What is back step?

Answer 1

Backstep welding is a technique to avoid distortion while welding on thin sheets. In the backstep technique, the general progression of welding may be left to right, but each bead segment is deposited from right to left. As each bead segment is placed, the heated edges expand, which temporarily separates the plates at B. As the heat moves out across the plate to C, expansion along outer edges CD brings the plates back together. This separation is most pronounced as the first bead. With successive beads, the plates expand less and less because of the restraint from the prior welds.