How to understand mechanical drawings?

Machinery is a rigorous and highly practical subject. As far as drawings are concerned, even if there is not a clear place, it can not be used to guide the practical application. Drawings are the language used by engineering and technical personnel to communicate. Non-professionals have difficulty in reading mechanical drawings. At first glance, it seems to make sense, but on closer inspection, it doesn't seem so. It is said that amateurs look at the fun, experts look at the door, but for mechanical drawings, do not see through can not communicate work, so mechanical drawing is the factory technical personnel must grasp the knowledge.

1.Types of mechanical drawings

There are many types of mechanical drawings, including assembly drawings, schematic diagrams, schematic diagrams, parts drawings, BOM tables, etc. First of all, you must determine what kind of drawing you get, so that you can know what the drawing expresses and what it expresses. In terms of expression, to what extent.

2. How to understand mechanical drawings?

1. First of all, it is necessary to clarify what type of drawing you get, whether it is an assembly drawing, a schematic diagram, or a part drawing, or a BOM table. Different types of drawings have different information and emphases to be expressed;

2. First look at the object described by the drawing, namely the title of the drawing; Although each person and each company will have the same drawings, but everyone basically follow the national drawing standards, a drawing is made to show people, if there are too many special places, others can not understand it will lose its meaning. So first look at the title bar (bottom right) inside the object name, number, quantity, material (if any), scale, unit and other information;

3. Determine the view direction; standard drawings have at least one view. The concept of view comes from the projection of descriptive geometry, so the basic three-view concept must be clear. This is the basis for understanding drawings. If you understand the relationship between each view on the drawing, you can basically understand the general shape of the product expressed by the drawing; According to the principle of projection to represent the shape of the object, the object can be placed in any quadrant. Generally, the method of placing the object in the first quadrant to obtain the projected view is called the first angle projection method, so the second, third, and Four-corner projection.

The first angle method is widely used in European countries (such as the United Kingdom, Germany, Switzerland, etc.); the third angle method is the same as the direction in which we view the object, so the United States, Japan and other countries use this projection method; the Chinese national standard CNSB1001 stipulates, Both the first angle method and the third angle method are applicable, but they cannot be used at the same time in the same drawing.

4. Correspond to the key structure of the product through the view; this is the key point of the view, which requires accumulation and spatial imagination;

5. Determine the size of the product; you only need to take a rough look at this, and have a general concept. If you are a manufacturer, you can look at it when you use it;

At this point, as long as you have read the drawings, and the above 5 points can be understood from the drawings, you can be regarded as a layman who can understand the drawings;

6. Mechanical drawings (all of which are standard product processing drawings here) express all the design data used in the mechanical industry such as the structure, size, material, precision, etc. of a part or component or a machine, and the materials have been seen before entering the industry. and the structural part, but there is still a lot of information in the drawings. Since almost all the mechanical information is in the drawings, there are thousands of pages in the mechanical design manual. Every dimension and every expression in the drawings has a certain degree of attention. Both mean a lot of basic knowledge;

7. The accuracy of the product in the drawing: the mechanical size (such as the diameter of a cylinder) is not just a size, whether the tolerance is marked (+-0.XX) or the size is not marked, it is a range, which is The concept of mechanical (dimensional) precision must always exist. Because mechanical parts are generally mass-produced, precision is required to control the size of each part (they cannot be the same size, and there will definitely be errors in production) within a certain range. Similarly, parts and components also have geometric tolerances (there are also annotations or not). The unmarked accuracy (tolerance) is stipulated in the national standards, and some drawings and technical requirements will state that accuracy is the soul of mechanical parts, which requires a certain amount of accumulation;

8. The process of the product in the drawing: the process is simply how to manufacture (assemble) this component. Although the mechanical drawing does not have the direct information expression of the process (process), it contains the basic process. It is meaningless if a part is designed but cannot be processed. How to process it must be considered by the designer, and it will also be expressed in the drawing;

9. The surface roughness of the product in the drawings: the roughness determines the requirements for use, and also limits the requirements for processing methods. The roughness that can be achieved by different processing methods is different; for example, an element (a bearing Inner hole) size, position, shape tolerance requirements for its roughness, will imply its processing technology requirements (grinding);

10. Heat treatment of the product: heat treatment makes the processing feasible, and the performance meets the requirements of use. The heat treatment also has a certain relationship with the selected material and processing technology;

11. Product surface treatment: Surface treatment is generally proposed in the technical requirements, and surface treatment also has a certain relationship with the material;