GB814608A - Method of and apparatus for electric resistance welding - Google Patents

Abstract

814,608. Welding by pressure. FRUNGEL, F. Nov. 8, 1955, No. 31854/55. Class 83 (4). In electric resistance spot welding a heavy current of short duration is passed through the workpieces by electrodes maintained in contact therewith throughout welding and the major portion of the metal melted by the current is ejected from the weld area, to effect cooling thereof, at least partly by electromagnetic forces produced by the current. In an embodiment two crossing wires 3, Fig. 1, are engaged by electrodes 6, 7 connected to a single-turn secondary 3 of a transformer 1 and pressed together by jaws 10 acting through resilient members 11. A condenser charged from a source of more than 2000 volts, preferably voltage stabilized, is connected to the transformer primary to provide a pulse of welding current. Molten metal is ejected as indicated by arrows 13 when the current pulse flows. In a modified apparatus for double spot welds main electrodes 6, 7, Fig. 2, are connected to the transformer by flat conductors 4, 5 and a pair of counter electrodes 6a, 7a together with a bridge member 12 complete the circuit. Although rubber is used as the resilient means 11 springs may be used and these means need only be on one side of the work. In a further modification two pairs of main electrodes may be arranged above two pairs of counter electrodes and the pairs of main electrodes are connected to flat conductors, the electrodes connected to one flat conductor passing through holes in the other conductor. A switch 21, Fig. 5, may be provided to ensure that the condenser 16 is not discharged until a predetermined pressure has been applied by the electrodes. When the pressure has been reached a contact 21a closes the switch to actuate a magnetically operated switch 20 between the condenser and transformer. The electrodes contact with work over a larger area than that of the contact between the workpieces and the natural frequency of the electrodes system should be high, e.g. above 100 cycles per second, to maintain the work surfaces in contact during welding. The inductance of the electrode circuit should be low, e.g. less than 1, preferably 0.1, microhenry and the current impulse should rise by 1000 amps. in 1 microsecond to eject particles with a velocity of 5 metres per second. Oxide resulting from the welding is collected. Platinum and platinum-rhodium can be welded in the manufacture of thermo elements, tungsten can be welded to contact bodies and steel wires &c. can be welded.