Wear of the Tungsten Electrode at the TIG Arc-Spot Welding of Dissimilar Metals

Micro-TIG welding experiments have been used for the welding of the contacts of special lamps. Since the welded materials were different, the welded joint was a heterogeneous bound. For the joints a 0.6 mm Ni-Mn alloy or 0.4 mm Mo wire were inserted onto the hole of AISI 304 type austenitic stainless steel sheet, with a wall thickness of 0.35 mm. The micro-TIG welding was completed with a welding machine of which control characteristics corresponded to all the requirements necessary for TIG arc-spot welding. The goal of the experiments was to find the optimum regarding the quality of the lamps’ welded joints that correspond with the needed production quality level. The problems that occurred throughout the welding process were due to the very high melting point of the Mo. Also, using optical microscopy and scanning electron microscopy have performed a proper testing in parallel with the experiments. The details, revealed that the geometry of the joint and the resistance depend very much of the arc length, shielding gas velocity and especially of the tip geometry of the tungsten electrode and its wearing. Regarding to the electrode’s wearing, there have been determined the tip angle, the tapering and the effect of the electrode’s material composition. The latter parameter was investigated for unalloyed, thorium-oxide, cerium-oxide and lanthanum- oxide alloyed electrodes.