What is the purpose of a back bar in welding?

The purpose of a back bar in welding is to support the weld bead. When welding, particularly in processes like arc welding, molten material is deposited to create a weld. The back bar serves as a backing material that can help control the shape and size of the weld pool. By providing support, it helps to ensure that the weld bead maintains its form and integrity, contributing to the strength and quality of the joint.

The other options, while they may pertain to aspects of welding, do not accurately describe the function of a back bar. For instance, cooling the weld area is often achieved through other means, such as using cooling agents or controlling the heat input, rather than through the back bar itself. Similarly, things like insulation from heat or cleaning the welding area are unrelated to the primary role of a back bar, which focuses specifically on the structural support of the weld.