EXPERIMENTAL INVESTIGATION AND MODELLING OF MACHINING OF DIFFICULT TO CUT MATERIAL USING INTERNALLY COOLED CUTTING INSERT

Abstract

Titanium alloys find applications in various types of industries, including chemical, aerospace, petroleum and automobile sectors. The superior qualities like corrosion resistance, toughness, fatigue strength, hot hardness etc., make these alloys suitable even for harsh environments and their machining plays an essential aspect in the product development. Ti- alloys are generally considered as difficult to cut materials, due to their inherent metallurgical properties like low thermal conductivity, adhesiveness, etc. Machining of Ti6Al4V leads to localized heating and high temperatures in the machining zone and it leads to excessive tool wear and low surface quality. Additionally, high temperatures also adversely affect the surface integrity (i.e. micro hardness, residual stress etc.) of the machined component, which will directly affect the fatigue strength and productive life of the part. Generally, conventional cooling technique have been used during the machining of Ti-alloys to normalize the heat effect. These techniques consume a huge amount of coolant, i.e., 5-10 liters/min during process operation. Most lubricants and coolants being used during machining are petroleum-based emulsions that affect the environment and are also very expensive. The coolant costs can be as high as 70% of the total machining costs. Besides this, excessive use of the coolant can threaten human health and the environment seriously. Therefore, in the recent years, research has been focused towards the development of new cooling techniques in order to minimize the consumption of the coolant and its adverse effects. One of the solutions can be the introduction of internal cooling, which is one of the most advanced techniques for machining difficult to cut materials. In this approach, the coolant flows through the channel built inside the tool or tool holder to absorb the heat generated at the tool tip. This avoids localized heating which in turn reduces the tool wear and increases the surface quality. Powder metallurgy is a traditional method used for developing the cutting insert. This process includes mixing, compaction and sintering of the powder. Modern sintering techniques such as Spark Plasma Sintering, Hot Isostatic Pressure, and Microwave sintering have successfully eliminated the limitation of the traditional sintering technique, i.e., the long sintering time. From the research studies conducted on the fabrication of tool using traditional sintering so far, it has been found that developing the cutting insert with an internal channel is a complex and challenging task. Hence, the present research focused on developing novel cutting inserts with inbuilt channels for coolant flow during turning of Ti6Al4V. Initially, a Computational Fluid Dynamics simulation was performed for cutting insert having internal channel. It was found that the channel design and placement inside the cutting tool did not affect its original strength. However, this channel design further helped in promoting the heat transfer effect since a significant temperature drop was observed during the heat transfer simulation. It has also been seen that the inlet pressure of the coolant played a vital role in heat distribution in the cutting insert. Besides, the channel profile further enhanced the heat transfer effect from the tool tip (i.e. localized heat region).