There are materials that due to their properties are not suitable for projection welding. This can be extended to thin cross section in other materials that could be projection welded in heavier gauges. The basic problem being that the material must be strong enough to withstand the force applied during the squeeze portion of the weld cycle. If the projections collapse before the weld/heating cycle begins, there is no longer a projection to concentrate the heat. It collapsed. The weld will fail. Materials that are generally not candidates for projection welding are brass, copper and red brass. Aluminum in some forms can be projection welded.
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 weld schedule parameters are readily available in the 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.
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