Estimated reading time: 11 minutes
Hydraulic press brake machine is a widely used bending machine, which has already been hydraulicized. As an important part of sheet metal processing equipment, the press brake machine plays an irreplaceable role and plays a decisive role in the quality, processing efficiency and accuracy of the product.
The hydraulic system consists of two working hydraulic cylinders that move in parallel to form a vertical downward pressure to drive the mold on the bending beam to perform bending work. As the brain of the bending machine, the hydraulic control system mainly controls the synchronous operation of the bending process and the positioning of the hydraulic cylinder when the machine is working at full load.
Components of hydraulic system
- Oil Pump (The high-pressure gear pump is usually connected to the main motor)
- Hydraulic tank
The hydraulic oil tank is usually welded inside the machine, with a built-in oil filter, and an external motor, oil pump, high-pressure valve, control valve and electronic system.
- Synchronous servo valve
The servo valve is usually installed on the top of the cylinder. The output flow of the servo valve is mainly controlled by DNC and servo amplifier. These output flows mainly control the speed of the slider during the entire stroke. The servo motor runs faster, the bending speed becomes slower, and the slider moves from the bottom dead center to the top dead center.
- Hydraulic cylinder
For most press brake machine, the oil cylinders are generally installed above the left and right sides of the bending machine. The oil cylinders are used to provide machine pressure. The pressure generated by the oil cylinders directly acts on the slider, and then acts on the bending workpiece through the slider.
- Protection system
DNC controls the protection of the entire stroke. From the beginning of the machine tool operation, DNC monitors the time and stroke of the hydraulic oil during the entire stroke. This can also be referred to as hydraulic oil leakage monitoring.
- Filling valve
The filling valve is located at the top of the cylinder. When the slider moves quickly, the oil in the oil tank flows into the oil cylinder through the filling valve. When bending, the filling valve is closed.
- Oil filter
Generally, the oil filter accuracy is 10 microns, and the maximum pressure is 400 bar. If the filter is clogged or the hydraulic oil is changed, the filter element should be replaced.
Operation of the hydraulic system
Start the oil pump
The motor rotates in the direction marked by the pump arrow, that is, clockwise, driving the axial piston pump to run. The oil enters the valve plate and the electromagnetic overflow valve return tank through the pipeline. When the No. 19 valve is closed, the No. 20 cylinder lower chamber The oil keeps the slider at a fixed position.
The rapid downward movement of the bending machine is generated by the weight of the bending machine beam and various accessories and the pressure of the oil. During this process, the rodless cavity of the hydraulic cylinder is filled with oil through the filling valve. The rod cavity will generate back pressure and the oil will flow back quickly. The fast-forward movement starts from the top dead center. After a short deceleration stage, the speed of the slider slows down at a certain distance close to the bent sheet.
When No. 9 YV1, No. 24 YV6, No. 13 YV4, No. 17 YV5 electromagnets work, the slider quickly descends, and the descending speed is adjusted by the No. 18 valve. The oil in the lower chamber of the No. 20 cylinder passes through No. 19, No. 18, and No. 17 No. enters the oil tank, and the oil in the upper cavity of cylinder 20 is injected through the No. 21 valve.
When the slider is lowered to the limit switch, the No. 9 YV1, No. 8 YV2, No. 11 YV3, No. 13 YV4, and No. 24 YV6 electromagnets work, and the slider enters the working speed. If the sliding block is not synchronized, it will be automatically corrected by the No. 15 valve, and the sliding position of the sliding block is restricted by the mechanical stop in the oil cylinder.
The bending phase starts with pressure build-up in the rodless cavity. On the one hand, the bending speed is limited by the amount of oil supplied by the oil pump, and on the other hand, it can be adjusted by the proportional valve directional valve. At the same time, the directional valve also controls the synchronous operation of the bending beam and the positioning of the bottom dead center. The limit of the bending force is accomplished by the proportional relief valve to limit the pressure of the pump. The corresponding given values of speed, synchronization, positioning and pressure all come from the CNC.
The operating time of No. 9 YV1, No. 8 YV2, No. 11 YV3, No. 13 YV4, and No. 24 YV6 electromagnets is controlled by a foot switch or button to realize the jog distance when the slider is lowered, and the descending speed of the slider is changed from No. 16 For valve adjustment, the upward movement of the slider is controlled by No. 11 YV3 and No. 24 YV6. Similarly, the length of the electromagnet’s working time can realize the upward jog distance of the slider.
The decompression of the rodless cavity starts when it reaches the bottom dead center, or after a short holding time, so that the material has enough time to shape and further improve the dimensional accuracy of the part. Both holding and decompression are completed by the proportional directional valve in accordance with the instructions of the CNC.
In order to improve processing efficiency, the decompression time must be as short as possible, but in order to avoid unloading impact in the entire system, it is required to extend the decompression time as much as possible. In short, the decompression curve should be as stable as possible and not too steep. The optimization of the whole process is achieved through the proportional directional valve.
Main cylinder return back
The flow rate of the pump and the pressure-bearing area of the rod cavity of the hydraulic cylinder determine the maximum return speed, which is close to the maximum speed in most cases.
The return stroke also requires synchronous operation, from the beginning of the decompression of the rod cavity to the end of the top dead center.
At the moment of the return stroke, the No. 8 YV2 electromagnet is required to reset for 2 seconds to relieve the pressure, and then the No. 11 YV3 and No. 24 YV6 electromagnets work, the slider returns, and the return speed is constant.
Pressure adjustment of the machine
No. 6 high pressure relief valve and No. 11 electromagnetic relief valve are to ensure the rated force of the machine. The No. 14 overflow valve adjusts the return force of the machine so as not to damage the machine due to overload. The working pressure in the hydraulic system can be read from the No. 7 pressure gauge. The nitrogen charging pressure of the No. 10 accumulator is mainly the pressure required to operate the No. 19/No. 21 valve.
Working principle of CNC press brake hydraulic system
During normal operation, the motor starts to drive the oil pump, the pressure is normal, the A valve acts, and the small cylinder rises; three large cylinders rise at the same time, and the large cylinder simultaneously sucks the tank hydraulic oil. Of course, the suction port has a one-way valve. When it encounters resistance, The solenoid valve B is energized, the three large cylinders are loaded with oil pressure, and the bending works. The pressure is controlled by the servo valve. When returning, the A and B valves are our of energized, and the C valve is energized. This completes the sheet metal bending work.
The electro-hydraulic control system in the CNC bending machine can be divided into an open-loop control system and a closed-loop control system. The beam of the bending machine is the main control part of the system.
- Closed-loop system
Closed loop is also called a feedback control system. The system compares the measured value of the system output with the expected given value to generate a deviation signal, and then uses the signal deviation to control and adjust, so that the output value can be close to the desired value. For example, people first have a preliminary perception of the driving direction of the car in the brain. During the driving process, people observe the driving direction of the car with eyes, and compare the driving direction of the car with the expected direction. In this process, the direction is continuously adjusted, and finally the driving direction of the car is constantly close to the target direction, thus forming a closed-loop control.
Closed-loop control is based on the operating conditions of each part of the machine tool, with high accuracy and response speed. Since the closed-loop control system involves many elements, compared with the open-loop system, the structure of the whole system is more complicated and the price is higher.
- Open-loop system
Open-loop is compared to closed-loop, that is, open-loop control does not feed back the current system control results. For example, throw things. Once something is thrown out, people cannot control what is thrown out. Because once things leave the hands of people, people’s control over things stops immediately.
Therefore, in the open loop system of the bending machine, the accuracy of bending depends on the accuracy of each part of the machine tool. The system cannot control and compensate for the parameter changes produced during the bending process, resulting in low bending accuracy. Once the outside of the machine tool is disturbed, the internal parameters of the machine tool will change. However, in terms of system design, the open-loop design is simpler and more stable. Whether it is the installation of the machine tool in the early stage, or the maintenance of the subsequent machine tool, it is easier.
The slider rotates quickly and slowly, and the time pauses too long
- Check whether the oil level of the fuel tank is too low, the filling port is not flooded, and the upper cavity of the cylinder is filled with liquid during fast forwarding, causing insufficient filling. For the above reasons, add the oil from the oil tank of the bending machine to more than 5mm above the filling port so that the filling hole is completely flooded.
- Check whether the fast forward speed is too fast, causing insufficient filling. For the above reasons, the fast forward speed can be reduced by modifying the parameters of the hydraulic system of the press brake.
- Check whether the filling valve is fully opened. If it is due to oil contamination, the valve core of the filling valve will not move flexibly and become stuck, causing insufficient filling. Need to clean the filling valve and reinstall it to make the spool flexible.
The hydraulic system of the hydraulic press brake has no pressure
- Whether the solenoid coil of the proportional relief valve is energized and whether the voltage of the proportional solenoid coil meets the requirements. For the above reasons, please check the related electrical reasons.
- Check whether the cartridge valve of the bending machine is stuck or the main spool is stuck, and the damping orifice is blocked. If it is because of the above reasons, please disassemble the overflow valve, clean it, and reinstall it.
- The phase modulation of the three-phase power supply causes the motor to reverse.
The return stroke of the slider is normal, the fast forward is normal, the manual cannot be slow down, and the folding plate of the bending machine is weak
- Check whether the “two-position four-way” reversing valve of the control filling control oil circuit is working properly, if it is, the filling valve is not closed, so that the upper cavity is connected to the filling port of the fuel tank, and pressure cannot be built. The reason that the valve cannot work normally is that it is not powered on or is stuck.
- Check whether the filling valve is stuck. If so, please clean the filling valve and reinstall it to make the valve core flexible and free.
The return speed of the slider is too slow, and the return pressure is high
This type of failure is mainly caused by the failure of the filling valve of the press brake to open.