Living in the Material World
We've all heard at one time or another—from a parent, a coach, or a teacher—a reference to "what you're made of." It probably referred to what you could do or withstand, but since we're all made of pretty much the same stuff, the meaning of the phrase was more figurative than literal. When you're an injection molded part, however, "what you're made of" literally determines a great deal of what you can do or withstand.
At Protomold, we keep dozens of resins in stock and have access to hundreds more. But the three most often requested are ABS, polycarbonate, and 33 percent glass-filled Nylon. This is not to say that these are the three most widely used resins for injection molding, just that they are the most used by Protomold customers.
ABS
ABS is a good, inexpensive, general purpose resin. It is widely used for the cases of hand-held electronic devices, the housings of power tools and many other products we use every day. The material is tough enough to take a licking in everyday use, and while it may scuff from rough handling, it is less subject to breakage than a lot of other plastics.
Another plus for ABS is its excellent moldability characteristics. It is somewhat susceptible to sink and can be damaged by solvents, but if you design parts carefully, it is possible to produce well-formed parts without serious shrink, sink, or internal stress. It is important to maintain relatively even wall thickness in designing parts in ABS, though not quite as critical as with other, more shrink-prone materials. In general, ABS is opaque, although a clear version of the material is available.
POLYCARBONATE
Polycarbonate is considered a "higher-end" resin. While it does cost more than ABS, it is just a medium-cost resin. It can be very strong, so much so that it is used for bulletproof windows. And while it is often chosen, because of its transparency, for use in lenses and light pipes, it can also be opaque. Because of its high strength, it is used to make cases and housings which need a stronger material than ABS.
Polycarbonate does have some shortcomings, including a tendency to sink. If a polycarbonate part is not properly designed, the surface of overly thick area can sink significantly during cooling. In some instances, shrinkage may not show on the surface, but internal shrinkage may cause a void inside the part, seriously weakening the finished piece. Proper design and avoiding thick/thin geometries will help prevent such problems. Also, polycarbonate is susceptible to petroleum-based solvents. In some applications, polycarbonate can be blended with other resins, like ABS, to achieve a compromise on both properties and cost.
GLASS-FILLED NYLON
Glass-filled nylon is the strongest of the three resins addressed here. Common glass-filled nylons are medium-cost resins, though some specialized versions of the material can be very costly. The material resists many solvents and hydrocarbons, but is attacked by some acids and bases. (You should research your application and environment before finalizing your resin choice). And with the addition of glass fiber, nylon is very heat resistant. With up to three times the strength of polycarbonate, this material is used for protective or structural parts that need to withstand a great deal of stress.
On the other hand, glass filled nylon is the most shrink-prone of the three resins being discussed. Nylon itself is very subject to shrinkage as it cools, and the addition of fiberglass can cause differential shrinkage relative to the direction of resin flow during mold filling and contributing to warp. For this reason, if the strength, heat resistance, and chemical compatibility of this material are needed, good design is critical in preventing distortion of the finished parts.
For more information, visit Protomold's Resin Guide
View Protomold's stocked resins list
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Design Guidelines
As always, you can visit the Protomold Design Guide for helpful Rapid Injection Molding design information.
European colleagues? Tell them about Protomold Europe!
Who's going to win the Super Bowl on February 4th?:
Last month's question/results:
Teflon was:
- Synthesized in 1949 by Swiss chemist Albert Teffle
- Developed for the military to lubricate artillery shells
- Initially developed as a fabric protectant
- The result of a failed attempt to produce an adhesive
- Discovered by a chemist working with freon gas
The correct answer is
E. Discovered by a chemist working with freon gas.
The responses are represented in the following chart:
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Solidworks World 2007
February 4-7, 2007
Morial Convention Center
New Orleans, LA
Booth #401
Pacific Design
and Manufacturing Show
February 13-15, 2007
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Anaheim, CA
Booth #3716
National Manufacturing Week
September 25-27, 2007
Donald E. Stephens
Convention Center
Rosemont, IL
Booth #4130
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