Research On Tool Path Reuse In NC Machining Of Free-Form Surface

With the rapid development of modern industry,the proportion of products with free-form surface in the modern manufacturing industry is growing,and the demand of market makes the NC machining technology of free-form surface products must be improved.The free-form surface has a high degree of freedom,and the morphological features are complex and diverse,so the tool path planning is an important part of complex free-form surface NC machining,and it is also a difficult point in the study.Free-form surface has more complicated programming content and higher production cost,it will effectively improve the NC machining level to reuse the existing machining examples.In this paper,a method of "reuse of similar tool paths" is proposed to generate the tool path of free-form surface.The user extracts the features of the preprocessed surface and retrieves the similar machining instances in the database according to the feature similarity,and extracts the tool path information of NC machining.Then the machining trajectory of new surface is generated by the cutter path mapping algorithm.Based on the 3D open source function library Open CASCADE(OCC)and Microsoft Visual Studio 2010(VS2010)programming development environment,this paper researches the NC machining planning of free-form surface expressed by B-spline,and writes a prototype system for cutting tool path generation of free-form surfaces NC machining.For free-form surface with typical application in engineering,tool path generation is automatically realized by reusing method,and the results of tool path generated by the system are compared with the results generated by Master CAM software.And the rationality of the research results is verified through practical processing.Firstly,a feature extraction algorithm for free-form surface NC machining is proposed.According to the curvature,the features of free-form surface are defined as4 types of convex,concave,saddle and flat.The boundary tracing algorithm is designed to extract the each characteristic boundary of the mixed feature surface.By extracting different features of surface,the surface region with a single curvature feature is obtained.Secondly,aiming at the extracted single feature region,a similarity comparison algorithm for free-form surface with single curvature is proposed.Surface is a set ofcurves.With the idea of reducing dimension,the algorithm uses a cluster of parallel planes to cut the surface to be compared to get the intersection curves,and converts the similarity comparison of 3D surfaces to the similarity comparison of 2D intersecting curves,simplifying the problem of surface similarity evaluation.Then,the tool path mapping algorithm is studied.Designing the mapping rules and the algorithm of generating B-spline curves on free-form surface,and mapping existing trajectories onto the surface to be machined,and NC machining tool path of free-form surface is automatically generated to realize the reuse of trajectory.It verified by experiment,the machining quality and efficiency of mapping trajectory meet the requirements.Finally,the tool path simulation of surface three-axis NC milling is carried out in Master CAM software.In contrast to the simulation results of tool path algorithm in the paper,the effect of trajectory mapping is analyzed and discussed.Through three-axis NC milling machine tool in the experimental center,the effectiveness and feasibility of tool path reuse are verified by practical machining.