HIGH-POWER LASER SOURCES ENABLE HIGH-QUALITY LASER WELDING OF COPPER

摘要

Copper and copper alloys are more and more in demand for industrial applications due to their high electrical and thermal conductivity. However, the optical and thermal material properties make laser welding of copper a very challenging task. Due to the low absorptivity of only a few percent (< 10%) at the wavelength of about 1μm and the high heat conductivity comparatively low feed rates of less than 10 m/min are needed to achieve welds with penetration depths of several millimeters using commercially available lasers with a few kW (< 6 kW) of power. In previous work it was shown that weld defects such as spatters, melt ejections and pores are very likely to occur within this parameter range. As these weld defects degrade both, the mechanical and the electrical properties of the weld seam it is important to minimize the number of such weld defects. In this paper the approach using a 16 kW disk laser to weld copper is discussed. The number of weld defects was analyzed serving as weld quality criteria. Welds were made at different laser power levels, feed rates and focal diameters and the resulting weld quality was compared. For every weld the thermal efficiency was calculated and identified as a key indicator of the reduction of weld defects. It is shown that above a thermal efficiency of about 35% welds in pure copper with reduced or even completely without weld defects were generated with penetration depth of up to 9 mm.