Innovative micro-tool manufacturing using ultra-short pulse laser ablation

The continuously growing demand for micro-electro-mechanical systems (MEMS) with decreasing feature sizes necessitates adjusted manufacturing solutions. Micro-milling fulfills the high requirements for precision and reliability placed on the final product. The employed tools have diameters in the range of 50-300 mu m and are commonly manufactured by grinding. However, a reduction in tool diameter leads to a decrease in stiffness in the fourth power and the introduced load in grinding causes a high scrap rate. Furthermore, the flexibility in tool design is limited to the attributes of the grinding wheel. These restrictions in micro-tool manufacturing can be avoided by using ultra-short pulse (USP) laser ablation. This process allows a force-free 2-D and 3-D machining across a broad range of materials without wear formation. By using a USP laser, a wide range of customer-oriented applications in the micrometer scale can be addressed. Also, it leads to precise ablation with minimal thermal and mechanical damage. This paper provides knowledge on the manufacturing of micro-tools made of tungsten carbide with small diameters and high aspect ratio. For the desired tool geometries, necessary process parameters are evaluated and their physical limits are shown and discussed. An innovative CAM-system has been programmed to allow the manufacturing of advanced geometries using a 4-axis laser machine test bench developed by ETH Zfirich. A 515 nm wavelength laser beam is capable of providing flawless tools with diameters as low as 50 mu m and aspect ratios up to 6. Due to precise calibration, the tool run-out is decreased to < 5 mu m. Providing multiple teeth at smaller diameters and individually shaping of each tooth is feasible using a beam radius < 10 mu m and a pulse duration of 1 ps. A form deviation to the target geometry below 5 mu m evidences high repeatability. The cutting edge is exposed after being struck by a focused ion beam. In the cross-section, the cutting edge radius is determined to be < 3 mu m. By mastering the multi-axis laser ablation process, micro-tools for machining ductile and brittle workpieces are presented. The performance of the micro-tools is analyzed in subsequent milling experiments. Enabling optimization of the tool geometry leads to higher flexibility compared to ground micro-tools. The laser-processed tools enhance the range of micro-structuring. Pitch distances of structures in the range of the tool diameter with extreme aspect ratios are realized in ductile and brittle materials.