Basic Theory of Rapid Prototyping

快速成型属于离散/堆积成型。它从成型原理上提出一个全新的思维模式，即将计算机上制作的零件三维模型，进行网格化处理并存储，对其进行分层处理，得到各层截面的二维轮廓信息，按照这些轮廓信息自动生成加工路径，由成型头在控制系统的控制下，选择性地固化或切割一层层的成型材料，形成各个截面轮廓薄片，并逐步顺序叠加成三维坯件，然后进行坯件的后处理，形成零件。

Rapid prototyping belongs to discrete/stacked molding. It proposes a new thinking mode from the perspective of forming principles, which involves meshing and storing 3D models of parts made on a computer, layering them to obtain two-dimensional contour information of each layer of cross-section, and automatically generating processing paths based on these contour information. Under the control of the control system, the forming head selectively solidifies or cuts layers of forming materials, forming thin slices of each cross-section contour, And gradually stack them in sequence into three-dimensional blanks, and then perform post-processing of the blanks to form the parts.

产品三维模型的构建。由于RP系统是由三维CAD模型直接驱动，因此要构建所加工工件的三维CAD模型。该三维CAD模型可以利用计算机辅助设计软件（如Pro/E，I-DEAS，Solid Works，NX等）直接构建，也可以将已有产品的二维图样进行转换而形成三维模型，或对产品实体进行激光扫描、CT断层扫描，得到点云数据，然后利用反求工程的方法来构造三维模型。

Construction of a three-dimensional model of the product. Since the RP system is directly driven by a 3D CAD model, the first step is to construct a 3D CAD model of the workpiece being processed. This 3D CAD model can be directly constructed using computer-aided design software such as Pro/E, I-DEAS, Solid Works, NX, etc. It can also convert existing 2D drawings of products to form a 3D model, or perform laser scanning or CT tomography on product entities to obtain point cloud data, and then use reverse engineering methods to construct the 3D model.

三维模型的近似处理。由于产品往往有一些不规则的自由曲面，加工前要对模型进行近似处理，以方便后续的数据处理工作。由于STL格式文件格式简单、实用，目前已经成为快速成型领域的准标准接口文件。它是用一系列的小三角形平面来逼近原来的模型，每个小三角形用3个顶点坐标和一个法向量来描述，三角形的大小可以根据精度要求进行选择。STL文件有二进制码和ASCⅡ码两种输出形式，二进制码输出形式所占的空间比ASCⅡ码输出形式的文件所占用的空间小得多，但ASCⅡ码输出形式可以阅读和检查。典型的CAD软件都带有转换和输出STL格式文件的功能。

Approximate processing of 3D models. Due to the fact that products often have irregular free form surfaces, the model needs to be approximated before processing to facilitate subsequent data processing work. Due to its simple and practical format, STL format files have become a quasi standard interface file in the field of rapid prototyping. It uses a series of small triangle planes to approximate the original model, with each small triangle described by 3 vertex coordinates and a normal vector. The size of the triangle can be selected based on accuracy requirements. STL files have two output formats: binary and ASC II. The binary output format takes up much less space than the ASC II output format, but the ASC II output format can be read and checked. Typical CAD software has the ability to convert and output STL format files.

三维模型的切片处理。根据被加工模型的特征选择合适的加工方向，在成型高度方向上用一系列一定间隔的平面切割近似后的模型，以便提取截面的轮廓信息。间隔一般取0.05mm～0.5mm，常用0.1mm。间隔越小，成型精度越高，但成型时间也越长，效率就越低，反之则精度低，但效率高。

Slicing processing of 3D models. Select an appropriate processing direction based on the characteristics of the processed model, and approximate the model by cutting a series of planes with certain intervals in the molding height direction to extract the contour information of the cross-section. The interval is generally 0.05mm~0.5mm, commonly 0.1mm. The smaller the interval, the higher the forming accuracy, but the longer the forming time, the lower the efficiency. Conversely, the accuracy is low, but the efficiency is high.

成型加工。根据切片处理的截面轮廓，在计算机控制下，相应的成型头（激光头或喷头）按各截面轮廓

Forming processing. According to the cross-sectional profile processed by slicing, under computer control, the corresponding forming head (laser head or nozzle) follows each cross-sectional profile

成型零件的后处理。从成型系统里取出成型件，进行打磨、抛光，或放在高温炉中进行后烧结，进一步提高其强度。

Post processing of formed parts. Remove the molded parts from the molding system for polishing, polishing, or sintering in a high-temperature furnace to further enhance their strength.