Download Design for Assembly - Design and Dissemination - Lecture Notes and more Study notes Development Economics in PDF only on Docsity! Design for Assembly Background When assembly is taken into account during the design process, several good things should happen. Quality and reliability are improved because there are fewer parts, and the device is simpler to put together. In the U.S., one often tries to limit number of jobs required. This goal does not necessarily fit in developing countries. Scale may be different because transportation challenges lead you to a more decentralized manufacturing model. Finally, hand workmanship means less strict standardization (less repeatability). Assembly methods include • Manual assembly • Fixed automatic assembly • Flexible automatic assembly What considerations affect the choice of methods? For manual assembly, the cost is fixed per unit regardless of the production volume. Fixed automatic assembly (i.e. injection molded part), the more units produced, the closer you get to just the cost of the materials (spreading fixed tooling costs and capital). Robotic or flexible assembly allows capital costs to spread across multiple uses, making cost per unit non-linear at lower volumes. Hands-on Assembly Exercise Groups of two students disassemble and then reassemble two items – a small keychain flashlight and a container of dental floss. How long does it take to take all the pieces apart? What’s the part count? What do you notice about the way the parts fit together? The flashlight had 18 pieces. Takes 1-5 minutes to take apart, and 6 minutes to “infinite” (i.e. parts broke during disassembly) to put back together. Note in particular the challenges posed by six very small screws. Docsity.com Floss container took just a few seconds to disassemble, only 3 or 4 parts. The case has several segments, hinged, making assembly much easier. No tools needed. What does this say about principles of good Design for Assembly: • Connected pieces or segments • Small parts are harder to work with • The fewer tools required, the better • Any clues to alignment are helpful • Deformable parts are a problem • Snap-fit assembly (vs. screws) reduces part count, simplifies assembly. Design Guidelines for Manual Assembly. Try to make it so there’s only “one way” – e.g. one sequence or one orientation for things to happen. Don’t hide important parts. Try to make everything self-aligning. Jigs and fixtures for manufacturing are quite helpful. If you take care with the jig, then each manufactured part is easily made, as it inherits the quality of the jig. (Photos courtesy of DISACARE. Used with permission.) Continuing…imagine what a pain it would be if 3 of six screws where Philips head, and 3 were slot head screws. Loose wires are particularly prone to getting tangled during assembly. Design Guidelines for Automated Assembly Reduced part count: floss container used to have a separate “lid” snapped in, but that’s not needed. Instead, the entire package can be made from a single hinged piece of plastic. Ask: does one part need to move relative to other parts during actual use? If not, maybe it can be manufactured as a single segmented part. Docsity.com
