A chip-tool interface lubrication technique for improvement in machinability of en-31 steel

Abstract

Machinability of a material provides an indication of its adaptability to a machining process. In general, machinability is defined as ease of machining of a material, characterized by low cutting force, high material removal rate, good surface finish, accurate and consistent work-piece geometrical characteristics, low tool wear rate and good curl or chip breakdown of chips etc. In this research work different concentrations of various solid lubricants in SAE-40 oil were applied to the chip-tool interface by a new technique and their effect on various machinability parameters of EN-31 steel were studied under turning operation. In the new technique solid-liquid (mixture) lubricant was applied with a brush at the machining zone, so that the lubricant seeps into the chip-tool interface. This reduces the chip-tool interface temperature and lubricates the surface, and makes cutting easy. All the machinability parameters studied were found to improve by this technique, the amount of lubricant that seeped to the chip-tool interface was negligible, thus a true minimum quantity lubricant (MQL) cutting or near dry (ND) cutting conditions were achieved. EN-31 steel was selected for machinability studies, because it is widely used in automotive industry for the production of axle, roller bearings, ball bearings, shear blades, spindle, forming and molding dies, etc. Turning is the main machining process for the production of these parts. Therefore EN-31 steel was chosen for the machinability studies under turning operation. The machinability criteria chosen for this study were, chip-tool interface temperatures, cutting forces, specific cutting force, power consumption, surface roughness, tool wear rate, chip thickness, chip micro hardness, chip-tool contact length, shear angle, cutting ratio, type of chip formed and coefficient of friction. Cutting velocity, feed rate, depth of cut and tool nose radius were the machining variables used.