Machine tool for combines micro milling an laser ablation processes
Small and medium lot sizes of parts containing micro structures, needed for micro dies and moulds for injection moulding e. g., can be produced economically by milling with tools of low nominal diameter. An alternative production technique that affords huge latitude concerning geometry features and machinable work piece materials is laser ablation. This paper introduces a machine tool that enables the two production techniques mentioned before, without removing the workpiece from the workspace. Thereby the specific benefits of each technique can be fully utilised and complex geometries with features in the scale of some micrometers can be machined, even in difficult-to-cut materials. In Addition to the process modules, the machine tool contains an optical measurement module, with which the geometry of the workpiece can be acquired. The measurement module bases on the chromatic-coded principle and it determines the distance between the optical probe and the workpiece surface with an accuracy of less than one micron. The optical probe is moved by the machine tool axes and generates a 'cloud' of measuring points. The laser ablation process operates with pulsed light in the UV-regime (pulse duration 15 ps, repetition rate 500 kHz, average power 10 W) and the focus diameter is in the range of 10 mym The focus of the laser beam is moved by a scanner unit in x- and y- direction, the movement in z-direction is realised by use of a dynamic beam expander, which is placed at the beam entrance of the scanner. The envisaged machine tool allows combined laser ablation processes and milling processes on the basis of the machined geometry after one process step. Therefore, the workpiece does not have to be removed from the workspace what would cause realignment errors.