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Comparing 1070 nm and 515 nm Wavelength Laser Beam Sources in Terms of Efficiency for Laser Microwelding Copper
M. Hummel, A. Häusler, A. Olowinsky, A. Gillner and R. Poprawe

Copper is classified as an ideal material for electronic components due to its high electrical conductivity. With society’s increasing interest in alternative energy storage systems, the demand for copper increases and processes for contacting electronic components for battery and fuel cells are gaining in importance. One method to do so is laser microwelding, which is characterized as a high-precision joining process in the micron range. Fibre lasers with a wavelength in the near infrared range (NIR) have established themselves for this purpose. In these joining processes, material properties of copper such as high thermal conductivity and low energy absorption of infrared (IR) radiation cause significant difficulties such as process instabilities as well as pore and spatter formation. Newly developed laser beam sources in the visible wavelength range (VIS) prove to be an alternative to conventional fibre lasers. An increase in absorption of the electromagnetic wave from <5% (1070 nm) to >55% (515 nm) of copper at ambient temperature, leads to higher energy coupling and a more stabilized energy input into the material during the process. In this work the influence of the green wavelength of 515 nm on absorption, energy coupling during the laser welding process and the process dynamics is investigated on Cu-ETP and CuSn6. Blind welds with a frequency doubled 515 nm disc laser are conducted and compared to investigations with a fibre laser at 1070 nm. The reflected radiation from the materials surface is observed by using photodiodes while melt pool dynamics are observed by high speed imaging. The results obtained by the experimental method can be used for the quantitative comparison of laser welding processes as well as for the validation of simulative keyhole and welding models.

Keywords: Green laser, 515 nm, disc laser, 1070 nm, copper, laser welding, absorption, energy coupling

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