Cryogenic orthogonal turning of Ti-6Al-4V
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ORIGINAL ARTICLE
Cryogenic orthogonal turning of Ti-6Al-4V Analysis of nitrogen supply pressure variation and subcooler usage Benedict Stampfer1 · Philipp Golda2 · Robert Schießl2 · Ulrich Maas2 · Volker Schulze1 Received: 23 April 2020 / Accepted: 14 September 2020 / Published online: 28 September 2020 © The Author(s) 2020
Abstract Cooling of machining operations by liquid nitrogen is a promising approach for reducing cutting temperatures, increasing tool life and improving the workpiece surface integrity. Unfortunately, the cooling fluid tends to evaporate within the supply channel. This induces process variations and hinders the use of nitrogen cooling in commercial applications. In this work, the coolant is applied via the tool’s rake face during orthogonal turning of Ti-6Al-4V. The effect of a nitrogen supply pressure adjustment and a subcooler usage—proposed here for the first time for machining—is analyzed in terms of process forces, tool temperatures and wear patterns, taken dry cutting as a reference. Thereby, reliable cooling strategies are identified for cryogenic cutting. Keywords Orthogonal turning · Liquid nitrogen · Adaptive cooling
1 Introduction Cooling strategies of machining processes are economically and ecologically relevant, since high efforts arise for the supply, maintenance and disposal of conventional cutting fluids. Hence, the substitution of these cutting fluids is a promising approach moving towards environmental friendly production. In the machining of low strength materials such as aluminum alloys, dry cutting strategies and minimum quantity lubrication are used [1]. These strategies however are not suited for Ti-6Al-4V, which is a commonly applied titanium alloy and a difficult to machine material [2]. The high strength and low heat conductivity of Ti-6Al-4V lead to high cutting temperatures and diffusion of the chemical reactive titanium into the tool material [3]. This causes adhesion of titanium carbides on the rake of tungsten carbide tools. The adhered material Benedict Stampfer
[email protected] 1
wbk Institute of Production Science, Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany
2
Institute of Technical Thermodynamics (ITT), Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany
is occasionally torn away by the chip, resulting in crater wear [4]. As those mechanisms are temperature sensitive, a small increase of the cutting parameters may cause rapid tool wear. Arrazola et al. [5] identified a cutting velocity of 90 m min−1 as critical value when turning Ti-6Al-4V. Machining with elevated cutting parameters hence demands for effective process cooling. Consequently, machining of Ti-6Al-4V is regarded as a test case for improved cooling concepts in this work. High pressure cooling is a strategy which is suited for difficult to machine materials, but unfortunately issues associated with the cleaning of parts and energy consumption are critical [2]. An approach which overcomes the needs of maintenance and
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