main aim of Module 3C1/3P1.

5

Introductory Example: Materials into Products

Consider manufacture of an aluminium bike frame

Designer identifies optimum material:

heat-treatable aluminium alloy

(good stiffness and fatigue resistance at low weight; reasonable cost; recyclable)

But how might the tubing and frame be made?How does the processing influence the outcome?

low weight; reasonable cost; recyclable)


Overview of Module: Materials in Design and Manufacturing

Extract aluminium : Hall-Heroult process

An introductory example: aluminium bike frame

Cast + homogenise large ingots


6


Extrude into tube, and heat treat





Assemble frame by arc welding


7


Process step Comment

Extract/recycle aluminium Dominant step in environmental impact(“embodied energy”) and impurity control


( embodied energy ) and impurity control

Cast + homogenise large ingots Composition determined (while liquid)Coarse microstructure, poor properties (but good for economies of scale)

Extrude into tube, and heat treat Large shape change in one stepDesign of equipment itself is complex


Deformation refines cast microstructure (“wrought product”)

Thermal history key to achieving properties

Assemble frame by arc welding Strength loss due to local thermal historyCommon source of defects, residual stress


Designers need to know about manufacturing:• to design products that can be made to the target specification (geometry, properties, cost) • to enable sustainable design and ability to recycle/re-use, minimising life cycle impact

To sum up the messages in this example: turning materials into products requires understanding and control of the coupling between materials, processing and design.

Material producers/manufacturers need to worry about:• achieving required material properties and precision, with low variability• avoiding defects: both scrap during production, and origin of later failures in service• ever faster productivity and lower costs• efficient re-use of factory waste and recycled material• environmental impact of processes

H ti i i t i l d l ti i l ith ti


Hence optimising material and process selection is complex, with many competing constraints on the problem.

The core skills are:- knowing what the relevant issues are;- knowing where to go for the information.

i.e. successful materials processing and design depends on good knowledge management.

8

“Shaping, metals”

“Shaping ceramics”

Process-material compatibility matrix (using CES data) = viable combination

Coupling: Material-Process compatibility

Shaping, ceramics

“Shaping, polymers”

“Shaping, composites”


Processes clearly cluster by material class.The same is true for joining and surface treatment (not illustrated here).

Coupling: Material-Process compatibility

Zooming in further, classes of alloys subdivide, with associated process combinations:

e.g. aluminium alloys

Casting alloysAge hardening

Non age hardening

Die casting,

Investment casting ….

(Heat treatment)

Wrought alloys

Non age hardening

Age hardening

Non age hardening

(Heat treatment)

Rolling, Forging,

Extrusion ….

(Heat treatment)

And so it goes on:

e.g. age hardening wrought alloys 2000, 6000, 7000 series alloys(Al-Mg + Cu Si Cu-Zn respectively)


(Al Mg + Cu, Si, Cu Zn respectively)

Clearly the number of process-material combinations grows very rapidly.

Leading questions are therefore:(i) Just how deep do we need to go to reveal the technical challenges and complexities

that matter in making products?

(ii) How do parameters and features of the design also influence the outcome?

9

Coupled design problems: examples from casting design

(1) Successful mould filling

• Depends on maintaining fluidity in melt until mould is completely full

This in turn depends on:

• Viscous drag through sections of varying• Viscous drag through sections of varying size and aspect ratio

• Temperature history of melt (i.e. viscosity, onset of solidification)

The temperature history depends on:

• Pour temperature in the crucible

• Thermal properties of alloy and the mould

• Size and shape of the casting


Size and shape of the casting

NB: A successful outcome depends on the underlying physics, combining the following:

• Alloy detail (viscosity/solidification sensitive to composition – phase diagram)

• Process type (ceramic mould, metal mould etc) and process variables (pour temperature)

• Design detail (size and shape)

Coupled design problems: examples from casting design

(2) Effect of product size on properties

• Strength, toughness and ductility depend on many aspects of microstructure:

- grain size and shape- segregation

Small copper alloy casting: clarinet keys

Large copper alloy casting:

Examples:

- precipitates

These in turn depend on:

• Composition and phase diagram

• Cooling history from melt to room temperature

As before, cooling history depends on:

• Pour temperature, alloy and mould properties, casting size and shape

Large copper alloy casting: ship propellor


NB: Hitting target properties means hitting target microstructure, again determined by physical coupling between material, process and design parameters.

• Variability in properties reflects in-process variation (e.g. lack of control of pour temperature)

• Ranges in material property data (e.g. in CES) partly reflect the wide range in process histories and consequent properties achievable.

10

“Manufacturing Tasks”

The examples above show that the relevant, discriminating complexities are apparent at the level of a manufacturing task: a subset of processes applied to a subset of materials.

Module 3C1/3P1 considers different manufacturing tasks, working from primary shaping (casting metals, polymer moulding…..) through to heat treatment and joining.

In each task, the level of specification of process and material is always as general as possible, while capturing the essence of the problem:

e.g. casting productivity: effect of size: same principles apply to all metals;properties of castings: some different issues in cast irons, cast aluminium alloys, etc.

For each manufacturing task, the aim is to understand (and sometimes analyse) the underlying process physics (thermal, deformation history and microstructure evolution):

Key inputs:


y p• process variables (material temperatures, cooling procedures,

flow/deformation rates of liquids and solids, material-workpiece thermal and frictional contact etc.);

• material variables (composition, phase transformations, thermal and thermomechanical properties as f[temperature, strain-rate] )

Key outputs: • properties, defects, residual stress, limits to production rate, power consumption

Failure analysis: learning from mistakes

Processing builds in microstructure, defects and residual stresses: all factors in failures.The same knowledge of materials, processing and design therefore feeds directly into

failure analysis.

Failure falls into two categories:In-process scrap: expensive, but easily recycled, and not hazardous to publicFailure in-service: at best, expensive; at worst, serious loss if life, and litigation

Failures often due to multi-stage nature of processing: interactions between one processing step and microstructure/defects inherited from an upstream process step (probably in a different company in a different country)

In-service failures bring in new factors, with performance influenced by service conditions (e.g. temperature, corrosive environments).


Many failures originate from joining:- process physics and microstructure/defect evolution can be complex- geometric complexity: joints inherently introduce stress concentrations- last step: greatest scope for interaction with (perhaps poorly known) earlier stages

(probably in a different company, in a different country).

11

Failure analysis: example from welding

Oil-rig disaster: Alexander Kielland, 1980See: Easterling K.E., Introduction to Physical Metallurgy of Welding;

http://en.wikipedia.org/wiki/Alexander_Kielland_(Platform) + External link to animation

• Design modification: hydrophone mount welded to bracing member in oil rig structure

Technical cause of failure:

• Welding process introduced cracks

• Steel near weld embrittled (martenite, + hydrogencorrosion)

bracing member in oil-rig structure

• 6mm fillet weld led to fatigue crack, and failure

• Rig over-turned in 14 minutes; 123 out of 212 died

Fracture of bracing member


)

NB: Coupled underlying physics again responsible:

• Alloy detail (wrong hardenability, particularly in steel used for design modification)

• Process variables (wrong heat input, poor quality control)

• Design detail (weld geometry influences cooling history)

(But human error also played a significant role…..).

Summary: core themes in the course

(1) Whatever the manufacturing task, and the level of detail being considered, it is helpful to consider design requirements in the three categories:• technical: can it be done?• quality: can it be done well enough?• economic: can it be done cheaply enough?

(2) The outcome of a manufacturing task often depends on coupling between:design, material, process variant and operating parameters

(4) Material property data covers all possible processing outcomes (may be a wide range). It is essential to recognise that “the best” is not necessarily guaranteed in a given design: there may be a process-constrained “knock-down factor”.

(3) Avoiding failure, or analysing those that occur, also requires consideration of:service conditions


design: there may be a process constrained knock down factor .

(5) Final choice of material, processing conditions and design detail must often be made simultaneously.

(6) Microstructure evolution and process physics are central throughout; in a nutshell:Composition + Processing Microstructure + Properties

12

Structure of Module 3C1/ 3P1

Introduction (HRS)

Casting (HRS)Deformation Processing, Wrought Alloys (HRS)Heat Treatment of Steels (HRS)

Polymers and Composites (IMH)Powder Processing (IMH) Surface Engineering (IMH)Joining and Welding (IMH)Failure Analysis (IMH)

HRS: Dr Hugh Shercliff

IMH: Prof Ian Hutchings


General References on Manufacturing Processes:

Kalpakjian S., MANUFACTURING PROCESSES FOR ENGINEERING MATERIALS, Addison Wesley, CUED Library JN49

Edwards S.L. and Endean M., MANUFACTURING WITH MATERIALS, Butterworths, CUED Library JA146

Ashby M.F., Shercliff H.R., Cebon D., MATERIALS: ENGINEERING, SCIENCE, PROCESSING & DESIGN, 1st edition 2007, or 2nd edition 2009, Butterworth-Heinemann, CUED Library JA199

Ashby M.F., MATERIALS SELECTION IN MECHANICAL DESIGN, 3rd edition 2005, or 4th edition 2011, Butterworth-Heinemann, CUED Library JA163

http://www-materials.eng.cam.ac.uk/mpsite


p g p(“Process Encyclopedia” under “Design and Technology”)

CD-ROM “Material Selection and Processing”(in some college libraries, and on PWF)

Cambridge Engineering Selector (CES) EduPack 2011 or 2012(downloadable from CUED Computing pages)

ENGINEERING TRIPOS, PART IIA MANUFACTURING … · 2012-09-26 · physical coupling between...

Documents

Transcript of ENGINEERING TRIPOS, PART IIA MANUFACTURING … · 2012-09-26 · physical coupling between...