An orbiting welding head for welding tubing and the like together. A U-shaped tube clamp unit has a pair of jaws in which two tubing sections to be welded together are held with the edges of such tubing sections in abutment against each other. A welder unit is incorporated in a cassette having a housing with an electrically non-conductive outer wall portion. This cassette is inserted into the U-shaped tube clamp and removably joined thereto by means of a locking ring. The welder unit has a welding electrode which protrudes from a horseshoe shaped rotatable electrode drive member. This drive member has a ball bearing support which comprises a plurality of ball members which protrude from the rotatable drive member at the opposite side faces thereof and which ride in respective grooved races formed in the main body of the cassette. The drive member is rotatably driven by means of a motor driven gear train. The welding electrode is thus rotatably driven around the interface between the tube sections to be joined together in effecting the welding operation.