An Investigation of Alternative Path Planning Strategies for Machining of Nickel-Based Superalloys

Abstract

Nickel-based superalloys play a crucial role in elevated temperature applications where high strength and high resistance to corrosion and creep resistance are required. These environments are largely found in the aerospace, nuclear power and gas turbine industries. Due to the properties that make them suitable for their end use they remain a challenge to manufacture. In the machining of nickel-based superalloys high cutting forces and tool wear occur greatly reducing their machinability. Although there have been multiple recent studies on the machining of such alloys, the field remains vastly unexplored. A limited amount of research has been done in tool path methods, as most previous research focuses on finding optimal machining parameters to curtail the difficulties in machining while keeping the tool path constant. An alternative tool path, trochoidal milling, has been identified to combat the difficulties in machining superalloys and combines linear motion with uniform circular motion, reducing chip load in exchange for increased machining time. Although this method has been shown to reduce flank wear on tools it suffers from notch wear at the depth of cut line.In this study the authors propose and evaluate a new tool path termed variable depth milling (VDM) to reduce or eliminate the occurrence of notch wear in nickel-based superalloys. In this method the axial depth of cut is varied across the tool in a linear fashion, progressing from a maximum depth of cut value to zero in an upward ramping fashion. This work characterizes the effects of trochoidal milling and variable depth milling techniques and compares them against a traditional milling technique, end milling. In order to compare these alternative tool path approaches directly to end milling the authors utilize relatively new metrics 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 trochoidal milling was superior to end milling in terms of productivity, where trochoidal could machine at least seven times more material than end milling with the same amount of tool wear with similar efficiency as end milling. It was demonstrated that VDM eliminated the formation of notch wear in the cutting tool at the expense of a slight decrease in productivity and efficiency.