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I've been working on a design that requires a plastic snap feature. I've assumed up to this point that the material will be injection molded ABS, with material properties I pulled off of matweb.

After several dozen iterations on the design, I've pushed the geometry of the snap as far as possible give the geometric conditions of the feature and I'm right on the edge of acceptable (Factor of safety of ~1.1). If my loading conditions end up being too conservative or any features of my part come out slightly out of spec I could easily have parts that fail. I'd be much more comfortable with an FOS up above 1.8.

Ideally I'd like to lower the Youngs modulus of my material and I'm wondering if ABS can have its material properties 'toyed' with by using a different formulation of the plastic. Also, how consistent are material properties of injection parts?

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  • $\begingroup$ check out companies such as : fluorotec.com/blog/… $\endgroup$ – Solar Mike Sep 10 '17 at 17:54
  • $\begingroup$ Teflon has some other undesirable health concerns I'd like to avoid $\endgroup$ – Diesel Sep 11 '17 at 3:34
  • $\begingroup$ So any other companies that make plastic or variants of ABS that may have the property of not harming health? $\endgroup$ – Solar Mike Sep 11 '17 at 6:26
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Yes, the proportions of acrylonitrile, butadiene, and styrene can vary within some ranges. However unless you will be able to polymerize it yourself you will have to use a commercially available polymer.

I would look as product information sheets for bulk polymer pellets sold for injection molding. From those you will be able to see the real available range of properties like youngs modulus, tensile strength, shore hardness.

In terms of mechanical anisotropy throughout the part, some could exist, but it will be difficult to determine the magnitude of such effects. These effects primarily arise from the differential cooling rates of different areas of the part due to part geometry (which can induce internal stresses). To mitigate these effects its helpful to pay attention in design to uniformity in part thickness so that cooling rates are kept similar.

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