What is the main purpose of using a filler material in welding?

The main purpose of using a filler material in welding is to strengthen the joint. Filler material is added to the weld pool during the welding process, which allows it to fuse with the base metals being joined. This incorporation of filler material enhances the mechanical properties of the weld, often matching or exceeding the strength of the base materials.

When filler material is used properly, it contributes to a defect-free weld and is essential in creating a strong and durable bond between the materials being welded. It also helps to fill any gaps and contours in the base metals, ensuring a more comprehensive and cohesive joint configuration. This is particularly crucial in applications where the weld joint must withstand high stress and fatigue, making it vital for the structural integrity of the final product.

In contrast, the other choices primarily address different aspects of the welding process that are not directly linked to the primary role of filler material. For instance, oxidation control, cost, and cooling rates are important considerations in welding but do not define the primary function of filler material, which is fundamentally to enhance strength and stability in the joint.