Effects of Helium Pressure on Characteristics of TIG Arcs and Mechanical Properties of Welds

概要

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Characteristics and the behavior of arcs and the feasibility of welding of mild steel plates by TIG arc welding process were investigated in the pressure range from 0.1 to 5.1 MPa. As the cathode, 2% thoriated tungsten of 4 mm in diameter and 30° in vertex angle was used. Results obtained are summarized as follows : (1) Arc voltage increases with an increasing pressure. V_A+V_K is 11.5V in 0.1 MPa and it decreases with an increasing pressure. It remains about 9.3V over 0.6 MPa. (2) The arc column constricts and the diameter of the arc decreases with an increasing pressure. As the result, the current density in the center of the arc increases considerably. (3) The area of the cathode spot decreases and therefore the cathode mode of arc changes from the normal mode to the cathode spot mode with an increasing pressure. Then, the erosion of tungsten tips increases. The erosion in He atmosphere is much worse than in Ar atmosphere. (4) The depth of penetration of a mild steel plate increases with an increasing pressure. Therefore, the optimum welding current for penetration welding of a thin mild steel plate decreases considerably with the pressure. (5) Sound penetration welds of mild steel plates of 3.2 mm in thickness can be obtained in the pressure range up to 3.1 MPa. (6) Welded joints obtained in the pressure range up to 3.1 MPa have sufficient tensile strength and Charpy impact value.
社団法人溶接学会の論文
1990-04-01