Compact air bearing spindle for manufacturing and application of micro end mills

• Applicant: Professor Dr.-Ing. Jan C. Aurich
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491400536

To ensure sufficient cutting speeds the production of microstructures with tools with very small diameters is only feasible with tool spindles with high rotational speed. In addition, such tool spindles must guarantee minimal runout of the tool which is a measure of the deviation of the tool from the ideal rotational movement. Due to the very small tool diameters, the tool’s runout has significant influence on the machining result in form of deviations between the structure to be produced and the structure produced. Tool runout also increases tool wear and can lead to tool breakage. In addition, micro milling tools are optimized for a defined ratio of feed velocity, rotational speed and cutting edges. For an optimum machining result, this ratio, the feed per tooth, should constantly assume the previously defined value. However, due to rapid changes in the feed direction during micro milling, such as when milling curves, there are often temporary deviations of the feed per tooth from the nominal value. This leads to lower surface qualities and increased tool wear.The objective of the proposed research project is to develop and apply an air bearing spindle with pneumatic drive, pneumatic speed control and integrated tool production. The tool production and use without reclamping avoids the radial runout that inevitably results from clamping and unclamping the tool in different positions in the tool holder, leading to a higher dimensional accuracy of the milled structures. Moreover, the pneumatic drive concept eliminates interactions caused by electromagnetic interference fields of electric drives, which in previous investigations led to a significant increase of the spindle’s runout. Counter-rotating turbines are used to accelerate and decelerate the rotor, and are operated in dependence on the feed rate. The pneumatic speed control thus allows the feed per tooth of the micro end mills to be kept constant during rapidly changing feed velocities, which means that optimum cutting parameters can be set constantly. In addition, the pneumatics are almost wear- and maintenance-free. The spindle will achieve a speed of 300,000 min-1 with minimal tool runout (< 1 µm). Due to its compact dimensions, the spindle can also be integrated into desktop machine tools, which are increasingly being used in micromachining.After completion of the research project an air bearing tool spindle with pneumatic speed control will be available for the production and application of micro milling tools, which guarantees a permanently constant feed per tooth.

• DFG Programme: Research Grants