Quality improvement of copper welds by laser microwelding with the usage of spatial power modulation

Abstract

Laser welding of copper is gaining more and more importance to create electrical contacts due to the high temperature resistance and high achievable mechanical loads. However, laser welding of copper in the past was always associated with low process stability. By using high brightness fiber laser sources, small laser spots can be generated which allows keyhole-based deep penetration welding even in copper with high quality. Unfortunately, a small spot size and keyhole welding lead to a small connection area between the two joining partners. To avoid this, spatial power modulation - a linear feed with superposed circular motion - has been introduced. By using an additional parameter, oscillation frequency, and amplitude, in conjunction with spatial power modulation, we can increase not only the connection area but also the stability of the laser welding process and quality characteristics of the welds. In addition to the conformity of the weld depth, the surface roughne ss of the weld is a measure of the quality. Especially in interconnection of lithium ion cells and high power electronics, the consistency of the weld depth influences the connection area, which is essential for the current-carrying capacity. The quantity of weld defects and irregularities has a direct impact on the surface roughness of the weld. This paper presents recent results on the influence of the spatial power modulation on quality characteristics during laser microwelding by analyzing the weld via three-dimensional longitudinal cross sections and via laser measuring of the weld surface. Experimental investigations are supplemented by finite element simulations which enable a detailed analysis of the influence of the laser scanning strategy on the geometry of the fusion zone

Overlap joining of aluminium and copper using laser micro welding with spatial power modulation

“…The increased width is accompanied by a slight reduction of the weld depth, as the actual path speed is increased due to the oscillation movement. Although linear feed rate and laser power are the same, the overall cross-sectional area is increased [7].…”

“…An increase of the process stability and a better controllability of the melt pool dynamics can be observed [7,8]. Furthermore, the efficiency of the welding process could be increased using a spatial power modulation [9].…”

“…For laser beam welding, common fibre lasers with infrared wavelength (1070 nm) can be used. High focusability leads to high intensity for enabling a stable keyhole welding process [7]. This process step is recommended to achieve an efficient weld seam because of the increased energy incoupling inside the keyhole.…”

Processing of Keyhole Depth Measurement Data during Laser Beam Micro Welding

“…To apply these fast movements, mostly, galvanometric scanners are used. 3,4,8 Depth measurement during laser welding Depth measurement methods for laser beam welding can be divided into destructive and non-destructive methods. Performing parallel longitudinal cross sections with a distance of 20 mm 3 shows threedimensional weld seam shapes comparing the weld depth consistency using laser micro welding with and without spatial power modulation.…”

“…Nevertheless, it is only possible to visualize a single plane of the weld seam with this analysis method. Investigations to achieve a threedimensional weld seam model have been done by Haeusler et al, 3 with multiple parallel cross sections.…”