In metal welding, a strong weld is a fundamental requirement when using a resistance spot welding machine. A simple image might suggest that more weld points equate to a stronger weld. Therefore, some might argue against this, believing that more welds will result in a stronger weld. However, this is a misconception. In multi-spot welding, there are requirements for the spacing between weld points; the closer to these requirements, the stronger the welds. If the weld point spacing is not within the acceptable range, it can be counterproductive. Irregular and non-standard weld point spacing can lead to poor weld quality.
The main cause of this problem is current shunting at the weld points. When the spot spacing is too small, current shunting easily occurs, resulting in insufficient heating in the welded area. During spot welding, the current flowing through the non-welded area is called current shunting. The current shunting effect at the weld point is related to the resistivity of the workpiece material and the conductive path. In reality, each weld point represents a current path. When spot welding is used, there are two main factors: the resistance at the first spot and the resistance in the adjacent areas during welding. The resistance at the first spot is significantly lower than in the area being welded, meaning the resistance at the second spot is greater. Since the current flows from the first spot, the quality of the second spot is lower than that of the first.
The smaller the distance between two weld points, the worse the quality of the subsequent welds. If the spacing is too small, the current shunting can be significant, potentially even affecting the formation of the next weld point.
Therefore, in spot welding, when welding multiple spots, a suitable weld point spacing must be designed; otherwise, the welding effect will be affected. The appropriate spacing range varies depending on the weld point size, welding material, workpiece geometry, different welding methods (collision, parallel), and different welding head structures, and should be evaluated based on the actual situation.
Furthermore, it should be noted that when using an AC spot welding machine, the impact of the weld point spacing on the welding quality is greater than that of a DC spot welding machine with a high-frequency inverter, because the current is less concentrated, the welding time is longer, and the current shunting will be more severe.