Class16DesignforAssembly Plastic Design

7/28/2019 Class16DesignforAssembly Plastic Design

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© Daniel E Whitney

DFA

• Goals of this class: – Place DFA in context

– Learn basic principles of Design for Assembly

– Understand background and history – Understand its strong and weak points



© Daniel E Whitney

“The Multiplier” According to Ford and GM

or: Why Is DFM/DFA Important?

• For every product part, there are about 1000

manufacturing equipment parts*

• Or, for every toleranced dimension or feature on a

product part, there are about 1000 toleranceddimensions or features on manufacturing

equipment

• Such “equipment” includes fixtures, transporters,dies, clamps, robots, machine tool elements, etc*Note: Ford’s estimate is 1000, GM’s is 1800. Both are informal estimates.



© Daniel E Whitney

A Few Quotes

• Just because you can make something doesn’t

mean you can manufacture it.

• It’s very hard to make cheap [low cost] stuff - you

get buried by your mistakes.

• I don’t understand why it won’t assemble. It passed inspection.

• Word came down that we couldn’t use screws. So

we used snap fits. Then word came down that ithad to pass a drop test. So we dropped it and it

fell apart...



© Daniel E Whitney

Goals of DFM/DFA

• Historically, conventionally – reduce costs, simplify processes

– improve awareness of manufacturing issues during design

• More broadly (a goal of this course) – align fabrication and assembly methods to larger goals

• ability to automate, systematize, raise quality, be flexible

• access to assembly-driven business methods like delayedcommitment

• innovative designs, outsourcing (Siemens intake manifold)

• Inevitably pushes DFM/DFA earlier into the productdevelopment process where it blends with architecture(see AITL Basic Issues and Product Architecture classes)



© Daniel E Whitney

Complete Outsourced Subassembly

AIR

CLEANER

FUEL INJECTORS

INTAKE AIR

TEMPERATURE

SENSOR

INTAKE MANIFOLD

THROTTLE BODY

FUEL PRESSURE

REGULATOR

INTEGRATED

FUEL RAIL

AIR FLOW

SENSOR

IDLE SPEED

CONTROL

Courtesy Siemens VDOAutomotive. Used with permission.



© Daniel E Whitney

The Assembly from Heaven*

• Can be assembled one-handed by a blind personwearing a boxing glove

• Is stable and self-aligning• Tolerances are loose and forgiving

• Few fasteners

• Few tools and fixtures

• Parts presented in the right orientation

• Parts asymmetric for easy feeding• Parts easy to grasp and insert

*Dr Peter Will, ISI









© Daniel E Whitney

Characteristics of Traditional DFA

• Uses an easy to understand metrics-driven approach (metrics

story about demurrage)

• Uses a relative cost and time metric

• DFA in the small simplifies each assembly step

– single parts

– manual assembly

– small parts

– uses many context-free metrics to assess difficulty levels of

feeding and handling

• DFA in the large emphasizes part count reduction – It is essentially another force in product architecture

– Advanced plastics make part count reduction more attractive









© Daniel E Whitney

Part Count TradeoffsONE PART PER

µ FUNCTIONMANY

SIMPLEPARTS

LOTS OFINTERFACESIN ASSEMBLY

LOTS OFLOGISTICS,FAB ACTIVITY,

& ASSY ACTIVITY

EXTRA WEIGHT,EXTRA FAULT

OPPORTUNITIES

EXTRA CHANCESFOR ERRORS

QUALITY ISCREATEDDURING

ASSEMBLY

FLEXIBILITYIS POSSIBLE

DURINGASSEMBLY

EXTRA"SUPPORT"

COST

PARTS CONSOLIDATION:FEWER PARTS AND LESS

FASTENING

MORE FUNCTIONSHARING

FEWER BUTMORE COMPLEX

PARTS

MORE ACTIVITYDURING FAB,LESS DURING

ASSEMBLY

QUALITY CREATEDDURING FAB

PARTS COSTMORE

PARTS TAKELONGER TODESIGN ANDPROTOTYPE

FEWER OPPORTUNITIESFOR ON-LINE FLEXIBILITY

PART COUNT TRADEOFFS





© Daniel E Whitney

DFM Strategies

Example Products:

High performance computers

Telecommunications equipment

DFM Strategy:

Avoid long lead time tooling

Use standard components

Minimize production risk

Example Products:

Machine tools

Electrical distribution equipment

DFM Strategy:

Avoid expensive tooling

Use standard components

Other issues likely to dominate

Example Products:

Blank videocassettes

Circuit breakers

DFM Strategy:

Use traditional DFM

Combine and integrate parts

Consider automatic assembly

Example Products:

Notebook computers, Toys

DFM Strategy:

Minimize complexity of mostcomplex part

For complex parts, use processes

with fast tool fab

Apply traditional DFM to less

time-critical parts

Low Lifetime Production Volume

D e v e l o p m e n

t T i m e C r i t i c a l

D e v e

l o p m e n t T i m e

N o t C r i t i c a l

Source: Ulrich, Sartorius, Pearson, Jakiela, “DFM Decision-making”, Mgt Sci, v 39 no 4, Apr 1993.

High Lifetime Production Volume



© Daniel E Whitney

Questions of Scope

• When can DFA be applied?• When should DFA be applied?

• What information is needed before DFA can be

applied?

• What should the designers’ priorities be?

• Can/should DFA be separated from “the rest” of product design?



© Daniel E Whitney

The Pump Redesign

• See Redford & Chal, pp 118-119• What are the differences between the old and new

designs?

– from the POV of product function – from the POV of assembly

• What are we looking at in this example?



© Daniel E Whitney

R e d f or d - C h a l P

um pR

e d e s i gn

Ball

Ball

Valve

Valve

Courtesy of Alan Redford. Used with permission.



© Daniel E Whitney

The Pneumatic Piston Redesign*

• Was the original function completely understood?• Was it preserved in the redesign?

*Product Design for Assembly by Boothroyd and Dewhurst, workbook 1991







© Daniel E Whitney

DFA at Sony

• Applied to products like Handicams• “Our designers take assembly into account early.”

• Method:

– concept designs are sketched in exploded views

– each concept is subjected to DFA analysis and scored

– concept selection criteria include DFA score

• A Sony engineer made a complete exploded view

drawing of a Polaroid camera in 20 minutes!



© Daniel E Whitney

D

F A a t

D e n s o

L



© Daniel E Whitney

How to Do DFA

• Make a structured bill of materials

• Identify every part mate and understand it

• Choose a reasonable assembly sequence

• Use the tables to estimate handling and mating times

• Label theoretically necessary parts, excluding all fasteners• Calculate

• This ranges from 5% for kludges to 30% for good designs

assembly efficiency =3* # of theoretically needed parts

total predicted assembly time



© Daniel E Whitney

Handling Times

S =α + β

No handling difficulties Part nests or tangles

Thickness > 2mm <2mm Thickness > 2mm <2mmSize>15mm 6mm<size

<15mmSize>6mm Size>15mm 6mm<size

<15mmSize>6mm

Symmetry

( )

0 1 2 3 4 5

S < 360° 0 1.13 1.43 1.69 1.84 2.17 2.45

360°<S<540° 1 1.5 1.8 2.06 2.25 2.57 3540°<S<720° 2 1.8 2.1 2.36 2.57 2.9 3.18S=720° 3 1.95 2.25 2.51 2.73 3.06 3.34

α ≤180° α = 360°

0 1 2

4 4.1 4.5 5.6

For parts needing one hand only

For parts needing two hands(Courtesy of Boothroyd Dewhurst, Inc. © 1999.) Used with permission.



© Daniel E Whitney

Insertion Times

(Courtesy of Boothroyd Dewhurst, Inc. © 1999.)

Secured by separate operation or part No hold ing dow nrequ ired

Ho lding dow nrequ ried

Secured r igh t aw ay by snap fi t

Easy toalign

No t easyto align

Easy toalign

No t easyto align

Easy toalign

No t easyto align

0 1 2 3 4 5

No access

or visiondifficulties

0 1.5 3.0 2.6 5.2 1.8 3.3

Obstructedaccess or restrictedvision

1 3.7 5.2 4.8 7.4 4.0 5.5

Obstructed

access andrestrictedvision

2 5.9 7.4 7.0 9.6 7.7 7.7

Part inserted but not secured immediately, or secured by snap fit

Easy to align No t eas to align0 1

No access or vision difficulties

3 3.6 5.3

Restricted visiononly

4 6.3 8.0

Obstructedaccess only

5 9.0 10.7

Part inserted and secured immediately by power screwdriver. Note: add 2.9 s to get power tool.

Used with permission.



© Daniel E Whitney

A Few Conceptual Questions

• What’s a “base part?” – remember the alternator - the nut is the “base” in the

only assembly sequence family that achieves assemblywithout reorientation

– different types of “product structure” exist (Arch. class)

• What do you mean “difficult?” – for manual assembly, Boothroyd has some time-baseddata (originally derived from grad students)

• Why avoid screws? – 25 years ago’s reasons may not apply any more

– see Blonder video



© Daniel E Whitney

Manual vs Automatic Assembly DFA

• What’s easy for a person

– reorienting the assembly

– quickly eyeballing the part (story about bad filament)• What’s easy for a machine

– picking up little parts

– using tools that are like tweezers

• Part jams occur most often in feeder tracks

– Denso: perfect parts don’t jam!

• A different balance between gross motion and fine

motion times

• Different ways of “inspecting”

i hi A bl li bili l i



© Daniel E Whitney

Hitachi Assembly Reliability Evaluation

Method



© Daniel E Whitney

Design for Recycling and Reuse

PRODUCT ORSUBASSEMBLY

SINGLE

PART

MULTIPLE

PARTS

REUSE,

RECYCLE,

OR DUMP

SINGLE

MATERIAL

MULTIPLE

MATERIALS

SOME PARTS

CAN BE REUSED

NO PARTS

CAN BE

REUSED

CHOOSE DISASSEMBLY

METHOD THAT

PRESERVES

REUSABLE PARTS

CHOOSE DISASSEMBLY

METHOD THAT SEPARATE

PARTS INTO GROUPS

OF LIKE MATERIALS

NO PARTS

CAN BE

REUSED

RECYCLE

OR DUMP

A

TO A TO A



© Daniel E Whitney

Greg Blonder Video (17 min of 1:45)

• Talk given at Bell Labs Jan 16, 1990

• Has been analyzing precision consumer products

for about 5 years• Takes about a day to analyze each one

• Takes apart and analyzes a $100 Canon camera

• Classifies ~ 400 parts including 60 screws (!)• Tells what it means to get high assembly yield

• Tries to explain it to a high level executive

• Discusses shutter and flash subassemblies

• He later became a VP of Lucent

Documents

Class16DesignforAssembly Plastic Design