ISSUE 114 AUTUMN 2024 LASER WELDING


HIGH-POWER LASER WELDING:


A COMPARATIVE STUDY OF Cu & Al RAGAVENDRAN MEENAKSHISUNDARAM Laser welding is widely used in various


industries, such as aerospace, nuclear, automotive, and medical. There is an increasing appetite for high-power batteries in diverse industrial sectors. Some batteries require relatively thick tabs and bus materials to deliver the required power, which are mainly made of aluminium or copper. The dissimilar laser welding of aluminium and copper is challenging, attributed to several factors such as reflectivity (reduced laser absorption), intermetallic formation, cracking, and differences in thermophysical and mechanical properties. Welding of thick and dissimilar materials in lap configuration can be carried out using high-power lasers with wobbling technology.


The welding of dissimilar materials, especially highly-conductive and reflective materials such as aluminium and copper, makes using laser beams more challenging. Welding these materials poses several inherent problems including lack of fusion, incomplete penetration, keyhole instability due to high heat input-producing porosities of varying sizes, and cracking due to incompatibility in chemistry and wide variations in the physical and mechanical properties at room and processing temperatures.


Experimental details and materials


This article describes the joining of thick sheets of copper and aluminium, each 2 mm, in a lap joint configuration - this configuration is widely used and applicable in the electronics and battery industries. Three lap joints, copper to copper (Cu-Cu), copper to aluminium (Cu-Al), and aluminium to copper (Al-Cu), were made using an IPG 8 kW high-power laser in continuous wave mode. This laser has two switchable scanner heads with a maximum coverage area of about 200 mm x 200 mm.


The study aimed to determine whether the acceptable welds of thick sections in these configurations could be fabricated using high- power laser welding with wobble technology. Welds of 50 mm in length were produced in all three material configurations. The aim was to fully penetrate the top section and partially penetrate into the bottom sheet. This condition was chosen to replicate the ideal situation in battery welding. The welds were fabricated with and without beam wobbling.


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The laser system used in this study is shown in Figure 1. The battery modules welded using the laser system with wobble technology are shown in Figure 2.


The wobble parameters have great influence on the weld shapes, i.e., the top and bottom dimensions of the welds. The wobble parameters, namely amplitude and frequency, substantially determine the heat distribution, temperature gradient and molten metal flow


rate. The wobble amplitude is essential in making welds compliant with industrial requirements, whereas the wobble frequency effect on penetration depth and interface width is limited. The penetration depth is reduced when the wobble amplitude and frequency increase. The decrease in maximum temperature required for welding the bottom material is reduced due to the fast movement of the laser beam and scanning over a large area compared to


THE LASER USER


Figure 1: Laser welding with inline process monitoring and material handling robot.


Figure 2: EV battery modules are assembled and welded at AMRC Northwest utilising an 8-kW laser welding facility.


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