Force is used for two main reasons. One is to contain the weld nugget and prevent expulsion and the other is to strengthen the weld by forging the solidifying weld nugget. It is easy to see that if welding force is changed these actions will be affected to some degree. Expulsion could increase or decrease and the resultant weld strength could also increase or decrease.
Generally all spot welding electrodes are made from a copper alloy. During the resistance welding operations if their tensile strength is exceeded they will bend or collapse and fail from the mechanical force being exerted on them. RWMA Fig 18.3 in the RWMA Manual 4th Edition, shows the relationship of electrode weld face size, applied force and maximum capability. Similar information is shown in the following table.
Resistance welding tapers are precision tapers for attachment of electrodes to resistance welding holders. They are meant for quick and easy attachment and removal. If the weld forces used in the application are excessive for the size of the taper, the male taper can be driven into the female taper and ruin the tooling. Electrode removal may become difficult or impossible and further use of the holder is compromised. RWMA Fig 18.3 in the RWMA Manual 4th Edition, shows the relationship of electrode weld face size, applied force and maximum capability.
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