Influence of laser parameters on tensile shear strength of copper welds

Abstract

The electrification of the power train in the automotive industry leads to the requirement of electrical connectors with high current carrying capacities. These interconnections are often realized with the ultrasonic bonding technology. On the one hand the substitution of ultrasonic welding by laser welding allows an increase of ribbon cross section by a factor of five and thus a similar increase of the maximum transferred current. On the other hand the increased cross section leads to higher loads (at least by a factor of 5) during the loop forming process. To minimize the weld seam dimension, which can resist the applied force, it is necessary to understand the mechanical properties of laser welded lap joints.The influence of different laser parameters on the ultimate tensile shear strength is investigated, based on realistic specimen geometries (10 mm x 0.3 mm). The variable parameters are: Laser wavelength (515 nm, 1030 nm and 1070 nm), focal diameters (45 µm, 50 µm, 150 µm and 300 µm), temper conditions of the base material (soft, semi hard, hard), process parameters (laser power 0.6 kW - 4 kW and feed rate 50 mm/s to 800 mm/s) and welding strategy (line welding, spatial beam modulation). The material used is Cu-ETP (>99.9 % Cu). For all the investigated parameters the observed failure mode was fracture in the fusion zone.The ultimate tensile shear strength for all experiments is around 188 N/mm² with a high reproducibility and for parameter changes in the order of one magnitude. This is in contrast to the stated relation between laser parameters and the mechanical properties. This contrast will be discussed.