Micro Milling

J. Fleischer, M. Deuchert, C. Kühlewein, C. Ruhs
Institute of Production Science (wbk), Universität Karlsruhe (TH), Kaiserstrasse 12, 76131 Karlsruhe, Germany

Abstract

The geometry of micro milling tools currently in use have been adopted from macro tools, assuming that chip formation and process kinematics are analogical in both types of tools [1]. Experience has proved that micro tools respond to influences in a very different way than macro tools [2]. Oftentimes, structural details such as the rake angle and the twist angle impede further miniaturization and are impossible to achieve with conventional manufacturing techniques. Therefore it is necessary to get a comprehensive understanding of the entire process by taking a structure mechanical and cutting technological approach to micro milling tools in order to be able to optimize them. Another objective consists in the production of these miniaturized milling tools by means of force-free procedures such as laser ablation and electrical discharge machining.
The present state of research already puts the deficits of the currently available tools on display. Insufficient manufacturing tolerances of ±10 μm, constitute a substantial change of cutting conditions for the commonly used lateral infeed or feed per tooth of a few micrometers. Sometimes, only one cutting edge is engaged, which results in increased wear and, therefore, reduced durability, increased cutting forces, minor surface quality and a higher probability of milling cutter breakage. For that reason, a single-edged geometry has been proposed. It guarantees clear adjustment of the process parameters feed per edge and lateral infeed. For that purpose, stability analyses of simple stylus geometries have been conducted by means of FEM simulations. The resulting tool with a diameter down to 30 μm was machined on the EDM-machine at the wbk (Sarix SX 100). First tests have been carried out that prove the ability of these tools to cut steel.

G. Bissacco (a), T. Gietzelt (b), H.N. Hansen (c)

(a) Department of Mechanics and Innovation (DIMEG), University of Padova, via Venezia 1, 35131Padova, Italy
(b) Forschungszentrum Karlsruhe Institut für Mikroverfahrenstechnik, 76021 Karlsruhe, Germany
(c) Department of Mechanical Engineering (MEK), Technical University of Denmark (DTU), Produktionstorvet 2800 Kgs. Lyngby, Denmark

Abstract

This paper discusses the issues related to force measurement in micro milling and presents the results of the experimental investigation performed in an on going Cross Divisional Project within the 4M network of Excellence, aiming at force analysis and process characterization in micro milling. Reliable force measurement in micro milling is shown to be a challenging task. Measured forces are affected by contributions coming from the machining system. Based on the performed measurements, tool engagement has been demonstrated to occur at each tooth passing, even at feeds per tooth as low as 2 μm.