Geometry-Dynamics Modeling In Five Axis Numericalcontrol Milling And Cutting Parameters Optimization

Geometry-dynamics modeling in five-axis numerical control milling with cutting parameters optimization is one of the key technologies to manufacturing the vital parts independently in national projects. It is also an effective way to improving the productivity and precision in manufacturing enterprises. However, some important questions remain as follows. In the stage of tool path generation and optimization, the commercial CAM software in general lack of the analysis of global approximation between the surface enveloped by tool motion and the design surface via fine-tuning of the discrete cutter locations. In the stage of selection and optimization of the cutting parameters, the effective modeling, simulations and the quantitative uncertainty analysis in five-axis machining process are absent. The cutting parameters optimization is traditionally developed based on the deterministic parameter model, thus the obtained nominal optimization results are not the real ones as expected in practical machining.This thesis aims to solving the problems given above arising from the studies and shop floor. The relationships of the contents of this paper are rational motion design of rigid point-line—swept surface generation of tool spatial motion—tool path optimization—robust cutting parameters optimization. The tool path optimization and cutting parameters optimization in five-axis numerical control machining of complex surfaces are detailed to improve the productivity and precision from a geometry way as well as a dynamics way. In the studies of the model of geometry—dynamics in five numerical control milling and robust cutting parameters optimization, the main content and innovative ideas are presented as follows:The cutting tool is viewed as the rigid point-line from a respective of kinematics, and then the study of the cutting tool motion can be transformed into that of the rigid point-line. The mapping of the point-line rational motion to the hyper-plane curve in dual quaternions space is constructed. The rational motion design of the rigid point-line is developed. In the frame of rigid point-line motion design, the problem of design of rational ruled surface is transformed into that of hyper-plane curve design in dual quaternions space. The design and optimization of the cutting tool orientation curve, which is a sphere NURBS curve is viewed as the curve design and optimization in quaternion space. The experiment, optimization of cutting tool orientation curve in five-axis machining of blade structures, indicates that the overcuts in the machining are eliminated and the quality is improved after optimizing the tool orientation curve.The individual cutter locations are viewed as the discrete spatial point-lines and the continuous tool path is generated by using the rational motion method. The analytical swept surface of typical cutting tool used in five-axis motion is developed based on the double parameters envelope theory of sphere congruence. The problem of global tool path optimization is then transformed into that of the comparison of two surfaces, i.e. designed surface and the swept envelop surface. Optimization of five-axis tool path is modeled as fine tuning of initial cutter locations under the minimum zone criterion which requires to minimize the maximum geometrical deviation between the design surface and the envelop surface.The finite shell element model of workpiece is developed, and the material removal process in milling is treated as the perturbation of the workpiece geometry. The effect of material removal on the modal shapes of blade structure in high-speed machining is predicted by using the matrix perturbation theory, as a result the varying dynamics of workpiece are obtained and the modal shape experiments are reduced. The experiment results validate the theoretical predictions. Considering the uncertainties in workpiece-tool, the interval finite element characteristic matrices of workpiece-tool are obtained using the interval arithmetic. Upper and lower bounds of dynamic responses of the tool are derived based on the interval arithmetic.Based on the sensitivity analysis, considering the uncertain parameters in five-axis machining, the upper and lower bounds of chatter lobes and the dynamic responses of tool are obtained. The multi-object optimization problem with uncertain parameters is transformed into the single-object optimization one with deterministic parameters. In practical five-axis machining of blade structure, considering the uncertain parameters of modes of tool system, the robust optimization model is developed, in which the optimization object is to maximize the spindle speeds and minimize the tool vibration amplitudes, and the constrained condition is to keep the machining process un-chatter. Comparing with the deterministic model, the results of the robust model guarantee the stability of the milling process and improve the surface quality of the blade structure.