Spot Welding
Questions and Answers
A cosmetic weld is a resistance weld on a surface where a typical weld indentation would not be permitted. The middle of the hood of your car is a good example. Welds on medical instruments would be another case. To prevent these indentations from showing most of the heat input must be made from the other side of the part.
Generally “C” flat faced electrodes are used on the cosmetic side and care is taken to not over heat the part. Usually the weld nuggets are run in the lower range of the quality specification to reduce the heat affected area.
Reference RWMA Resistance Welding Manual 4th Edition
The proper electrode material can be determined from published weld schedules based on the work pieces being spot welded. These weld schedules can be found in AWS Standard C1.1, Recommended Practices For Resistance Welding and RWMA The Resistance Welding Manual. Your electrode supplier is another source. Spot welding requires a few initial decisions to be made to set up a good welding process. Most of these evolve around pressure, current and time.
Dressing an electrode means mechanically machining or forming the face of the worn electrode back to its original geometry. All resistance welding electrodes wear during use. In the case of spot welding this appears in the form of what is referred to as mushrooming. The weld face of the electrode begins to spread out perpendicular to the length of the electrode.
All electrodes wear and in the case of spot welding they mushroom. Therefor the face must be dressed back to original shape to maintain weld quality. If the weld face size is not controlled within some reasonable parameters there will be insufficient current to maintained the required weld nugget.
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