Seam welding drive shafts carry current, deliver force and rotate during the seam welding operation. Duty cycles, currents and forces are high. The shaft operates in a housing which is filled with conductive grease and has current carrying shoes which ride on the shaft to deliver current. Eventually these conductors and the shaft wear and service is required. Sometimes people ask if they can the buildup the worn shaft with new copper and machined it back to size? They are suggesting the use of plasma or some welding process to lay down this layer of copper. Unfortunately the resultant laid on copper has some amount of porosity when compared to the original copper it is replacing. This soft porous copper will not wear well or conduct the high currents experienced in seam welding.
Knurl Driven Seam Welder
The second issue is that the conductive shoes are probably worn. They will need to be machined or replaced. The shaft and the shoes have to be machined to exacting specifications so that they will match up properly. The shaft in turn rides on bearing surfaces and must be machined for this.
The best alternative is to work with a reputable machine builder and have them replace the shaft and rework or refurbish the drive housing unit for the machine. This would update the contact shoes, bearings, shaft, grease and water cooling for the machine.
Reference: RWMA – Resistance Welding Manual Section 4