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

本研究的目的是通过建立焊接等离子体的定量描述来促进对高速、极深激光焊接工艺的基本理解。激光材料加工已迅速取代或补充了生产线上的许多传统制造技术。随着工业激光器能够经济地提供非常高的功率，10KW到20KW，它们开辟了以超过2米/分钟的速度焊接超过10毫米厚的金属板的应用。超高功率激光焊接的关键问题之一是控制和克服焊接过程中产生的剧烈等离子体。过量的等离子体会吸收、反射或重新聚焦激光束，导致激光束穿透不足、烧穿、焊缝形状不规则或光束传输光学污染。PI与普渡大学、日本大阪大学和卡特彼勒公司建立了密切的研究合作关系，试图提供更完整的等离子体及其对激光吸收机制的影响。理论建模的重点是表征由激光束形成的进入工件的毛细管锁孔内的等离子体电子温度和密度。实验将主要在大阪大学及其附属工业实验室进行，使用最先进的2KW CO2和8KW二极管泵浦Nd:YAG激光器。除了促进对高能激光与材料相互作用的基本理解外，此次合作还将提供一个有效的机会，将大阪大学集团在激光焊接方面的经验和专业知识与普渡大学的学术研究小组和行业合作伙伴卡特彼勒结合在一起。这将促进向工业的技术转让以及对工业从业人员的培训。

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.