Shaped laser beam profiles for heat conduction welding of aluminium-copper alloys

Heat conduction welding is often used where weld seams with a high surface quality and the exact retention of the chemical composition are needed. This study investigates the influence of intensity profiles in laser beam welding with laser powers up to 3.2 kW. The resulting process windows for heat conduction mode welding, the melt pool shape, the process stability and the dynamics, and the produced surface roughness are analysed. Therefore, three different intensity profiles are created with diffractive optical elements and the process dynamics are monitored with two high-speed cameras. Before analysing etched cross sections with respect to microstructural properties, the surface roughness is measured on all produced samples with a laser scanning microscope. With beam shaping, we found that a high peak intensity does not necessarily lead to an instable melt pool and that the distribution itself plays the major role. The use of shaped beam profiles leads to a more stable process and an enlarged heat conduction process regime compared to a defocussed multimode spot of the same size. Applying shaped laser beam profiles surface roughness close to laser polished surfaces can be achieved while also simultaneously enlarging the weld cross section area.