Metal cutting process is one of the most important industrial processes in which metal parts are shaped by removal of unwanted material in the production of mechanical components. Removal operations are performed on the atomic, micro and macro scales and metal is removed as a plastically deformed chip. In these operations, produced chip experiences severe friction with tool rake face. Metal cutting involves concentrated shear along a rather distinct and the chip-tool contact zone. These variables, however, have effects on one another and cannot be considered independently. The three most widely used cutting operation are turning, milling and drilling. Turning is a continuous cutting process using a single-point tool that removes unwanted material and milling is an intermittent cutting process using a multi-point tool such as rotating cutter. Drilling process is a continuous cutting process using a multi-point tool and material is removed from workpiece by a drill. Drilling process is usually the most efficient and economical method of making a hole in a solid body. However, there have been no analytical method to assess drilling process based on the shear and frictional characteristics. In this paper, procedures for analyzing shear and frictional processes of drilling have been established by adopting an equivalent turning system to drilling. A series of drilling experiments were carried out with varying feed, velocity and drill shape factors on the workpiece of SM45C and SS41 steels. Using the experimental results, the cutting characteristics including shear in the primary shear zone and friction in the chip-tool contact region of drilling process have been analyzed. The specific cutting energy tends to decrease exponentially with increase of feed rate.
In drilling of SM45C steel, 35-40% of the total energy is consumed in the friction process. While in case of SS41 steel, 25-35% of the total energy is consumed in the friction process. These are greater than that of turning process in cutting of the same work materials.