Investigation on turning of AISI 1040 steel with the application of nano-crystalline graphite powder as lubricant

The past few decades have witnessed significant advancements in turning processes, cutting tools and coolant/lubricant chemistry. These developments have enhanced the machining capabilities of hard materials when machining at higher cutting conditions. Turning, being characterized by the development of high temperatures at the cutting zone, is critical with respect to the tool life and surface finish apart from other machining results like the forces generated. This phenomenon of heat generation at the cutting zone plays a negative role during turning operations due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation. Cutting fluids and solid lubricants are generally used to overcome the problem of heat generation at the cutting zone. The use of cutting fluids in the conventional way may not effectively control the heat generated in turning operation. Moreover, cutting fluids are a major source of pollution. With the advancement in technology, nano-level particulate solid lubricants are being used nowadays in machining operations, especially grinding and turning. The present work deals with the investigation of using nano-level particulate graphite powder as a solid lubricant and various tests were conducted by machining AISI 1040 steel using tungsten carbide inserts. The experiments were conducted by taking into account the parameters like feed rate ranging from 0.05 mm/rev to 0.125 mm/rev, cutting speed ranging from 51 m/min to 192.6 m/min and depth of cut from 0.25 mm to 1 mm. Four levels of each parameter are considered for experimentation. The results indicate that with the decrease in the nano-sized graphite powder, there is an increase of cutting forces – feed force, cutting force and thrust force. The temperatures at the tool–chip interface also increases with the decrease in the lubricant size. It is found that the surface roughness of the workpiece after machining deteriorated due to the size of the lubricant particle.