GMA (MIG) plug welds join two or more lap pieces together and are used to replace factory spot welds. What type of weld is this?

• A. Lap weld
• B. Seam weld
• C. Butt weld
• D. Plug weld

Answer: (D)

Plug welding is the technique used to join overlapping lap pieces by welding through a pre-punched hole in one sheet so the weld fuses to the underlying sheet. In MIG (GMAW) welding for collision repair, this method re-creates factory spot welds, giving a series of discrete welds that hold the panels together without forming a long seam. The welds penetrate through the hole and bind both sheets, which is exactly what’s needed when replacing spot welds. By contrast, a lap weld runs along the overlapped seam, a seam weld is continuous along a seam, and a butt weld joins edges end-to-end; none of those match the function of inserting welds through holes to connect the sheets.