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DFMA ± Design for Manufactureand Assembly

Shin Ta LiuPh.D. CSSBB, CQE, CRE

Principal Consultant

Lynx Systems

12529 Cloudesly Dr 

San Diego, CA 92128

Web site: www.lynxsys.net

Email : shin@lynxsys.net

Phone: 858-366-4951

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DFSS Process

DCDOV

Goals Tools

Define Obtain customers needs and wants

Translate customers needs andwants to VOC list

Market/Customer Research, Kanoanalysis, stakeholders analysis,operation cross walk

Concept Development Develop DesignFeature/functional requirementsbased on VOC

QFD. TRIZ, Axiomatic Design

Design Development Identify engineering andprocess parameters based onthe design features/functionalrequirements

CTX, DFX, DOE, Taguchimethods

Optimize Design Identify optimal settings for theengineering and processparameters based on theperformance, robustness,production and other requirements.

RSM, FMEA update, sensitivityanalysis, Taguchi Methods

Verify Capability Establish the designedproduct/process is capable of 

meeting the design target andrequirements.

Verification/qualification tests,validation tests, simulation,

statistical analysis

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DFMA process

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DFMA Algorithm

Determine criticality of a part

a part is critical if  

 ± - move relative to all other parts already assembled, or  ± - different material than all being assembled

 ± - separated from other parts assembled.

Physical coupling of ³un-critical parts with a ³criticalpart´

Reassess assembly time for new configured parts Analyze the manufacturability of new configured part

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DFMA Example

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DFMA Example 1 Analysis

Total actual assembly Time T1= 163 s

Theoretical total part count is 4 and averageassembly time is 3 s. Theoretical assembly

time T2= 4 x 3 s = 12 s Calculate Design Efficiency :

or 7.362%

07362.0163

12

1

2!!!

 s

 s

T 

T L

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DFMA Recommended

redesign

Bushes are integral to the base

Snap-on plastic cover replaces standoff ,cover ,plastic bush, six screws.

Using pilot point screw to fix the base,

which redesign to be self-alignment.

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DFMA- An Improved DesignDFMA- An Improved Design

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DFMA Worksheet for an Improved Design

38.4

3.3

7.1

7.1

10.0

3.8

2.9

Assembly Cost(cents)

4.2

46.0 4 7 TOTALS

4.0 0 1 Plastic Cover  

0 1 Setscrew 8.5

1 1 Sensor  Subassembly

12.0 0 2 Motor Screw

4.5 1 1 Motor  Subassembly

3.5 1 1 Base

AssemblyTime(s)

TheoreticalPart Count

Number   Item

8.5

- - Thread leads 5.0

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DFMA Cost Differential Worksheet

Totals

Cover screw(4)

Cover  

Plastic bush

End-plate Screw

Endplate

Standoff(2)

Setscrew

Motor Screw(2)

Bush(2)

Base (Aluminum)

Item

Old Design

21.73 35.44

0.40

8.00 Plastic Cover (includetooling)

8.05

0.10

0.20

5.89

5.19

0.10 Setscrew 0.10

0.20 Motor Screw(2) 0.20

2.40

13.43 Base (nylon) 12.91

Cost, $ Item Cost,$

New Design

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DFMA ±Calculate Total Saving

Total Saving =

Saving from Assembly Time Reduction+ Saving from parts reduction

= $0.95 + $13.71

= $14.66

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Improved Assembly Design Efficiency

Total actual assembly Time T1= 46 s

Theoretical total part count is 4 and averageassembly time is 3 s. Theoretical assembly

time T2= 4 x 3 s = 12 s Calculate Design Efficiency :

or 26.087%

26087.046

12

1

2!!!

 s

 s

T 

T L

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Design for Assemblability & 

Manufacturability-Summary

Design Guides:

Minimize the number of setup and stages. Analyze the existing manufacturing and assembly function. Revisit the physical structure (of the design) which customize

to the local processing capability Apply the most appropriate (not latest) technology.

Use Axiomatic design to create Modular design of the parts. Design for minimum number of parts using physical coupling Choose the appropriate material for easy manufacturing Apply the layer assembly principles.