Electron beam and gas tungsten arc welding under microgravity

Abstract

Electron Beam (EB) and Gas Tungsten Arc (GTA) welding were performed using both microgravity and terrestrial conditions and the effects of gravity on bead shape and bubble behavior were investigated. The drop-shaft type system was used to obtain a 10 s microgravity of 10(exp -5)g at the Japan Microgravity Center (JAMIC). Small-size systems for both EB welding and GTA welding were developed, and EB welding was carried out in a high vacuum under microgravity, which simulates conditions very similar to those in space. It was found that a flat bead is formed under proper conditions and a large amount of metal can be welded at once in any welding position. When aluminum alloys were welded in a high vacuum under microgravity, several pores were observed in all the welds including the bead-on-plate welds. It was established that the bubbles were formed by the production of Al2O gas. By comparing the pore distribution in the terrestrial environment with that in the microgravity environment, the bubble behavior in the molten pool was investigated and the following conclusions reached. Blowholes grow by combining with other blowholes after their formation, though wormholes do not combine with other wormholes or blowholes. Gravity does not significantly affect either the movement or the combination of bubbles smaller than a critical size. Gravity does affect the movement of bubbles larger than a critical size, though it does not affect their combination.