"Expanded Figure" Projection and View PPT Courseware 2

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"Expanded Figure" Projection and View PPT Courseware 2

The essence of drawing an expanded diagram is to find the actual shape of the surface of the workpiece.

Three-dimensional surfaces are divided into two categories:

developable surface

A surface that can be accurately developed according to a real shape, such as a plane solid surface, or a curved surface in which two adjacent prime lines are parallel to or intersect each other.

non-developable surface

Surfaces that cannot be expanded accurately, such as spheres, torus, etc., are generally expanded using approximate expansion methods.

Approximate expansion of non-developable surfaces

The essence of the approximate expansion of a non-developable surface is to divide the non-developable surface into several smaller parts, and then treat each small part of the surface as a developable surface, so as to perform an approximate expansion.

For example, the spherical surface can be divided in several ways, such as the following diagrams (a), (b), (c), etc. Below, we will take the expansion of a sphere as an example to illustrate the principle of approximate expansion.

Approximate cone method

Draw several horizontal parallels on the sphere and divide the sphere into equal parts, then each small part can be approximately regarded as a cone, as shown in Figures (a) and (b).

(c) The figure shows the two-sided projection of the ball, and the expansion diagram of each cone can be drawn accordingly.

Approximate trapezoidal method

Divide the surface of the sphere into equal cones, and then divide the cone into equal parts into trapezoids, as shown in Figure (a). When blanking, you can cut into small trapezoidal units as shown in Figure (b), and weld each trapezoidal unit into a cone. As shown in Figure (c), it is finally welded into a round ball.

Approximate deformation method

As shown in Figure (a), it is a tank-shaped container whose structure consists of a cylinder and upper and lower hemispheres. When making the spherical part of a container from steel plates, the steel plates obtained from blanking are generally heated and bent to plastically deform the steel plates and then welded.

Considering the convenience of cutting materials and processes, the hemispherical surface can be decomposed into a top plate and eight identical side plates, and then the following method is used to approximate the expansion of the spherical surface, as shown in Figures (b) and (c) , called the approximate deformation method.

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Update Time: 2024-06-26

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