Characterizing Keyhole Plasma Intensity and Absorption Mechanisms for Improving High Speed, Very Deep Penetration Laser Beam Welding

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The objective of this research is to advance the fundamental understanding of high speed, very deep laser welding processes by estabishing a quantitative descriptions of the welding plasma. Laser material processing has rapidly replaced or complemented many conventional manufacturing techniques in production lines. As industrial lasers become capable of delivering very high power, 10KW to 20KW, economically, they open up applications to weld sheet metals over 10 mm thick at speeds over 2 m/min. One of the most critical issues in very high power laser welding is to control and overcome violent plasma generated during welding. Excess plasma can absorb, reflect, or refocus the laser beam resulting in insufficient penetration, burn-through, irregular weld shape, or contamination of the beam delivery optics. The PI has formed a close research collaboration involving Purdue University, Osaka University, Japan and Caterpillar, Inc. in an attempt to provide a more complete picture of plasma and its effect on laser absorption mechanism. The theoretical modeling will focus on characterizing plasma electron temperature and density inside the keyhole which is a capillary into the workpiece created by the laser beam. Experiments will be conducted mainly at Osaka University and affiliated industrial laboratories using state-of-the-art 2KW CO2 and 8KW diode-pumped Nd:YAG lasers. In addition to advancing the fundamental understanding of high energy laser interactions with materials, this collaboration will provide an effective opportunity to bring the experience and expertise in laser welding of the Osaka University group together with the academic research group at Purdue and the industry partner, Caterpillar. This will promote technology transfer to the industry as well as training for industry practioners.