Force prediction and stability analysis of plunge milling of systems with rigid and flexible workpiece

Time domain simulation model is developed to study the dynamics of plunge milling process for system with rigid and flexible workpiece. The model predicts the cutting forces, system vibration as a function of workpiece and tool dynamics, tool setting errors, and tool kinematics and geometry. A horizontal approach is used to compute the chip area to consider the contribution of the main and side edge in the cutting zone and to deal with any geometric shape of the insert. The dynamic chip area is evaluated based on the interaction of the insert main and side cutting edges with the workpiece geometry determined by the pilot hole and surface left by the previous insert. For the case of system with a flexible workpiece, the workpiece dynamics, as well as its variation in the axial direction with respect to hole location, is considered in the simulation. Cutting tests with single and double inserts were carried out to validate the simulation model and predicted stability lobe for both systems with rigid and flexible workpiece and to check the correctness of the cutting coefficient model. Good agreement was found between the measured and the predicted cutting forces and vibration signals and power spectra. This indicates the ability of the model to accurately predict cutting forces, system vibration, and process stability for process planning prior to machining. The results show dominance of workpiece dynamics in the axial direction for systems with flexible workpiece due to its flexibility as compared to the tool axial rigidity. On the other hand, chatter behavior was found to occur due to tool lateral modes for case of rigid workpiece.