Quality improvement of the surface of laser micro welds by using a dual beam setup

Laser micro welding on functional surfaces, for example, in medical engineering applications or in food industries, is gaining more and more importance. The ongoing development of high-brilliance laser beam sources allows processing of parts in the micron range with a minimum of energy input. Nonetheless, the welding process reduces the surface quality of the processed part. Every weld defect or irregularity in the molten pool has a direct impact on the surface roughness and therefore on the quality of the weld, which can cause increased expenditure for post-processing cleaning or damages on sensitive objects. By using a spatial power modulation – a linear feed with superposed circular motion – the molten pool dynamic can be influenced to achieve a more stable process, leading to a decreased surface roughness. Furthermore, an additional laser source can heat up and extend the end of the molten pool on the surface to decrease the dynamics of the molten pool even more. To achieve this, the second laser source is focused with a larger spot diameter to avoid a second keyhole generation and to create a longer molten pool with a shallower solidification front and a more stable fluid dynamic. As a further parameter, the output power of the continuously-emitting laser beam source can be modulated with a varied frequency and amplitude. This paper presents recent results on the influence of the spatial and temporal power modulation method in connection with a second laser source on the surface roughness during laser micro welding via laser measuring of the weld surface.