Bending in sheet metal refers to the process of changing the angle of the sheet or workpiece, such as bending it into a V-shape or U-shape. Generally, there are two methods for sheet metal bending: mold bending, used for complex structures, small volume, and large-scale production of sheet metal structures, and press brake bending, used for processing larger-sized or lower-volume sheet metal structures.
These two bending methods have their own principles, characteristics, and applicability.
1.1.1 Mold Bending:
For structural components with an annual processing quantity of over 5000 pieces and relatively small part sizes (generally around 300x300), the consideration is given to using punching and stamping molds for processing.
1.1.1.1 Common Bending Molds:
To extend the life of the mold, it is advisable to use rounded corners as much as possible in the design of parts.
A too small bending edge height is not conducive to forming even with bending molds. Generally, the bending edge height L ≥ 3t (including wall thickness).
1.1.2 Press Brake Bending:
Press brakes are divided into ordinary press brakes and CNC press brakes. For sheet metal bending with high precision requirements and irregular bending shapes, CNC press brakes are generally used. The basic principle is to use the bending blade (upper die) and the V-shaped groove (lower die) of the press brake to bend and shape the sheet metal.
Advantages: Convenient clamping, accurate positioning, and fast processing speed. Disadvantages: Low pressure, capable of processing only simple forms, and relatively low efficiency.
1.1.2.1 Basic Forming Principle:
1) Bending Blade (Upper Die):
The selection is mainly based on the shape requirements of the workpiece.
2) The lower die is generally a V=6t (t is the material thickness) die.
There are many factors that affect the bending process, mainly including the radius of the upper die's arc, material, material thickness, strength of the lower die, and the size of the lower die's die orifice.
Basic principles of bending sequence:
1) Perform bending from the inside to the outside.
2) Perform bending from small to large.
3) Bend special shapes first, then bend general shapes.
4) The previous process should not affect or interfere with the subsequent process after forming.
1.1.2.2 Bending Radius:
When bending sheet metal, there should be a bending radius 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 bending point, while a too large bending radius can result in bounce-back.
1.1.2.3 Bending Springback:
1) Springback angle △a = b - a
Where b is the actual angle of the workpiece after springback, and a is the angle of the mold.
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 area. This prevents the completion of the bending process or may cause bending deformation due to interference.
