A Study on Performance Enhancement of Cutting Tools through Perforated Surface for the Machining of Titanium Alloy using PCD Inserts

Abstract

In the manufacturing industry, high-speed machining technology has been widely used in metal cutting due to its remarkable advantages in improving the productivity. However, the cutting tools have minimum tool life when used for machining difficult-to-cut materials such as titanium alloys and nickel-based alloys. Titanium alloy (Ti-6Al-4V alloy) is one of the widely used materials in the application of aerospace industries, military applications, automobile industries and biomedical implants. Rapid tool wear is the main issue in machining these difficult-to-cut materials due to the high heat generation in the machining zone and high chemical reactivity at higher cutting conditions. The heat produced at shear zone during machining of Ti-6Al-4V alloy is highly centralized and temperature increases rapidly. Tribological properties at the toolchip contact area can be improved by using a number of methods like Minimum Quantity Lubrication (MQL) and surface coatings. The surface texturing technology is a promising approach in this regard. Many researchers have discussed with different surface texturing patterns such as parallel, perpendicular and elliptical micro/nano textures on cutting inserts. These surface textures helped in improving the tribological properties. The present work is focused on surface textures with micro-hole patterns on cutting inserts, under the MQL environment. In this process, the lubricant surrounded in the micro-holes at the tool-chip interface could be squeezed to the cutting interface to reduce friction under proper viscosity and sliding speed. A novel configuration of holes and tunnels in the inserts has been tried out successfully. The present work is divided into three phases while machining of Ti-6Al- 4V alloy using the micro-hole patterned cutting insert under MQL environment. In the first phase, the modelling and simulation of micro-hole patterned cutting inserts were developed using Finite Element Analysis software. In this phase, different micro-hole patterns were developed on PolyCrystalline Diamond (PCD) cutting insert using CAD modelling and later static and dynamic analysis were carried out. From the results, it was observed that cutting inserts with micro-holes embedded on rake face and flank face had lower stress concentration. Hence, proved that cutting inserts with micro-holes withdifferent hole configurations had no adverse impact on mechanical properties of cutting tool materials. In the second phase, optimization strategy is applied to identify the right configuration of surface texture and experiments were conducted based on the one factor at a time approach to study the behaviour of individual process parameters like cutting velocity, feed rate and depth of cut on the performance indexes such as cutting temperature, machining vibrations, tool flank wear, Material Removal Rate (MRR), chip-morphology and surface integrity (surface roughness, surface topography and microhardness) under MQL environment machining using normal and modified cutting inserts. It is evident from the experimental results that machining with modified inserts significantly improved the machining performance and quality of the product. One more finding, out of the present work, is the mitigation of serrated chips, when compared to chip formation in machining of Ti-6Al-4V alloys with normal inserts. The chip formation with less shear bands were obtained during machining process due to the improvement in the thermal stability property caused by a reduction in cutting temperature through micro-hole patterns. A best feasible micro-hole configuration for the machining of Ti-6Al-4V alloy under MQL environment was arrived at, as a unique solution. In the third phase, the modified PCD insert with the chosen pattern of micro-holes was compared with Polycrystalline Cubic Boron Nitride (PCBN) inserts, for machining of the Ti-6Al-4V alloy. From the experimental results, it was found that modified PCD insert had better efficiency in reducing the cutting temperatures and also reduces the tool wear by increasing the wear resistance properties due to the micro-pool lubrications when compared to modified PCBN inserts. Another important outcome of this research is the development of prediction model using Adaptive Neuro-Fuzzy Inference System (ANFIS) to assist in validation. This method is a combination of two soft-computing methods of ANN and Fuzzy logic. Fuzzy logic helps in the transformation of the human knowledge and the ANN helps in the learning process and reduces the rate of errors in the determination of rules in fuzzy logic. In this research, gauss membership function model was developed for the prediction ofoutput parameters. The comparison made between the predicted values derived from ANFIS and experimental values proved that the gauss membership function adaptation achieved accuracy of 96 % with 4-5% prediction error. Thus, a unique surface texturing consisting of micro-holes and tunnels in the PCD inserts, for machining Ti-6Al-4V alloy has been successfully developed, tested and validated.