Understanding tool chip interaction through experimental and numerical analysis during vibration assisted turning of AISI D3 steel

Abstract

Vibration Assisted Turning (VAT) is a hybrid machining process where the material is machined with the help of a tool vibrating at ultrasonic frequency. VAT results in significant changes in process characteristics compared to conventional machining, like reducing the machining forces and tool wear. The chips produced during the machining operation can provide valuable insight into the process characteristics like machining zone temperature, friction at the tool-chip interface and chip load that primarily alter the process performance. One can understand and have a better control on the machining process performance by studying the formation of these chips and the tool-chip interaction. The work presents an experimental and numerical study to analyze the chip formation during VAT while machining AISI D3 steel. The chips formed while machining at different vibration amplitudes were observed to be of different colors, widths, and thicknesses. These were found to correlate to the forces generated and the surface integrity produced. A decrease in the chip width and thickness was observed with an increase in the amplitude that helps to reduce the chip load and hence forces. Also, the temperature at the machining zone increased with an increase in amplitude as seen from different color of chips produced and carbon content of the chip. The numerical model, developed to analyze the effect of the vibration amplitude on the contact pressure at the chip-tool interface, showed that the average contact pressure reduced upon applying ultrasonic vibration to the tool, thereby reducing the coefficient of friction and frictional forces. Also, with increase in vibration amplitude, the coefficient of friction was found increasing but it still remained lower than that in conventional turning. The study would help to understand the reduction the overall machining forces and chip morphology and thereby to have a better control on the process performance.