A scratch can be introduced before heating, during forming, at release, or in downstream handling. Its shape and orientation usually identify the stage.
Straight parallel marks may come from sheet extrusion, transport rollers, or stacking. Curved or directional marks that match tool withdrawal suggest release contact. Random fine scratches often result from dust trapped under protective film or between finished parts.
Trace the origin
The sheet should be inspected under directional light before loading, after masking removal, after forming, and after trimming. Protective film must be compatible with the heating cycle and kept clean. Tool and fixture contact surfaces should be checked for embedded chips or damaged padding.
Polishing the finished part is not a process correction. The handling route, separators, cleaning method, and operator contact points should be controlled so the surface reaches forming without damage and leaves the cell without abrasive contact.