Designing a new part is a complicated process. Typically there are a number of problems to overcome. A few important considerations might include a few of the following:

• The mechanical function and design of the overall product

• The mechanical function or design of a particular subcomponent of the larger product

• Selecting the proper material for both a prototype part and a mass-manufactured, marketable product (ideally these are the same)

• Finding the appropriate machinery suited to create a prototype of the part in the chosen material (typically a CNC machine with sheet stock of the material or a 3D printer with a specially designed material cartridge

• Design considerations for production (e.g. tool design for injection molded manufacturing).

There are a vast number of considerations when building a part in general. In this blog we want to focus on things to consider when choosing the particular plastic for your prototype part. What should you consider when trying to make such a decision?

Here are three quick steps to point you in the right direction:

1. Determine the Purpose of the Particular Part

   - Different plastics are suited to different functional purposes. Is the part mechanical, load bearing, purely aesthetic? Does it experience friction? How does it relate with the other parts in the larger device?

2. Choose the Appropriate Stock Material

   - The general availability of plastics is variable. Commonly used plastics like ABS or Delrin® (a common acetal) are typically in stock from a supplier. Other plastics may require special ordering and/or increased pricing.

   - Consider the material’s availability as a sheet, rod or pipe (e.g. for use in a CNC machine), or as a printable material for use in an FDM (3D printer). Typically FDM machines are the best option when trying to match production plastics. You can mimic some plastics with other 3D printing options such as SLA or SLS, but you typically can’t use the same exact material. SLA materials start off as liquids and are cured when hit with a laser. The process causes some inherent differences in the end product. SLS is similar to SLA except that a powdered material (typically Nylon) is hit with a laser to fuse it with another surrounding powder. This can be a good option if the end part will be nylon. You can read all about 3D printing here.

   - Consider the plastic’s ability to be prototyped. Again, different plastics are more suitable to CNC machining (e.g. polypropylene) while others can be easily 3D printed (e.g. ABS).

   - Consider the material’s feasibility as an injection moldable polymer. Will you use the same material for a prototype as you will in final manufacturing?

   - Consider the plastic’s recyclability after use by the consumer. If so, make sure to use a thermoplastic as opposed to a thermoset material. Read more on thermoplastics here and recyclable plastics here.

3. Design, Engineer, and Construct a Prototype Part

   - Consider whether you want to construct a single prototype or whether you want create 300-1000 injection moldable prototypes for testing prior to mass production. If a few hundred to a thousand injection moldable prototypes are desired then an injection molding tool will need to be designed and built (“tools” are typically steel or aluminum blocks with an internal cavities that represents the negative of your prototype part). Mold flow software like Solidworks Plastics will be very useful in such a case.

If you want to read about some common plastics that are likely to be useful for your prototype part design projects, consider the following blogs:

Acetal (Polyoxymethylene; POM): A very common low-friction plastic that is useful for applications like gears.

Polypropylene (PP): A very flexible plastic that is best known for its application in living hinge geometries.