Prediction of Microstructural Changes and Residual Stresses in Hard Machining

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This grant provides funding for the development of a computational tool for analysis and prediction of microstructure changes and residual stresses generated in cutting of hardened steels using single-point tools. The computational tool will be used to establish the optimal parameter values for cutting speed, feed, depth of cut and tool geometry that yield favorable residual stresses and a workpiece surface free of undesirable microstructure changes (e.g., white layer formation) in two-dimensional cutting of a hardened steel material. To achieve this goal, analytical models of the metallurgical phase transformation occurring in quenching of steels will be developed and combined with a coupled thermo-mechanical updated Lagrangian finite element model of the two-dimensional cutting process developed using the ABAQUS Standard finite element code. In order to validate the complete model, orthogonal cutting experiments will be performed with bearing steel (e.g., AISI 52100) as the workpiece material and PCBN tool material using cutting parameters determined from the model. Existing material property data and/or elevated temperature high strain-rate tests will be used to establish the material flow-stress models to be used in the simulations. The microstructure of the machined workpiece samples will be characterized using optical and scanning electron microscopy while residual stresses will be measured using X-ray diffraction. If successful, the results of this research will provide the capability of accurately simulating surface generation in machining of hardened steels and determining an optimal window of cutting conditions to produce surface characteristics that enhance the service-life of hardened steel components. This will in turn help to reduce cost, improve part quality, and promote the industrial use of hard machining technology. On a fundamental level, the proposed research will advance current physical understanding of material and cutting process interactions in hard machining, particularly from a standpoint of workpiece microstructure changes (e.g., white layer formation) and residual stresses. The proposed research will also provide a solid framework for future development of a three-dimensional model for simulating hard machining processes such as turning and milling.