Why does the press brake need a crowning system?
Bending accuracy
When it comes to bending workpieces, there are two key factors that determine its accuracy:
- Angle accuracy: This is primarily related to the deviation in the height direction of the die system, as depicted by Ty in Fig. 1.
- Dimensional accuracy: This is primarily related to the deviation in the front and rear direction of the die system, as shown by Tx in Fig. 1.
Fig. 1 Tx and Ty schematic
The greater the depth of the upper die of the press brake into the lower die, the smaller the bending angle.
Based on Figure 2, it can be calculated that when bending a 2mm carbon steel plate to 135° using the V12 lower die, a height direction deviation of 0.045mm can result in an angle deviation of 1.5°.
Fig. 2 Influence of height direction deviation on angle deviation
Further reading:
Deflection deformation of press brake
When a workpiece is bent using a press brake, the upper and lower beams may experience deflection and deformation due to their structural characteristics and the bending force applied, as illustrated in Figure 3.
Fig. 3 Deflection and deformation diagram of upper and lower beams
Currently, there is an inconsistency in the depth of the upper die entering the opening of the lower die along the full-length direction of the workpiece. This inconsistency can cause excessive deviation of the bending angle of the workpiece along its full-length direction.
This inconsistency typically results in a workpiece with a large middle angle and smaller angles at both ends, as depicted in Fig. 4.
Fig. 4 Schematic diagram of bending angle
Therefore, to ensure consistency of bending angle along the entire length of the workpiece, a crowning system needs to be introduced in the press brake.
Why does press brake need mechanical crowning system?
As mentioned above, when the press brake bends the workpiece, the upper and lower beams, due to their structural characteristics, undergo deflection deformation under the bending force. This can lead to excessive deviation of the bending angle of the workpiece in the full-length direction.
However, the crowning system can effectively compensate for the deflection deformation of the press brake. By using the crowning system on either the upper or lower beam, the consistency of the bending angle can be ensured throughout the length of the workpiece.
The crowning system is divided into two categories:
- Hydraulic crowning system
- Mechanical crowning system
1. Hydraulic crowning system
The hydraulic crowning system operates on the principle of embedding several hydraulic cylinders in the lower beam of the press brake. Each hydraulic cylinder can be controlled separately, causing the lower beam to form a certain bulge, as illustrated in Figure 1.
Theoretically, using more hydraulic cylinders increases the number of compensation points, resulting in higher compensation accuracy.
Hydraulic crowning is a discrete compensation method that is built-in.
To achieve a high-resolution compensation effect and high bending accuracy, the number of hydraulic cylinders and their hydraulic control system must meet higher requirements, resulting in a more complex overall structure and a higher cost of the press brake.
It is not possible to retrofit the hydraulic crowning system onto an existing customer press brake.
Fig. 1 Schematic diagram of hydraulic crowning system
2. Mechanical crowning system
The mechanical crowning system utilizes the filling method to compensate for the lower beam/lower die. Its main principle involves generating various compensation curves by means of the mutual movement of a pair of deflection compensation wedges, as demonstrated in Figure 2.
Fig. 2 Schematic diagram of mechanical crowning system
There are many types of mechanical crowning systems available in the market.
Let’s take the example of Wila’s mechanical compensation workbench. It falls under the category of external, relatively continuous compensation. This system can be directly installed on the lower beam of the press brake and is suitable for both new and old press brakes.
The compensation curves of this system can be adjusted continuously for various applications, as demonstrated in Fig. 3.
Further reading:
Conclusion
Both hydraulic crowning systems and mechanical crowning systems can effectively compensate for the deflection deformation of the press brake.
The difference between them lies in the accuracy or resolution of compensation, as well as the cost of the press brake caused by the different structural designs.
For high-precision bending applications, we recommend selecting the mechanical crowning system.
