Sheet metal bending refers to the process of changing the angle of a sheet or plate. It involves bending the sheet into shapes such as V-shape or U-shape. Generally, there are two methods for sheet metal bending:
One method is die bending, which is used for complex structures, small volume production of sheet metal structures.
The other method is using a bending machine, which is suitable for processing larger-sized or lower volume sheet metal structures. Currently, our company primarily uses bending machines for the bending process.
These two bending methods have their own principles, characteristics, and applications.
1.1.1 Die Bending:
For structural components with an annual production volume of over 5000 pieces and dimensions not too large (generally around 300x300), die stamping is usually considered for processing.
1.1.1.1 Common Bending Dies:
To prolong the lifespan of the dies, it is preferable to design parts with rounded corners. Having a too small bending edge height is not conducive to forming, so the bending edge height should generally be L ≥ 3t (including the material thickness).
1.1.2 Bending Machine Bending:
Bending machines can be divided into ordinary bending machines and CNC bending machines. For precise requirements and irregularly shaped sheet metal bending, CNC bending machines are generally used. The basic principle is to use the bending blade (upper die) and V-shaped groove (lower die) of the bending machine to bend and shape the sheet metal.
Advantages: Convenient clamping, accurate positioning, and fast processing speed.
Disadvantages: Low pressure, suitable only for simple shaping, and lower efficiency.
1.1.2.1 Basic Forming Principle:
The selection of the upper die mainly depends on the shape requirements of the workpiece.
The lower die is generally V=6t (t refers to the material thickness).
There are many factors that affect the bending process, including the upper die's radius of curvature, material, thickness, lower die strength, and the size of the lower die's die opening. The left side represents the upper die, and the right side represents the lower die.
The basic principles of the bending sequence are as follows:
1) Perform bending from the inside to the outside.
2) Perform bending from small to large.
3) First bend special shapes, then bend general shapes.
4) The previous process should not affect or interfere with subsequent processes after forming.
1.1.2.2 Bending Radius:
When bending sheet metal, a bending radius is required at the bending point. The bending radius should not be too large or too small and should be appropriately selected. A too small bending radius can cause cracking at the bend, while a too large bending radius can result in springback.
1.1.2.3 Springback:
The springback angle (Δα) is calculated as the difference between the actual angle of the workpiece after springback (b) and the die angle (a).
1.1.2.4 Interference Phenomenon during Bending:
For secondary or multiple bending, interference often occurs between the bent workpiece and the tool, as shown in the black areas. This prevents the completion of the bending process or may cause bending deformation due to interference.
1.1.2.5 First-time Edge Crushing:
The method of first-time edge crushing involves using a 30-degree bending blade to bend the sheet metal to 30 degrees and then flatten the bending edge.
The minimum bending edge size L is determined by adding 0.5t (t refers to the material thickness) to the minimum bending edge size described in 1.3.2.2. Edge crushing is generally suitable for materials such as stainless steel, galvanized sheet, and aluminum-zinc-coated sheet. It is not suitable for electroplated parts as acid may be trapped in the crushed edge.
1.1.2.6 180-Degree Bending:
The method for 180-degree bending involves first using a 30-degree bending blade to bend the sheet metal to 30 degrees, then flatten the bending edge and remove the spacer.
The height H should be selected from commonly used sheet metal sizes, such as 0.5, 0.8, 1.0, 1.2, 1.5, 2.0. It is generally not advisable to choose a higher height.
1.1.2.7 Triple Folding and Edge Crushing:
First, perform the bending and then crush the edge.
