Uneven wall thickness is a material-distribution problem, not simply a heating defect. The sheet stretches according to local temperature, unsupported area, contact sequence, friction, and geometry. Two parts with the same final shape can have very different thickness profiles.
Hot regions thin more readily, but early tool contact can preserve or freeze thickness depending on where it occurs. A plug may push too much material into one wall while starving the opposite side. Incoming gauge variation and residual sheet orientation can add a directional bias.
Build a thickness map
Measurements should cover the flange, sidewalls, radii, base, and all cavities. The map should then be compared with the thermal field and first-contact pattern. A repeatable asymmetry suggests tooling or motion; a shifting pattern suggests heating, sheet position, or material variation.
Corrective actions may include pattern heating, plug geometry changes, controlled plug temperature, pre-stretch, reduced friction, or revised tool layout. Average thickness is not a sufficient acceptance criterion. Minimum local thickness and its location should remain stable through normal production variation.