NEW PERSPECTIVES ON THE CUTTING MECHANISM OF DIFFICULT-TO-MACHINE MATERIALS

Advanced aeroengine alloys such as titanium and nickel-based alloys are widely used for casingand compressor blades. Poor machinability of titanium and nickel-based alloys are due totheir inherent characteristics, including high hot hardness andstrength, causingsinificantdeformation of the cutting tool and workpiece during machining, lowthermal diffusivity, rapidwork hardening, causing a severe wear at the depth of cut line, and the saw-tooth chip formation. Forefficient and precise NC machining of these difficult-to-machine materials, an understanding ofthe cutting mechanism is essential. This paper provides an overview of the theories of saw-toothchip formation mechanism and the fracture criteria for the FEM simulation of segmentedchips. How to determine the flow stress at high deformation rates and temperatures in the cutting zone is then discussed. The interaction between strain, strain rateand temperature should be sufficiently considered. The temperature andresidual stress have aconsiderable influence on the distortion and machining precision for thin-wall structures as used inthe aerospace industry, which are also analyzed in this paper.