Material deformation analysis and characterization in metal cutting and laser assisted machining of silicon nitride

This study focused on material deformation and characterization in both metal cutting and laser assisted machining of silicon nitride ceramics. A general material constitutive modeling procedure was developed for large strain, high strain rates and a wide range of temperatures based on orthogonal machining experiments. A new strain rate model was developed which is easy to use and provides more accurate results. Hot machining tests were utilized to allow deformation analysis at high temperatures. A constitutive model for 1020 steel was obtained and was subsequently used in a finite element simulation of orthogonal machining. Distributions of the stress, strain, strain rate and temperature were obtained for the deformation zone. Average values of the predicted quantities were compared with experimental results, and the favorable agreement confirmed the validity of the FEM simulation and the constitutive equation. Laser-assisted machining (LAM) of silicon nitride (Si3N 4) was evaluated for its potential to become an economically viable process in fabricating precision ceramic parts. On-line measurements of cutting force and workpiece temperature were performed, and tool wear and surface integrity were examined. Tool wear characteristics were determined as a function of workpiece temperature, which was measured using a laser pyrometer. Optical microscopy was used to determine tool wear/failure mechanisms, while application of scanning electron microscopy to heated and machined surfaces, as well as to chips, was used to infer material removal mechanisms and the extent of damage caused by LAM. The sub-surface damage of parts produced by LAM was compared with that of typical ground parts. The constitutive modeling method for orthogonal machining was extended to three-dimensional LAM. A new approach was formulated for determining the shear angle associated with segmented chip formation in LAM. The LAM experiments were used to develop and validate a constitutive model for silicon nitride