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IPPD 4/25/00 DFM

Lecture 19Design for Manufacture

Design for Assembly

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DFM

Designs decisions will have significantimpact on the costs associated with themanufacture of the product

Piece part costs

Cost of quality

yield

process precision

Set-up costs Labor content

Throughput

Flexibility

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Design for Manufacture

Broad term applied to a variety of tool,guidelines, and methods to ensure

Low cost parts

Piece parts are built using the lowest costprocess possible

Design dimensions/tolerances are specifiedwith thought.

Low cost assembly

DFA Low cost processes

Processes are designed to target the critical tofunction characteristics

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Tradeoffs

Piece part simplicity vs. assembly time

Variety vs. integrality

Manufacturability vs. performance

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DFM Iteration

Process selection

material

requirements

volumes

tolerances

part complexity

setup costs

expertise

Design for the process

ensure that the product

can be made with the

process

exploit some of the

benefits of the process

General Design Guidelines

Reduce part count

DFA

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DFM Support Processes

Simultaneous Engineering / Cross-functionalteams

Design for Manufacturing Reviews

DFM Guidelines

DFM Metrics

Simulation software

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Simultaneous Engineering / Cross-

functional teams

Simultaneously design the product and theprocess

Prevents over-the-wall design

Cross-functional teams continually evaluateeach others work and have input on thewhole product/process design

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DFM Reviews

Formal reviews where experts are brought into evaluate the manufacturability of theproduct

Formalized gate

Problems

Often not taken seriously

we never can get design to makechanges, well just wait until we get it tomake it manufacturable

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DFM Guidelines

Formalized lists of guidelines for a specificmanufacturing process

Developed by manufacturing to generaterules for design to follow

Can be either computer based or book based

Heuristics rather than quantitative

Problems

Just sit on the desk - never used

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WorseBetter

Design for Adhesives

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IPPD 4/25/00 DFMWorse

Better

Two-directions

Single direction

Guideline: Reduce number of

setups. Benefits both time

and variation.

Guideline: Reduce number of

setups. Benefits both time

and variation.

CNC Guidelines

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Design for Assembly

Reduce assembly time by

Integral parts

Remove fasteners

Minimize assembly time

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Minimize part count through integral parts

Identify

parts that can be made of the same material

parts that dont move relative to each other

parts that do move but can use

integral joints

flexures

Problems

Reduce modularization

Increase complexity Benefits

Reduced assembly

Reduced tolerance stack-ups

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Minimize assembly time

Easy to get part

parts dont tangle

Easy to orient part

symmetrical orveryunsymmetricalparts

Easy to assemble

parts self aligning

lead-in chamfers

Vs.

Vs.

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Minimize fasteners

Options

Press fits

Adhesives

Snap-fits

Integral parts

Problems

fasteners are stronger

fasteners can be used to locate parts temperature insensitive

less sensitive to part variation

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DFM metrics

Quantitative evaluations that are used to puta metric on the manufacturability of a product.

The goal is to improve the metrics throughdesign changes

Examples

Boothroyd and Dewhursts complexity

Yield

# of manuf. Rule violations

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Boothroyd and Dewhurst Complexity

factor

Total number of parts

Total number of part types

Total number of interfaces

NPNTN

i

Complexity=

NT+

NP+Ni

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Yield

Calculation of the number of parts that will notpass inspection.

Ways to calculate

Models of the product

Statistical correlation with historical data

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Yield based on Model

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4

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-0.1 -0.05 0 0.05 0.1

Upper

Inspection

Limit

Lower

Inspection

Limit

Predicted

system

variability

Parts that fail inspectio

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Yield based on Statistical Analysis

Use historical data to determine the productcharacteristics that are highly correlated withyield problems

SMT example

Process technology

Number of parts

Number of interconnects

Volume .

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Simulation software

Used to simulate the as built state of aproduct

Examples

Mold flow (injection molding)

CNC simulations

Problems

Dont give guidance on the changes

Time consuming

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Collect the DFM guidelines and review

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Fixtured vs. Determinate Assembly

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Fixtured vs. Determinate

Fixtured Determinate

Locaiton Fixtures Precisionholes

Flexibility of

fixture

Low High

Precisionrequirements

Low High

Ability to

rework

Low High

AssemblyTime

High Low

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Sub-assemblies

Build ups

Parts (bulkheads, doors, etc) are built up ofmany parts that are assembled indedicated fixtures

Monolithic

parts are machined out of a large

forging, or

billet

to make a single piece

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Monolithic vs. build up

Monolithic Build upNear net shapeforging

Billet

Cycle time High Low flexibleAbility to increasethroughput

Low Low/med high

Crack resistance Med Med. High"Quality" High/med High Med/low

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IPPD 4/25/00 DFM

Lecture 20:

VARIATION RISK MANAGEMENT, THEROLE OF QUALITY

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