Which method requires high accuracy in the preparation of the metals before welding?

The method that requires high accuracy in the preparation of the metals before welding is TIG welding. This process, known as Tungsten Inert Gas welding, involves the use of a non-consumable tungsten electrode to produce the weld. Because of the precision required in controlling the heat and maintaining a stable arc, the edges of the materials being welded need to be clean, properly fit, and accurately prepared. This is crucial for achieving a high-quality weld with good penetration and minimal defects.

TIG welding is often used for welding thin materials and when the appearance of the weld is important, such as in aerospace or automotive applications. The attention to detail in metal preparation enhances the effectiveness of the inert gas shielding, which protects the molten weld pool from contamination. This high level of preparation is less critical in processes like MIG welding or arc welding, where some level of contamination may be tolerated, and the equipment is typically more forgiving regarding fit-up. In resistance welding, the focus is more on the application of pressure and the electrical current rather than the meticulous preparation of edges.