Design for Manufacturing

Design for Manufacturing

Chapter 11EIN 6392, Product Design

Summer 2012

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Product Design and DevelopmentKarl T. Ulrich and Steven D. Eppinger4nd edition, Irwin McGraw-Hill, 2000.Chapter Table of Contents 1. Introduction2. Development Processes and Organizations3. Product Planning4. Identifying Customer Needs5. Product Specifications6. Concept Generation7. Concept Selection8. Concept Testing9. Product Architecture10. Industrial Design11. Design for Manufacturing12. Prototyping13. Product Development Economics 14. Managing Projects

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Planning

Product Development Process

ConceptDevelopment

System-LevelDesign

DetailDesign

Testing andRefinement

ProductionRamp-Up

How can we emphasize manufacturing issues throughout the development process?

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Outline DFX concept DFM objectives DFM method Mfg. cost estimation DFM impacts DFM examples

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Understanding Manufacturing Costs Manufacturing Cost

Components Assembly Overhead

Standard Custom Labor Equipmentand Tooling

Support IndirectAllocation

RawMaterial Processing Tooling

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Definition Design for manufacturing (DFM) is a

development practice which emphasizes manufacturing issues throughout the product development process.

Successful DFM results in lower production cost without sacrificing product quality.

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Three Methods to Implement DFM Organization:

Organize cross-functional teams Design Rules:

Exercise best practices specialized by the firm

CAD Tools: Apply CAD systems such as the

Boothroyd-Dewhurst DFA software

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Introduction DFM is part of DFX DFM often requires a cross-function team DFM is performed through the development

process

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Major DFM objectives Reduce component costs Reduce assembly cost Reduce production support costs

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The DFM Process (5 steps)1) Estimate the mfg. costs2) Reduce the costs of components3) Reduce the costs of assembly4) Reduce the costs of supporting

production5) Consider the impact of DFM

decisions on other factors.

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Estimate mfg. costs Cost categories

Component vs. assembly vs. overhead Fixed vs. variable Material vs. labor

Estimate costs for standard parts Compare to similar part in use Get a quote from vendors

Estimate costs of custom made parts Consider material costs, labor costs, and tooling costs Depend on the production volume as well

Estimate costs of assembly Summing up all assembly operations (time by rate)

Estimate the overhead costs A % of the cost drives

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Reduce the costs of components Identify process constraints and cost drivers Redesign components to eliminate processing

steps Choose the appropriate economic scale for

the part process Standardize components and their processes Adhere the black-box component

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Reduce the costs of assembly

Integrate parts (using the Boothroyd method)

Maximize ease of assembly Consider customer assembly (do-it-

yourself) technology driven products

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Reduce the costs of supporting production

Minimize systematic complexity (such as plastic injection modeling for one step of making a complex product)

Error proofing (anticipate possible failure modes in the production system and take appropriate corrective actions early in the development process)

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Considering impacts Development time Development cost Product quality External factors such as

component reuse and life cycle costs

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Design for Manufacturing Example:1993 GM 3800cc V6 Engine Design

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DFM example Exhibit 11-15 on Page 230 Unit cost saving of 45% Mass saving of 66% (33 Kg.) Simplified assembly and service procedures. Improved emissions performance Improved engine performance Reduce shipping costs (due to lighter

components) Increased standardization across vehicle

programs.

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Cost Appendices Materials costs

Exhibit 11-17 on page 235 Component mfg. costs

Exhibits 11-18/21 on pages 236-239 Assembly costs

Page 242 for common products Page 243 for part handling and

insertion times

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Design for X – Design principles

Part shape strategies: adhere to specific process design guidelines if part symmetry is not possible, make parts very

asymmetrical design "paired" parts instead of right and left hand parts. design parts with symmetry. use chamfers and tapers to help parts engage. provide registration and fixturing locations. avoid overuse of tolerances.

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Standardization strategy use standard parts standardize design features minimize the number of part types minimize number of total parts. standardize on types and length of linear materials and

code them. consider pre-finished material (pre-painted, pre-plated,

embossed, anodized). combine parts and functions into a single part.

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Assembly strategies 1 design product so that the subsequent parts can be added to

a foundation part. design foundation part so that it has features that allow it to

be quickly and accurately positioned. Design product so parts are assembled from above or from

the minimum number of directions. provide unobstructed access for parts and tools make parts independently replaceable. order assembly so the most reliable goes in first; the most

likely to fail last.

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Assembly strategies 2 make sure options can be added easily ensure the product's life can be extended with

future upgrades. use sub-assemblies, especially if processes are

different from the main assembly. purchase sub-assemblies which are assembled and

tested.

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Fastening strategies 1 use the minimum number of total fasteners use fewer large fasteners rather than many small fasteners use the minimum number of types of fasteners make sure screws should have the correct geometry so that

auto-feed screwdrivers can be used. design screw assembly for downward motion minimize use of separate nuts (use threaded holes). consider captive fasteners when applicable (including

captive nuts if threaded holes are not available).

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Fastening strategies 2 avoid separate washers and lockwashers (make it be

captivated on the bolt or nut so it can still spin with respect to the fastener)

use self-tapping screws when applicable. eliminate fasteners by combining parts. minimize use of fasteners with snap-together features. consider fasteners that push or snap on. specify proper tolerances for press fits.

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Assembly motion strategies fastened parts are located before fastener is applied. assembly motions are simple. Assembly motions can be done with one hand or robot. assembly motions should not require skill or judgment. products should not need any mechanical or electrical

adjustments unless required for customer use. minimize electrical cables; plug electrical sub-assemblies

directly together. minimize the number of types of cable.

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Automation handling strategies 1 design and select parts that can be oriented by automation design parts to easily maintain orientation use parts that will not tangle when handled in bulk. use parts what will not shingle when fed end to end (avoid

disks). use parts that not adhere to each other or the track. specify tolerances tight enough for automatic handling. avoid flexible parts which are hard for automation to

handle.

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Automation handling strategies 2 make sure parts can be presented to automation. make sure parts can be gripped by automation. parts are within machine gripper span. parts are within automation load capacity. parting lines, spruces, gating or any flash do not

interfere with gripping.

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Quality and test strategies product can be tested to ensure desired quality sub-assemblies are structured to allow sub-assembly

testing testing can be performed by standard test instruments test instruments have adequate access. minimize the test effort spent on product testing consistent

with quality goals. tests should give adequate diagnostics to minimize repair

time.

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DF Maintenance strategies 1 provide ability for tests to diagnose problems make sure the most likely repair tasks are easy to perform. ensure repair tasks use the fewest tools. use quick disconnect features ensure that failure or wear prone parts are easy to replace

with disposable replacements provide inexpensive spare parts in the product. ensure availability of spare parts.

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Maintenance strategies 2 use modular design to allow replacement of modules. ensure modules can be tested, diagnosed, and adjusted

while in the product. sensitive adjustment should be protested from accidental

change. the product should be protected from repair damage. provide part removal aids for speed and damage

prevention. protect parts with fuses and overloads

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Maintenance strategies 3 protect parts with fuses and overloads ensure any sub-assembly can be accessed through one door or

panel. access over which are not removable should be self-supporting

in the open position. connections to sub-assemblies should be accessible and easy to

disconnect. make sure repair, service or maintenance tasks pose no safety

hazards. make sure sub-assembly orientation is obvious or clearly

marked.

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Maintenance strategies 4 make sure sub-assembly orientation is obvious or clearly marked. provide means to locate sub-assembly before fastening. design products for minimum maintenance. design self-correction capabilities into products design products with self-test capability. design products with test ports design in counters and timers to aid preventative maintenance. specify key measurements for preventative maintenance programs include warning devices to indicate failures.

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Axomatic design Axiom 1

In good design, the independence of functional requirements is maintained.

Axiom 2 Among the designs that satisfy axiom 1, the

best design is the one that has the minimum information content.

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Axiomatic design- corollaries Decouple or separate parts of a solution if functional requirements are

coupled or become coupled in the design of products and processes. Integrate functional requirements into a single physical part or

solution if they can be independently satisfied in the proposed solution.

Integrate functional requirements and constraints. Use standardized or interchangeable parts whenever possible. Make use of symmetry to reduce the information content. Conserve materials and energy. A part should be a continuum if energy conduction is important.

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DFA Method: Boothroyd and Dewhurst Apply a set of criteria to each part to

determine whether, theoretically, it should be separated from all the other parts in the assembly.

Estimate the handling and assembly costs for each part using the appropriate assembly process - manual, robotic, or high-speed automatic.

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Three criteria Is there a need for relative motion? Is there a need for different materials Is there a need for maintenance?

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Design for Assembly RulesExample set of DFA guidelines from a computer manufacturer.1. Minimize parts count.2. Encourage modular assembly.3. Stack assemblies.4. Eliminate adjustments.5. Eliminate cables.6. Use self-fastening parts.7. Use self-locating parts.8. Eliminate reorientation.9. Facilitate parts handling.10. Specify standard parts.

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Design for Assembly

Key ideas of DFA: Minimize parts count Maximize the ease of handling parts Maximize the ease of inserting parts

Benefits of DFA Lower labor costs Other indirect benefits

Popular software developed by Boothroyd and Dewhurst.

http://www.dfma.com

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To Compute Assembly Time

Handling Time+ Insertion Time

Assembly Time

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Method for Part Integration

Ask of each part in a candidate design:1. Does the part need to move relative to

the rest of the device?2. Does it need to be of a different material

because of fundamental physical properties?3. Does it need to be separated from the

rest of the device to allow for assembly, access, or repair?

If not, combine the part with another part in the device.

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Videocassette DFM Exercise

2 billion worldwide annual volume 7 major producers of 1/2” cassette

shells JVC licenses the VHS standard

dimensions, interfaces, light path, etc VHS cassette shells cost ~$0.25 each What is a $0.01 cost reduction worth?

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DFM Strategy is Contingent

CorporateStrategy

ProductionStrategy

ProductStrategy

DFMStrategy

Design for Manufacturing

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