EML 4550: Engineering Design Methods Design for Manufacturing and Assembly (DFMA) (Examples)
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
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?
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
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)
Holes • Keep L/D < 3 whenever possible • Do not specify holes that ‘turn corners’
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
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
Symmetry Illustration of principle: Which part can be ‘aligned’ with minimum rotation? How many axes of symmetry?
Fastening • Consider the least expensive fastening method that meets the requirements
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
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 Handling
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?