Warping is a dimensional change that occurs as the formed part cools and internal stresses rebalance. It may appear immediately after release, after trimming, or hours later. The timing helps identify the cause.
Uneven mold temperature, different cooling rates on the tool and air sides, nonuniform wall thickness, premature demolding, and asymmetric geometry are common sources. A trim operation can also release stress that was held by the surrounding web.
Diagnosis
The part should be measured on the tool, immediately after release, after full cooling, and after trimming. A change while still on the mold points toward cooling or tool temperature. A change only after release indicates insufficient stiffness or shrinkage constraint. A change after trim indicates locked-in stress or inadequate trim support.
Cooling should be balanced rather than merely extended. Wall distribution, mold circuits, airflow, fixtures, and release temperature may all require adjustment. A cooling jig can hold geometry, but it should not be used to conceal severe molded-in stress.