Spot 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.
To adequately cool the electrodes we need to minimize their time at high temperatures so we need a lot of water flow. RWMA recommends 1.5 gallons/minute at the coldest temperature water available. Any compromise does not mean you will produce discrepant welds. It only means you will not produce as many good welds before dressing of the electrodes is required. This means down time in your production schedule which means fewer parts out the door each day. The recommended water flow rate is 1.5 gallons of water/minute per electrode. You can successfully produce good welds at 1.0 gal/min and 0.5 gal/min.
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.
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