Laser-arc combination welding displays the same features as those found in laser welding, namely deep welding, high welding speed, etc. It also has an advantage over laser welding in for example, it improves on tolerance in size accuracy. There is however a significant difference in the penetration depth and cross section shape caused by the distance between the laser and arc. The welding mechanism is quite complex, as mentioned above, and radiation phenomena is observed in the narrow groove extending from the front in the travelling direction when welding with a laser-arc combination of CO{sub}2 laser welding of 5kW and MIG welding of 10kW. The relationship between the cross section of the bead and this radiation phenomena was surveyed. The following results were obtained. (1) In the case of 0mm distance between the laser and MIG arc on the material surface, the position of plasma radiation is the entrance to the groove. In the case of 20mm, the positions are separately, the entrance and the bottom. In the case of 10mm, the radiations are a combination between the entrance and the bottom in the depth direction. (2) The maximum cross section of the bead is obtained on the condition of 20mm distance between laser and MIG arc and the material surface of the laser focusing point.
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