Hydraulic Press Brake

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Hydraulic Press Brake
Hydraulic Press Brake
Hydraulic Press Brake

Press Brake Not Descending Synchronized (Causes And Solutions)

1. Overview

Wc67y-250 / 4000 hydraulic press brake has high labor productivity and high bending accuracy for bending metal sheets.

It is stable and reliable, easy to operate, with inching or continuous travel.

It can keep the pressure, especially has the same force in the whole working stroke.

Users only need to equip with different molds to bend the sheet metal into the required shape.

Because the speed of the return movement of this kind of press brake is several times higher than that of bending (using fast movement in return can greatly improve the production efficiency), it is found that the cylinder of the press brake will be out of sync when it drops rapidly, which affects the quality of the product.

2. Cause analysis of desynchrony

1) Analysis from the piston cylinder:

The main reason is that the piston cylinder has internal leakage, that is, the gap between the piston and the oil cylinder is too large to cause leakage,

The leakage in the left and right cylinders is not exactly the same, which makes the movement speed of the two cylinders different.

2) Analysis from the oil inlet pipeline:

As shown in Fig. 1, when the press brake descends rapidly, on the one hand, the oil pump supplies oil to the oil cylinder through the synchronous valve;

On the other hand, the top oil tank 1 feeds oil to the oil cylinder through one-way valve 2 through the natural height difference,

These two kinds of oil supply oil to the upper chamber of the oil cylinder to make the oil cylinder descend rapidly,

Since the flow in the valve circuit after the synchronization valve is approximately equal, so only the flow from the tank through the check valve 2 into the oil cylinder 3 is considered.

Fig. 1 Oil supply analysis of oil cylinder

1- Oil tank; 2 – Check valve; 3 – Oil cylinder.

Fig. 1 Oil supply analysis of oil cylinder

The structure of check valve 2 is shown in Fig. 2.

P1 is the inlet pressure and P2 is the outlet pressure.

For the two check valve inlet pressure, P1 can be regarded as atmospheric pressure, so it is equal.

When P1 is the same, the smaller P2 and the greater P, the greater the flow rate Q through the check valve.

Fig. 2 Check valve structure

Fig. 2 Check valve structure

It can be seen from the above that the two hydraulic cylinders will not be completely synchronized when they are started, so the pressure P in the upper chamber of the two cylinders is not the same, and the pressure difference between the front and rear of the two check valves will not be the same.

Therefore, the flow from the oil cylinder through the one-way valve into the two cylinders is not the same, which also leads to the movement of the two cylinders is not synchronized.

3) Analysis from the oil return pipeline:

When the press brake descends rapidly, the motion damping on the return oil circuit is not equal, resulting in the difference of the back pressure in the lower chamber of the piston, so the flow rate of the return flow of the two cylinders is not equal.

As a result, the speed of the two cylinders’ rapid descent is not equal, that is, out of synchronization.

3. Solution

1) For hydraulic cylinders, in order to make the leakage in the two cylinders equal, on the one hand, it should try to make the selection accuracy of left and right pistons, cylinders and other parts (including dimensional accuracy, position accuracy such as coaxiality, roundness, etc.) consistent.

On the other hand, the hydraulic circuits of the two hydraulic cylinders should be designed as the same as possible.

2) For the oil inlet pipeline, in order to ensure that the flow through the two check valves is equal, on the one hand, it should try to make the center of gravity of the movable frame in the geometric center of the two cylinders;

On the other hand, the mechanical damping between the piston and the piston rod and between the piston rod and the end cover should be close as far as possible to ensure that the mechanical damping of the two piston cylinders is similar when they drop rapidly.

3) For the oil return pipeline, in order to ensure that the return flow of the two cylinders is equal, it is necessary to make the return oil resistance of the oil return pipeline similar, that is, the pipe diameter, pipe length, pipe bending number and pipe bending angle should be basically the same.

4) Mechanical rack and pinion drive is used to force synchronization.

The setting of the device is shown in Fig. 3.

The rack is installed on the left and right of the connecting frame of the press brake, and is meshed with the gear on the rack.

The rack is used as the guiding device and the error correction is made by the meshing of the gear and the gear.

As long as the manufacturing accuracy of the rack and gear is guaranteed, the two working cylinders of the press brake can achieve very high synchronous accuracy.

Fig. 3 Schematic diagram of gear rack drive with forced synchronization

Fig. 3 Schematic diagram of gear rack drive with forced synchronization

4. Effect

Through the cooperation of users, designers and manufacturers, the whole process of manufacturing, assembly and commissioning has been effectively improved.

Judging from the current use, the structure is simple and compact, the operation is stable, basically without noise.

Thus, the quality of the bending steel plate is guaranteed and the bending efficiency can meet the requirements.

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