GMA Welding for Collision Repair Welding Practice Test

In MIG welding, the most direct signal that fusion is insufficient is a lack of fusion—where the weld metal does not bond to the base metal or to a previous weld bead. This shows up as a gap or seam at the weld interface where the metal should have melted together, leaving a discontinuity instead of a continuous weld. It happens when heat input is too low, travel speed is too fast, joint prep is inadequate, or contamination prevents melting. Porosity consists of gas pockets trapped in the weld, not a failure to fuse; crater cracking occurs at the end of the bead from thermal stress, not from a lack of fusion; and dents are surface deformations from impact or handling, not fusion issues. To address lack of fusion, increase heat input or adjust technique, ensure clean, properly prepared joints, and maintain stable travel to promote full melting and bonding.