METHOD AND DEVICE FOR SMALL ELECTRIC CURRENT PLASMA ARC WELDING

摘要

PURPOSE:To hold the small electric current plasma arc stably and to facilitate the automation of sheet welding by generating a plasma jet with a prescribed flow rate of a working gas thence inducing the plasma arc with an instantaneously large flow rate and returning the same to the prescribed flow rate. CONSTITUTION:A three-way valve 12 is operated to communicate a pipeline 11 with a pipeline 13 in which a prescribed flow rate of a working gas flows, whereby the prescribed flow rate of the working gas is supplied into a chamber 4 in a nozzle tip 2. Thence, potential is applied between an electrode 1 and the tip 2 by an auxiliary electric power source e, whereby a plasma jet 8 is generated, but no plasma arc 7 is generated because the flow rate of the working gas is small. Next, the valve 12 is operated to communicate the pipeline 11 with a pipeline 14 to supply the gas at the flow rate larger than the steady flow rate, at which this gas is ejected through a nozzle port 5 to arrive at base metals 6, whereby electric current is induced between the base metals 6 and the electrode 1 in the tip 2 and the arm 7 is generated. Immediately the flow rate of the working gas is changed over to the prescribed flow rate by the valve 12, but once the plasma arc 7 is generated, the arc 7 is maintained stably even at the small flow rate.