Unfolding and blanking of ventilation pipe processing: In ventilation engineering, the shapes of pipes and parts made of metal and non-metallic sheets are various, and some parts must be processed and fabricated by the basic method of unfolding and blanking. The so-called unfolding refers to laying the surface of pipe fittings on the sheet according to the actual size according to the requirements of the pipe fitting construction drawing (or setting out drawing). The drawn figure is the unfolding drawing, and the quality of the unfolding drawing is good or bad, It directly affects the quality of spiral air duct and components and the use efficiency of materials.

展開下料的步驟：展開下料的基本步驟是：熟悉圖形，形體分析，求直線的實長或平面的實形，確定展開方法和畫展開圖等。

Steps of unfolding blanking: the basic steps of unfolding blanking are: getting familiar with graphics, shape analysis, finding the real length of a straight line or the real shape of a plane, determining the unfolding method and drawing the unfolding diagram.

熟悉圖紙展開下料前，要認真熟悉施工圖紙，了解需要展開的管件或部件的內容，它在通風工程的部位、與何種管件相連接，它在圖紙上尺寸的大小，用哪種材料制作等。對于復雜的管件和部件需要反復仔細地對施工圖進行閱讀和分析，必U型全部看懂，如果圖紙有錯誤或看不懂或設計不合理，應向有關部門提出。

Be familiar with the drawings. Before spreading and blanking, first of all, be familiar with the construction drawings carefully, understand the contents of the pipe fittings or components to be spread, the position of the ventilation project, the pipe fittings to be connected, the size of its dimensions on the drawings, and the material to be used. For complex pipe fittings and components, it is necessary to read and analyze the construction drawings repeatedly and carefully. All U-shapes must be understood. If the drawings are wrong or cannot be understood or the design is unreasonable, it should be reported to the relevant departments.

形體分析通風和空調工程中的通風管件和部件都是由幾何圖形構成的，對形體的分析的目的就是把復雜的幾何形體分解成簡單的幾何形體，通過分解，便能找到恰當的展開方法，一般需要展開的部件多為殼體，殼體有平面殼體和曲面殼體。

Shape analysis The ventilation pipe fittings and components in ventilation and air conditioning engineering are all composed of geometric figures. The purpose of shape analysis is to decompose complex geometric figures into simple geometric figures. Through decomposition, you can find the appropriate expansion method. Generally, the parts to be expanded are shells, which include plane shells and curved shells.

1)、平面殼體：它是由一組平面形成的殼體，主要有棱柱形和棱錐形兩種。前者棱形相互平行，后者棱形豐交一點，通常按棱線的多少有三棱、四棱柱形及三棱、四棱錐形。正棱柱殼體：底部為正多邊形，棱與底平面相垂直。正棱錐殼體：底部為多邊形，而錐項投影與底部正多邊形相重合，不重合者為錐形殼體。經過剖切，殼體可出現各種截體。棱柱形殼體（截體）的特點是：各棱對不同投影面相互平行或分別交于一點。棱錐形殼體（截體）的特點是：各棱的投影相交于一點。多面殼體，它的四棱延長線不相交于一點。

1) Plane shell: it is a shell formed by a group of planes, mainly including prismatic and pyramidal shells. The former is parallel to each other, while the latter is rich in intersection. Generally, according to the number of prisms, there are three prism, four prism and three prism, four pyramid. Regular prism shell: the bottom is regular polygon, and the edge is perpendicular to the bottom plane. Regular pyramid shell: the bottom is a polygon, and the projection of the cone is coincident with the center of the regular polygon at the bottom, otherwise it is a conical shell. After sectioning, various sections of the shell can appear. The characteristics of prismatic shells (truncated bodies) are that the edges of different projection planes are parallel to each other or intersect at a point respectively. The feature of pyramid shaped shell (truncated body) is that the projection of each edge intersects at a point. The extended lines of the four edges of a polyhedral shell do not intersect at a point.

2)、曲面殼體：表面為曲面，或曲面、平面兼有的殼體稱為曲面殼體。曲面殼體可分為：旋轉或非旋轉兩種殼體。

2) Curved shells: shells with curved surfaces or both are called curved shells. Curved shells can be divided into rotating or non rotating shells.