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Projection welding is performed with many style projections - rings, dimples and slots to name a few. The sizes and designs will depend upon the material being welded its thickness and the design and location for the projection. Some projection welding does not require a design as in cross wire welding. Merely place the two wires in contact at 90 deg and they are ready to weld. Two flat pieces of low carbon steel however require a projection of some sort. The thickness of the material also plays a part in the height and diameter of the projection. Material composition factors into the design.
Welding guns use special copper alloy arms/adapters which function as electrode holders. They attach to the gun on one end and have a cap taper at the other for the electrode.
Projection welding parameters are readily available in published weld schedules referenced below. In general they have relatively short weld times and perform very well as documented. There are cases in which the circumstances in manufacturing are not ideal and variations from the standard are necessary. When this is present a change in the weld schedule may help.
Repeat or pulsing refers to repeating the weld and hold portion of a weld schedule. Normally there is a very short off period of one or two cycles with continued application of force between the two weld sequences. This gives you the ability to dissipate the heat energy a little further into the part away from the center of the weld nugget.
Aluminum has a tendency to form voids or cracks in the weld nugget as it solidifies. These voids are generally not desirable. In many cases this condition can be improved with good force follow up or application of a secondary forging force near the end of the weld cycle.
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