The electro-hydraulic synchronization system of the CNC press brake is composed of the following eight parts:
① Drive assembly
② Pressure control valve unit
③ Closed loop control valve unit
④ Closed loop proportional valve amplifier
⑤ Hydraulic cylinder
⑥ Position detection system
⑦ CNC system
⑧ Electrical system, etc
The position synchronization of the two piston cylinders during the stroke and the positioning of the stroke end point are realized by the electro-hydraulic synchronous servo system, which has high synchronization accuracy and repeated positioning accuracy.
See the below figure for the working principle of the press brake synchronization system.
Fig. 2 Schematic diagram of synchronous control
The oil output from the drive assembly enters the hydraulic cylinders on both sides through the pressure control valve unit and the closed-loop control valve unit, drives the ram to move downward (or upward), and is detected and fed back to the CNC system and the electrical system through the position detection system at both ends of the ram, and then the CNC system gives the processing signal to the closed-loop proportional valve amplifier, and then the closed-loop control valve unit distributes the oil to the hydraulic cylinders at both ends, so as to achieve the purpose of synchronization at both ends of the ram.
It has high synchronization accuracy and repeated positioning accuracy.
For the hydraulic system principle and action sequence of hydraulic components of the CNC press brake machine, please refer to the hydraulic schematic diagram of the CNC press brake (Fig. 3) and the action sequence table attached to the upper right corner.
Fig.3 Hydraulic schematic diagram of the CNC press brake
For the layout of the hydraulic components, please refer to figure 4 of the pressure control valve group of the hydraulic system and figure 5 of the closed-loop control valve group. The component serial number and code in the figure are the same as those in Figure 3.
Fig4. Pressure control valve group of the hydraulic system
Fig.5 closed-loop control valve group
When the machine is working, the ram needs to go through eight stages to complete one stroke:
- 1: Fast downward;
- 2: Slow downward;
- 3: Press and maintain the pressure;
- 4: Pressure relief;
- 5: Fast upward;
- 6: Decelerate upward;
- 7: Slow to dead center;
- 8: Stop at top dead center.
Phase 1
Operate the down button to power on 4Y3 and 4Y5.
When 4Y3 is powered on, port a and port t of lift valve (III-2) are connected, port P is closed, so that the upper chamber of cartridge valve (III-5) is connected with the oil tank, and open cartridge valve (III-5); When 4Y5 is powered on, ports P and B of proportional servo valve (III-1) are connected, ports A and T are connected, and the throttle port is the maximum.
At this time, due to the opening of (III-5) valve, the oil in the lower chamber of the two oil cylinders quickly returns to the oil tank through port A and T of (III-5) valve and (III-1) valve, and the oil pressure required to support the ram is lost at the same time.
Due to the self weight of the ram, the piston drops rapidly, the volume change rate of the upper chamber of the oil cylinder is greater than the flow of the oil pump, the upper chamber of the oil cylinder generates negative pressure, and the oil in the oil tank is pressed into the upper chambers of the two oil cylinders through the filling valve (IV). The ram forms a rapid downward operation under no-load.
Phase 2
When the ram moves down quickly to reach the set value, give 4Y5 a new parameter value through CNC system to reduce the throttle port of the proportional servo valve (III-1) to slow down.
Phase 3
Work advance boost: 4Y3 is powered off, 1Y2 is powered on, 4Y5 is powered on, and the proportional servo valve (III-1) is connected at ports P-B and A-T.
4Y3 loses power, the lifting valve (III-2) resets (Port P-A is connected and port T is closed), so that the valve (III-5) is also closed at the same time, the oil circuit in the lower chamber of the oil cylinder is cut off, and the pressure required to support the ram is quickly generated, so that the ram cannot fall freely;
1Y2 is powered on, the port P-A and port B-T of reversing valve (II-7) is connected. Close the control port of the charging valve, close the charging valve, and cut off the passage between the upper chamber of the oil cylinder and the oil tank.
At this time, the oil output by the oil pump enters the upper chamber of the oil cylinder through the fine oil filter (II-9) and port P-B of the proportional servo valve (III-1), and the proportional overflow valve (II-5) establishes pressure through the electromagnet 1Y1, forcing the ram to move downward against the supporting force and material pressing force of the lower chamber of the oil cylinder, and the oil in the lower chamber of the oil cylinder returns to the oil tank through port P-A of the overflow valve (II-5) and port A-T of the proportional servo valve (III-1).
In this way, the pressing and boosting process is completed.
Phase 4
When 1Y1 is powered off, the system oil begins to relieve pressure, while 4Y5 is powered on, and P, A, B and T port of the proportional servo valve (III-1) are closed to achieve the force balance of the upper and lower cavities of the oil cylinder.
Phase 5
After pressure relief, 1Y2 is powered off and 1Y1 and 4Y5 are powered on.
1Y2 de energized directional valve (II-7) is reset, port P-B is connected and port A-T is connected.
Because port P-B is connected, the charging valve (IV) is opened to connect the oil return path between the upper chamber of the oil cylinder and the oil tank; 4Y5 is energized, and port P-A and port B-T of proportional servo valve (III-1) are connected.
At this time, the oil output by the oil pump flows into the lower chamber of the oil cylinder through the fine filter (II-9), port P-A of the proportional servo valve (III-1), the one-way valve (IV-11) and the valve (III-5), and the proportional overflow valve (II-5) establishes pressure through the electromagnet 1Y1 to make the ram move upward rapidly, and the hydraulic oil in the upper chamber of the oil cylinder returns to the oil tank through the charging valve (IV).
Phase 6&7
When the ram rises to a certain position, 1Y1 continues to be powered on, while changing the electrical signal of 4Y5 to change the opening of the proportional servo valve (III-1) and close it slowly, so as to slow down the rise and slow down to the top dead center.
Phase 8
When the ram reaches the top dead center, 1Y1 loses power and the ram stops running, so that the machine tool completes a full stroke.
Under the control of the synchronous servo system of a press brake machine, the ram of the CNC press brake can always be parallel to the workbench in the process of rapid approach, working stroke, end point positioning and return.
When the ram tilts under the action of various disturbances and eccentric loads, the position detection system at both ends of the ram detects and feeds back the deviation value to the computer, and adjusts the parameters such as the flow and pressure of the oil entering the oil cylinder through the proportional servo valve to keep the positions of the two pistons synchronized, so as to keep the ram parallel to the workbench.
