EML EML 4550: Engineering Design Methods Design for Manufacturing and Assembly (DFMA) (Examples)

EML Design For X (DFX) nA successful design must consider all relevant considerations throughout the life cycle of a product by analyzing the causes and effects of the product. nA common set of design guidelines for X includes: lAssembly lEnvironment lManufacturing lQuality lReliability lSafety lServiceability

EML Definitions nDesign for Manufacturing (DFM) lConcerned with reducing overall part production cost §Minimize complexity of manufacturing §Use common axes and common processes nDesign for Assembly (DFA) lConcerned with reducing product assembly cost §Minimize number and complexity of assembly operations §Individual parts may be more complex in design nTrade-off between DFM and DFA ===> DFMA lWhy?

EML Principles of DFM (DFM Guidelines)(DFM Guidelines) nSimplify and reduce the number of manufacturing operations nStandardize materials and use common parts nDesign for efficient joining nOpen tolerance as much as possible nAllow over-travel in part design nAvoid special tooling and frequent tool changes nSelect materials for best manufacturability nSpecify ‘acceptable’ surface finish for functionality nMachine for one primary axis whenever possible

EML Grooves nConsider degree of difficulty in cutting grooves nUse as big a radius as possible in corners (sharp edges are difficult to cut and keep uniform)

EML Holes nKeep L/D < 3 whenever possible nDo not specify holes that ‘turn corners’

EML Plastic injection molding nMinimize wall thickness variations to allow for uniform cooling rate (warped parts) nFeatures should be on top or sides of part to allow for ease of forming nConsider molding + machining as an option

EML Principles of DFA (Guidelines for Assembly)(Guidelines for Assembly) nMinimize part count nDesign parts with self-locating features nDesign parts with self-fastening features nMinimize reorientation of parts during assembly nEmphasize ‘top-down’ assemblies nStandardize parts nEncourage modular design

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

EML Self-locating parts

EML Self-locating parts

EML Top-down assembly

EML Fastening nConsider the least expensive fastening method that meets the requirements

EML Design efficiency nA quantitative measure of time and cost required to assemble a product nA rating which can be used to judge the effectiveness of a current design (a benchmark for future improvements) nDesign efficiency is the end result measure as calculated by the Boothroyd-Dewhurst process lSymmetry of parts (repeatability for orientation) lSize and thickness lHandling time lInsertion time Boothroyd & Dewhurst complexity factor

EML Handling Handling Time nHow many hands required? nAny grasping assistance needed? nEffect of part symmetry on assembly nIs part easy to align/position? Insertion time nIs part self-securing? nNeed to hold down? nWhat fastening process? nEasy to align/position? Handling difficulty n Size n Thickness n Weight n Fragility n Flexibility n Slipperiness n Stickiness n Necessity for using: lBoth hands lOptical magnification lMechanical assistance

EML

BDI criteria for part minimization (Column 9) nIf the answer to ALL THREE of these questions is NO, then the part is a candidate for elimination (“0” in column 9) lDuring 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) lMust the part be of a different material than all other parts already assembled? Only fundamental reasons concerned with material properties are acceptable lMust the part be separate from all other parts already assembled because otherwise necessary assembly or disassembly of other separate parts would be impossible?

EML BDI Example