Tool wear and chip analysis after the hard turning of AISI D6 steel assisted by LN₂

Abstract

Sustainability is a concept which is widely considered nowadays, including in factories where machining operations are present. The search for methods able to improve the performance of industrial processes without damaging the environment or the worker’s health has been the main goal of several investigations. In this context, cryogenic machining is a technique that has been studied as an alternative to the use of mineral oil-based cutting fluids, mainly in the machining of titanium and nickel alloys. Investigations on the cryogenic machining of hard tool steels are still scarce in the literature. This article presents results from a series of turning trials under dry and cryogenic conditions using a hardened AISI D6 tool steel bar (57 HRC) as the workpiece. For the cryogenic machining tests, liquid nitrogen was delivered to the flank face, rake face and on both faces of PCBN inserts. The main cutting parameters (cutting speed, feed rate, and depth of cut) were kept constant during the trials. Tool wear and chip morphology were the output variables studied. The results show that the liquid nitrogen was able to reduce the cutting tool wear, providing a tool lifetime around 50% longer compared with the dry process. Moreover, the frequency of chip segmentation was diminished under cryogenic conditions in comparison with the dry process.

Keywords:

• Cryogenic machining
• hard turning
• AISI D6 tool steel
• PCBN
• tool wear
• chip morphology

Acknowledgments

The authors would like to thank CAPES, for granting a scholarship to Welber Vasconcelos Leadebal Jr. the Graduate Program in Mechanical Engineering at UFRN, the Department of Physics at UFRN for providing the LN₂ used in this investigation, Professor Álisson Rocha Machado for donating the PCBN inserts and the workpiece material used in this study and Sandvik Coromant for donating the toolholder.