Research On Auto Hollowing STL Model Algorithm For Stereolithography Apparatus

Stereolithography(SL) has been researched earliest in Rapid Prototyping(RP) domain, which can generate parts with high accuracy and has been widely used. With the development of SL, SL device now can produce very large dimension parts. The larger the part is, the more raw and processed materials and machining process time will be consumed. By the research result of the SL process characteristic, the SL device can process hollow part in stead of solid part. This process can reduce the consumption of expensive photosensitive resin and the processing time. The popular 3D model format file in RP domain is STL file and hollowing the STL model is the precondition of processing the hollow part, so the algorithm of automatic hollowing STL model is researched in this thesis.After study the merits and demerits of the predecessors'work of automatic hollowing algorithms, this thesis present an improved algorithm for hollowing STL model based on vexel representation and space offsetting algorithms. The algorithm still use vexels express the STL model, but use"bit"instead of"byte"to store the vexels, so the vexels'storage space is reduced. Space offsetting method is used to find and remove all the discrete vexels round the model surface, the left vexels make up of the hollow body of the model. This method is very simple and faster than other method. Combined the processing characteristic of SL system, the algorithm automatic add inside frame support structure in hollow model. Finally, the algorithm cut the STL model and the left vexels into slices, and than smooth the vexel slice contours, export the hollow part's NC path file in stead of exporting the hollow model's huge size STL file.At last, this algorithm as a hollow module integrated with PowerRP SLA software, has been applied in SL rapid prototyping system. This algorithm can hollow out any arbitrary complex STL model in a short time. And it has performed very well by time and space complexity analysis. The results of the hollow part's manufacture process and actual experiment data analysis have proved that making hollow part indeed improved the utilization of expensive photosensitive resin, decrease the processing time and machine wastage, and finally economize the machining cost of part.