GB1280727A - A method and device for plasma-arc welding - Google Patents

Abstract

1280727 Welding by fusion INSTITUT ELEKTROSVARKI IMENI EO PATONA 15 Oct 1969 50626/69 Heading B3R [Also in Division H2] In plasma arc welding of small gauge sheet metals, e.g. of aluminium or its alloys, wherein a constantly burning pilot arc, between a non- consumable electrode 1 and a water-cooled copper nozzle 2, is supplied from a D.C. source 3, alternating voltage pulses (W 1 , W 2 ), respectively positive and negative with respect to the workpiece 4, are supplied respectively to the nozzle 2 to destroy surface oxide films and to the electrode to form the main fusing arc. As shown, the pulses (W 1 , W 2 ) are supplied respectively from a point a and a tap b of the secondary winding of a transformer 5 the primary winding of which is supplied by A.C. through an adjustable choke 9. During the positive voltage half-cycles the pulses (W 1 ) are supplied to the nozzle through a diode 7, a thyristor being arranged to be closed to avoid short-circuiting of the secondary winding part a, b by the pilot arc. At the beginning of the negative voltage half-cycle, a controlling circuit (not described) opens the thyristor 6 so that the pulse (W 2 ) is supplied therethrough to the electrode. The thyristor 6 may operate to provide groups of pulses of adjustable pulse number and group frequency. In Fig. 4 (not shown), the points a, b coincide, and the means 6 may be a non-controllable diode. When using a transformer 11 with a variable falling voltage characteristic (Fig. 5, not shown), the diode 7 is replaced by a thyristor (13) so controlled as to avoid arc-hampering loading of the secondary winding part a, b by the pilot arc when welding reverse polarity current lags.