Which term describes the depth of weld fusion into the base metal?

• A. Stitch
• B. Porosity
• C. Penetration
• D. Burn through

Answer: (C)

Penetration describes how deep the weld metal fuses into the base metal. It’s about how far the fusion travels from the surface toward the root of the joint. Adequate penetration means the weld has fused deeply enough to transfer the stresses, giving the joint strength. If penetration is too shallow, the weld doesn’t fuse far enough into the base metal, weakening the joint. If penetration is excessive, it can burn through the metal, creating holes. In collision repair, you aim for the right amount of penetration to restore strength without causing burn-through, while avoiding other issues like porosity from gas bubbles or a stitched pattern that doesn’t provide full fusion. Porosity, burn-through, and stitch describe other weld qualities or defects, not how deep the fusion goes.