What is the bending process in sheet metal fabrication?
The bending of sheet metal refers to the processing of changing the angle of the sheet or plate. Such as bending the sheet into a V-shape, U-shape, etc. In general, there are two methods for sheet metal bending: one method is die bending, which is used for sheet metal structures with complex structures, small volume, and mass processing; the other is bending machine bending, which is used for It is suitable for processing sheet metal structures with relatively large structure sizes or small output.
Two bending methods
At present, the bending of the sheet metal fabrication factory's products is mainly processed by bending machines.
These two bending methods have their own principles, characteristics, and applicability.
For structural parts with an annual processing volume of more than 5,000 pieces and the size of the parts is not too large (generally 300X300), it is generally considered to open a stamping die for processing.
Commonly used bending dies
Commonly used bending dies, as shown in Figure 1-1: In order to prolong the life of the die, the parts should be designed with rounded corners as much as possible.
If the flange height is too small, it is not conducive to forming even if a bending die is used. Generally, the flange height L≥3t (including wall thickness).
Bending by bending machine
There are two types of bending machines: ordinary bending machines and CNC bending machines. The precision requirements are high, and the bending of sheet metal with an irregular bending shape is generally bent by a CNC bending machine. The basic principle is to use the bending knife (upper die) and V-shaped groove (lower die) of the bending machine. Sheet metal parts are bent and formed.
- Advantages: Convenient clamping, accurate positioning, and fast processing;
- Disadvantages: low pressure, only simple forming can be processed, and the efficiency is low.
Basic principles of forming
The basic principle of bend forming is shown in Figure 1-2:
- Bending knife (upper die): The form of the bending knife is shown in Figure 1-3. During processing, it is mainly selected according to the shape of the workpiece.
- Lower die: The lower die is generally V=6t (t is the thickness of the material) die.
There are many factors that affect the bending process, mainly including the arc radius of the upper die, the material, the thickness of the material, the strength of the lower die, and the die size of the lower die. See Figure 1-3 for the upper die on the left and the lower die on the right.
4 Basic principles of the bending sequence
- Bend from inside to outside;
- Bending from small to large;
- Bend special shapes first, and then bend general shapes;
- After the previous process is formed, it will not affect or interfere with the subsequent process.
The bending forms seen are generally as shown in Figure 1-4.
When the sheet metal is bent, a bending radius is required at the bending point. The bending radius should not be too large or too small and should be selected appropriately. If the bending radius is too small, it is easy to cause cracking at the bend, and if the bending radius is too large, the bending is easy to rebound.
Bending and spring back
Figure 1-5 Schematic diagram of bending and spring back
Springback angle Δα=b-a where
- b——the actual angle of the workpiece after spring back;
- a—The angle of the mold.
Interference phenomenon during bending
For two or more times of bending, there is often interference between the bending workpiece and the tool. As shown in Figure 1-6, the black part is the interference part, so the bending cannot be completed, or because of the bending interference lead to bending deformation.