In situ X-ray tomography investigations on laser welding of copper with 515 and 1030 nm laser beam sources

摘要

A paramount challenge in laser micro welding is to design welding processes both highly energy efficient and precise regarding weld depth and surface roughness. With society's increasing interest in alternative energy storage systems, the demand for copper connections increases and processes for contacting electronic components for batteries and fuel cells are gaining in importance. Fiber lasers with a wavelength in the near infrared range have established themselves for this purpose [1,2]. However, the high thermal conductivity and low energy absorption of infrared radiation of copper cause significant difficulties such as pore and spatter formation. An increase in absorption of the electromagnetic radiation from 5 % (1030 nm) to 55 % (515 nm) of copper at room temperature, leads to a higher energy input into the material during the process which promotes lasers in the visible wavelength range as a more efficient alternative to near infrared lasers [3]. In this work, we investigate in situ X-ray tomography experiments during laser beam welding of copper with 515 nm and 1030 nm laser beam sources. Both lasers are equipped with similar optical setups to achieve identical focal diameters on the material surface. We investigate the difference in the geometric shape of the keyholes during the process. A wide range of laser parameters is investigated to create a basis for comparison with our numerical keyhole model [4]. It is found, that a significant difference in the depth of the keyhole depending on the wavelength occurs. A higher sensitivity to the variation of feed rate and laser power is observed for the 1030 nm laser source than for the 515 nm laser source.