Please cite this article in press as: Pu Z, Singh A. High speed ball nose end milling of hardened AISI A2 tool steel with PCBN and coated carbide tools. J Manuf Process (2013), http://dx.doi.org/10.1016/j.jmapro.2013.05.005 ARTICLE IN PRESS G Model JMP-174; No. of Pages 7 Journal of Manufacturing Processes xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Journal of Manufacturing Processes j ourna l h o me page: www.elsevier.com/locate/manpro Technical paper High speed ball nose end milling of hardened AISI A2 tool steel with PCBN and coated carbide tools Zhengwen Pu, Anshul Singh ∗ Diamond Innovations, Inc., 6325 Huntley Road, Worthington, OH 43085, USA a r t i c l e i n f o Article history: Received 18 May 2013 Accepted 31 May 2013 Available online xxx Keywords: High speed machining (HSM) PCBN Ball nose end milling Hardened steel Surface integrity Die/mold a b s t r a c t High speed machining (HSM) of tool steels in their hardened state is emerging as an attractive approach for the mold and die industry due to its potential for significant cost savings and productivity improvement. An experimental study was conducted to investigate the tool wear mechanism and surface integrity in high speed ball nose end milling of hardened AISI A2 tool steel using coated tungsten carbide and polycrystalline cubic boron nitride (PCBN) tools. It is found that coated carbide tools can only be used at low speed (120 m/min) while high content PCBN tools are suitable for HSM range (470 m/min). PCBN tools produce a damage free workpiece with better surface finish and less work hardening. Despite the higher tool cost, HSM with PCBN tools lead to reduction in both total cost and production time per part. © 2013 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. 1. Introduction High speed machining (HSM) of tool steels in their hardened state is emerging as an attractive approach for the mold and die industry since machining and polishing take up more than 50% of the total production time [1]. Significant cost saving and productiv- ity improvement can be achieved through HSM compared with the traditional method where workpieces go through rough machining in pre-hardened state, electrical discharge machining (EDM) after hardening and finally manual polishing to the required surface fin- ish [2]. A 67% reduction in machining time and 58% reduction in cost was achieved by using the HSM method for manufacturing an AISI H13 die compared with the traditional method [2,3]. In addi- tion, it was reported recently that the HSM approach led to better surface integrity and improvement of fatigue life in machining of AISI H13 workpieces compared with the traditional method [4]. The definition of HSM varies with the workpiece materials. The HSM range for alloyed steels is about 500 m/min [1]. Coated car- bides are the most common cutting tools used currently for die and mold manufacturers due to its low cost. However, the cutting speed used is normally in the range of 100–300 m/min, which does not take full advantage of the HSM technique [5]. It is also reported that white layers were produced under all testing conditions when ∗ Corresponding author. Tel.: +1 614 438 2132; fax: +1 614 438 2829. E-mail address: anshul.singh@diamondinnovations.com (A. Singh). machining hardened P20 steel (41 HRC) at relatively high speed (301–754 m/min) with TiAlN coated carbide end mills [6]. Polycrystalline cubic boron nitride (PCBN) tools are claimed to be more suitable for HSM of hardened steels by several researchers [2,4,5]. The cutting speed is in the range of 300–1200 m/min depending on the workpiece materials. It was reported that 8 times longer tool life was achieved by PCBN tools compared with TiAlN- coated carbide when machining hardened D2 steels at 500 m/min [5]. A white layer free surface and compressive residual stresses were reported in HSM of hardened H13 steels using PCBN tools at the cutting speed 300 m/min and the fatigue life of the machined component was increased 30% compared with the traditional method where EDM and manual polishing were employed [4]. Despite the known benefits of PCBN tools, there is still limited knowledge on the influence of CBN content in the PCBN tools on tool life. Most researchers employed low content PCBN tools (about 45 vol.% cubic boron nitride) for milling of hardened steels [4,7]. Low content PCBN tools are normally recommended for hard tur- ning of hardened steels due to their good chemical resistance and may not be suitable for hard milling applications where the cut- ting is more interrupted. Also, there is few studies on the surface integrity generated by PCBN tools in the HSM range, especially for cold work tool steels with hardness >60 HRC. These two prob- lems are addressed in the current study. Ball nose end milling of hardened A2 cold work steel at 64 HRC is conducted using both TiAlN coated carbide tools and PCBN tools with different CBN content. The tool wear mechanism and surface integrity are investigated. 1526-6125/$ – see front matter © 2013 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jmapro.2013.05.005