Optimization Of Tool Size,Locations,and Orientations In Multi-Axis Machining Of Blisk Channels

Blisks are key parts of a fan or compressor stage in new jet engines.The computer numerical control(CNC)machining technology is relevant to blisk's surface quality and producing time,which is a bottleneck in developing China's aviation weapons.Due to their specific structures with narrow channels and overlapped blades,the blisks are considered as typical complex parts with multiple geometric constraints.Geometric and kinematic issues in multi-axis milling of blisks are difficult to be solved.The presented work focuses on key technologies in multi-axis milling of blisks,which covers machinability analysis,accessible region of tool orientations calculations,process planning in plunge milling,and tool orientation smoothness in finish milling.The main contents and innovative achievements are as follows:(1)Comprehensive methods are proposed to evaluate the machinability in machining blisks.At first,machining features are extracted according to the specific structures of blisks,among which the blade features are parametrically reconstructed as needed.By checking interference between blisks and cutters with different diameters,the maximum collision-free tool diameter is calculated for multi-axis milling of blisks.The minimum global tool length is then obtained by considering the solved collision-free tool length on each tool orientation to guarantee that the tool holder has no interference with blisks.In viewing of the constraints of tool size and length-diameter ratio,an approach to evaluate the machinability of blisks is then proposed as three stages,which are rough judgment,reachability calculation,and detailed evaluation.After that,an interactive tool selecting and machining region determining method is proposed for actual machining of blisks by considering geometric and rigid constrains of the cutter,accessible region of tool orientations,smoothness of tool orientations,and completeness of tool paths(2)The accessible region of tool orientations is figured out in multi-axis machining of blisks.An approach to calculate collision-free tool orientations in machining blisks is proposed by searching the start and inner critical points of surface profiles without collision detection.After that,the accessible region of tool orientations is obtained by combining single accessible region of each checking surface,via rearranging and recombining the search critical points.The proposed approach is verified to be efficient and accurate to solve the accessible region in multi-axis milling of blisks.Then a bidirectional mapping relationship of tool path and axis movements of a specific machine tool is established according to its structures.Based on that,the accessible region is decoupled on each rotating axis and then rebuilt under their limit constraints(3)Optimization models are established to plan the multi-axis plunge milling process of blisks.To solve boundary paths in multi-axis plunge milling of blisk channels,tool locations and residual material on machined blades are calculated in specific orientations.Then the optimization models to plan boundary paths are established and solved based on the calculated residual material.To plan inner paths,total length of tool paths is optimized to be minimal to improve the plunge milling efficiency,under the constraints of cutter overlap ratio and the maximum height of residual material.To smooth the variant cutting load in multi-axis plunge milling,a mathematic model is established to calculate cross sections of the removed material.After that,a mechanical model of multi-axis plunge milling is proposed to schedule the federate by the lateral force,axial force,and torque.The results show that the proposed method can improve the machining efficiency and smooth the cutting load.(4)The methods to plan tool orientations and improve the cutter rigidity are proposed in multi-axis finish milling of blisks.A kinematic constraint model is firstly established and planning principles are proposed to smooth tool orientations.Then a constrained model to evaluate the smoothness of tool orientations is proposed based on the overall strain energy of speed curve of rotating axes.To solve this model,a practical method is then presented,which is able to deal with the kinematic constraints of machine tool,accessible regions of tool orientations,and singular problems in multi-axis machining.When the tool orientations are optimized,the maximum collision-free space inside of the channel is calculated to improve the cutter rigidity in two approaches.One approach shortens tool length by locating the tool holder into the channel.The tool holder selecting and tool length calculating methods are then presented.The other approach optimizes the geometric structure of two taper cutters to enlarge the effective tool diameter,which can also efficiently improve the cutter rigidity in multi-axis finish milling of blisks.