Spot Welding

Questions and Answers

Water flow measurement is critical to insure that the components of the resistance welder and especially the electrodes are receiving the proper amount of cooling water during operation.

Open Drain - The simplest method if you are using an open drain is to run the exit water line from each component on the welder into a bucket for one minute and measure the water in the bucket. the ideal amount for the electrodes is 1.5 gallons/minute.

In order to lengthen electrode life, cooling the electrode is essential. The water temperature should be the colder the better for electrode life. A large amount of cold water is a requirement. The best temperature for the electrode is the coldest that you can provide. If your plant had a source of water from a well this would be perfect since the water would be about 50 something degrees Fahrenheit year round. While this is great for the electrodes, this temperature for the electrical equipment and electronics is not good during a humid summer. Electronics does not do well with condensation dripping all over it. Transformers may not hold up if they are sweating. So even though the electrodes might do well the weld machine might do poorly with lots of condensate.

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.

During the resistance welding process the electrode face is subjected to extreme temperatures for short periods of time. To prevent premature wear, water cooling is necessary for the resistance welding electrodes. The technical term for this wear and resultant deformation is annealing. In the case of spot welding the face will begin to take on the shape of a mushroom. As this face grows the weld quality suffers and eventually weld quality failure occurs. Prevention or retarding this mushrooming is very important. One of the most important items to control is the time at temperature that the electrode weld face sees. One method of control is by cooling the electrode. The second benefit of this is that it will also cool and solidify the weld nugget during the hold period of the weld cycle.

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