design for manufacture and assembly _dfma_ - mechanical science

7/30/2019 Design for Manufacture and Assembly _DFMA_ - Mechanical Science ...

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TAM 302 Design for Manufacture & Assembly 1

TAM302Engineering Design Principles

Syl labus Top ic:Design for Manu factu re &

Assemble (DFMA)Int roduct ion

Course I nstructor :

Mike PhilpottDirector of Concurrent Design & Manufacture Lab

Associate Professor of Mechanical Science & Engineering

[email protected]


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$95

$10

$25

$8

$75

$100

$55

$400

$0.30

$60,000

$1.20

$5,000

x3

Piece-part costs

Tooling costs

Mfg. Alternatives:Investment/Cash Flow

Decisions

Trade off:Recurring Costs versus Non-Recurring Costs

Example: $60,000 tooling investment = $0.30 per part$5 tooling investment = $95 per part


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$95

$10

$25

$8

$75

$100

$55

$400

$0.30

$60,000

$1.20

$5,000

x3

Piece-part costs

Tooling costs

Mfg. Alternatives:Investment/Cash Flow

Decisions


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DFM: where M =Primary Mfg. Process

Select theManufacturingProcess

Improve thedesign formanufacturability

AnalyzeCost

Broad processknowledge

Comparativecost knowledge

Do's & Don'ts(Rules/checklist)

Cost-of-features

knowledge

Quote Hist. data Models Software


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Design ForAssembly (DFA)

Assembly typically occupiesbetween 40% and 60% of thetotal production period.

SelectAssemblyMethod

Analyze forAssembly

Improve thedesign

Manual Robotic Specialpurpose

DFA principles BDI handbook Software (BDI,Sapphire, AEM)

$

%

Combine Eliminate Simplify


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TAM 302 Design for Manufacture & Assembly 6DFAExample


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Assembly LaborHours per Car

U.S. (Big 3)

Japan

Europe

16

25

36

Data Source: Detroit Free Press



DFA onFord Taurus

Savings resulting from the use ofDFA techniques on Ford's TAURUSCarline have been estimated to be

> $1 billion.



NCR 2760 Point-of-saleTerminal

Assembled blindfolded at DFA conf. in 1.5 mins. Reduced number of parts by 80% Reduced number of vendors by 65% Eliminated special assembly tools Estimated lifetime labor cost redn. of $1.1 million Estimated savings from elimg. 1 screw $12,500



Design ForAssembly (DFA)

Assembly typically occupiesbetween 40% and 60% of thetotal production period.

SelectAssemblyMethod

Analyze forAssembly

Improve thedesign

Manual Robotic Specialpurpose

DFA principles BDI handbook Software (BDI,Sapphire, AEM)

$

%

Combine Eliminate Simplify



DFAPrinciples

A. 'Product' Design forAssemblyThe design of the entire product with a view tooverall ease of assembly.

B. 'Component' Design forAssemblyThe design of each component for ease ofassembly to its neighbors.



A. 'Product' DFAPrinciple #1.

1. Design for minimumnumber of parts

Is there a way that reduces the number ofrequired parts?

Are all components essential or can their

functions be achieved by modifying anexisting component?

Can components be combined into one andmanufactured as an integral multifunctional

component?



Ex. Application ofPrinciple #1.

New design= 3 parts

Old design= 8 parts


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Old Design = 25 parts New Design = 2 parts

Ex. Application ofPrinciple #1.


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2. Minimize number of

fasteners and their components Use snap fits where possible Use press fits where disassembly is not required Consider molded hinges, straps, or hook-unders Rationalize fasteners - types, lengths etc.Use one piece fasteners with lead in pilots Design geometry for automatic alignment



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Hook-under design tominimize number offasteners

Ex. Applications ofPrinciple #2.


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Use single-piecefasteners, withguide pilots

orinserts


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Snap fits - can bedesigned for ease ofassembly &disassembly

Recess for

release ofsnap


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Living hinges& straps


Hinges, strapsand/or snap fits:

Snap fits


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Rocker-box example:Good ergonomics / style


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3. Design the product for

assembly from one direction Where possible assemblies should bedesigned so that a base piece is established,and remaining parts assembled from one,ideally vertical (Z) direction.

It is difficult to feed components in from theside.



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4. Avoid the need to

turn the assembly over If previously placed components have not beenfastened, they may move out of position.

Datum and location points change, andcomplicate the assembly process, which leadsto jamming and assembly failure.



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5. Standardize on Components,

Materials, and FastenersComponents can be difficult to differentiate,

particularly small similar shaped ones.

It is relatively common for feeders to becomejammed because wrong parts have been fedin by operators.

Considerable savings in storage, inventory,ordering etc.



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6. Provide location surfaces that areclosely related to datum surfaces

This ensures a known location tolerance for theautomatic placing of components.

Care should be taken to avoid tolerance build-up.



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7. Consider ease ofdisassembly for maintenance,

service, repair, and recycling Integral snap fits, press fits, and retaining clips

(circlips) allow compact designs, but if care isnot taken, result in impossible disassembly

Disassembly is frequently necessary due toincorrect assembly, the need to service/repair,and now the requirement to recycle



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8. Adopt a modular design

philosophy for the product group Allows model variations to be accomplished ata sub-system level. Subassembly volumesincrease, total parts decrease.

Modular sub-assemblies may be built andtested by specialist teams (higher quality).


Modular Design


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Modular DesignAssembly time reduced from 540 hrs to 180 hrs

Design time per crane =350 man hrs - 18hrs

Fabrication time = 1500 hrs to 550 hrs


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9. Avoid the need forassembly adjustments

Eliminating adjustments will usually reduceassembly time considerably; and reduce

service / maintenance

Equipment going out of adjustment is one of

the biggest causes of customer dissatisfaction. Spring loading can be used effectively to avoidassembly adjustment and to eliminateadjustment for wear.



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10. Minimize assemblysteps and extra operations

Each assembly step or operation must beresourced

Mistakes in assembly are one of the greatestcause of product malfunction and customerreturns. The fewer the steps the fewer theopportunities for error.

Extra operations such as applying grease,sealants, turning part over etc. add to time andreduce assembly efficiency.

B 'C t' D i


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Feeding the components: from a bin, bulkfeeder (e.g. bowl feeder), or magazine, or

continuous strips. Orienting the components: by human operator,by the feeder tracks, and by the robot /workhead.

Positioning and Placing the components

B. 'Component' Designfor Assembly

The design of eachcomponent for ease ofassembly to its neighbors;i.e. the following tasks:

B 'C t' DFA


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1. Components should besymmetrical or haveexaggerated assymetry

Symmetrical shapeshave a predictablerest aspect

Non-symmetrical shapes

have an unpredictableresting aspect

exaggerated assymetryand part falls on oneof its flat faces

B. 'Component' DFAPrinciple #1

B 'C t' DFA


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2. Components shouldhave the least numberof important directions

A

B

is betterthan

is betterthan

B

A

To reduce the chance of correctfeeding and positioning:


B 'C t' DFA


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Where possible make chamfers and lead-in anglesgenerous, and avoid sharp corners, to avoid jamming:

3. Provide Lead-in orChamfers


OR

B 'Component' DFA


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Often a small design change can eliminate thetendency of components to tangle. Close ends andkeep material thickness greater than gaps and slots:

4. Components should befree from burrs andflash, and be smooth in surface finish.

B. Component DFAPrinciple #4 & #5

5. Design parts to prevent tangling:

B 'Component' DFA


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Loosely tolerancing non-functional dimensionscan cause problemsif the feeding andorienting method is

not considered -jamming may occurif components are at extremes of limit:

Feeder / Hopper

Delivery

Tube

Parts

t

B. 'Component' DFAPrinciple #4 & #5

6. Consider the dimensionsimportant to feeding and orienting

design for manufacture and assembly _dfma_ - mechanical science

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