Research On Automatic Segmentation Equal Thickness Layering Algorithm Based On STL Model In Rapid Prototyping

Rapid prototyping is a new strategy for fast fabrication,which hierarchically segments the 3D data model into a series of 2D slicing planes before the additive manufacturing process(the so-called layer-by-layer stacking principle).However,the current uniform thickness hierarchical algorithm,which is the most widely applied to hierarchical processing,will lead to a great increase in number of layers and a reduction of the prototyping efficiency,when applied to cylindrical parts with slope changes in a certain direction.For this reason,this paper presents an automatic segmented equal thickness stratification algorithm,the process of segmentation is added before uniform-thickness layering of cylindrical parts.In other words,the model is first segmented into multiple components,which is then processed by the uniform thickness hierarchical algorithm.Research on the above problem is mainly embodied into the followings:(1)At present,STL model has become a standard format for rapid prototyping,aiming at the common problem of large holes across pages during 3D scanning of parts without engineering drawings in the research objects,an end cover is exampled,and a hole filling and model reconstruction strategy which combines reverse engineering software and GABP algorithm is proposed in this paper to acquire a complete STL model.After the complete STL model is read into the Matlab software,the local topological relationship among the triangular facets is created using two public vertices between two neighboring facets.Then,the dihedral angel is calculated against the triangular facets with the topological relationship,the common edge of the triangular surface larger than the threshold value is regarded as the characteristic edge.Public edges of the above triangular facets are extracted,and the line segments of the characteristic edges are fit using the data structure of an undirected graph to get a complete segment boundary;the triangular surfaces within adjacent boundaries are fitted to obtain segmented blocks,in each of which triangle facets are ordered simplifiedly in three steps to quickly position the triangular facets in the process of layering.The layer thickness within the allowable error range of the tip in each block is calculated,And this layer thickness value is taken as the layer thickness of the segment;The intersection of the layered facet and the triangular facet is acquired with the compiled intersection algorithm,and the contour line of such intersection is then obtained using the method of intercepting while outputting.(2)In order to verify the validity of the proposed uniform thickness hierarchical algorithm,a double-nozzle FDM printer for experimental purpose is built for verification of prototyping.The principal computer part will automatically segment the objects in the contour line cambium layer generated by the uniform thickness hierarchical algorithm,storing the polygon vertices of the contour line in the path list in sequence and writing the starting point flood fill algorithm to generate the filling path.The contour and the filling path determined are then converted into the G-code command code universal for printers.The slave computer is responsible for hardware design of the built double-nozzle printer,and manufacturing of the prototype,by selecting frame materials,and designing the three-axis motion system,the nozzle system and the control board.The G-code code of the printing path generated by the test model in the above-mentioned uniform thickness hierarchical algorithm is imported into the slave computer to verify the real prototype.This paper verifies the proposed hierarchical algorithm from perspectives of theoretical layering simulation and actual prototyping.The result shows that: compared to the direct uniform thickness hierarchical algorithms,the algorithm works better in reducing the number of layers of the test model,shortening the time of and improving the efficiency of prototyping.In addition,the innovation and shortcomings of this paper are summarized,and the future development trend of this field is prospected,which lays a certain foundation for further understanding the segmentation stratification algorithm based on STL model.