Gpu-Based Tool Feasibility Space Computation And Whole Tool Orientation Optimization For 5-Axis High Efficiency Machining

The advantages of 5-axis NC machining depend on the control of tool orientations: (1) The accessibility can be improved by changing tool orientations. Then the complicated shapes such as aerospace impeller, turbo blade and marine propeller can be machined. (2) Only the small-diameter cutters can be used when the surface is machined in a confined space. The use of short tool overhang length will be allowed if the tool orientation is optimized. The rigidity of the whole milling system will then be increased. (3) Simple and efficient tools can be used to machine complicated surface if tool orientations are reasonably generated. The highly efficient flank milling is allowed to machine aerospace impeller by using 5-axis machine tool. (4) The cutting area in a cutter will also be controlled by controlling tool orientations. The cutting force can be decreased, the surface quality can be improved and the cutter wear can be reduced. Theoretically, the tool orientations can be any point of the Gauss Sphere in 5-axis NC machining. In fact, the feasible tool orientations are only a limit area in the Gauss Sphere because of the constraints about collision avoidance and work space. For improving machining efficiency and quality, the tool orientation of each CL (Cutter Location) data should be optimized based on the feasibility area.The access-based whole tool orientation optimization method is studied for 5-axis high efficiency NC machining of complicated shapes in this dissertation. It is necessary to consider some important factors in a practical cutting process when tool paths are generated. The factors consist of geometrical constraints (collision avoidance, machining precision, work space and fixture), kinematic constraints (singularity, velocity, acceleration and jerk), dynamic characters (rigidity and stability) and physical factors (cutting force) in the cutting process. How to optimally consider the four factors in the process of tool path generation is the key problem to improve manufacturing efficiency and quality of 5-axis NC machining. It is also the most challenging aspect in the research of tool path generation. Existing commercial general CAM software mainly focus on the method to satisfy the geometric constraints. We investigate the algorithms to wholly optimize tool orientations for 5-axis NC machining based on the feasibility space. The most obvious advantages of the method are that the dynamic characters and cutting force are also considered besides the geometric constraints. The three factors are considered by wholly smoothing tool orientations, generating the safe and shortest tool length and interpolating dual-NURBS tool path. The main research work and the novel contributions are listed as follows:Firstly,a novel algorithm is proposed to efficiently calculate the cutter accessibility cone by using graphics hardware. Based on the definition of cutter location point, the problem to determine the global accessibility cone is changed into the problem to check the complete visibility of the disk and the cone surface. Then the GPU-based algorithm is proposed to check the cutter global accessibility. The methods to improve the computational efficiency are also discussed. The computational examples show that the time complexity of this algorithm is almost linear. Comparing with the exsiting algorithms such as C-configuration (Chell A. Roberts, 2007) and visibility cone (S. Sarma, 2000), the proposed algorithm is much more efficient. Though the triangle number in the obstacle model of this method is about 10 times as of the simulation algorithm (Gershon Elber, 2005), the average computational time to check the accessibility of one cutter location is only the 3.76% of the simulation algorithm.Secondly, collision-free and orientation-smooth tool path are generated in the feasible space. The machining efficiency is improved by globally smoothing tool orientations. The feasibility cone is first selected from accessibility cone by considering the geometric constraints. Considering the constraints of tool orientation transition between two neighbor cutter contact points, the tool orientations are finally determined by globally smoothing tool orientations along the CC points. The cutting experiment of a complicated marine propeller shows that the cutting efficiency can be improved obviously by smoothing tool orientations. The cutting time is decreased from 51 minutes to 34 minutes. Only 66.67% of origin cutting time is used.Thirdly, considering the computation speed and the relationship between cutting force and tool orientation, a novel mesh-based algorithm is proposed to optimize tool orientations. Based on the feasibility cone at each mesh point, the tool orientations at mesh points are first generated by globally smoothing tool orientations. The tool orientations at other CC points are finally determined by interpolation. The obtained tool orientations are smooth not only along the feed direction but also along the pick-feed direction. The algorithm is applied to machine a turbo blade. Only the accessibility cone of 900 cutter location points are necessary to computed for a tool path consisting of 13845 cutter location points. The computational efficiency is improved. The validity of the generated tool path is finally proved by a cutting experiment.Fourthly, the use of shorter cutters without collision is a key advantage of 5-axis machining because the rigidity is greatly affected by the slenderness ratio of the cutter. An algorithm is proposed to optimize the safe and shortest tool length for 5-axis NC machining based on the safe and shortest tool length along an accessible tool orientation. The collision avoidance and tool orientation smoothness of the tool path are imposed as the constraints on the optimization model. Comparing with the existing algorithm (Y.R. Hwang, 2003), the obtained tool length can be obviously decreased by the proposed algorithm. The algorithm is applied to generate the tool length for the machining of the complicated marine propeller. The tool length is reduced from 55mm to 40mm. The cutting experiment shows that the machined surface quality is improved by using the shorter cutter. Fifthly, the method to generate dual-NURBS tool path is investigated for 5-axis NC machining because of the obvious advantages of NURBS interpolation in dynamic characteristics. The smooth dual-NURBS tool paths are interpolated by a rational motion described by a dual quaternion curve. The analytical envelope surface of a conical cutter under the rational motion is studied. The close solution of the characteristic point of a general cutter under the rational motion is also discussed. Furthermore, the singularity of the characteristic point is also considered. An algorithm is proposed to generate tool path for the flank milling of a conical cutter. The experiment is adopted to compare the dual-NURBS tool path and linear tool path. The result shows that cutting time is reduced from 15.384 seconds to 3.38 seconds. Furthermore, the better efficiency and dynamic characteristic are both achieved when dual-NURBS tool path are used.Sixthly, the software (SurfMilling V1.0) has been developed to implement the access-based whole tool orientation optimization algorithms. The functions of this software include accessibility cone computation, safe and shortest tool length generation, tool orientation optimization, dual-NURBS tool path interpolation and post-process. The tool path can be automatically generated based on the input obstacles, cutter geometry and CC points (or CL points). The software is introduced by using an example about the finishing machining of a turbo blade and the tool path is confirmed by a cutting experiment. The obtained turbo blade satisfies the technical requirements of Shanghai Turbine Co. Ltd.