What does a filler rod do in the welding process?

A filler rod plays a crucial role in the welding process by providing a source of additional material that helps to fill the joint between the two pieces of metal being welded. When welding, especially in processes where a joint gap exists, the filler rod melts and flows into the joint, ensuring that a strong bond is created as the base materials fuse together. This is particularly important in situations where the base metals alone would not fill the gap adequately or where additional strength is needed in the weld.

The filler rod not only helps in creating a more uniform weld but also contributes to the overall integrity and strength of the final weld joint. This is essential for the performance of the welded structure in practical applications, where the joint must withstand various stresses and forces.

In contrast, the other options do not accurately describe the primary function of a filler rod. While heat is certainly a factor in welding, the filler rod itself does not directly increase the arc's heat, nor does it serve a cooling function or offer protection against fumes. Understanding the filler rod’s role helps in grasping fundamental welding techniques and enhances the quality of welds made in practice.