www.engineeringnews.co.nz 33 Easy assembly If a product must be assembled, attempt to make the task easier by orienting the various screws and connectors in such a way that all are accessible from the same side, thus minimising part flipping and rotating. Use common hardware wherever possible, so the worker doesn’t have to reach for different hand tools. Poke yoke (mistake proof) the assembly by designing in alignment pins and guiding features to avoid mismatched parts. And spend a little time in the assembly room: Knowing the issues that emerge at this stage often yields big improvements in part design. Over and out Often, two or more components can be moulded together. Rather than welding, gluing, or screwing a rubber grip onto a plastic instrument case, overmoulding creates a permanent bond with no need for secondary assembly processes. The two plastics must be chemically compatible, but an array of material combinations and colours are available. Similarly, the aforementioned threaded inserts can be placed into the mould before pressing cycle start on the injection moulding machine, permanently fixing the metal inserts in the plastic. A large assortment of bushings, pins, and fasteners can be moulded directly into plastic parts, saving time and simplifying designs. Proto Labs currently doesn’t supply common off-the-shelf inserts but expects to do so at some future point. Liquid silicone rubber parts Due to its “cold set” properties, extremely agreeable flow characteristics, and disregard for traditional moulded part concerns like sink and knit lines, liquid silicone rubber (LSR) is breaking many of the rules of injection moulding. LSR parts probably aren’t going to reduce assembly part count, but they do eliminate many moulding headaches and are often a great alternative to other “squishy” materials. Complex gaskets and seals can be accurately formed, and because LSR is biocompatible, heat resistant, and withstands sterilization, is a material of choice for many medical and food applications. LSR is also forgiving of large variations in wall thickness, and undercuts are easily accommodated. For the right application, it offers big advantages. Looking at alternatives It’s a great time to be in manufacturing. Technologies and materials only dreamt of a few decades ago are now turning the design and engineering world on its head. Industrial 3D printing is one of these. Quantities permitting, parts that once required construction of an injection mould or setup and programming of a CNC machine tool can now be 3D printed in a fraction of the time and cost. What’s more, the “free complexity” that comes with 3D printing often produces one-piece BOMs, thus eliminating assembly, and with part materials suitable for long-term use. Proto Labs has multiple 3D printing options available, including processes that can build plastic, metal, and elastomeric parts. Of course, some multipart assemblies are best done the old-fashioned way, by machining individual pieces and assembling them. Yet even here, the rules of designing for manufacturability and assembly apply. Keep things simple, don’t make what you can buy off the shelf, explore all your manufacturing options, and understand the rules of each. Stick close to the guidelines and you’ll be designing cost-effective and efficient multipart assemblies in no time.
EN-June2017-eMag2
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