Internal Stress：You Should Know When Machining Plastic

If you're a mechanical engineer and ignore stress release in plastics, you're missing a fundamental piece of the puzzle.

Your POM or PP CNC part warps. First reaction? ...  “Poor machining.”

Most of the time, that's not the case.

The deformation didn't start on the machine - it was already locked inside the material during manufacturing.

Here's what many overlook: Different plastics, different behaviour.

-  POM, PP, Nylon: high internal stress. Machine them, and warping is almost inevitable.
-  ABS:  much more stable. Stress releases, but deformation stays minimal.

Same geometry. Same toolpath. Different plastic. Completely different result.

So before you point fingers at the machinist, ask yourself: “Did I design for the right material?” Choosing the correct plastic upfront saves time, cost, and scrap.