Study on Smooth 2D tool-orientation Field Generation for Complex Surface Five-axis Machining
Author:Huang Kun Tao
Supervisor:fang feng zhou gong hu
Five-axis machining technology has two more rotary degree-of-freedoms than three-axis machining.More freeform surfaces can be machined by five-axis machine tools.However,tool path generation is with more difficult problems in five-axis machining.Quality of tool orientation generation plays a key role in complex freeform surface machining process.In this thesis,the investigation of tool orientation generation is focused on.Based on the current available relevant theories and relevant approaches,the thesis is to carry out the study on smooth 2D tool orientation field generation for five-axis complex surface machining.The main contents of the thesis are summarized as follows.(1)A five-axis tool path generation algorithm framework based on 2D smooth tool orientation field(TOF)is designed.First of all,several key points on surface are confirmed,and then the respective key tool orientation vectors are confirmed also by users.They should be selected at the key positions to avoid tool path collision and gouge.2D TOF function on the surface is calculated by key points and key tool orientations.And tool path can be generated via TOF function.In order to assess the tool path generated by the algorithm framework,the smoothness of TOF is analyzed.Volatility indices that assess the smoothness of TOF are constructed based on calculus of variation.The volatility indices represent the whole quality of TOF.To adapt to the computer calculation,the indices obtained from parametric surface are also discrete via finite difference method and finite element method.(2)The concept of cut-off obstacle is proposed based on the space topological relationship between surface,tool motion space and obstacle.Existence of continuous TOF is decided by the shape and position of cut-off obstacle.To select key surface points and key tool orientations by our given strategies can not only ensure continuous TOF generation,but also improve the smoothness of the TOF.For 2D machining,3 types of cut-off obstacles are analyzed.For each type of obstacle,existence of continuous TOF is analyzed via the variation of tool orientation motion FC space on the surface.(3)The 2D TOF calculation algorithm is presented.Based on radial basis function,a tool orientation constructing algorithm framework is constructed.The algorithm framework provides two TOF expressions,that is,radial basis function and spline expression.Different types of distance definitions are provided to adapt to different types of surfaces.Besides geometric space distance definition and parametric distance definition,surface shortest distance is used in surfaces on which there exist two points with large difference between space distance and surface shortest distance.And mapped cylinder distance definition is used in half-open surfaces on which there exists one parameter is closed.Allowing for uneven distribution of key surface points,distance weighted correction algorithm is studied based on Voronoi diagram.This work reduces quantity of key surface points.(4)The optimization algorithm of 2D TOF calculation is proposed.An optimization model is constructed that combine with both TOF smoothness and key tool orientation fitting.The multiplier optimization algorithm is adopted to solve the model.A TOF on the surface with optimized smoothness that fit the key tool orientations can be calculated.Compared with radial basis function algorithm framework,distance definition is with no necessary.With calculation experiment,a model with thousands of nodes can be solved with several seconds.A blisk triple-hubs surface that is multiply connected domain is adopted for calculation and machining experiment.For multiply connected domain surface,region-divided tool path generation is traditional strategy.Tool path generated by the two strategies are compared.Machining trace steps that exist in region-divided tool path are disappeared.