Preliminary Study on Arc Welding in Vacuum

Welding technology in space is required to repair the space station. Arc welding in vacuum should be more conventional than electron beam welding because of low voltage operation. Preliminary study on vacuum arc welding is presented in this paper. Arc was ignited by separating an arcing electrode (cathode) from the welding piece (anode). The former is composed of a rod with round tip, however the latter of a screw/nut set. Both of them are made of stainless-steal (SUS304). A pulsed-arc current up to approx. 3kA with duration of about 15-20ms was fed from a power supply that was consisted of a low-voltage LC circuit (135 muH/0.04F/550V) with a crowbar diode. The screw/nut seemed to be uniformly melted by eye. The tensile strength of the welded piece was measured after welding test. However it was low in comparison with a TIG welding piece performed in an atmospheric pressure. One-dimensional thermal conduction was analyzed in a finite welding piece. The calculated result showed that the melting depth could be over 1mm when the arc current flows for more than 10-15 times longer than that in this experiment. Further investigation is required to find appropriate conditions (arc current, arc discharge mode, welding material, etc) to realize satisfactory arc welding in vacuum