Understanding of BIW Welding Fixtures

A: The 3-2-1 locating logic breaks once compliance exceeds a few tenths under weld load. ISO 1101 is about functional relationships, not just geometry, and a floating arm shifts under gun force even if the drawing tolerance looks fine.

A: Once spatter layers reach roughly 0.2–0.3 mm, operators scrape them off, and that repeated removal drives adhesive wear. The others exist, but they don’t move the pin location fast enough to blow Cp/Cpk.

A: With ±0.8 mm variation, you need constraint without over-constraint. One round plus one diamond manages 4 DOF while letting thermal strain bleed off instead of storing it until gun release.

A: Flatness and level within ~0.1 mm/m set the reference. Pin true position comes next. Clamp repeatability only matters once the datums are real; reversing the order hides root cause.