To avoid burn-through when welding an open butt joint on a vehicle, which technique may be used?

• A. Lap welds
• B. Stitch welds
• C. Full-penetration weld
• D. Double pass welds

Answer: (B)

Heat control is the key when welding thin automotive sheet metal like an open butt joint. A continuous weld concentrates heat in a small area, which can cause burn-through in these thin panels. Stitch welds—short, intermittent welds spaced along the joint—limit heat input per pass and give the metal time to cool between spots. This approach reduces the risk of burning through while still providing adequate joint strength when performed correctly, and it also helps minimize distortion in the panel. Other methods, such as full-penetration or double-pass welds, require more heat and increase the chance of burn-through on thin metal; lap welds, while useful in other joints, can complicate an open butt seam on a vehicle surface.