How to Deal With Press Brake Hydraulic Valve Pressure Failure ?

The hydraulic valve of the CNC hydraulic press brake is mainly used for the bending of workpieces. It is assembled by frame, slider, worktable, hydraulic cylinder, hydraulic proportional servo system, position detection system, numerical control system, and electrical system. The bending machine can always keep the position of the slider synchronized (parallel to the table) under conditions of no-load speed, working speed, and return speed, and can achieve high-precision positioning at the end of the stroke. Therefore, it is widely used in the bending of components in industries such as automobiles, shipbuilding, containers, construction machinery, construction mechanisms, metal structures, light poles, and power poles.

Next, we will analyze the hydraulic valve system of the CNC hydraulic bending machine, sort out the possible causes of failures such as no pressure on the workers, and introduce the working principle and troubleshooting of the filling valve.

Fault Description

When the CNC hydraulic bending machine is running, under the control of the CNC system and the hydraulic servo system, the slider needs to go through the following 6 stages to complete a stroke: fast descending, decelerating descending, pressing and maintaining pressure, releasing pressure, fast ascending and stopping at the top dead center. In this paper, for the convenience of analysis, the 6 stages are combined into 3 stages, namely fast forward, work forward, and fast return (fast rewind).

Now the failure phenomenon of the bending machine in the work is: that the slider can go down quickly, but the pressure is obviously insufficient when pressing the material, and the bending operation cannot be completed.

Overview of Hydraulic System

System hydraulic principle:

1—Liquid filling valve 2—Proportional servo valve

3—Relief valve 4—Cartridge valve 1

5—Proportional relief valve 6—Cartridge valve 2

7—Oil filter device 8—Hydraulic pump

• Slide down quickly (fast forward)

When 4Y5 (cross) and 4Y3 are powered on, the oil in the lower chamber of the hydraulic cylinder quickly returns to the oil tank through cartridge valve 1 and the proportional servo valve, and at the same time loses the oil pressure required to support the slider. The weight of the slider drives the piston to drop rapidly, and the upper chamber of the hydraulic cylinder instantly forms a negative pressure, “sucks open” the filling valve, and a large amount of oil enters the upper chamber of the hydraulic cylinder from the oil tank through the filling valve, and the slider runs down quickly.

• Work-in pressurization

When the slider goes down to the switching point, 4Y3 loses power, the cartridge valve is closed, and the oil in the lower chamber of the hydraulic cylinder generates pressure through the relief valve. So that the slider cannot fall freely. At this time, 1Y1 is energized, so that the proportional relief valve establishes the system pressure, 1Y2 is energized, the filling valve is closed, and the oil enters the upper chamber of the hydraulic cylinder through the proportional servo valve, forcing the slider to move downward to complete the pressing action.

• Quick return of the slider (rewind)

4Y3 is energized, cartridge valve 1 is turned on, and 4Y5 is energized (straight-through). At this time, the oil output by the oil pump enters the lower chamber of the hydraulic cylinder through the proportional servo valve and the cartridge valve 1, and 1Y1 remains energized, and the proportional relief valve continues to be established. pressure. At the same time, when 1Y2 loses power, the filling valve is opened under the action of the control oil circuit pressure, and the oil in the upper chamber of the hydraulic cylinder returns to the oil tank quickly through the filling valve (a large amount), and the slider completes the rapid return action.

Failure Analysis And Troubleshooting

According to the failure phenomenon, analyzing the schematic diagram of the hydraulic system, it can be seen that there is no pressure in the bending machine, and the reason for the failure is speculated as follows.

Cause of issue:

1. The 1Y1 electromagnet of the proportional relief valve in the pressure control valve group is not energized. At this time, the proportional relief valve is an ordinary relief valve, and the system cannot build up enough pressure.
2. The taper hole of cartridge valve 2 in the pressure control valve group is worn or the seal is invalid, etc., the valve port is not closed, so that when the system pressure builds, the oil passes through the cartridge valve port and returns directly to the fuel tank, and the system has no pressure.
3. The valve port of the filling valve cannot be closed normally, the valve core is damaged or the seal fails [2], the upper cavity of the hydraulic cylinder is connected with the oil tank through the inner cavity of the filling valve, and when the bending machine is working, the oil flows from the upper cavity of the hydraulic cylinder through the oil tank. The fill valve goes directly back to the tank, causing a lack of pressure.

According to the elimination method from simple to difficult, the troubleshooting process of the fault point is as follows.

Troubleshooting

• Check whether the proportional relief valve in the pressure control valve group is energized normally. Check the proportional relief valve in the working state of the bending machine, the contact 1Y1 light is on, the proportional relief valve operates normally, and the failure of the proportional relief valve is eliminated.
• Check cartridge valve 2 of the pressure control manifold. Disassemble cartridge valve 2, check the wear of the taper hole, and reinstall the valve core after cleaning. If the pressure of the bending machine is still insufficient, the failure of the cartridge valve can be temporarily eliminated.
• Check the solenoid reversing valve of the oil circuit controlled by the charging valve. When the bending machine is working, the electromagnetic reversing valve is in a closed state, the charging valve is instructed to close, and the electromagnetic reversing valve is normal.
• Check the filling valve. Dismantling the filling valve, it is found that the locking bolt at the end of the filling valve is loose and falling off, and the pilot valve core is damaged, which causes the pilot valve port to be in a normally open state, and the filling valve cannot be tightly closed.

Estimated reading time: 6 minutes