EML 4550: Engineering Design Methods
Design for Manufacturing and Assembly (DFMA)
(Examples)
EML4550 2007
1
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)
EML4550
2007
Holes
 Keep L/D < 3 whenever possible
 Do not specify holes that ‘turn corners’
EML4550
2007
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
EML4550
2007
Symmetry
Illustration of principle: Which part can be ‘aligned’ with minimum rotation?
How many axes of symmetry?
EML4550
2007
Self-locating parts
EML4550
2007
Self-locating parts
EML4550
2007
Top-down assembly
EML4550
2007
Fastening
 Consider the least expensive fastening method that meets the
requirements
EML4550
2007
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?
EML4550
2007
Handling difficulty
 Size
 Thickness
 Weight
 Fragility
 Flexibility
 Slipperiness
 Stickiness
 Necessity for using:
 Both hands
 Optical magnification
 Mechanical assistance
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
EML4550
2007