Behavior of hardened steel grinding using MQL under cold air and MQL CBN wheel cleaning

Abstract

Nowadays, environmental concern and the search for environmentally friendly techniques have contributed to industrial development towards sustainability. Production without social and environmental impact is one of the main goals of engineering research. Although analysis is carried out, some manufacturing processes still require studies, such as grinding, for example. In this process, the interaction between the grinding wheel and workpiece generates a significant amount of heat, due to shearing, friction, and scratching caused by the contact of the numerous abrasive grains with the workpiece surface. The heat generated at the interface has a more intense flow to the workpiece, which can cause several microstructural damages, as well as providing shape errors and increased grinding wheel wear. Thus, the application of cutting fluid is indispensable to minimize the harmful effects caused by heat to the grinding wheel and the workpiece during the process. However, the industry commonly uses soluble cutting fluid, having oil in its composition, in addition to chemical components that prevent its degradation, due to recirculation in the system and the need to avoid the accumulation of bacteria, whereas its application has a flow rate of tens of liters per minute. These cutting fluids will be discarded at some point, which will require complex waste treatment processes for proper disposal. An alternative to this type of application is the minimum quantity lubrication (MQL), which consists of a few milliliters per hour, but which has low refrigerant power. Some techniques have been developed to enhance its application and make it more refrigerant, such as the application of a jet of compressed air directed to the grinding wheel cutting surface to perform the cleaning, minimizing the heat generation by the reduced agglomeration of chips in the grinding wheel pores. Therefore, this work analyzed the cylindrical plunge grinding of hardened steel workpiece with cubic boron nitride grinding wheel on different cooling conditions, comparing the conventional cutting fluid application method (flood) with the MQL technique, MQL simultaneously with the wheel cleaning jet (MQL + WCJ) and MQL with cutting fluid applied at 0 °C (MQL + CA). The performance of each method was analyzed by using the measurements of surface roughness (Ra), roundness error, diametral wheel wear, power consumed during the process, specific energy grinding, microhardness, and microstructural analysis to investigate possible modifications of the microstructure of the workpiece. It was found that in none of the cases, there were microstructural alterations, but the MQL application method presented the worst values of the variables among the techniques studied, whereas the application on low temperature showed potential to be used in a large scale. Nevertheless, the MQL application method applied simultaneously with the wheel cleaning jet (WCJ) has presented the closest values of the conventional method; it becomes the most feasible method for application in the industry towards the protection of the environment and health of the workers.