4M Knowledge base - papers

A Friction Model for Microforming

H.J. Jeon, A.N. Bramley
Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK

Abstract

For the simulation of metal forming processes, input data relating to the tool-workpiece interface is necessary. For microforming applications the tool/workpiece interface conditions tend to dominate the process and it has been found that traditional methods of modeling the interface are not realistic. This paper describes an approach that seeks to describe friction by modelling the geometric surface roughness of the tool as opposed to the use of the traditional empirical friction coefficient or factor. This finite element based model has been validated experimentally in terms of loads and metal flow using the ring test and actual surface measurements. It enables more accurate and also more flexible modeling of friction. As such it will be very suitable for microforming applications.

Submitted on May 19, 2008 - 15:23.

Geometry Optimization of Micro Milling Tools

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.

Submitted on August 6, 2008 - 14:13.

Simulating electroplated micro surfaces in 3-D

A H. J. Jeon (1), J Low (1), A. R. Mileham (1), A.N. Bramley (1), C. Johal (2)
1 Department of Mechanical Engineering, University of Bath, BA27AY, UK
2 Glacier Vandervell Bearings Ltd, Rugby, UK

Abstract

This paper describes the development, comparison and validation of a 3-D model of the electroplating process. It is based on the current density distribution that is generated using the Finite Element Method (FEM) and is used together with Faraday's law of electrolysis and various material and electrolyte values to determine the local plating depth. It has been developed initially to model the depth of the micro layer deposited on the work surface of an automotive engine’s "big end" shell bearing. Actual plating trials were conducted in a series of controlled laboratory experiments using an industrial type jig and industrial plating conditions. These consisted of a steel cathode (the bearing) and a lead anode. The results described here, in this paper, show good agreement between the 3-D simulation and the actual plating depth and profile and are considered to validate the model sufficiently for it to be used for electroplating tooling design and micro-electroforming.

Submitted on May 19, 2008 - 15:26.

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