Effects of Cutting Parameters over Turning of UDIMET® 720 Superalloy in a Broaching Process Simulation

Abstract

The nickel-based alloy “UDIMET® 720” has been used for several years to manufacture components in turbomachines. Its physical properties allow it to keep high mechanical strength when subjected to high temperatures. However, those properties also cause its low machinability. Turbomachine design requires the use of rotating parts assembled and submitted to high thermo-mechanical stresses. Fir-tree slots machined by broaching are used to create the bond between turbine discs and blades. Currently, the broaches are made from high speed steel which is restricted to low speed and feed hence limiting the productivity. In order to go faster, a solution is to use carbide tools. However, this material is more sensitive to shock and it is then necessary to precisely identify cutting conditions for the optimal design of broaches. Furthermore, cutting phenomena are different and can affect the machined surface integrity for this critical workpiece.A large experimental campaign has been done by turning to reduce tool costs and to highlight the effects of cutting parameters on tool wear and machined surface quality. In order to optimize the productivity, the effect of cutting conditions on cutting forces is taken into account. To determine the broach geometry composed of several teeth, the effects of rake angle, cutting edge preparation and clearance angle are presented. In order to simulate the broaching process, a specific test has been designed on a lathe. This allows us to include specific disturbances like interrupted cut, temperature variation, lubrication discontinuity, and difficulty to liberate the chip.