Development of electrostatic solid lubrication system for improvement in machining process performance

Liquid lubricants have traditionally been used to control the high heat generation in machining; however, the use of cutting fluid has become more problematic in terms of both employee health and environmental pollution. Minimization or possible elimination of cutting fluids substituting their functions by some other means is emerging as a thrust area of research in machining. Solid lubricant assisted machining is a novel concept to control the machining zone temperature without polluting the environment. The focus of this study is to explore the possibility of application of graphite as a lubricating medium in drilling of AISI 4340 steel, as a means to reduce the heat generated due to friction, towards finding an alternative to conventional coolants. To this end, an optimized solid lubricant application method, electrostatic solid lubrication experimental setup has been envisaged for effective supply of solid lubricant mixture as a high velocity jet and at an extremely low flow rate to the machining zone, thus meeting environmental requirements. The process performance is judged in terms of thrust force, tool wear, chip thickness, hole diameter and surface finish of machined workpiece keeping the other conditions constant. A comparison with the results obtained in wet and dry machining is also provided. The results obtained from the experiments show the effectiveness of the use of the solid lubricant as a viable alternative to wet and dry machining through reduction in the cutting zone temperature and favourable change in chip–tool and work–tool interaction. The proper selection and application of solid lubricant can lead to low cost, and this concept could emerge as an effective alternative to conventional coolants.