Research On Tool Path Generation For Five-Axis Wide-Stripe Milling

Sculptured surfaces have been widely used in the aerospace,automobile and other fields,and the wide-stripe numerical control machining has shown its advantage in the machining efficiency.The envelope surface for a non-ball-end cutter can be highly approximated the design surface by adjusting the tool orientation to increase the machining stripe width.Current studies focus on point milling with flat-end cutters and torus cutters,and flank milling with cylindrical cutters and conical cutters.Owing to the two added rotational motions,five-axis machining can greatly improve the precision and efficiency of complex parts machining.However,there are still some difficulties in five-axis tool path generation for wide-stripe machining,such as interferences detection and avoidance,machine tool motions smoothness,singularity avoidance and chatter-free tool orientation selection.Methods of wide-stripe tool path generation for five-axis flank milling with rotary cutters and point milling with flat-end cutters are investigated in this study.The main research is listed as follows:1)By representing the swept envelope of a generic rotary tool as a sphere-swept surface,the necessary and sufficient conditions for tangent continuity of two adjacent swept tool envelopes are derived.It is shown that the cutter location positions of the second tool path are uniquely determined while the unit vector representing the tool orientation should satisfy a linear constraint.This constraint function can be incorporated into the existing tool path optimization models for single-pass flank milling to generate multi-pass flank milling paths.This study can solve the following problems:(1)the two adjacent envelope surfaces can be blended smoothly with the tangent continuity conditions;(2)the geometric deviations between the envelope surface and the target surface can be controlled when generating a tool path.The proposed method can extend the flank milling strategy to sculptured surface machining.2)The evaluation method of cutter stiffness is proposed,and a tool profile optimization method for five-axis impeller machining with flank milling is developed.It can seek the cutter with maximal stiffness under the interference-free premise,avoiding repeated attempts when selecting a cutter.The point-to-surface distance function is utilized to characterize the required geometric constraints: constraint of machining accuracy,constraint of tangency between the ball-end of the cutter and the hub,and constraint of collision avoidance between the cutter and the adjacent blade.A mathematical model is then developed to optimize the cutter profile considering the cutter stiffness and geometric constraints.After the optimal profile of the cutter is obtained,a flank milling tool path with this cutter is then generated.3)To avoid incoherent movements of the two rotary axes of a machine tool during five-axis machining,approaches to generate five-axis flank milling tool paths with smooth rotary motions of the machine tool are presented.The tool path smoothness is characterized by the motions of the two rotary axes,and incorporated into the global tool path optimization model as the optimization objective.In the tool path optimization model,the point-to-surface distance function is utilized to measure the geometric deviations.Thereafter,the smoothness tool path optimization model considering geometric deviations is developed.Two approaches are developed to generate smooth tool paths:(1)adjusting the tool orientations in the workpiece coordinate system to smooth the rotary axes motions;(2)optimizing the rotary axes motions directly to make them smoothness.Both the numerical examples and machined surface indicate the effectiveness of the proposed methods.4)To increase the machining width of five-axis sculptured surface machining with flat-end cutters,decreasing the number of tool paths,a model of optimum tool path generation with flatend cutters considering tool orientation and feed direction simultaneously is developed.This model takes the machining width as the objective,and the requirements of smooth cutter motion,machine tool performance,interference-free between the cutter and the design surface,as well as machining stripe widths overlap are considered.The relationship between machining width and tool posture is highly non-linear,and the Differential Evolution(DE)algorithm is suitable for solving this model.However,when the dimension of the solution is high,the DE algorithm is easy trapped into a local optimum.To get the global optimal tool paths,a hybrid algorithm,combing the DE algorithm and the sequence linear algorithm,is proposed to solve the model.5)The effects of lead and tilt angles on the five-axis process dynamics with flat-end cutters are studied.The discrete vector method is adopted to obtain the cutter-workpiece engagement in five-axis flat-end milling for cutting force prediction.A general formulation for the dynamic milling system is then developed by analysing the process mechanics and dynamics.Finally,the proposed integration method is used to predict the stability limits in flat-end milling with different tool orientations.Effectiveness of the strategy is validated by conducting experiments on five-axis flat-end milling.On the basis of the point-to-surface distance function and modelling of the cutter swept envelope,tool path optimization models considering requirements of interference-free,geometric deviation,smooth cutter motion and machine tool motions are developed in this dissertation,generating tool paths for five-axis wide-stripe milling.The five-axis process dynamics with flat-end cutters is also investigated,providing the basis for tool path generation considering the geometric and physical constraints.