Evaluating the effectiveness of PCD tools on machinability of titanium alloy Ti-6Al-4V in high speed end milling under various wet cutting conditions

Abstract

Superior properties of titanium alloy Ti-6Al-4V over many other materials like higher strength to weight ratio, ability to maintain strength at elevated temperatures (around 500°C) and ability to resist against corrosion in severe environmental conditions have made them as an excellent choice for using them in many aerospace and bio-medical industrial applications. But the properties which had made them an ideal choice for most practical applications severely hinders their machinability and therefore is renowned as difficult to machine material. The low thermal conductivity of titanium alloys does not allow the generated heat to dissipate away quickly and thus results in chemical reaction with cutting tool materials at higher temperatures. Several researchers have tried to reduce tool-chip interface temperature, increase tool life and surface quality with carbide tools by applying different cutting fluids like water based emulsions flood cooling, oil flood coolant, minimum quantity lubrication MQL and various liquid nitrogen LiN cryogenic cooling techniques and has found some advantages of MQL & LiN cooling in terms of not only in improved surface roughness & tool life but also in controlling the hazardous environmental impact by eliminating the use of hazardous and expensive traditional flood coolant equipment. Moreover the thrust for higher quality and productivity has directed the attention of researchers on using super hard cutting tool materials for machining of titanium alloys. Super hard cutting tool like polycrystalline diamond PCD, Poly Cubic Boron Nitride PCBN and Binderless CBN inspite of their higher cost has many advantages over carbide tools like higher thermal conductivity, lower wear rate and high hot strength. Studies have shown that PCD tools can give better tool life and surface roughness as compared to carbide and PCBN tools. The studies on evaluating the effectiveness of PCD insert in high speed end milling of titanium alloy has not yet considered the effect of different types of cooling strategies. Therefore there is need to study the effectiveness of PCD tools in various wet cutting conditions and find optimal coolant which can help to increase tool life and can provide better surface quality and therefore this study is specifically designed to address above mentioned issues. Four different type of coolants “water based flood cooling, oil based flood coolant, MQL and LIN cryogenic cooling technique has been applied and their effect on tool-chip interface temperature, tool edge temperature, cutting forces and stresses acting on tool edge are observed using Finite element, FE numerical simulations. FE numerical simulations are widely employed in academic research field because it provides fast & reliable results and thus eliminates expensive experimentation costs which otherwise is always required. Results have shown that the LiN cooling technique has shown clear advantages over MQL and flood coolant techniques in terms of temperature near the tool rake face and in reducing cutting forces and stresses acting on cutting edge. Therefore from the study it can be concluded that LiN cooling can be used for machining of titanium alloys with PCD inserts for getting maximum productivity and part quality.