Projection Welding

Questions and Answers

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.

Cooling is possibly the most important factor in electrode life. Proper water tube location will insure water flow as close as possible to the working face with the proper flow and temperature water. In each resistance welding application after the weld schedule is determined and the proper pressure, current and time (PCT) are set another important factor for electrode life is water cooling. Even with the proper setting every electrode will see very high temperatures and forces on its face. Over time this creates the traditional mushrooming of the weld face. To slow this face wear down we must reduce the time at high temperature that the weld face sees. Proper water cooling of the electrode is critical.

Water for the electrode should always come directly from the water manifold and not be plumbed to use water from another weld machine component. Cooling water is the most important item to insure electrode life. Therefore the amount of water and its temperature are very critical.

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.

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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