A feasibility study has been conducted to determine whether a hollow cathode arc (HCA) can be used for a welding heat source in space, that is high vacuum and microgravity conditions. The HCA method enables the arc discharge to form under low pressure conditions by purging a small amount of gas through the centre of the hollow cathode. The characteristics of HCAs under low pressure conditions have been experimentally investigated, in particular the melting properties and voltage-current characteristics. Results show that the penetration profile and arc characteristics of the HCA method are sensitive to process parameters such as gas flowrate, arc length, and inner diameter of the electrode, and that the penetration in HCA melting is extremely deep under the conditions of low gas flowrate and long arc length.

Characteristics of hollow cathode arc as welding heat source: arc characteristics and melting properties

GHTA (Gas Hollow Tungsten Arc) welding experiments were conducted under a simulated space environment that consists of vacuum and microgravity. A vacuum chamber for the experiments was placed in the aircraft cabin. Aluminum and titanium plates were employed as work pieces. The experiments prove that the arc discharge phenomena, the welding phenomena, and the microstructure of welded metal receive almost no effect from gravity. Moreover, it is also demonstrated that the weld metal of the plate welded under the simulated space environment hangs down less than that of the plate welded on the ground.

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GHTA Spot-Welding Experiments of Aluminum and Titanium Plates under a Simulated Space Environment

As a welding method in space, the authors have proposed the GHTA (Gas Hollow Tungsten Arc) welding method in the previous papers, where some GHTA welding experiments have been conducted under the condition of low pressure (10-2 Pa) and/or the micro-gravity. In the present paper, a feasibility study has been conducted whether the method can be used under such a high vacuum condition (10-5 Pa) as on the space station orbit. As a result, it is made clear that the GHTA method is quite feasible under the high vacuum condition and its melting process strongly depends on the operating gas species such as Ne, Ar and Kr. Increasing the flow rate of operating gas decreases the mass of metal vapor from molten pool and the use of a heavy operating gas such as Kr also decreases the mass of metal vapor.

宇宙ステーション軌道圧力での ghta 溶接実験

A feasibility study has been conducted to determine whether gas hollow tungsten arc (GHTA) welding can be used for welding in space. As described in a previous paper by the present authors, the GHTA method has been tested in a simulated space environment using aircraft. The test result shows that the method is most promising as a welding process in space. In the present paper, some fundamental characteristics of the GHTA in a vacuum chamber, such as discharge characteristics and plasma properties, have been elucidated and the results of melting tests on stainless steel plate using the GHTA method have been compared with those obtained via a conventional gas tungsten arc method under atmospheric pressure.

Gas hollow tungsten arc characteristics under simulated space environment

GHTA Spot Welding Experiments of Aluminum and Titanium Plates under Simulated Space Environment

GHTA (Gas Hollow Tungsten Arc) welding experiments were performed in a simulated space environment using aircraft. A vacuum chamber for GHTA welding test was placed in the cabin of the aircraft and the microgravity environment was produced by a parabolic flight of the aircraft.Spot welding tests on stainless steel plates and girth welding tests of stainless steel pipes were performed in the vacuum chamber under microgravity condition.The results are summarized as follows, (1) GHTA method makes it possible 'to form a stable arc and weld stainless plates and pipes in the simulated space environment.(2) Experimental results show that the arc configuration and the melting characteristics of GHTA are insensitive to the gravity.(3) The weld bead formation is affected significantly by the gravity. The flat weld with full penetration, as is expected, is formed both in the spot welding and the girth welding under the microgravity condition.(4) The butt joints of pipes welded by GHTA process in the simulated space environment have no defect good joint strength and the bead appearances is quite satisfactory.

Teppei Kohno

Papers

GHTA Welding Experiments under Simulated Space Environment in Flying Laboratory.

GHTA Spot-Welding Experiments of Aluminum and Titanium Plates under a Simulated Space Environment

GHTA Spot Welding Experiments of Aluminum and Titanium Plates under Simulated Space Environment