Investigation of Trochoidal Milling in Nickel-Based Superalloy Inconel 738 and Comparison With End Milling

Abstract

Nickel-based superalloys are designed for use in extreme environments and are getting progressively better for these environments, therefore much harder to machine. They play a crucial role in elevated temperature applications where high strength, high resistance to corrosion and creep resistance are required. Machinability suffers as a result of these properties and harsh machining conditions occur, resulting in high cutting forces and tool wear. To combat the difficulties in the machining of nickel-based superalloys, such as poor thermal diffusivity and high levels of abrasive wear, trochoidal milling was introduced as an alternative method of milling. This method of milling combines linear motion with uniform circular motion, reducing chip load in exchange for increased machining time. Industry is averse to its widespread adoption due to increasing cycle times when compared to conventional milling methods, however it has been shown that overall productivity can be improved due to less tool wear with a more predictable behavior. This work characterizes the effects of trochoidal milling and provides a comparison of trochoidal milling with a traditional milling technique, end milling, for the machining of Inconel 738. In order to compare the trochoidal and conventional machining approaches directly, metrics of productivity normalized to tool wear are introduced. The normalized metrics introduced in this study aim to provide a more representative comparison of productivity and efficiency characteristics: volumetric material removal per unit tool wear (MR/VB) and the material removal rate per unit tool wear (MRR/VB). It was found that significantly higher volumetric material removal is possible using trochoidal milling, and fewer tools are needed; material removal rates that competitive with end milling can be achieved. When the amount of time spent on tool change for the same volume of material removal is considered, material removal rate of trochoidal milling can even be higher than end milling, indicating that better productivity and efficiency of the process is possible at reduced tooling costs.