SME DFM Tech Paper

1. TP05PUB214
TECHNICAL PAPER 2005 Society of Manufacturing Engineers ■ One SME Drive ■ P.O. Box 930
An Account of the Use of DFA/DFM
Tools in Modern Manufacturing
Enterprises
author(s)
TOM PAGE
Loughborough University
Loughborough, Leicestershire, England
abstract
This paper provides an account of the role of design for manufacture (DFM) and
design for assembly (DFA) in modern manufacturing enterprises. Software tools for
integrated design for manufacture are presented with trend data on the use of such
tools. A decision model for design for manufacture and assembly is also discussed
for the purpose of highlighting the key features of these methodologies.
terms
Design for Assembly
Design for Manufacture
Integrated Design Tools
Concurrent Engineering
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3. An Account of the Use of DFA/DFM Tools
in Modern Manufacturing Enterprises
T. Page, Department of Design & Technology,
Loughborough University, UK
Abstract: This paper provides an account of the role of Design for Manufacture
(DFM) and Design for Assembly (DFA) in modern manufacturing enterprises.
Software tools for integrated design for manufacture re presented with trend data
on the use of such tools. A decision model for design for manufacture and
assembly is also discussed for the purpose of highlighting the key features of
these methodologies.
Keywords: DFA, DFM, Integrated software tools, Concurrent Engineering
DFM / DFA
ƒ Concurrent Engineering
ƒ Design for Manufacture (DFM)
o What is DFM?
o Principles of DFM
ƒ Design For Assembly (DFA)
o What is DFA?
o Principles of DFA
ƒ Integrated Design Tools
Concurrent Engineering
ƒ Concept
o Consumers demand products that meet design requirements at the
lowest price
o Manufacturability issues have the greatest effect on product cost
o Designers can directly affect the cost of products by considering
manufacturability issues during the product design phase
ƒ Practice
o First recognized by Japanese manufacturers in the late 1970’s
o Concurrent engineering attempted to bridge the gap between
design and manufacturing
o Best design practices were documented and organized into rules
and guidelines
o Beginning of DFM
Design for Manufacture
ƒ What is DFM?
o Fundamental tool of concurrent engineering
o Essentially a system of design principles, guidelines and rules
o System narrows the region for an optimal design solution
o Increases the probability of a sound design solution

4. 2
Design for Manufacture
ƒ Where did DFM come from?
o Old System - “School of Hard Knocks”
o Designers learned good design practices on the job by trial and
error
o Experience divided good designers from bad
ƒ New System - DFM
o Good design practices documented and organized
o Inexperienced designers learned best design practices from
beginning
o Design learning curve flattened
Principles of DFM
ƒ Reduce the total number of parts
o Most fundamental concept
o Greatest opportunity for cost savings
ƒ Develop modular designs
o Builds in versatility of manufacture and redesign
ƒ Use standard components
o Reduced cost
o Shorter lead time
ƒ Design parts to be multi-functional
o Reduces total number of parts in product
ƒ Design parts to be multi-use
o Reduces total number of parts in system
ƒ Design for ease of fabrication
o Select optimum materials and processing
o Eliminate secondary operations
ƒ Avoid use of separate fasteners
o Reduces handling and feeding
o Increases product quality
ƒ Minimize assembly directions
o Downward assembly direction is optimal
ƒ Maximize compliance
o Use design features to facilitate assembly
o Use chamfers and solid base parts
ƒ Minimize handling
o Symmetrical parts reduce handling
o Asymmetries should be exaggerated to reduce handling errors
o Avoid flexible components
o Reduce packaging materials
Design for Assembly
ƒ What is DFA?
o Quantitative product simplification tool
o Reduces scope of design problem
o Relates design decisions directly to cost

5. o Increases effectiveness of subsequent application of DFM
3
techniques
o Potential savings
ƒ 20-40% Manufacturing cost reduction
ƒ 100-200% Assembly productivity increase
Principles of DFA
ƒ Two step approach
o Reduce the total number of parts
ƒ Similar to DFM principle
ƒ Quantitative method
ƒ Uses theoretical minimum as baseline
o Estimate handling and assembly costs
ƒ Based on practical data
ƒ Generates estimated costs before detail design begins
ƒ Efficiency index relates disparate manufacturing processes
o Reduce the number of parts
ƒ Determine the theoretical minimum
o Parts must meet three criteria to be indispensable:
o There is relative motion between the part and all other
parts already assembled
o The part must be made of a different material or be
isolated from all other parts already assembled
o The part must be separated from all parts already
assembled because necessary assembly or
disassembly would otherwise be impossible
ƒ Estimate handling and assembly costs
o Select assembly processes
ƒ Six alternatives
o Manual Assembly (MA)
o Manual with Mechanical Assistance (MM)
o Automated assembly, Indexing-transfer (AI)
o Automated assembly, Free transfer (AF)
o Automated, Programmable assembly (AP)
o Automated, programmable Robot assembly (AR)
o Calculate assembly cost
ƒ Additional input data
o Projected market life
o Number of parts
o Projected production volume
o Company investment policy
o Calculate assembly design efficiency
ƒ Em = 3 * Nm / Tm
Em = Manual assembly design efficiency
Nm = Theoretical minimum number of parts
Tm = Total assembly time
Assumptions:
- Parts are easy to handle
- One third of parts are
secured completely after
insertion

6. 4
ƒ Re-design product
o Reduce number of parts to theoretical minimum
o Reduce excessive handling and assembly costs
ƒ Re-evaluate assembly design efficiency
ƒ Repeat process within budgetary constraints
ƒ Proceed to DFM analysis
Integrated Design Tools
ƒ DFA Software
o BDI-DFM released in 1981
ƒ Developed by Boothroyd-Dewhurst, Inc.
ƒ Became industry standard for concurrent engineering
processes
ƒ Reduced part costs as well as assembly costs
ƒ Allowed designers to estimate assembly times
ƒ Highlighted areas of potential improvement
ƒ Quickly indicated the effects of design changes on assembly
time and cost
ƒ Appeared in mid-1980’s
ƒ Provided guidance in the selection of materials and
processes
ƒ Generated piece part and tooling cost estimates at all stages
of product design
ƒ Trade-off analysis of design alternatives
ƒ Trade-off analysis of process alternatives
ƒ Quickly spread to many industries
DFM Software
2003 National DFM Survey of Leading Design Engineers Prepared for Galorath Incorporated

7. DFM Software
Purposes for which DFM is used in your company/division
2003 National DFM Survey of Leading Design Engineers Prepared for Galorath Incorporated
5
DFM / DFA Discussion
ƒ Manufacturers of DFM / DFA software
o Commercial software vendors
o Boothroyd-Dewhurst (BDI) software
ƒ BDI-DFA
ƒ BDI-DFM
ƒ Decision Model
o Functions?
o Processes?
o Interface / OS?
Commercial Software Vendors
ƒ Boothroyd Dewhurst Inc
ƒ Galorath Incorporated
ƒ EASE Inc.
ƒ Manufacturers Technologies
ƒ Valor Computerized Systems
ƒ IBM
ƒ Cadence
ƒ Mentor Graphics
ƒ Avanti Technologies Inc
BDI Software
BDI Software

8. 6
ƒ Design for Assembly
o Product simplification through DFA
ƒ Design for Manufacture
o Aids in the selection of materials and processes
o Provides piece part and tooling cost estimate
o Feedback to Design for Assembly
ƒ Design for Service
o Improve the serviceability and maintainability
ƒ Design for Environment
o Environmental impact of the final design
BDI-DFA Software
ƒ Structure Chart
o Build complete list of items and operations directly on the Structure
Chart
o Entries appear as blocks in a tree form showing the structure of the
product
ƒ DFA Questions Window
o Perform a basic DFA analysis by answering questions on
ƒ part geometry
ƒ handling and insertion difficulties
ƒ minimum part criteria
ƒ Suggestions and Graphs for Redesign
BDI-DFM Software
ƒ The main program in BDI DFM software is
ƒ DFM Concurrent Costing
ƒ Detailed programs also available for
ƒ Machining
ƒ Injection Molding
ƒ Sheet Metalworking
DFM Concurrent Costing
ƒ part cost estimation as they are being designed
ƒ tooling cost estimates
ƒ investigate alternative materials and processes
ƒ provides details of cost drivers that allow for discussions with suppliers
ƒ compare designs with competitors products to determine market feasibility
and target costs

9. 7
DFM Machining Module
ƒ user develops a process chart where machining processes are graphically
displayed
ƒ The software calculates the optimum speed, feed and cost for the given
process and materials
ƒ This information is added to the process chart and the user can continue
to add machining sequences
Output
ƒ the designer has a process chart for the component, total component cost
and a list of optimum speeds and feeds
DFM Injection Molding Module
ƒ Provide the component cost of an injection molded part
ƒ Estimates the mold cost, processing cost and materials cost for the part
ƒ Process parameters, such as optimum number of cavities, set up time, set
up cost, and mold time are estimated by the software
ƒ Allows designers to see the cost impact of tolerance and finish
specifications which can then be optimized by "what if" analysis
ƒ This software also useful in evaluating vendor quotes
DFM Sheet Metalworking Module
ƒ The software estimates
o the per part cost of sheet metal dies
o primary shaping and forming costs (blanking, bending, etc.)
o secondary operations costs (deburring, painting, etc.)
o material costs (cost impact of using a different material or gage
thickness)
o compare processes such as stamping verses turret press work
Output
ƒ The costs are presented to the user in report or graphical format defining
the primary operations, number of dies, typical press force, cycle time per
part, machine rate, operation cost per part, set-up time, and die cost
Decision Model
ƒ Decision Table
o What functions must the software support?
ƒ Design for Manufacture
ƒ Design for Assembly
ƒ Design for Service
ƒ Design for Environment
ƒ Cost Estimation

10. 8
Decision Model
ƒ What processes must the software support?
o Mechanical Assembly
o Electrical Assembly
o Machining
o Fabrication
o Plastic Molding
o Finishing
o Welding
o PCB Fabrication
o IC Assembly
Is a specific interface support required?
ƒ Pro-Engineer
ƒ CATIA
Is a specific operating system required?
ƒ Windows OS
ƒ UNIX OS