Research And Implementation Of Porous Structure Model Representation And Fabrication Based On Selective Laser Sintering

Porous structures have been widely used in aerospace,automobile,footwear and chemical materials due to their special functions such as absorbing,shock absorption and lightweight.However,there are many problems when using selective laser sintering to fabricate porous structure: The traditional model representation method uses STL format to present the internal cell characteristics of porous structure,which produces STL files of more than 100 megabytes in size and greatly reduces the transmission and slicing efficiency of the model.The traditional zigzag scanning strategy tends to cause local heat concentration,warping and over burning when sintering repeatedly inside the cell.This paper focuses on the scanning strategy of small cell structure representation and optimization of local heat concentration for porous structure.In view of the model representation method,a hybrid representation of boundary representation and function representation is proposed to represent the porous structure.The traditional three-dimensional model boundary representation is used to represent the external surface of the model,and the spatial function method is used to represent the internal cell structure.The triply periodic minimal surface function is used as the function representation to represent the external surface of the internal cellular structure.Finally,two kinds of representation methods are synthesized to achieve the accurate representation of porous structures.Furthermore,a bitmap slicing algorithm based on the Axis-Aligned Bounding Box and a bitmap-based variable power constant speed scanning strategy are proposed for the manufacturing of porous structures.Topology is used to reconstruct the adjacent trianglecommon edge relationship of STL model,and then the outer contour is obtained by finding the intersection point of tangent plane and triangle at a specific height.And the internal cell contour of STL model is obtained by using the triply periodic minimal surface space function equation.Aiming at the obtained two-part contour,this paper takes the Axis-Aligned Bounding Box of STL model as bitmap,and calculates the number of pixels with length and width distribution on the bitmap based on the size of bitmap and the resolution of pixels.And then the gray value is set according to the position relationship between each pixel unit and the contour area,and the gray value of all the pixels is set to get the final slice bitmap.The strategy of variable power and constant speed scanning is to make the laser scanning at a constant speed.The power of the laser changes according to the gray value of the bitmap.Because the scanning speed is constant in the manufacturing process and the laser will not jump frequently in the local area,the problem of local heat concentration can be greatly reduced.The experimental results show that the size of the porous structure model file represented by the traditional STL can be reduced from 100 Mega to Mega,and the cellullar structure with the pore size as low as 1.8 mm can be fabricated.In addition,the influence of local heat concentration on the forming accuracy can be reduced prominently.