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One of the applications of the micromilling technology is to machine micro features on moulds by direct machining of hardened tool steels. However at this moment, this process is not industrial applicable because of the encountered problems, such as the big tool deflection, severe tool wear, and pre-mature tool breakage. A detailed examination of current commercial micro endmills showed that the geometry of micro endmills is mainly derived from macro endmills, which has been proved to be not suitable for micro hard milling application in experiments. Based on the experimental observations, the guidelines for the design of micro endmills for the micro hard milling application were generated. These guidelines were applied in the re-design of the micro endmill with the help of analytical modeling and Finite Element Analysis. The main purposes of the new design are to increase the strength of the cutting edge corner of the micro endmill and to improve the micro tool stiffness. The preliminary experiments with the new designed endmills showed that the new geometry has improved the tool performance largely.

This paper discusses the influence of runout on the calculation of the coefficients of mechanistic force models in micromilling. A runout mode is used to study the change of chip thickness, tool angles, and immersion period of two cutting edges of micro endmills due to runout. A new method to find the cutting coefficients was proposed based on the observations.