アーク溶接における溶込みの生成機構に関する一考察

抄録

The authors have investigated the penetration mechanism of the base metal in TIG arc welding process in D.C.S.P.
When the arc is fixed perpendicular to the base metal, three typical shapes of penetration, i.e. Simple, Central and Peripheral Penetration Types, are observed as shown in Photo.1. The mechanism of the first type can be clearly explained by the theory of heat conduction. The second type appears under heavy current. The strong plasma stream which becomes remarkable under heavy current digs deeply the central part of the molten pool, and consequently makes the penetration deep at the center. The last type is observed when the arc is held long and continued for a considerably long time. The formation of this type may be explained by the internal convection in the molten pool. As the surface temperature at the center of the molten pool is higher than that at the peripheral zone, a surface flow the center to the peripheral zone will be generated by the difference in surface tension. Thus the peripheral zone is melted effectively. The phenomena of the surface flow and the internal convection were examined with paraffin models.
In the case when the arc is traveling, the relations between the welding conditions and the penetration of bead are as follows;
i) Generally, the shape of the penetration becomes wide and shallow when the vertex angle of the cathode is decreased under small current and slow traveling speed. Under heavy current, the depth of penetration increases as the vertex angle becomes small. This is due to the strong plasma stream in the neighbourhood of the cathode with sharp vertex angle.
ii) Photo 4. shows the relation of the bead form when the welding speed is increased. At the higher speed, an exposure of solid surface is observed at the bottom of molten pool due to the driving force of arc plasma.