Why Does Resistance Spot Welding Machine Stick When Welding Galvanized Plates？

Resistance spot welding is a widely used technique in various industries for joining metal sheets together. However, when working with galvanized plates, welders often encounter a peculiar issue – the welding machine tends to stick. In this article, we will delve into the reasons behind this phenomenon and explore possible solutions.

Understanding the Problem

Resistance spot welding involves passing a high electrical current through two pieces of metal, creating a localized melting point that fuses them together. When welding galvanized plates, the outer layer consists of zinc, which has a lower melting point than steel. This zinc layer can melt before the steel does, leading to the welding electrodes sticking to the plates.

Causes of Sticking in Galvanized Plate Welding

1. Zinc Vaporization: During the welding process, the high heat causes the zinc layer to vaporize. This vapor can rise and condense on the welding electrodes. As a result, the electrodes become coated with zinc, leading to adhesion with the workpiece.
2. Electrode Contamination: The zinc coating can also contaminate the welding electrodes, reducing their conductivity and causing them to stick to the plates.
3. Uneven Zinc Coating: In some cases, the galvanized plates may have an uneven zinc coating. This non-uniformity can lead to variations in the welding process and increase the likelihood of sticking.

Solutions to Prevent Sticking

1. Electrode Maintenance: Regularly clean and maintain the welding electrodes to prevent zinc buildup. Special anti-stick coatings or dressings are available to reduce adhesion.
2. Proper Welding Parameters: Adjust the welding parameters, such as current, time, and pressure, to minimize the heat input. This can help control the zinc vaporization and reduce sticking.
3. Use of Copper Alloys: Consider using copper alloy welding electrodes. Copper has a higher melting point than zinc and is less likely to stick to the workpiece.
4. Surface Preparation: Ensure that the surfaces to be welded are clean and free from contaminants. Proper surface preparation can reduce the risk of sticking.
5. Avoid Overlap Welds: Minimize overlapping welds, as they can trap molten zinc between the plates, increasing the chances of sticking.
6. Ventilation: Implement proper ventilation to remove zinc fumes from the welding area, preventing electrode contamination.

The issue of a resistance spot welding machine sticking when welding galvanized plates can be attributed to the unique properties of zinc and the challenges it presents during the welding process. By understanding the causes and implementing the suggested solutions, welders can improve their efficiency and reduce the occurrence of sticking, ensuring high-quality welds in their galvanized plate applications.