Influence of Filler Metal on Weld Bead Penetration and Shape in Automatic TIG Arc Welding
Itsuro Tatsukawa, Shinobu Satonaka, Masayoshi Inada
In the present work, bead-on-plate welds of mild steel and aluminum alloy are made with an automatic TIG arc welding machine, the traveller and filler rod feeder of which have been made to be driven by individual stepping motors manually and automatically controlled, and welding thermal cycles, weld bead shape and penetration are examined. Detailed discussions cover the heat flow in filler rod as well as in parent plate and the cross-sectional configuration of weld bead in connection with the process variables such as welding heat and ratio of feed speed to travel speed, i.e., length of rod deposited per unit weld length. The main results are summarized as follows:
The traveller and feeder, individually, are smoothly driven at accurate speeds with acceptable step response. By increasing the welding heat, both the penetration depth and the cross-sectional area of molten base metal are increased linearly, and the bead width is increased by increments reduced with welding heat. For a given welding heat, increasing the ratio of feed speed to travel speed decreases the cross-sectional area of molten base metal as well as the high temperature region in parent plate during welding, and increases the ratio of bead width to penetration depth. The temperature distribution along the filler rod during welding can be approximately derived from the quasi-steady-state one dimensional heat conduction theory, and a fraction of the welding heat which is transferred into the filler rod is 2 to 5 percent and increases with an increase in feed speed of the filler rod.
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