Deep draw rupture occurs when local strain exceeds the sheet’s available elongation or when a hot region loses enough melt strength to fail. The tear usually develops near a corner, plug contact line, or wall transition where strain is concentrated.
A simple depth-to-opening ratio cannot predict every part. Plan shape, corner radii, wall angles, material anisotropy, forming temperature, strain rate, and contact sequence all change the true draw demand.
Distinguish hot and cold failure
A cold failure tends to split sharply with limited thinning. A hot failure shows pronounced necking, extreme local thinning, or a stretched edge around the opening. If the failure moves when heater zoning changes, the thermal profile is involved. If it remains fixed at a tool feature, geometry or material distribution dominates.
Pre-stretch and plug assist should distribute material before the highest-strain region forms. Starting gauge or material grade may need revision when the geometry has no stable process window. Increasing heat alone is risky: it can trade brittle rupture for melt-strength failure.