EML4550 2007 1

EML 4550: Engineering Design Methods

Design for Manufacturing and Assembly (DFMA)(Examples)

EML4550 2007

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

EML4550 2007

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?

EML4550 2007

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

EML4550 2007

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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Holes

Keep L/D < 3 whenever possible Do not specify holes that ‘turn corners’

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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

EML4550 2007

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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Symmetry

Illustration of principle: Which part can be ‘aligned’ with minimum rotation?How many axes of symmetry?

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Self-locating parts

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Self-locating parts

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Top-down assembly

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Fastening

Consider the least expensive fastening method that meets the requirements

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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

EML4550 2007

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

EML4550 2007

EML4550 2007

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?

EML4550 2007

BDI Example