If you’re looking for a plastic part that is resistant to impact, low-friction, and can be easily machined into prototype parts prior to large scale injection molded manufacturing, then acetal is probably the one you want. Acetal, also known as Polyoxymethylene, and frequently identified by the three letter acronym POM, has fairly unique properties that are relevant for a number of common engineering applications. You can read about the specifics here, but in the meantime, here are a few examples of common situations where you might want to use acetal:
Gears: Acetal is a great choice for plastic gears because the typical objective in such a device is to minimize the friction resulting from contact. Acetal is very slippery (i.e. it has a very low coefficient of friction) and therefore minimal energy is lost in the internal contact interaction between gears. Want to learn about gears as a mechanism, read here.
As a “Point of Contact”: What we mean by this is a plastic part that is physically touching another surface (presumably made of some other material). A few examples are useful:
- Think of the small plastic piece on the bottom of a couch that allows it to slide more easily across the floor without damaging either the floor or the leather.
- Another relevant application might be as a guitar pick, a pinch valve, or a plastic buckle. Anything where low-friction is a highly desirable characteristic.
Turning raw acetal stock into a prototype part typically starts by choosing the particular brand you wish to work with. Definitely the most popular and readily available product is known as Delrin®. This is DuPont’s trademarked name for their specific product formula (an acetal homopolymer). You can read about some of the specific differences between homopolymers and copolymers as well as some other available acetal brands here.
Typically we use Solidworks Computer Aided Design followed by programming the CNC machine to manufacture prototypes out of Delrin® sheet stock; raw material that is provided by DuPont wholesalers in both white and black colors. Although there has been some experimenting re: 3D printing with acetal, currently neither Stratasys nor 3D Systems (the two major technology providers in the 3D printing space) are doing it. This indicates that acetal is likely difficult to print with. From the prototype design and manufacturing perspective, we would have to make major adjustments to our machinery to print in such a material. As a result, we typically print using ABS plastic while using the CNC machine for prototype parts with special material requirements (such as the requirement that they be made from acetal).
Curious about 3D printing with Acetal? It’s possible, but definitely not likely - especially from a professional design shop. The reasons for this are fairly simple. First, ABS is an extremely convenient material to print with (read more about ABS here). Second, companies like Stratasys may require shops to pay large license fees to print in alternate materials. Third, adjusting a 3D printer’s specifications to print in different materials is time consuming. Repeated switching back and forth is not practical. A design shop could buy an additional machine to print in alternative materials and thus escape the time it takes to make the adjustments, but such an endeavor is expensive and typically not justified by the low volume of requests to print in specialty materials. An easier solution is to CNC machine prototypes out of the specialty material or to print prototypes in a common material like ABS and then develop tooling for injection molded prototypes in the actual material from this starting point.