Spot welding electrodes have a large influence on the resistance welding process. Their alloy and face size contribute to the development of the proper weld nugget. All of this assumes that the electrodes have been installed properly. This means proper water cooling and water tube location and good alignment. Alignment means that the face of the electrode is square and parallel to the part being welded. In addition the upper and lower electrodes faces should line up vertically with each other. The goal is to apply all forces on the same central axis. This prevents the electrodes from imparting and twist or distortion into the part during the welding operation.
When the material is thick and the projection starts to collapse the metal sometimes needs a place to flow to in order to get out of the way of the two parts coming together. This can be done by projection design. Frequently a small cavity or depression is formed into the part around the base of the projection. Excess material can flow into this area and let the two parts come into more intimate contact.
Platen mounted (PM) holders are designed to be used with press type welder platens or they can be used as components of any specialized weld fixture. They are offered in two body sizes which match the standard T-slot spacing of standard RWMA welders.
A universal holder is a simple non ejector style straight barrel holder. Instead of a taper for electrode attachment it is threaded for use of threaded adapters. The threaded adapters allow welding in line with the barrel length or at right angle or 30 degrees.
High pressure holders are required at forces above 2400 lbs.. Tapers are no longer practical at these levels per RWMA Manual Fig 18.3. At these high forces the electrode tapers fail because they are continually forced deeper and deeper into the holder taper. High pressure holders use mechanical attachment that mount by means other than a taper and this is not an issue.
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