What does the process of ‘preheating’ aim to achieve in welding?

The process of preheating in welding is primarily aimed at reducing internal stresses and preventing cracking. When metal is welded, the heat from the welding process can create rapid temperature changes and gradients, which may lead to uneven cooling. This discrepancy can cause internal stresses that may result in cracking, especially in high-strength steels or materials that are thick.

By preheating the area to be welded, the temperature differential is minimized, allowing the metal to expand uniformly. This controlled heating helps to reduce the risk of thermal shock, promotes a smoother transition during welding, and allows for a more consistent metal structure. Preheating also helps to ensure that any moisture, oil, or contaminants are removed from the metal surface, further supporting the integrity of the weld.

While other options may represent important aspects of the welding process or subsequent finishing processes, they do not accurately reflect the primary goal of preheating, which is fundamentally about managing the thermal dynamics of the material to produce a sound weld.