Journal of Materials Processing Technology 210 (2010) 212–218 Contents lists available at ScienceDirect Journal of Materials Processing Technology journal homepage: www.elsevier.com/locate/jmatprotec Capability of high pressure cooling in the turning of surface hardened piston rods D. Kramar ∗ , P. Krajnik, J. Kopac Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, 1000 Ljubljana, EU, Slovenia article info Article history: Received 16 June 2008 Received in revised form 3 February 2009 Accepted 4 September 2009 Keywords: Fluid power products Hard turning High pressure cooling Machinability Tool wear Chip breakability abstract An experimental study was performed to investigate the capabilities of dry, conventional and high pres- sure cooling (HPC) in the turning of surface hardened piston rods used in fluid power applications. Machining experiments were performed using coated carbide tools at cutting speeds up to 160 m/min. The cooling capabilities are compared by monitoring of chip breakability, process regions of operability, cooling efficiency, tool wear, tool life and cutting forces. Test results showed that dry cutting could not be performed due to long and ductile chips that were formed for all investigated cutting conditions. In comparison to conventional cooling the significant increase of cutting speed and feed rate region of oper- ability was recorded when machining with HPC. Tool life analysis proved a five times increase in tool life when machining with HPC. Furthermore HPC also improved chip breakability and reduced coolant consumption. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The research goal relates to an improvement of hard turning in order to increase its technological capability and to extend the region of process operability. This can be achieved by applying HPC that can reduce the coolant consumption in comparison with con- ventional cooling as well as improve the machinability of surface hardened steel. End-users of fluid power products require surface hardened components such as hydraulic cylinders and piston rods in order to improve their wear behaviour. In the manufacturing chain, the inductive hardening process is followed by a finishing operation that generates the component’s final geometry. Traditionally, the finishing operations are grinding processes, but within the last years the performances of hard cutting operations have drastically improved. The study of Klocke et al. (2005) has shown that hard cutting offer a higher flexibility, increased material removal rates and the possibility of machining with reduced coolant consump- tion. As presented by Rech and Moisan (2003) hard turning usually employs high cutting speeds and advanced cutting tool materials such as CBN, PCD and ceramics. Hard cutting with coated carbide tools, low cutting speed and conventional cooling, usually results in significant problems concerning extremely long chips and severe adhesion wear mechanisms. By applying HPC at flow rate 1.4 l/min, the friction and the heat induced in the tool–chip interface can be reduced. It is expected that HPC assisted hard turning with coated ∗ Corresponding author. Tel.: +386 1 4771 737; fax: +386 1 2518 567. E-mail address: davorin.kramar@fs.uni-lj.si (D. Kramar). carbide tools and cutting speeds in the range of 90–160 m/min can be performed. According to Klocke and Eisenblätter (1997) coolant has a direct influence on the manufacturing economics. Therefore, by abandon- ing conventional cooling and using dry or HPC assisted machining, the cost related to the usage of coolant can be reduced. Weinert et al. (2004) have shown that besides an improvement in the economic efficiency of the machining process, dry machining principles can also contribute to the health of machine tool operators and envi- ronment concerns. In this investigation the capabilities of dry, conventional and HPC in hard turning are compared. All machining experiments are performed with coated carbide tools and cutting speeds up to 160 m/min. The performances of different cooling condi- tions are assessed on the basis of chip breakability, regions of operability, cooling efficiency, tool wear, tool life and cutting forces. 2. Analysis of existing work To achieve higher wear resistance, the piston rods are inductive hardened before the finishing operation. In the hard turning of steel, the thermal influence can lead to high temperatures and structural alterations of the workpiece material, causing the change of piston rods mechanical properties. The thermal impact mainly depends on the maximum temperature reached in the cutting zone as well as the cooling capability. Klocke and Eisenblätter (1997) have stated that many materi- als such as high-temperature alloys (titanium and nickel based), hardened steels and other hard to machine materials cannot be 0924-0136/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2009.09.002