13 Design for Manufacturing

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Design for Manufacturing

Teaching materials to accompany:

Product Design and DevelopmentChapter 13

Karl T. Ulrich and Steven D. Eppinger5th Edition, Irwin McGraw-Hill, 2012.


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Produc t Design and DevelopmentKarl T. Ulrich and Steven D. Eppinger

5th edition, Irwin McGraw-Hill, 2012.

Chapter Table of Contents:1. Introduction2. Development Processes and Organizations3. Opportunity Identification4. Product Planning5. Identifying Customer Needs6. Product Specifications

7. Concept Generation8. Concept Selection9. Concept Testing10. Product Architecture11. Industrial Design12. Design for Environment

13. Design for Manufacturing14. Prototyping

15. Robust Design16. Patents and Intellectual Property17. Product Development Economics18. Managing Projects


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Outline

DFX concept

DFM objectives

DFM method

Mfg. cost estimation

DFM impacts DFM examples


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Design for Manufacturing Example:

GM 3.8-liter V6 Engine


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Understanding Manufacturing Costs


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Definition

Design for manufacturing (DFM) is a development

practiceemphasizing manufacturing issues

throughout the product development process.

Successful DFM results in lower production cost

without sacrificing product quality.


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Introduction

DFM is part of DFX

DFM often requires a cross-function team

DFM is performed through the developmentprocess


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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. costs

2) Reduce the costs of components

3) Reduce the costs of assembly4) Reduce the costs of supporting

production

5) Consider the impact of DFM decisionson 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 thepart 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 ofmaking a complex product)

Error proofing (anticipate possible failure

modes in the production system and take

appropriate corrective actions early in thedevelopment 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 13-15 on Page 274

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 13-17 on page 279

Component mfg. costs Exhibits 13/18-21 on pages 280-283

Assembly costs Page 286 for common products

Page 287 for part handling and insertion times on

Ex. 13-23

Cost structures for firms on Ex 13-24.


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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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Design for X

Design principles

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 fromthe 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 mostlikely to fail last.


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Design for X

Design principles 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 thatauto-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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Design for X

Design principles 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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Design for X

Design principles 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 electricaladjustments unless required for customer use.

minimize electrical cables; plug electrical sub-assembliesdirectly together.

minimize the number of types of cable.


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Design for X

Design principles 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 tohandle.


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Design for X

Design principles 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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Design for X

Design principles 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 consistentwith quality goals.

tests should give adequate diagnostics to minimize repairtime.


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Design for X

Design principles 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 replacewith disposable replacements

provide inexpensive spare parts in the product. ensure availability of spare parts.


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Design for X

Design principles 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 damageprevention.

protect parts with fuses and overloads


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Design for X

Design principles 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 andeasy to disconnect.

make sure repair, service or maintenance tasks pose nosafety hazards.

make sure sub-assembly orientation is obvious or clearlymarked.


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Design for X

Design principles 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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Design for X

Design principles Axomatic Design by Nam Suh

Axiom 1

In good design, the independence of functionalrequirements is maintained.

Axiom 2

Among the designs that satisfy axiom 1, the best

design is the one that has the minimuminformation content.


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Design for X

Design principles Axiomatic design- corollaries

Decouple or separate parts of a solution if functional requirements arecoupled 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 proposedsolution.

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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Design for X

Design principles 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 theassembly.

Estimate the handling and assembly costs foreach part using the appropriate assembly

process - manual, robotic, or high-speedautomatic.


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Design for X

Design principles 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 handlingparts

Maximize the ease of insertingparts

Benefits of DFA

Lower labor costs

Other indirect benefits

Popular software developed byBoothroyd 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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Three Methods to Implement DFM

1.Organization: Cross-Functional Teams

2.Design Rules: Specialized by Firm

3.CAD Tools: Boothroyd-Dewhurst Software


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DFM Strategy is Contingent

CorporateStrategy

ProductionStrategy

ProductStrategy

DFM

Strategy


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Other Images


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13 Design for Manufacturing

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