Research On Tool Path Planning Method For Complex Surface Machining Based On STL Model

With the increasing use of complex surfaces in the industrial field,CNC machining technology for complex surfaces has received increasing attention.The STL format is one of the expressions of 3D complex surfaces,and the consistency between the STL model and the original surface model is high.Therefore,the numerical control processing method based on the STL model has been paid much attention by many scholars.Studying the tool path of complex surface machining based on STL model can effectively reduce the calculation amount of tool path planning,and improve processing efficiency,shorten the development cycle of products with complex shapes.In this paper,based on the STL format,the tool path planning algorithm for complex surfaces was studied.The research content of this thesis mainly includes the following aspects:(1)The STL model file redundant data filtering algorithm was studied.The original data information of the STL file is discrete and there is a large amount of redundant information.The triangular patches data needs to be streamlined and stored according to a certain rule in order to make more convenient use of the data.On the basis of analyzing the characteristics of the STL file,this paper designed data structures such as point tables and surface tables;then the hash table method was used to identify and eliminate redundant data,and the data storage of point tables and surface tables was completed.It laid the foundation for subsequent STL information processing.(2)The offset algorithm of STL model was studied.In order to facilitate the calculation of the tool point data required for planning the tool path,the STL model is first offset.Using the point table data of the triangle patch,the first-order neighborhood triangle index value of the vertex was obtained,and then the corresponding neighborhood triangle data was extracted in the surface table,thereby obtaining the necessary information required;and then the offset vertex coordinates was obtained according to the calculation formula.Then the offset model of the original STL model was obtained.(3)The slicing algorithm of the STL model was designed.After the STL offset model is obtained,the model needs to be sliced in layers to obtain a two-dimensional contour polygon.Firstly,the intersection information of the relevant triangles and the tangent plane was obtained and stored in the temporary array,and the intersections repeating were seen as redundant information.Secondly the topological relationship and the order of the intersections were determined according to the redundant information,and the intersection of the known order was deleted from the temporary array.The ordered intersections had formed a closed polygon only when there was no information redundancy for the intersection in the array.Remaining closed polygons could be gained using above method.(4)The tool path planning algorithm based on slice information was studied.The two-dimensional contour data acquired by the slice is not smooth and affects the quality of the machined surface,so the smoothing of the two-dimensional contour is further performed.Firstly,the two-dimensional closed contour was segmented according to the preset threshold;the NURBS curve interpolation was performed on the part of the segmentation data that needs smoothing;then the NURBS curve was interpolated by the tolerance dispersion method to obtain the smoothing tool path.(5)G code was generated and machining simulation verification.In order to verify the feasibility of the proposed method,the STL model of the mouse surface was taken as an example,and the generated G code was verified in the Swarovski simulation sofitware.The effectiveness of the proposed method was proved by comparing the results of the simulation with the mouse CAD model in UG.The algorithm overcome the shortcomings of CNC machining based on CAD entity model,such as complex NC machining,low computational efficiency and poor versatility.