2D to 3D percussion drilling of thin metal foils using a fiber-based ultrashort pulsed laser robotic system

We report on 2D and 3D percussion drilling of thin metal foils using a six-axis articulated laser robot with flexible beam guidance of ultrashort laser pulses via a hollow-core fiber (HCF). Prior to drilling experiments, single-pulse ablations are conducted at different robot coordinates of thin transparent oxide layers to analyze the influence of HCF bending on beam characteristics and the resulting ablation pattern. In these experiments, we find a hexagonal ablation geometry of various sizes and different shape characteristics. To optimize the drilling quality in copper, brass, and mild steel foils, as being evaluated by the inlet and outlet diameters and the taper angle using laser scanning microscopy, a different number of pulses is applied in single-pulse and MHz burst modes. Our results show a material-dependent taper behavior due to different optical and thermophysical properties and dynamic in-hole processes. Furthermore, drilling brass and copper foils with two burst pulses in the MHz burst mode results in an average taper angle reduction of up to 31.5 %, which is mainly attributed to smaller inlet diameters and increasing heat accumulation inside the boreholes. 3D percussion drilling is performed on brass foils perpendicular to the workpiece surface within a large spatial area of 800 × 600 × 200 mm and workpiece inclinations ranging from −15° to 15° in the x- and y-directions. Experiments reveal a high consistency in the fabricated inlet and outlet diameters and tapers with small fluctuations, highlighting the potential of our novel laser robot for flexible 3D micromachining.