Design for Manufacturing

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Design for Manufacturing

• Chapter 11
• EIN 6392, Product Design
• Spring 2008

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Product Design and DevelopmentKarl T. Ulrich and
Steven D. Eppinger

• Chapter Table of Contents
• 1. Introduction
• 2. Development Processes and Organizations
• 3. Product Planning
• 4. Identifying Customer Needs
• 5. Product Specifications
• 6. Concept Generation
• 7. Concept Selection
• 8. Concept Testing
• 9. Product Architecture
• 10. Industrial Design
• 11. Design for Manufacturing
• 12. Prototyping
• 13. Product Development Economics
• 14. Managing Projects

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Product Development Process
Concept Development
System-Level Design
Detail Design
Testing and Refinement
Production Ramp-Up
Planning
How can we emphasize manufacturing issues
throughout the development process?
4
Outline

• DFX concept
• DFM objectives
• DFM method
• Mfg. cost estimation
• DFM impacts
• DFM examples

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Understanding Manufacturing Costs
6
Definition

• Design for manufacturing (DFM) is a development
  practice emphasizing manufacturing issues
  throughout the product development process.
• Successful DFM results in lower production cost
  without sacrificing product quality.

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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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Introduction

• DFM is part of DFX
• DFM requires a cross-function team
• DFM is performed through the development process

9
Major DFM objectives

• Reduce component costs
• Reduce assembly cost
• Reduce production support costs

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The DFM 5 steps

• Estimate the mfg. costs
• Reduce the costs of components
• Reduce the costs of assembly
• Reduce the costs of supporting production
• Consider the impact of DFM decisions on 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 the
  part 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 of making a
  complex product)
• Error proofing (anticipate possible failure modes
  in the production system and take appropriate
  corrective actions early in the development
  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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DFM example

• Page 230
• 45 cost saving
• 66 mass saving.

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Design for Manufacturing ExampleGM 3.8-liter V6
Engine
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Cost appendices

• Materials costs
• Page 235
• Component mfg. costs
• Pages 236-239
• Assembly costs
• Page 242 for some common products
• Page 243 for some component handling and
  insertion time

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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

• Standardization strategy
• use standard parts
• standardize design features
• minimize the number of part types
• minimize number of total parts.
• standardize on types and length of linear
  materials and code them.
• consider pre-finished material (pre-painted,
  pre-plated, embossed, anodized).
• combine parts and functions into a single part.

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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 from the 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 most likely to fail last.

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Design for X Design principles

• Assembly strategies 2
• make sure options can be added easily
• ensure the product's life can be extended with
  future upgrades.
• use sub-assemblies, especially if processes are
  different from the main assembly.
• purchase sub-assemblies which are assembled and
  tested.

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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 that auto-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
  electrical adjustments unless required for
  customer use.
• minimize electrical cables plug electrical
  sub-assemblies directly 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 to handle.

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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
  consistent with quality goals.
• tests should give adequate diagnostics to
  minimize repair time.

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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 replace with 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 damage
  prevention.
• 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 and easy to disconnect.
• make sure repair, service or maintenance tasks
  pose no safety hazards.
• make sure sub-assembly orientation is obvious or
  clearly marked.

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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
• Axiom 1
• In good design, the independence of functional
  requirements is maintained.
• Axiom 2
• Among the designs that satisfy axiom 1, the best
  design is the one that has the minimum
  information content.

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Design for X Design principles

• Axiomatic design- corollaries
• Decouple or separate parts of a solution if
  functional requirements are coupled 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 proposed solution.
• 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 the
  assembly.
• Estimate the handling and assembly costs for each
  part using the appropriate assembly process -
  manual, robotic, or high-speed automatic.

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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 handling parts
• Maximize the ease of inserting parts
• Benefits of DFA
• Lower labor costs
• Other indirect benefits
• Popular software developed by Boothroyd 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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Videocassette DFM Exercise

• 2 billion worldwide annual volume
• 7 major producers of 1/2 cassette shells
• JVC licenses the VHS standard
• dimensions, interfaces, light path, etc
• VHS cassette shells cost 0.25 each
• What is a 0.01 cost reduction worth?

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DFM Strategy is Contingent
Corporate Strategy
Product Strategy
Production Strategy
DFM Strategy