Due to their material properties such as high electrical and thermal conductivity, copper materials are more and more demanded for industrial applications. The same material properties make laser welding of copper a challenging task. Welds in copper at low velocities (v<10 m/min) with 1 µm wavelength lasers often suffer from defective weld seams with melt ejections and pores. Furthermore the absorptivity of pure copper is very low at this wavelength. On the one hand the absorptivity of copper strongly increases in the visible wavelength range. On the other hand a modulated laser power can reduce melt ejections.
A combination of these two approaches is presented in this paper. A frequency doubled thin-disk laser (λ = 515 nm) with a maximum fundamental mode cw output power of 200 W and a 5 kW 100 µm fibre delivered thin-disk laser (λ = 1030 nm) were used. In addition welds were made with modulated laser power. Results are presented for different copper alloys and the influence of the modulation frequency is discussed.