Unfolding and blanking of ventilation pipe processing: in ventilation engineering, the shapes of pipes and parts made of metal and non-metallic sheet materials are various, and some parts must be processed and fabricated by the basic method of unfolding and blanking. The so-called unfolding is to lay the surface of pipe fittings on the sheet material according to the actual size according to the requirements of the pipe fitting construction drawing (or setting out drawing), Directly affects the quality and material efficiency of spiral ducts and components.

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 for unfolding cutting: The basic steps for unfolding cutting include familiarizing oneself with graphics, analyzing shapes, finding the true length of a straight line or the true shape of a plane, determining the unfolding method, and drawing an 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 unfolding and blanking, first of all, be familiar with the construction drawings carefully, understand the contents of the pipe fittings or components to be unfolded, the position of the ventilation project, the pipe fittings to be connected with, the size of its size on the drawings, and the material to be used. For complex pipe fittings and components, it is necessary to carefully read and analyze the construction drawings repeatedly, and all U-shaped parts must be understood. If there are errors in the drawings, 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。

The ventilation pipes and components in ventilation and air conditioning engineering are all composed of geometric shapes. The purpose of analyzing shapes is to decompose complex geometric shapes into simple geometric shapes. Through decomposition, an appropriate unfolding method can be found. Generally, the components that need to be unfolded are mostly shells, which have flat 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) Flat shell: It is a shell formed by a set of planes, mainly consisting of two types: prism and pyramid. The former has parallel prisms, while the latter has more intersecting prisms. Usually, there are three prisms, four prisms, and three prisms and four pyramids according to the number of prisms. Regular prism shell: the bottom is a Regular polygon, and the edge is perpendicular to the bottom plane. Pyramid shell: the bottom is a polygon, and the cone projection coincides with the center of the bottom Regular polygon, otherwise it is a conical shell. After cutting, various types of cut bodies can appear on the shell. The characteristic of a prismatic shell (truncated body) is that the different projection surfaces of each pair of edges are parallel to each other or intersect at a point. The characteristic of a pyramid shaped shell (truncated body) is that the projections of each edge intersect at a point. A polyhedral shell with four extended edges that 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 shell: A shell with a curved surface or both surfaces is called a curved shell. Curved shells can be divided into two types: rotating or non rotating shells.