Red Seal Metal Fabricator (Fitter) Practice Exam

Why is preheating metal before welding often recommended?

1. To increase the visual appearance

2. To improve bonding of the weld

3. To reduce warping and cracking

4. To enhance the color of the metal

The correct answer is: To reduce warping and cracking

Preheating metal before welding is often recommended primarily to reduce warping and cracking. When metal is welded, the heat from the welding process can create sudden temperature changes, leading to thermal stresses within the material. These stresses can cause warping, which distorts the shape of the metal, and cracking, which compromises the integrity of the weld and the overall structure. By preheating the metal, the initial temperature of the workpiece is raised, allowing for a more even distribution of heat during the welding process. This helps to minimize rapid temperature fluctuations, reducing the risk of thermal stresses that lead to warping and cracks. Preheating also promotes better penetration of the weld, as the heat of the weld puddle is better absorbed by the preheated areas. While improving bonding and the overall look of the finished weld can be benefits of some preheating practices, the primary advantage lies in minimizing defects associated with temperature changes during welding.