Design for Manufacturability (DFM) 1) two takes: Bralla

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Design for Manufacturability (DFM)1) two takes
Bralla Anderson2) DFM process guidelines
(review) Design for Assembly (DFA)1) major
guidelines2) insertion time analysis

• TEC 316
• Dr. Lou Reifschneider

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Reverse Engineering Findings(crate full of
partshow things are made)

• Number of parts to make product?
• Types of fastening (assembly) methods?
• Variety of materials used
• Metal
• Plastic
• Other
• Processes used to make the majority of parts in
  products?
• Injection molding or die casting?
• Extrusion (plastics or metal)?
• Forming forging or rolling?
• Machined components?

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DFM DFA Defined

• DFM, Design for Manufacturability
• Design to minimize part count (save , improve
  reliability, and improve quality).
• Design to ease manufacturing by applying process
  specific rules later discussion.
• DFA, Design for Assembly
• Simplify methods of joining components and make
  more error proof and less costly
• Minimize parts count,
• Maximize the ease of handling parts,
• Maximize the ease of inserting parts.

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WHY Product Design is Important
70 of Cost committed BEFORE Detailed Product
Design
100
100
95
85
Committed Cost
85
70
75
Percent of Product Costs
50
40
Incurred Cost
DFM DFA
25
25
15
0
Concept Development
Preliminary System Design
Detailed Product Design
Process Tool Design
Production
Product Support
Product life-cycle phases / Time
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DFMA Methodology
Proposed Design
Estimate the Manufacturing Costs
Inventory, suppliers
Reduce Costs of Components
Reduce Costs of Assembly
Reduce Costs of Supporting Production
Impact of DFM on other factors?
Development time/cost, product quality
Recompute the Manufacturing Costs
Good Enough?
No
Yes
Acceptable Design
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General Design Principles for Manufacturability
The 10 Rules. (DFMH, 2nd Ed, Bralla G.) (1/2)

• 1) Simplicity. (fewest parts, simple shape, few
  precision adjustments) (easiest to make and
  least costly reliable)
• 2) Standard materials and components. (simplify
  purchasing and inventory)
• 3) Standardized design of product. (group
  technology)
• 4) Liberal tolerances. (tighter tolerance more
  )
• 5) Use the most processable materials. (mild
  steel vs. stainless steel), (ultimate tradeoff
  matl cost vs. cost to manufacture)

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General Design Principles for Manufacturability
The 10 Rules. (DFMH, 2nd Ed, Bralla G.) (2/2)

• 6) Teamwork with manufacturing personnel.
  (collaboration yields success) (value of ISU
  degree)
• 7) Avoid secondary operations. (adds )
• 8) Design appropriate to level of production.
  (lt1,000 machine gt1,000 cast) (tooling vs. high
  volume)
• 9) Utilize special process characteristics.
  (injection molding achieves color and texture
  during molding, can mold living hinges)
• 10) Avoid spec.machining process. (only spec
  final dimensions surface finish, allow
  machining expert to find best method)

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Rearrange connected items to improve assembly
efficiency and reduce costs
Increased Efficiency
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Approximate Relative Cost of Progressively
Tighter Dimensional Tolerances
Surface Finish ?
N.E.Woldman, Machinability and Machining of Metals
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Approximate Relative Cost of Progressively
Tighter Dimensional Tolerances Finer Surface
Finish
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Optimal Tolerance Balance

• Quality
• Safety
• Manufacturability
• Avoid Tolerance Block (all dims /-.005)
• .XXX /-.005 .XX/-.01,
• Critical dimensions tight tolerance.
• Low demand dimension looser tolerance (and
  cheaper parts)

10 rules
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Manufacturing Options Machine from Brass
or Injection Mold Glass Reinforced PET /lb
GR-PET gt /lb Brass BUT, Injection Molding
Permits gtgt Less material usage gtgt Faster
production times But tooling costs of IM is high.
Figure 8.03 Designing With Plastic by Hoechst
Celanese
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Product Design Process Selection is Driven by
Order Size
Machining
10/unit matl processing
Injection Molding
Total Cost
1/unit matl processing
Mold Cost 10,000
Fixture Cost 1,000
1,000 units
Number of Units Produced
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Part consolidation with alternative manufacturing
method injection molding
Figure 6.2.2 Design for Manufacturability
Handbook by Bralla, Ed.
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Injection Molding Permits gtgt Consolidation of
pieces into one molded part gtgt Reduction of
assembly cost
1st
2nd
Figure 8.02 Designing With Plastic by Hoechst
Celanese
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Anderson on DFX (DFM, DFA,)
ANDERSONS LAW NEVER MAKE A PART THAT CAN BE
PURCHASED FROM A CATALOG

• Design for Manufacturability Concurrent
  Engineering
• Dr. David M. Anderson

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Anderson on DFX (1/4)

• A1) Understand manufacturing problems/issues of
  current/past products. (learn from your
  mistakes and successes)
• A2) Design for easy fabrication, processing, and
  assembly. (easy repair, too)

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Anderson on DFX (2/4)

• P1) Adhere to specific process design
  guidelines molding, forging, machining.
• P2) Avoid right/left hand parts consolidate
  similar parts (suit case).
• P3) Design parts with symmetry ease of
  assembly
• P4) If part symmetry is not possible, make parts
  very asymmetrical allow for low-tech automated
  orientation.

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Anderson on DFX (3/4)

• P5) Design for fixturing part registration for
  machining and assembly (tooling pins on parts)
• P6) Make part differences very obvious.
  (color, markings, packaging)
• P7) Specify (liberal) optimal tolerances for a
  Robust Design. (but product still reliable)
• P8) Specify quality parts from reliable sources.
  See Rule of 10 ?

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Anderson on DFX (4/4)

• The Rule of 10 (cost to fix problem)
• part X sub-assm 10X final assm 100X dealer
  1,000X customer 10,000 X
• P9) Minimize Setups machining key dimensions on
  same setup (fixture)
• P10) Design to Minimize No. of Different Cutting
  Tools (tool changes more inventory) (use
  standard tool sizes)
• P11) Understand tolerance step functions and
  specify tolerances wisely.

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Injection Molded Part Guidelines

• Minimize wall thickness (less material, less
  cooling time, less warpage)
• Stiffness gained with ribs, not mass.
• Draft angle for mold release.
• Avoid sharp corners (stress) Rout Rin t
• Rib root 60 wall (minimize sink)
• Core thick sections, gradual thickness change.
• Gate into thick area, not thin.

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Machined Part Guidelines (1/2)

• Design holes to shape of tool. Tapped hole allow
  for space.
• Use standard dimensions Dont F.627 Do
  F.625
• Do not design impossible to machine hollows,
  overhangs,
• Internal pockets have radii Dont square inside
  or R.125, Do R.25
• Avoid thin walls
• Avoid drilling inclines faces.

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Machined Part Guidelines (2/2)

• Place hole away from corners (assembly)
• Provide access for tools (drill chuck)
• Avoid vibration
• work piece mill at end of thin section,
• tool mill deep pocket with narrow mill.
• Holes cannot change direction.
• Design for fixturing flats on cylinders.
• Avoid outside round corners need CNC vs.
  chamfer. (chamfer blocks going into blind pockets)

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Major DFM ThemesSimplify and Standardize

• Group Technology (GT)
• new products similar in design to existing (allow
  use of same fabrication or assembly machinery and
  methods),
• Supply Chain Management
• database of approved suppliers, easy access to
  acceptable component data
• Reduce complexity (and No. of Parts)
• reduce cost improve quality
• achieved w/ modular block assembly

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Why Reduce Part Count?
Parts
Operations
Machines
Inventory
Labor
Errors
Warehouse
Transport
Wages Benefits

All this adds to COT!
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Design for Assembly

• Assembly costs two components.
• Two Key Points
• Reduce number of discrete parts in the assembly.
• Design remaining parts so they are easy to make
  and assemble.

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The Four Aspects of DFA(Refer to handouts for
images)

• System design (Fig. 14.3, Otto Wood)
• modularize multiple parts into subassemblies,
  open access, parts should indicate orientation,
  standardized components.
• Handling components (Fig. 14.4, Otto Wood)
• max. symmetrymin. handling, avoid tangling
  nesting, color code similar geometry parts,
  orientation features.
• Insertion (Fig. 14.5, Otto Wood)
• mating features (chamfers), alignment features,
  from above, from same direction.
• Joining (Fig. 14.6, Otto Wood)
• fewer fasteners, no obstruction, access to tools,
  fasten on flats.

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DFA Guidelines (PDD, Otto Wood) (1 of 2)

• 1. Minimize part count.
• 2. Modularize multiple parts.
• 3. 14. 15. Assemble in open space, preferably
  vertically, and minimize change of orientation
  (set-ups).
• 4. 11. Place orientation features on
  components.
• 5. Standardize to reduce part variety.
• 6. Maximize part symmetry (eases assembly).

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DFA Guidelines (PDD, Otto Wood) (2 of 2)

• 8. 10. Eliminate parts that tangle or nest.
• 9. Color code parts of same geometry.
• 12. Design mating features for easy insertion.
• 13. Provide alignment features (chamfers).
• 16. Eliminate fasteners.
• 17, 18, 19, 20. Design for fastening tool access
  and ease of use.

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Restricted access for assembly of screws
Design A
Design B
Better Design for Assembly
Poor Design for Assembly
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Maximize Ease of Assembly

• Insert part from top of assembly.
• Part self-aligns.
• Part needs no orientation.
• One-hand operation.
• No tools needed.
• Single linear motion achieves assembly.
• Part is secure immediately upon insertion.

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To Eliminate Parts, Ask 3 Questions

• 1) Does part move with respect to mating parts?
• 2) Must adjacent parts be made of different
  materials for fundamental physical reasons?
• 3) If parts were combined, would assembly of
  other parts or field service be more difficult or
  unfeasible?
• If answer to all three is NO, then part in
  question could be eliminated by putting its
  function into some other part of assembly.

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Major Benefits of Part Reduction

• minimize defective part or assembly error,
• decrease total cost of fabrication assembly,
• improve chance to automate assembly

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Boothroyd Dewhurst Analysis of Manual Assembly
Methods

• Establish theoretical minimum handling times
  based upon shapes and sizes of components being
  assembled. (graphs)
• Assembly product record all steps.
• Define
• Decision matrix

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Ease Assembly Chamfer Geometries on Peg and Hole
Fig. 3.23 Design for Manufacturability Handbook,
Bralla
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Effect of clearance on insertion time
Fig. 3.24 Design for Manufacturability Handbook,
Bralla
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Effect of part size on handling time
Fig. 3.20 Design for Manufacturability Handbook,
Bralla
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Effect of part shape on handling time
Handling time
Figs. 3.17 3.18 Design for Manufacturability
Handbook, Bralla
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CASE STUDY John Deere Co. (Moline, IL) set a
company goal to reduce the cost of parts
purchased by its major equipment divisions.
There were two ways to meet that goal buy less
expensive parts or buy fewer parts. The first way
required legwork and shrewd bargaining. The
second required better product designs. And for
that, Deeres engineers were helped by Design for
Manufacture and Assembly (DFMA) software from
Boothroyd Dewhurst Inc. (Wakefield, RI). We
have two mandates for the cost management group
at John Deere reduce part costs and increase
product reliability, says Rich Norton, manager
of cost management. The process and materials
cost-estimating capabilities of DFMA software has
assisted in achieving both goals. DFMA
software combines two complementary toolsdesign
for assembly (DFA) and design for manufacture
(DFM). Engineers use DFA software to reduce the
assembly cost of a product by consolidating parts
into multifunctional designs. DFM software then
allows the design engineer to quickly judge the
cost of producing the new design and to compare
it with the cost of producing the original
assembly. An extensive library in the software
enables product developers to investigate
alternative materials and processes for producing
parts. The cost management group at John Deere
works with cross-disciplinary teams that include
members of the supply chain. The teams review a
bill of materials for a part to establish a
benchmark. They then perform DFM analyses of
materials and manufacturing processes to redesign
the part and provide the supplier with a
should-cost estimate based on the new
design. http//www.assemblymag.com/CDA/ArticleInf
ormation/features/BNP__Features__Item/0,6493,13058
3,00.html
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DFA In-Class Assessment Activity
Design A
Design B
Power Component