Plug-induced tearing begins at or immediately beside the plug contact region. It is usually repeatable and follows a plug edge, corner, or high-pressure contact point.
The sheet may be too cold, but plug geometry and motion often dominate. Sharp transitions, excessive penetration, high acceleration, misalignment, insufficient clearance, and poor pre-stretch concentrate strain before the sheet is supported by final forming pressure.
Correction
The tear should be mapped against plug position and stroke. Motion should be reviewed as a profile, including acceleration and deceleration, rather than a single speed value. Plug radii, clearance, alignment, and surface condition must be checked.
Pre-stretch may need to place more material beneath the plug before contact. Raising sheet temperature should be done cautiously because a hotter sheet may stop tearing but become too thin. The corrected process should meet minimum thickness as well as visual acceptance.