A New Compression-Torsion-Tribometer with Scalable Contact Pressure for Characterization of Tool Wear during Plastic Deformation

Marco Teller,Gerhard Hirt,Simon Seuren,Markus Bambach

doi:10.1155/2015/496515

Abstract

A contact pressure which reaches up to ten times the yield stress of the workpiece material is characteristic for cold extrusion processes. Common tests for friction and wear are limited to rather low contact pressures. Thus, the aim of this paper is to present a new compression-torsion-tribometer which is able to scale the contact pressure to a multiple of the yield stress of the workpiece. In order to enable a contact pressure that greatly exceeds the yield stress of the workpiece material, the workpiece specimen is encapsulated laterally. As main parameters, contact pressure, glide length, and relative velocity can be adjusted independently, thus allowing for multiple load cycles. The resulting torque is measured continuously as an indicator for wear. Afterwards wear can be also quantified by examination of surfaces. Hence, the developed setup enables a comparison of tool surfaces and coatings and a characterization of wear behaviour under high contact pressure.

Highlights

A characteristic of cold extrusion processes is the high contact pressure between workpiece and tool [1]
A contact pressure which reaches up to ten times the yield stress of the workpiece material is characteristic for cold extrusion processes
Common tests for friction and wear are limited to rather low contact pressures

Summary

Introduction

A characteristic of cold extrusion processes is the high contact pressure between workpiece and tool [1]. It can reach up to ten times the yield stress σy of the workpiece material [2]. The high stresses highly influence the lifetime of the tools in extrusion processes. For the determination of friction and wear, different methods were investigated in the past. On the one hand there are the “classical” experimental setups for friction measurement involving partial plastic deformations, for example, the pin-on-disk test, the stripdrawing test, or the draw-bending test [3]. There are measurement methods for friction involving bulk plastic deformations like the Burgdorf-ring-compression test [4], the conical tube-upsetting test by Kopp and Philipp [5], or a sliding-upsetting test by Hemyari [6]. A multiple performance of these experiments allows an estimation of tool wear

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Conclusion