4M Knowledge base - papers

A. Herreroa, L. Uriartea, J. Esmorisa, J.A. Sánchezb, L.N. Lopez de Lacalleb
a Fundación Tekniker, Avda. Otaola 20, 20600, Eibar, Spain
b Dpto. Ing. Mecánica, ETSII, Alameda Urquijo s/n, 48013, Bilbao, Spain

Abstract

The analysis of WEDM is still nowadays an important field of research due to the difficulties to measure the process characteristics: narrow gap (~10 mm), dirty environment (oil or deionised water), high frequency (>100 kHz), etc. Nevertheless, the WEDM technology has been improved thanks to the theoretical and empirical results of different research groups that have made use of state of the art technologies to measure temperature distributions, displacements, frequencies or electrical signals for spark characterisation. The accurate measurement of machined parts has also brought light to the machining process, being this aspect critical for the improvement of the EDM technology.

In the last years, the growing tendency to miniaturisation has promoted the research of production techniques capable to produce small components with very high precision. EDM technology, due to the low processing forces, was immediately identified as one applicable technology for the production of moulds and dies. The technological research in the field has been very important, reducing the minimum wire diameter from Ø0.1 mm to Ø0.02 mm, the machine components have evolved to provide a finer control of all process parameters, specially the wire traction force, the machine feed and the spark energy. Thanks to the research in WEDM, nowadays it is known that, during the process, electrostatic, electrodynamic, electromagnetic, dielectric and wire traction forces act on the wire. Many of these forces push and pull the part from the workpiece. The result of all these forces acting on the wire is an error of the machined shape that, in normal WEDM, is of only a few microns (3~20 mm depending on part height). This error is specially important when machining flat walls and machining corners in which the feeding direction change.

Despite using lower energy values, due to the origin of the different forces acting on the wire and the low tensile strength of wires smaller than Ø0.1 mm (considered as thin wires), the errors that can be found in miniature parts and microparts are bigger than the corresponding values in conventional WEDM. The present paper analyses the errors that appear when applying thin wire EDM (Ø0.03 mm) to the machining of 3 mm height components made of tungsten carbide, it presents the difficulties that are found when trying to characterise the errors in small components. A possible error analysis approach is presented and then the errors are discussed.

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.