Tool Orientation Optimization Based On Drive Constraints For Five-axis CNC Machining

The sculptured surface parts,like turbine runners,bladed disks,impellers and molds,playing a vital role in aerospace,energy and transportation.The surfaces are designed according to hydrodynamics,which are machined by multi-axis CNC technology due to the complexity of surfaces.Tool path planning is one of the most important procedures in multi-axis CNC machining,improper tool path will lead to abrupt changes in tool orientation,interference and collision,the machining accuracy and efficiency will be reduced.Currently,the studies on this issue mainly consist of three aspects,one is based on the geometry,like avoiding interference,improving machining accuracy and machining efficiency,the others are based on the kinematics and dynamics,like smoothing tool path,decreasing cutting force and torque.However,most of the tool orientation optimization methods are carried out in Part Coordinate System(PCS),the kinematical smoothness of drive axes is ignored.The thesis proposed a novel tool orientation optimization method for five-axis CNC machining of sculptured surface parts,taking both geometric and kinematical issues into consideration,a smooth and collision-free tool path can be acquired through the method.The optimization methods consist of angular acceleration minimization method and strain energy method.The aim of angular acceleration minimization method is acquiring tool orientations in general positions according to the given tool orientations.The drive axes positions are acquired firstly according to the initial tool path in PCS by the inverse kinematical transformation,the representative tool orientations are determined based on geometrical and kinematical characters.Then smooth tool orientations are acquired by the angular acceleration minimization method.For the strain energy method,the constraints are the feasible regions of representative tool orientations,and the objective function is the strain energy of the rotary axis,so the smooth rotary axis positions can be acquired by the optimization method.Finally the tool path can guarantee the smooth motion of the rotary axes and collision free is acquired.To verify the efficiency of this method,an experiment of simulation and real machining is performed on a typical sculptured surface part,a bladed disk.The simulation results show that the proposed method,as expected,can effectively reduce the magnitude of the angular acceleration and decrease the change of the tool orientation,so the kinematic and dynamic performance of rotary axes are improved.In the machining of the bladed disk,compared with the traditional method,the real feedrate after optimizing the tool orientation by the proposed method,especially at the leading edge and trailing edge,is increased greatly such that the machining efficiency is improved 13.5%,and since the drastic changes of tool orientation are avoided at the leading and trailing edges,an improvement of 31.6% of the surface roughness is also obtained.It demonstrates that our method can improve the efficiency and accuracy of 5-axis machining.In summary,the paper proposed a comprehensive method for tool orientation optimization,which has a great value in theoretical and practical significance.