Analysis of Ultrasonic Vibration Combined with Sustainable Cooling Strategies for Machining Difficult-to-cut materials

Abstract

The metal-cutting process induces a severe plastic deformation of the workpiece material at the deformation zones, generating heat. Machining difficult-to-cut materials further enhance heat generation, reducing tool life and degrading surface quality. Using cutting fluids to remove the heat from the deformation zone is a common approach used by metal-cutting industries. It is observed that the conventional synthetic oil-based cutting fluids are not bio degradable and require expensive treatment for disposal. In this regard, applying ultrasonic vibration combined with a sustainable cooling/lubrication strategy is proposed to enhance the machinability of difficult-to-cut materials and to reduce the consumption of conventional cutting fluids. An indigenously developed setup is used for implementing ultrasonic vibration to the cutting tool. MQL (minimum quantity lubrication) and LCO2 (liquid carbon dioxide) are employed for cooling and lubrication purposes. The machinability of Ti6Al4V and Inconel 718 is examined under the combined effect of ultrasonic vibration and cooling/lubrication strategies. The responses, such as tool wear, surface quality, power consumption, and cutting forces, are analyzed. The combination of ultrasonic vibration and LCO2 offers a significant reduction in tool wear and hence power consumption and specific cutting energy for both the workpiece materials, Inconel 718 and Ti6Al4V. Quantitatively, the UAT combined with LCO2 approximately reduced the flank wear by 35-70% and 32-60% for Ti6Al4V and Inconel 718, respectively. In the other phase of the thesis work, analytical and finite element models are developed to estimate the machining responses, considering the ultrasonic vibration. The analytical model is developed to predict machining forces and tribological characteristics under the effect of ultrasonic vibration. The developed analytical model is validated by conducting experiments on the SS 304 stainless steel. The analytical model showed a very good agreement at a lower value of cutting speed and feed rate. The tool wear and machining forces are estimated using finite element modeling and validated with experimental observations. The FEM and experimental results were in close agreement with an approximate error of 2-25%. In the extension of the thesis work, the downscaling of conventional machining is explored using different workpiece materials such as wrought Ti6Al4V, SLM Ti6Al4V, and Nimonic 90. Comparing the micro machinability of wrought and SLM Ti6Al4V, higher hardness and instability of the β phase at a higher temperature in the LPBF Ti6Al4V are mainly responsible for enhanced tool wear. On the other hand, equiaxed grains and balanced yield strength and hardness of wrought Ti6Al4V are primarily accountable for reduced tool wear.