Keyhole behavior during all position welding with high power Nd:YAG laser

Abstract

The keyhole behavior in flat, downward vertical, upward vertical and overhead welding was observed with X-ray transmission imaging system. The laser beam, where the pulsed beam of 2 ms width was superimposed to the modulated rectangular beam of 100 Hz frequency and 50 % duty at the delay time of 0 - 9 ms, was used in the welding. Under the formation conditions of sound beads without generation of sputters, the generation and collapse of a keyhole were repeated synchronizing with the modulated frequency of the laser beam in all welding positions.Moreover, in vertical welding, the molten metal was brought downward by gravity and blockaded the inlet of the keyhole. Then, bubbles often remained in the bottom of the molten pool, resulting in the formation of porosity. On the other hand, the penetration depth increased in the case of 1 - 2 ms of the delay time and in 4 ms of Td the penetration width increased without increasing the penetration depth in all welding positions. The penetration was the deepest in the overhead position welding and was the shallowest in flat position welding in all the ranges of the delay timeThe keyhole behavior in flat, downward vertical, upward vertical and overhead welding was observed with X-ray transmission imaging system. The laser beam, where the pulsed beam of 2 ms width was superimposed to the modulated rectangular beam of 100 Hz frequency and 50 % duty at the delay time of 0 - 9 ms, was used in the welding. Under the formation conditions of sound beads without generation of sputters, the generation and collapse of a keyhole were repeated synchronizing with the modulated frequency of the laser beam in all welding positions.Moreover, in vertical welding, the molten metal was brought downward by gravity and blockaded the inlet of the keyhole. Then, bubbles often remained in the bottom of the molten pool, resulting in the formation of porosity. On the other hand, the penetration depth increased in the case of 1 - 2 ms of the delay time and in 4 ms of Td the penetration width increased without increasing the penetration depth in all welding positions. The penetration was the deepest in t...