GB552701A - Improvements in or relating to electric resistance spot welding - Google Patents

Abstract

552,701. Electric-welding. DORRAT, J. A., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Dec. 13, 1941, No. 16111. [Class 83 (iv)] A machine for spot welding relatively large and thick sheets in ship-building &c. comprises a gantry the central bridging member of which carries a welding head supporting a pair of spaced depending electrodes movable with respect to a corresponding pair of fixed electrodes upstanding from the bed of the gantry, the movable pair being connected to opposite ends of a transformer or like and the fixed pair being connected together so that welding current passes from one movable electrode through the work at one spot and is conveyed externally of the work so as to pass to the other movable electrode through a second spot in series with its passage at the first spot. By simultaneously welding at two spots the inductance in the circuit is minimized and maintained relatively constant for different locations of the spot welds in relation to the margin &c of the sheet. Two pairs of electrodes 3, 3a, 4, 4a, may be used one electrode 3, 4 of each pair being movable and connected to the opposite poles of a transformer 6, the stationary electrodes 3a, 4a being connected directly together. The pairs of electrodes are spaced apart at such a distance that the electrical impedance in the plane of the sheet is high relatively to that of the transverse path through the sheets. The electrodes 3, 4, which may be spaced apart say 8 inches which is equivalent to twice the pitch of the spots in the finished work, are ciltried by separate slides 12, which are reciprocated by fluid pressure rams in guides in a head 15 carried by a frame 1 extending from an arm 1d projecting laterally from the bridge 1c of a gantry. The electrodes may be spaced about 5 feet from the limbs 1a, 1b of the gantry, and the frame 1f extends about 5 feet in front of the gantry so that long sheets say 5 feet wide and ¢ inch thick, may be passed straight through the gantry and moved through about 5 feet from one side to the other as well as being turned for effecting transverse welds. The electrodes 3a, 4a are secured by clamps to a copper or like conducting block 40 mounted on the top of a pillar 5. The electrodes 3, 4 are connected to the slides 12 through horizontal carriers 8, 9 provided at their rear ends with lugs 8c, 9c which are connected by short U-shaped flexible leads 26, 32 to conductors 28, 34. Such conductors are secured to flat conductor bars which are close together and pass through an insulating block 30 and are connected to the secondary terminals of the transformer which is mounted in the frame 1f.