I need an annular snap-fit for a plastic tube of inside diameter 8mm, requiring an undercut. Is this possible?

Question

This would require a groove on the inside surface of the tube, about 2mm from the end. I have looked into collapsible core technology, but unfortunately this would only work with larger diameter items. The item would need to be manufactured in large quantities, in the tens of thousands, so machining would probably not be an option. The plastic is fairly hard, so the core could not be removed without damaging the part.

Any ideas appreciated.

Answer 1

You could machine. If you do a lot, pretty cheap, especially if loose tolerances. However, folks usually try to modify designs of plastic parts to eliminate machining.

Can't really tell what you are doing from the description.

How about using a slightly tapered core with a step with reduced OD at the tip, extending into the tube from the backside. This basically reduces the tube ID at the face, leaving a step.

How about putting a feature on the OD, or on the pipe face?

Maybe extend the mating part so it goes Thur tube and locks to other end.

Leave ID smooth, on mating part have thin stamped part that holds onto sides of tube, like an inside out Tinnerman nut.

Insert could use self cutting threads on OD instead of snap fit.

Push pin through tube wall instead.

Use separate thermoform operation after molding to add feature.

Glue or weld also possible, but add process and other issues.