ORIGINAL ARTICLE Evaluation of tool life and workpiece surface roughness in turning of AISI D6 hardened steel using PCBN tools and minimum quantity of lubricant (MQL) applied at different directions Miguel Mandú Bonfá 1 & Éder Silva Costa 1 & Wisley Falco Sales 1 & Fred Lacerda Amorim 2 & Luis Henrique Andrade Maia 3 & Álisson Rocha Machado 1,2 Received: 7 December 2018 /Accepted: 19 March 2019 # Springer-Verlag London Ltd., part of Springer Nature 2019 Abstract The main objective of this work is to evaluate the tool life and the workpiece surface roughness when applying a vegetable-based cutting fluid by minimum quantity of lubricant (MQL) at three different directions (main tool flank face, secondary tool flank face, and overhead) in turning AISI D6 hardened steel with polycrystalline cubic boron nitride (PCBN) tools with Al 2 O 3 ceramic binder and TiN coating. Dry cutting was also tested for comparisons. Tool wear analyses were performed on the tools at the end of their lives within a scanning electron microscope (SEM). The application of the cutting fluid by MQL technique in the direction between the main tool flank face and the workpiece showed better results than the dry condition. The application of MQL through other directions (overhead and between the secondary tool flank face and the workpiece) also showed competitive results. Abrasion and adhesion were the prevailing mechanisms for the wear of the tools. Keywords AISI D6 steel . Hard turning . Minimum quantity of lubricant . PCBN tools . Tool lives . Surface roughness 1 Introduction The use of hardened steel tools for cold and hot works is growing in several practical applications in engineering, espe- cially when high wear resistance, toughness, and corrosion resistance, such as those for dies and molds, are demanded. These steels are used to manufacture tools for cold/hot pro- cessing of other steels and cast irons and nonferrous metals in various operations such as cutting, stamping, extrusion, and forging. Applications of round components of D6 steels are parts of complex stamping dies, molds for spinning pans and bottles, and molds for stamping cans among others. Heat treat- ment of these steels ensures high hardness, providing im- provement of mechanical properties such as ultimate strength and toughness [1]. Machining processes such as turning, drilling, and milling are normally used to manufacture dies and molds, which de- mands good machinability characteristics of the hardened tool steels. Hard turning appears as an alternative operation to con- ventional grinding with respect to effective cost, high produc- tivity, and a flexible machining process for ferrous materials components harder than 45 Rockwell C hardness (HRC) [2]. * Fred Lacerda Amorim fred.amorim@pucpr.br Miguel Mandú Bonfá miguelbonfa@yahoo.com.br Éder Silva Costa eder@ufu.br Wisley Falco Sales wisley@ufu.br Luis Henrique Andrade Maia luismaia@pucminas.br Álisson Rocha Machado alisson.rocha@pucpr.br 1 Faculty of Mechanical Engineering (FEMEC), Universidade Federal de Uberlândia (UFU), Av. João Naves de Ávila, 2121 - Campus Santa Mônica, Uberlândia, Minas Gerais 38400-902, Brazil 2 Mechanical Engineering Graduate Program (PPGEM), Pontifícia Universidade Católica do Paraná (PUCP), Av. Imaculada Conceição, 1155 - Prado Velho, Curitiba, Parana 80215-901, Brazil 3 Graduate Program in Mechanical Engineering, Pontifícia Universidade Católica de Minas Gerais - PUC Minas, Belo Horizonte, Minas Gerais, Brazil The International Journal of Advanced Manufacturing Technology https://doi.org/10.1007/s00170-019-03619-z