Contents lists available at ScienceDirect Journal of Manufacturing Processes journal homepage: www.elsevier.com/locate/manpro MoS 2 solid lubricant application in turning of AISI D6 hardened steel with PCBN tools Mauro Paipa Suarez a , Armando Marques b , Denis Boing c , Fred Lacerda Amorim d, ⁎, Álisson Rocha Machado a,d a Universidade Federal de Uberlândia – UFU, Faculty of Mechanical Engineering – FEMEC, Av. João Naves de Ávila, 2121, Uberlândia, MG, 38.400 902, Brazil b Federal Institute of Espírito Santo, Av. Rio Branco, 50 - Santa Lucia, 29056-255, Vitória, ES, Brazil c Brusque University Center, Department of Mechanical Engineering, Technology, Innovation and Manufacturing Center, R. Dorval Luz, 123 – Santa Terezinha, 88352 400, Brusque, SC, Brazil d Pontifícia Universidade Católica do Paraná - PUCPR, Mechanical Engineering Graduate Program - PPGEM, Av. Imaculada Conceição 1155 Prado Velho, 80.218 901, Curitiba, PR, Brazil ARTICLE INFO Keywords: Hard turning PCBN MoS 2 solid lubricant Minimum quantity of fuid – MQF Tool life ABSTRACT This research investigates the efect of the application of MoS 2 mixed with oil in the hard turning of AISI D6 cold work tool steel with PCBN tools. A 3 3 statistical factorial planning was used to run the tests, variables: cutting speed, feed rate; lubri-cooling conditions: dry cutting, pure oil applied by MQF (minimum quantity of fuid), oil mixed with solid lubricant (MoS 2 ) applied by MQF. The main tool wear mechanisms were abrasion, attrition (or adhesion), and difusion. The EDS of the PCBN confrmed the presence of MoS 2 , indicating that solid lubricant particles took place in the lubrication process at the cutting region. The results suggest that use of solid lubricant in hard turning may be a viable alternative to tackling the challenge of machining difcult-to-cut materials. 1. Introduction For over thirty years, the hard turning process has been proved as a feasible method for manufacturing quenched and tempering steel alloys (hardness above 45 HRC) in fnishing operations. The turning of har- dened steels is typically carried out using PCBN or oxide ceramic as the tool material. The process fexibility, material removal rate, set up time and environmental compatibility are the hard turning benefts when it is compared to the grinding process [1–3]. Furthermore, the high pre- cision hard turning tends to achieve ISO tolerance IT2 when combined with roughness Rz below 1 μm [4]. The hard turning prerequisites in- volve high stifness and dynamic stability of the machining system [5,6]. During the hard turning process, as a result of the chip formation mechanism, the austenitization temperature of the steel is easily achieved at the chip-tool interface [3,5,7]. The common practice of the hard turning is to machine without the application of coolant or lubricant fuids in order to keep the cutting region warm enough to maintain the strength of the work material in a level that facilitates material shearing [5], which is one of the greatest benefts of the hard turning based on the environmental compatibility of the production line. Furthermore, when using oxide ceramics, the application of a cutting fuid (i.e., wet/fooded cooling) may lead to early tool fracture due to the low thermal conductivity and fracture toughness of them [8]. On the other hand, in case of low volume of lubricant fuid application (i.e., minimum quantity of fuid – MQF, also known as MQL – minimum quantity of lubricant and NDM – Near dry machining), the friction force on the clearance surface and rake surface can be reduced, diminishing the heat generated and the temperature in the chip-tool interface in appropriate levels, increasing the tool per- formance [6,9,10]. Although not usual in an industrial environment, some successful application of cutting fuids, including the cryogenic cooling, in specifc hard turning cases have been reported [11,12]. Near Dry Machining (NDM) or Minimum Quantity of Fluid (MQF) is placed between dry machining and machining with food cooling, and it uses a spray of the mixture of compressed air and droplets of oil. When the MQF is compared to dry and food cooling, the literature has shown positive results in machining regarding the surface roughness, cutting forces, cutting temperature and tool wear [13]. The hard turning pro- cess of AISI 4340 (55 HRC) was experimented by Chinchanikar e Choudhury [14] using cemented carbide tools with several nanocoat- ings (AlTiN, multi-layer TiAlN/TiSiN, and AlTiCrN) under dry and MQF technique. Besides pointing AlTiCrN as the best coating, the results https://doi.org/10.1016/j.jmapro.2019.10.001 Received 29 January 2019; Received in revised form 26 August 2019; Accepted 1 October 2019 ⁎ Corresponding author. E-mail addresses: mauro.suarez@pitagoras.com.br (M.P. Suarez), amarques@ifes.edu.br (A. Marques), denis.boing@gmail.com (D. Boing), fred.amorim@pucpr.br (F.L. Amorim), alisson.rocha@pucpr.br (&.R. Machado). Journal of Manufacturing Processes 47 (2019) 337–346 1526-6125/ © 2019 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. T