Weld Quality, Destructive Testing, and Defect Identification
Inspect before you destroy
Weld quality starts with visual inspection: wet-out, bead profile, penetration, undercut, porosity, cracks, spatter, burn-through, and missed welds. Then use destructive tests on coupons that match the vehicle stack-same grades, thicknesses, coatings, and gaps. Common tests are the peel test for spot welds, the chisel test for fusion, and the bend test for GMAW.
What the tests tell you
A spot weld should pull a nugget from the coupon, not separate at the interface. A chisel test should show deformation before separation. A bend test should show ductile behavior without cracks. Record nugget diameter and failure mode against the OEM acceptance criteria.
Worked example
A peel coupon shows a 4 mm nugget with interfacial failure, but the OEM requires a 5 mm nugget with plug failure. The reasoning: interfacial failure means the weld did not grow enough; check tip condition and force first, then adjust current or time within the OEM window. Do not pass the weld because it “held.”
Traps
Testing a coupon of different thickness; calling spatter a cosmetic issue when it indicates gas or voltage problems; ignoring undercut on a visible panel; destructive-testing the vehicle instead of a coupon; forgetting that adhesive can change peel results.