Weld formation in microgravity

Abstract

In order to investigate the effect of gravity on the formation of a weld, gas tungsten arc (GTA) welding was performed both in a microgravity environment and in a terrestrial environment. The microgravity environment was produced for 10 sec with less than 10-5 G by a drop-shaft type microgravity system at Japan Microgravity Center (JAMIC). The material used was an aluminum alloy. It has become clear that in the microgravity environment, the weld bead is formed flatly and a large amount of metal can be welded at once and in any welding position though the weld shape is significantly affected by gravity in the terrestrial environment. When helium rather than argon is used as a shielding gas, the butt weld is formed more flatly because the arc pressure is reduced. Judging from the distribution of the grain structures in the weld, in the microgravity environment, the temperature gradient is smaller than that in the terrestrial environment, and the degree of the constitutional supercooling is higher due to the absence of the heat transfer by gravity.