This document discusses design for manufacturing and assembly (DFMA). It provides definitions and principles for design for manufacturing (DFM) and design for assembly (DFA). DFM aims to reduce production costs by simplifying manufacturing, while DFA aims to reduce assembly costs by making the product easier to assemble. The key is balancing DFM and DFA according to the DFMA approach. Guidelines are provided for both DFM and DFA, focusing on issues like part count, joining, tolerances, symmetry, and self-locating features. Metrics like design efficiency are also discussed for evaluating assembly difficulty and time.
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EML 4550: Engineering Design Methods
Design for Manufacturing and Assembly (DFMA)
(Examples)
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Design For X (DFX)
A successful design must consider all relevant
considerations throughout the life cycle of a product by
analyzing the causes and effects of the product.
A common set of design guidelines for X includes:
Assembly
Environment
Manufacturing
Quality
Reliability
Safety
Serviceability
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Definitions
Design for Manufacturing (DFM)
Concerned with reducing overall part production cost
Minimize complexity of manufacturing
Use common axes and common processes
Design for Assembly (DFA)
Concerned with reducing product assembly cost
Minimize number and complexity of assembly operations
Individual parts may be more complex in design
Trade-off between DFM and DFA ===> DFMA
Why?
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Principles of DFM (DFM Guidelines)
Simplify and reduce the number of manufacturing
operations
Standardize materials and use common parts
Design for efficient joining
Open tolerance as much as possible
Allow over-travel in part design
Avoid special tooling and frequent tool changes
Select materials for best manufacturability
Specify ‘acceptable’ surface finish for functionality
Machine for one primary axis whenever possible
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Grooves
Consider degree of difficulty in cutting grooves
Use as big a radius as possible in corners (sharp edges are difficult to
cut and keep uniform)
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Plastic injection molding
Minimize wall thickness variations to allow for uniform
cooling rate (warped parts)
Features should be on top or sides of part to allow for ease
of forming
Consider molding + machining as an option
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Principles of DFA (Guidelines for Assembly)
Minimize part count
Design parts with self-locating features
Design parts with self-fastening features
Minimize reorientation of parts during assembly
Emphasize ‘top-down’ assemblies
Standardize parts
Encourage modular design
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Design efficiency
A quantitative measure of time and cost required to
assemble a product
A rating which can be used to judge the effectiveness of a
current design (a benchmark for future improvements)
Design efficiency is the end result measure as calculated by
the Boothroyd-Dewhurst process
Symmetry of parts (repeatability for orientation)
Size and thickness
Handling time
Insertion time
Boothroyd & Dewhurst complexity factor
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Handling
Handling Time
How many hands required?
Any grasping assistance needed?
Effect of part symmetry on
assembly
Is part easy to align/position?
Insertion time
Is part self-securing?
Need to hold down?
What fastening process?
Easy to align/position?
Handling difficulty
Size
Thickness
Weight
Fragility
Flexibility
Slipperiness
Stickiness
Necessity for using:
Both hands
Optical magnification
Mechanical assistance
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BDI criteria for part minimization (Column 9)
If the answer to ALL THREE of these questions is NO, then
the part is a candidate for elimination (“0” in column 9)
During operation of the product does the part move relative to all
other parts already assembled? Only gross motion should be
considered (small motions that can be accommodated by elastic
hinges, for instance, should not count as positive answer)
Must the part be of a different material than all other parts already
assembled? Only fundamental reasons concerned with material
properties are acceptable
Must the part be separate from all other parts already assembled
because otherwise necessary assembly or disassembly of other
separate parts would be impossible?