Spot Welding

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Questions and Answers

Resistance welding electrode sizes are determined by referring to published weld schedules and looking up the recommended electrode size. Resistance welding electrode size is determined by the electrode body diameter and the electrode face diameter. These are determined by the work piece being welded and the forces and currents being used to develop a proper weld nugget.

The size 4 and 5 designate the body size of the electrode. A #4 electrode has a ½” body diameter with a 3/16” face diameter. A #5 electrode has a 5/8” body diameter with a ¼” face diameter. These are sizes established by the Resistance Welding Manufacturers Alliance (RWMA) and published in Bulletin 16 Section 18. All manufacturers produce to these standards here in the USA. There also is a size 6 and 7.  Size 7 is rarely used in cap form.  The charts below show data for RWMA caps and full size electrodes.

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.

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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