Cause: Poor or Varying Part Fit-Up

Fit-up is defined as a measure of the closeness or degree of contact between mating parts.

Description 

The metal being welded does not have intimate contact in the area to be welded. The application of welding force and current causes one or both sheets to distort.

Detection 

• Cracks & holes
• Excessive indentation
• Expulsion/burn through
• Inconsistent weld quality
• Mislocated/edge weld
• Missing or undersized weld
• Non-round Weld
• Poor Class A appearance
• Sheet metal distortion
• Stuck weld
• Interfacial expulsion
• Poor electrode life
• Visible gap between parts

Significance 

Quality, Workplace Issues, Cost, Downtime, Maintenance, Throughput (cycle time; PPH), are all potentially affected by this condition.

Subordinate Causes

• Joint design; design with built-in gap
• Fit-up gap from part dimensional variation
• Non-matching panel contour
• Part damage due to material shipping and handling
• Geometry, design, motion, and operating condition of locators
• Design and operating condition of clamps