Electrode sticking to the work piece generally is caused by excessive heating between the electrode and the work piece. In the Relative Resistivity Diagram RC has become too large. Any factor which would cause this is an issue that must be addressed to prevent this manufacturing problem. In many cases this condition is accompanied with excessive surface expulsion.
Electrode face mushrooming is the normal wear mechanism of a spot welding electrode. To slow this process or prevent excessive mushrooming one must control several factors in the welding process.
Expulsion of molten particles from between the two sheets of metal being welded can be caused by several items. All are related to causing excessive heat between the two work pieces or not containing the weld nugget during welding.
Force is one of the main inputs of the weld machine in the form of pressure exerted by the electrodes on the work piece. The main function of this force is to contain the weld by holding the work pieces together tightly during the welding operation. Stronger work piece materials require higher welding forces than weaker work pieces. With adequate force the contact resistance between the electrode and part is minimized and more energy is transmitted into the part to heat the interface between the two sheets being welded.
Pressure is one of the three major inputs of the machine, pressure, current and time. Pressure is called out as force in weld schedules. Force per square inch is pressure. When pressure is applied and the electrode makes contact with the part, there is a contact resistance at that joint. The amount of this resistance changes with the amount of force/pressure being applied.
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