Dfma

Design For Manufacturing/Assembly (DFM, DFA, DFMA) Much of the early and significant work on DFM and DFA was done in the early 1970s by Boothroyd and Dewhurst. Traditionally, product development was essentially done in several stages. The designer(s) (who usually had very good knowledge of materials, mechanisms, etc.) would design the product, and sometimes would construct working prototypes. Once the prototype was tested and approved, the manufacturing team would then construct manufacturing plans for the product, including the tooling etc. Often, different materials (e.g. different thickness or type of sheet metal), and different components (e.g. different sized screws etc), would be substituted by the manufacturing team. Their goal was to achieve the same functionality, but make mass production more efficient. However, the majority of the design remained unchanged, since the manufacturing engineers could never be sure whether a change would affect some functional requirement. Two things changed in the 1970’s: (i) Many new types of plastics were developed, and injection moulding technology became widely available, resulting in the possibility of low cost plastic components. An advantage of these new plastic materials was that they provided different material behaviour (e.g. many cycles of large elastic deformations without failure – a property useful in making snap-fit mating components). Thus pats that had to be made form metal and screwed together could just be made out of plastic and snap fitted. This reduced assembly time, assembly components, and production costs. (ii) Several companies were trying to bring their products to the market faster. One problem with the earlier method of doing things was that each time there was a design change made by the manufacturing engineer, product development was held up, waiting for the engineering change notice (ECN) to be approved by the designer. Often, this process introduced delays because the design engineer would be

References: Otto and Wood has a good chapter on DFMA Product Design for Manufacture and Assembly, Geoffrey Boothroyd, Peter Dewhurst, Winston Knight, 2nd Edition, Marcel Dekker, New York Several figures in these notes are from the or1gonal Boothroyd and Dewhurst workbook: Product Design for Assembly, Geoffrey Boothroyd and Peter Dewhurst, 1991, Boothroyd Dewhurst Inc. 15