Plug sticking occurs when the sheet adheres to the assist strongly enough to distort material distribution, mark the surface, or pull the part during plug withdrawal. The defect may look like drag lines, local thinning, or a delayed release from the plug.
Excessive plug temperature can promote adhesion, but roughness, contamination, incompatible coverings, high contact pressure, and long dwell are also common causes. Some polymers are more sensitive to surface chemistry than others.
Corrective action
The plug should be cleaned and inspected for pickup, wear, and damaged coating. Surface temperature and withdrawal timing should be checked during steady production. A release coating or lower-friction plug material may help when it is compatible with the polymer and downstream finishing.
Do not cool the plug so far that sticking is replaced by chill marks or tearing. The stable setting balances release, heat transfer, dimensional control, and material distribution.