Tony Holtz, applications engineer, Proto Labs Inc.

The range of choices available for a prototype or production process can be overwhelming. Here are a few tips to keep in mind when selecting a material for either stereolithography (SL) or injection molding applications.

One factor with materials is that there are a lot more materials available for injection molding than for SL. For SL, there are a dozen or so materials versus thousands for injection molding.

Second, injection molding uses actual thermoplastics. SL, on the other hand, uses resin-like materials because of the need to cure them with a UV light source. Thus, SL works with representations of injection molding materials.

For SL, Protolabs offers polypropylene-like, ABS-like, a glass-filled polycarbonate-like, and even a mimicry of die-cast aluminum. SL is one of the few technologies that offers clear materials to produce transparent parts, such as lenses or parts that show the internal workings of a design.

For injection molding, it offers any of the thousands of thermoplastic materials available.

Because SL materials are resin like, the material properties will not be exact matches to actual resins. In an ABS-like material, for example, the heat resistance, the elongation breaks, the tensile strengths, all the technical details behind the resin are not going to match that of a traditional ABS material. How much of a difference exists in their properties depends on such factors as the build orientation, thickness of the part, and others. In addition, the life of the part won’t be as long as a part made from the actual material. UV cured materials tend to break down more quickly than actual materials, either due to continued exposure to light or through age. Humidity is another issue with UV-cured material, as it will speed the breakdown of the material, causing objects to become brittle or change in color.

A tip is to produce a few test parts of the material you would like and explore the mechanical features to see if it’s close enough to fit the need.

Regardless of the SL material, SL parts are good for “show and tell” applications because of the fine feature resolution, and to check for part fit. If a designer needs to focus on other material capabilities, such as strength or thermal resistance, it’s best to consider other 3D printing technologies or injection molding.

Selecting a material for injection molding can be much more confusing than selecting materials for SL because of the number of materials available for injection molding.

With injection molded materials, there is a list of 100 or more materials in a family, which must then be broken down to individual materials within that family, which can range from hundreds to thousands of options. Materials range from ABS to rubbers to polycarbonates to glass-filled materials and so on. It can get overwhelming with injection molding to find that one perfect material, and that’s where material experts such as PolyOne or RTP Company can help.

Protolabs offers guidance here too. The engineering staff can suggest the right direction to explore based on what a customer requests. The better choice might be a polypropylene material when an ABS won’t work, for example.

Protolabs also supplies physical material samples of many of the resins it offers. The engineers will help customers compare features between ABS, polycarbonate, nylons, acetyls, and other materials. Samples of materials are also available free of charge.

Protolabs engineers have years of experience in addressing design and production questions, and they are always available to discuss options and choices with you.

Proto Labs Inc.
www.protolabs.com