injection molded flexible part


I’m new to this forum. What a wonderful idea for designers to share information.

I am designing a plastic part to be injection molded. For the ease and low cost of the mold to be built, I want to lay the part out flat in the mold. However, once out of the mold, the part needs to bend in half with about a 3/4 in. gap between the folds. (This doesn’t really make it a “live hinge” because it’s a one shot bend). The parts’ wall thickness will be around 1/16 in., but will probably need to be thinned at bend point. How much? What kind of radii need to be put in that area? Is there any data on the web that shows this? Can someone send me some? What kind of plastic should I chose? The part will be exposed to some water (splashing) and will be used outdoors. There is no structural stress put on it though. Infact, it’s largely covered by a piece of rubber.

~ Z

should be asking you. i normally ask the moldmaker.

my experience is that material dictates. choose material first. probably be a polyethylene or propylene. lots of variations in those. wall stocks drop down partly based on what will fill. and that depends on material, part complexity and gating. i’ve never seen regular parts with less than .040 thickness. but then some tooling people have different rules of thumb. obviously thin-wall technology lets you get thinner, but that’s usually on high-tech plastics, not outdoor products afaik.

Design News magazine used to have nice little How-To articles. might check online to see if they have them there now:

Try vinyl. Look at the plugs that are molded in pool float type products. There is no need to to thin the part or change the cross section. These plugs are molded flat, just as you described and folded over to plug the air hole.

is there one or two folds? if only one, Alcala makes a good point: mold flat.

It sounds like you want a rigid part that is bent after it is molded.

The part pops out of the mold all hot and soft, then it is pressed into a form to change the shape?

I’ve never seen this done. I think the plastic part could creep back to it’s original shape.
Could be possible with abs though.

Would probably be best to mold the part in the final shape.

If you want flexible part- krayton and santoprene are both good elastomers.