7 Notes for Reading Sheet Metal Unrolled Drawings

What is a sheet metal drawing?

Sheet metal fabrication processing engineering drawings also belong to the category of mechanical drawing. Mechanical drawing is a discipline that uses drawings to accurately represent the structural shape, size, working principle, and technical requirements of machinery. Drawings are composed of graphics, symbols, words, and numbers, and are technical documents that express design intent, manufacturing requirements, and exchange experience. They are often called the language of engineering.

Mechanical drawings mainly include part drawings and assembly drawings. Parts drawings express the shape and size of parts and the technical requirements for manufacturing and testing parts; assembly drawings express the assembly relationship and working principle between parts and components in the machine; express the structure and shape of parts. Graphics, commonly used are views, sectional views, and sectional views.

The view is the figure obtained by the orthographic projection method, that is, the part is projected onto the projection surface. According to the projection direction and the position of the corresponding projection surface, the views are divided into the main view, the top view, and the left view. Views are primarily used to express the external shape of a mechanism. Outlines that are not visible in the figure are indicated by dashed lines. When the part is projected onto the projection surface, there are two relative positions between the observer, the machine, and the projection surface. When the mechanism is located between the projection surface and the observer, it is called the first angle projection method. When the projection surface is located between the machine and the observer, it is called the third angle projection method. Both projection methods can express the shape of the mechanism equally well. The Chinese national standard stipulates the first angle projection method.

7 Notes for Sheet Metal Unfolding Drawings

1. Unless otherwise specified, the burr direction of the product shall be judged according to the principle of “burr inward”, and the expanded graphics shall be placed with the burr downward.
2. In the expanded image, all pixels except the circular hole must be connected in series to form a complex line, and all the pixels composed of short line segments must be redrawn as standard pixels (circles, straight lines).
3. The sharp corners of the shape are not processed, but they are chamfered according to the process in the engineering drawing.
4. Data annotation
   1. The expanded drawing must be in the form of linear annotation, the decimal point is accurate to two digits (UNIT2), the dimension annotation is placed on the DIM layer, and the origin of the coordinates should be selected at the lower left corner of the maximum external dimension, and the dimensions should be marked as complete as possible (except for the size or pixel density), However, it must be marked with the most external size, the broken line size, and the expanded size corresponding to the size marked on the product drawing.
   2. The shape, size, and height of the partial cross-sectional view and the partial cross-sectional view should be marked as complete as possible.
   3. All partial moldings such as tooth extraction, convex extraction, burr embossing, embossing, embossing, and embossing must be marked with their type, direction, and size in order (except for special cases).
   4. Indicate the 90∘ bending coefficients, and the size of the bending deformation area must be marked for non-90∘ bending.
5. Cutting
   1. When selecting punching and blanking, the minimum process gap can be set to 1.0, and can be adjusted appropriately according to the plate thickness (the process gap cannot be smaller than the plate thickness), and all the gaps and all types of holes in the punching must be based on the company’s specifications. The tool is adjusted to ensure the absolute consistency of the unfolding and the program;
   2. When laser cutting is selected, the minimum process gap can be set to 0.5, and appropriate adjustments can be made according to the thickness of the plate;
6. The spraying allowance needs to be adjusted
   1. Spraying wrinkle powder: If the customer’s requirement for the aperture size tolerance is above 0.2, there is no need to adjust the aperture size; if the customer’s requirement for the aperture size tolerance is below 0.2, the aperture size needs to be increased by 0.2, so that the aperture size after spraying meets the customer’s requirements. The aperture size matches
   2. Sandblasting powder/flat powder: If the aperture size tolerance is required to be more than 0.15, there is no need to adjust the aperture size; if the aperture size tolerance is required to be below 0.15, the aperture size needs to be increased by 0.15, so that the aperture size after spraying and The hole size required by the drawing is consistent with
   3. Spray paint: If the aperture size tolerance is required to be above 0.1, there is no need to adjust the aperture size; if the aperture size tolerance is required to be below 0.1, the aperture size needs to be increased by 0.1
7. Bending spray allowance adjustment
   1. If the bending size tolerance is required to be less than 0.2, it is necessary to reduce each sprayed surface affecting the required size by 0.1, so that the bending size after spraying is consistent with the required bending size;
   2. Sandblasting powder/flat powder: If the bending size tolerance is required to be more than 0.15, the bending size does not need to be adjusted; if the customer requires the bending size tolerance to be less than 0.15, it is necessary to reduce the size of each spray surface that affects the size required by the customer. 0.075, so that the bending size after spraying is consistent with the bending size required by the customer;
   3. Spray paint: if the customer requires a bending size tolerance of more than 0.1, there is no need to adjust the bending size; if the bending size tolerance is required to be 0.1 In the following cases, it is necessary to reduce each sprayed surface that affects the required size by 0.05, so that the bending size after spraying is consistent with the required bending size;