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Sheet metal does not yet have a comprehensive definition. According to a definition from a foreign professional journal, it can be defined as: Sheet metal is a comprehensive cold working process for metal thin plates (usually less than 6mm thick), including shearing, punching/cutting/compound operations, folding, welding, riveting, splicing, forming (such as car bodies), etc. Its significant characteristic is that the thickness of the same part remains consistent.
Sheet metal cutting and processing is an important procedure in the formation of sheet metal products. It includes traditional cutting and blanking, punching and processing, bending and forming methods and process parameters, various cold stamping die structures and process parameters, the working principles and operation methods of various equipment, and also new stamping technologies and processes.
For any sheet metal part, there is a certain processing process, which is known as the process flow. Depending on the structure of the sheet metal part, the process flow may vary, but generally, it does not exceed the following points:
1. Design and draw the part drawing of the sheet metal part, also called three views. Its function is to express the structure of the sheet metal part through drawings.
2. Draw the development drawing. That is, unfold a structurally complex part into a flat plate.
3. Blanking. There are many ways to perform blanking, mainly including:
a. Shear bed blanking. Using a shear bed to cut out the length and width dimensions of the developed shape. If there are holes or corners to be punched, transfer to a punch press combined with molds for hole and corner punching.
b. Punch press blanking. Using a punch press to form the flat plate structure of the part after development in one or more steps on the sheet. The advantage is short processing time, high efficiency, reduced processing costs, and is often used in batch production.
c. NC numerical control blanking. When performing NC blanking, the first step is to write the numerical control machining program. This involves using programming software to convert the drawn development drawing into a program recognizable by the NC numerical control machining machine. Let the machine follow these programs step by step to punch out the structural shape of the flat plate on a steel plate.
d. Laser blanking. Using a laser cutting method to cut out the structural shape of the flat plate on a steel plate.
4. Flanging and tapping. Flanging is also called stretching holes, which involves stretching a smaller base hole into a slightly larger hole, then tapping threads on the stretched hole. This increases its strength and avoids stripped threads. It is generally used for sheet metal processing where the material is relatively thin. When the material is thicker, such as 2.0mm, 2.5mm, and above, we can directly tap threads without flanging.
5. Punch press processing. Generally, punch press processing includes hole punching, corner cutting, hole punching and blanking, convex package punching, tear punching, stretching holes, etc., to achieve the processing purpose. Processing requires corresponding molds to complete the operation. Convex package punching has convex package molds, and tear punching has tear forming molds.
6. Press riveting. In our factory, frequently used press rivets include press rivet screws, press rivet nuts, press rivet screws, etc. The press riveting method is generally completed through a punch press or hydraulic press riveting machine, and they are riveted onto the sheet metal parts.
7. Bending. Bending is the process of folding a 2D flat plate into a 3D part. Processing requires a bending machine and corresponding bending molds to complete the operation. It also has a certain bending order; the principle is to fold first what will not interfere with the next step, and fold last what will cause interference.
8. Welding. Welding is the process of welding multiple parts together to achieve the processing purpose or single-part edge seam welding to increase its strength. The processing methods generally include CO2 gas shielded welding, TIG welding, spot welding, robot welding, etc. The selection of these welding methods depends on actual requirements and material types. Generally, CO2 gas shielded welding is used for iron plate welding; TIG welding is used for aluminum plate welding; robot welding is mainly used when the material is large and the weld seam is long. For example, in cabinet welding, robot welding can be adopted, saving much work time and improving work efficiency and welding quality.
9. Surface treatment. Surface treatment generally includes phosphating film, electroplating five-color zinc, chromate treatment, painting, oxidation, etc. Phosphating film is usually used for cold-rolled plates and electrolytic plates, and its main function is to coat a protective film on the surface of the material to prevent oxidation. Additionally, it enhances the adhesion of paint. Electroplating five-color zinc is generally used for surface treatment of cold-rolled plates; chromate treatment and oxidation are generally used for surface treatment of aluminum plates and aluminum profiles. The specific surface treatment method is selected based on customer requirements.
10. Assembly. Assembly refers to assembling multiple parts or components in a certain way to form a complete product. Attention should be paid to the protection of the parts, avoiding scratches and damage. Assembly is the final step in completing a product. If the parts cannot be used due to scratches or damage, rework will waste a lot of processing time and increase the cost of the product. Therefore, special attention should be paid to protecting the parts.