Basic Theory of Rapid Prototyping

快速成型屬于離散/堆積成型。它從成型原理上提出一個全新的思維模式，即將計算機上制作的零件三維模型，進行網格化處理并存儲，對其進行分層處理，得到各層截面的二維輪廓信息，按照這些輪廓信息自動生成加工路徑，由成型頭在控制系統的控制下，選擇性地固化或切割一層層的成型材料，形成各個截面輪廓薄片，并逐步順序疊加成三維坯件，然后進行坯件的后處理，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.

產品三維模型的構建。由于RP系統是由三維CAD模型直接驅動，因此要構建所加工工件的三維CAD模型。該三維CAD模型可以利用計算機輔助設計軟件（如Pro/E，I-DEAS，Solid Works，NX等）直接構建，也可以將已有產品的二維圖樣進行轉換而形成三維模型，或對產品實體進行激光掃描、CT斷層掃描，得到點云數據，然后利用反求工程的方法來構造三維模型。

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.

三維模型的近似處理。由于產品往往有一些不規則的自由曲面，加工前要對模型進行近似處理，以方便后續的數據處理工作。由于STL格式文件格式簡單、實用，目前已經成為快速成型領域的準標準接口文件。它是用一系列的小三角形平面來逼近原來的模型，每個小三角形用3個頂點坐標和一個法向量來描述，三角形的大小可以根據精度要求進行選擇。STL文件有二進制碼和ASCⅡ碼兩種輸出形式，二進制碼輸出形式所占的空間比ASCⅡ碼輸出形式的文件所占用的空間小得多，但ASCⅡ碼輸出形式可以閱讀和檢查。典型的CAD軟件都帶有轉換和輸出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.

三維模型的切片處理。根據被加工模型的特征選擇合適的加工方向，在成型高度方向上用一系列一定間隔的平面切割近似后的模型，以便提取截面的輪廓信息。間隔一般取0.05mm～0.5mm，常用0.1mm。間隔越小，成型精度越高，但成型時間也越長，效率就越低，反之則精度低，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。根據切片處理的截面輪廓，在計算機控制下，相應的成型頭（激光頭或噴頭）按各截面輪廓

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

成型零件的后處理。從成型系統里取出成型件，進行打磨、拋光，或放在高溫爐中進行后燒結，進一步提高其強度。

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.