New approach for cooling and lubrication in dry machining on the example of internal cylindrical grinding of bearing rings

This paper describes a new method of hybrid cooling and lubrication of the machining zone conducted in dry conditions on the example of internal cylindrical grinding of bearing rings. The idea of the method consists in simultaneous application of a cooling agent in the form of compressed cooled air generated by the cold air gun (CAG) nozzle and a solid antiadhesive and lubricating agent fed to the grinding zone in the form of an impregnate in grinding wheel. Hexagonal boron nitride hBN was used as impregnate. The method of hybrid supply of cooling and lubricating agents configured in such a way allows for dry machining process (without the use of liquid coolants), simultaneously performing the cooling and lubricating functions of liquid coolants in a different, more environmentally friendly form. The article presents the characteristics of a new hybrid method of cooling and lubrication of the machining zone, the results of simulation studies on the flow of compressed cooled air (CCA) and heat exchange in the grinding zone, as well as the results of experimental studies on the process of internal cylindrical grinding of 100Cr6 steel bearing rings using the described method. The conducted simulation tests made it possible to determine the most advantageous conditions of feeding the CCA stream into the grinding zone by means of a two outlet supply line for effective cooling of the grinding zone. The most important result of the experimental research was to demonstrate the possibility of five times longer wheel life in the dry grinding process by using the proposed hybrid method of cooling and lubricating in relation to grinding with a non-impregnated wheel without the application of cooling and lubricating agents. The application of the proposed hybrid method of cooling and lubrication significantly reduced the grinding wheel volumetric wear V-s and made it possible to carry out the machining in stable conditions with more than 4 times higher value of grinding ratio G. Proposed method show its advantages also in relation to workpiece and grinding wheel temperature as well as reduction of grinding wheel doggings. (C) 2020 The Authors. Published by Elsevier B.V.