Things You Should Know About Press Brake Crowning

Why does the press brake need a crowning system?

Bending accuracy

For bending workpiece, there are two most important accuracy:

(1) The angle accuracy is mainly related to the deviation of the height direction of the die system, as shown in Ty in Fig. 1.

(2) The dimensional accuracy is mainly related to the deviation of the front and rear direction of the die system, as shown in Tx in Fig. 1.

angle accuracy is mainly related to the deviation of the height direction of the die system

Fig. 1 Tx and Ty schematic

The deeper the depth of the upper die of the press brake into the lower die, the smaller the bending angle.

It can be calculated from Fig. 2 that when the lower die of V12 is used to bend 2mm carbon steel plate to 135 °, the height direction deviation of 0.045 mm can lead to the angle deviation of 1.5 °.

Things You Should Know About Press Brake Crowning 1

Fig. 2 Influence of height direction deviation on angle deviation

Further reading:

Deflection deformation of press brake

When the press brake bends the workpiece, due to its own structural characteristics, the upper and lower beams will produce deflection deformation under the action of bending force, as shown in Fig. 3.

Things You Should Know About Press Brake Crowning 2

Fig. 3  Deflection and deformation diagram of upper and lower beams

At this time, the depth of the upper die entering the opening of the lower die is inconsistent in the full-length direction of the workpiece, which will lead to the excessive deviation of the bending angle of the workpiece in the full-length direction.

The typical phenomenon is that the middle angle of the workpiece is large and the angle of both ends is small, as shown in Fig. 4.

Things You Should Know About Press Brake Crowning 3

Fig. 4 Schematic diagram of bending angle

Therefore, the press brake needs to introduce a crowning system to ensure the consistency of bending angle in the whole length.

Why does press brake need mechanical crowning system?

As mentioned above, when the press brake bends the workpiece, due to its own structural characteristics, under the action of bending force, the upper and lower beams will produce deflection deformation, which will lead to excessive deviation of the bending angle of the workpiece in the full-length direction.

The crowning system can effectively compensate the deflection deformation of the press brake.

Using the crowning system on the upper beam or lower beam can ensure the consistency of the bending angle in the whole length.

The crowning system is divided into:

  • Hydraulic crowning system
  • Mechanical crowning system

1. Hydraulic crowning system

The principle of the hydraulic crowning system is that several hydraulic cylinders are embedded in the lower beam of the press brake, and each hydraulic cylinder can be controlled separately, so that the lower beam can form a certain bulge, as shown in Fig. 1.

Theoretically, the more hydraulic cylinders are used, the more compensation points are, and the higher the compensation accuracy will be.

Hydraulic crowning belongs to built-in discrete compensation.

In order to achieve high-resolution compensation effect and achieve high bending accuracy, higher requirements are put forward for the number of hydraulic cylinders and their hydraulic control system, resulting in more complex overall structure and higher cost of the press brake.

The hydraulic crowning system cannot be applied to the upgrading of the existing press brake of the customer.

Things You Should Know About Press Brake Crowning 4

Fig. 1 Schematic diagram of hydraulic crowning system

2. Mechanical crowning system

The mechanical crowning system uses the filling method to compensate the lower beam / lower die.

Its main principle is to generate different compensation curves through the mutual movement of a pair of deflection compensation wedges, as shown in Fig. 2.

Schematic diagram of mechanical crowning system

Fig. 2 Schematic diagram of mechanical crowning system

There are many kinds of mechanical crowning systems in the market.

Take Wila’s mechanical compensation workbench as an example.

It belongs to external relatively continuous compensation.

It is directly installed on the lower beam of the press brake and can be applied to new and old press brakes.

For different applications, different compensation curves can be continuously adjusted, as shown in Fig. 3.

different compensation curves

Further reading:

Conclusion

Both hydraulic crowning system and mechanical crowning system can effectively compensate the deflection deformation of the press brake.

The difference between them lies in the accuracy / resolution of compensation, in addition to the difference in the cost of the press brake caused by the different design of the structure itself.

In dealing with high-precision bending applications, we recommend the selection of mechanical crowning system.

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