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Troubleshooting Common CNC Press Brake Faults: An Expert Analysis

Last updated:
August 24, 2023

Table Of Contents

Are you tired of dealing with frustrating faults in your CNC press brake?

Do you find yourself constantly troubleshooting and trying to fix issues with slow pressure build-up, excessive noise from the oil pump, or a ram that vibrates during slow descent?

Look no further than this comprehensive guide to troubleshooting common faults in CNC press brakes.

From identifying the root cause of the problem to implementing practical solutions, this article covers it all.

Whether you’re a seasoned professional or a novice just starting out, you’ll find valuable insights and practical tips to help you get your press brake back up and running smoothly.

So, sit back, relax, and let’s dive into the world of CNC press brake troubleshooting.

1. Excessive noise from the oil pump (heats up too quickly) and damage to the oil pump.

1. Leakage in the oil suction pipeline or low fluid level in the tank causing the oil pump to suck air.

2. Low oil temperature and high viscosity, resulting in high oil suction resistance.

3. Blockage of the suction port filter, dirty oil.

4. Pump damage due to improper installation or any impact damage.

5. Coupling installation problem, such as excessive axial tightness, motor shaft misalignment with the pump shaft.

6. Long reverse running time or lack of oil during pump testing after installation.

7. Blockage of the high-pressure outlet filter or flow rate not meeting the standard.

8. Oil pump suction failure (oil present, but air is present at the oil suction port of the pump).

9. If it is a plunger pump, it may be because the height setting of the return oil port pipeline is too low.

10. If it is a HOEBIGER oil pump, it may require venting.

11. High oil temperature leading to reduced viscosity (within 60°C).

12. Hydraulic oil containing water can cause blockage and damage to the high-pressure filter element.

2. No pressure in the system or inability to build up pressure.

1. Incorrect direction of the oil pump or damage to the oil pump.

2. Whether the pressure gauge is damaged.

3. Whether there is an electrical signal in the pressure control valve or whether the valve is blocked.

4. Blockage or jamming of the pressure insertion valve, unable to seal the oil.

5. The filling valve is stuck (the ram does not move down slowly).

6. The compensation amplifier is adjusted too small.

7. Pressure can only reach a certain value. Use a direct 24V method to determine if there is a problem with the valve or oil pump.

3. Slow pressure build-up (REXROTH hydraulic system).

1. The damping hole at the X port of the pressure valve may be blocked.

2. The insertion valve at the pressure valve may not be functioning properly.

3. Possible electrical problems: test the solenoid pressure valve with a direct 24V voltage or use an object to push the spool of the solenoid pressure valve.

4. Whether the high-pressure oil filter is blocked.

4. There is a sound of impact during rapid descent.

1. The impact sound may be caused by loose guide rail plates.

2. The position of the grating scale black strip may not be correct.

3. The setting value of the delay parameter before rapid descent may be too small.

5. The ram has no rapid descent action.

1. Whether there is an electrical signal in the rapid descent valve or whether it is stuck.

2. Whether there is an electrical signal in the electromagnetic proportional reversing valve or whether the spool is not moving or stuck (check feedback voltage).

3. The mechanical connection may be too tight, such as the guide rail plate or the oil cylinder being too tight.

4. The filling valve is closed and cannot be opened, which prevents oil from being sucked in.

5. Grating scale problem.

6. Whether the foot switch is intact, check the wiring.

7. After the slow descent valve receives power, the filling valve is closed, and oil cannot be sucked into the upper chamber.

6. The dwell time at the ram speed conversion point is too long.

1. There may be air sucked into the upper chamber of the oil cylinder, resulting in a long time for pressure to build up (leakage in the self-priming pipeline).

2. The flow rate of the filling valve or the self-priming pipeline may be too small, or the rapid descent speed of the ram is too fast, causing vacuum suction.

3. The filling valve is not completely closed, so the upper chamber pressure drops slowly.

4. After the slow descent valve receives power, the filling valve is closed, and oil cannot be sucked into the upper chamber.

5. The improper mid-position of the proportional valve causes different openings and asynchronous movement.

6. Try reducing the rapid descent speed to see if there is any pause.

7. The size of the rapid descent pressure has an effect on the closing of the filling valve. Exclude the rapid descent pressure.

8. Adjustment of the pressure parameter during the delay stage before working feed.

9. The damping hole in the control circuit of the filling valve may be too small, resulting in a pressure difference.

10. CNC system parameters (delay before slow descent).

11. CNC system parameters (reduction of gain parameter before slow descent).

7. The ram has no slow descent action.

1. Whether there is an electrical signal in the electromagnetic proportional reversing valve or whether the spool is not moving or stuck.

2. The system cannot build up pressure.

3. The filling valve may be stuck, or the sealing ring of the filling valve may be leaking.

4. Whether there is an electrical signal in the slow descent valve or whether it is stuck.

5. The back pressure may be too high, or the slow descent pressure may be too low.

8. The ram vibrates, oscillates, or makes noise during slow descent.

1. The pressure oil discharged from the cylinder contains bubbles.

2. The friction force of the ram guide rail is too large or there is no lubricating oil.

3. The gap between the mating surfaces of the guide rail plates is too large or uneven.

4. The frame or worktable may not be adjusted horizontally.

5. The balance valve may be blocked.

6. Check whether the rapid descent valve is energized and opened.

7. CNC system parameters (gain) or setting the working feed speed too high.

8. The back pressure valve may be loose, resulting in different resistance on both sides.

9. Whether the electromagnetic proportional valve coil has any bias, and whether the mid-position signal of the proportional valve is correct.

10. Whether the signal of the proportional servo valve is interfered with. Check the same way as above.

11. The sealing ring of the cylinder may hold the piston rod tightly, resulting in large resistance (try using PTFE hard seal rings).

12. The spherical washer on the grating scale is not installed, and the ram movement is not smooth. There may also be a problem with the communication line of the grating scale.

13. The pressure curve is incorrect, and the pressure is insufficient during working feed.

14. The pressure sealing O-ring of the filling valve produces a small amount of leakage.

9. Large synchronous deviation during slow descent.

1. Synchronous detection system failure (grating scale).

2. Proportional directional reversing valve.

3. Leakage of the rapid descent valve.

4. Large back pressure difference between both sides.

5. The oil temperature is too low.

6. Oil leakage between the upper and lower chambers of the cylinder.

7. CNC system parameters.

10. The ram oscillates or shakes when holding pressure at the bottom dead center during slow descent.

1. There may be a problem with the grating scale.

2. The pressure oil discharged from the cylinder contains bubbles.

3. The balance valve may be blocked.

4. CNC system parameters (gain).

5. Back pressure valve problems, with different resistance on both sides.

6. Problems with the electromagnetic proportional valve: the mid-position may not be correct.

7. The bolts that secure the oil cylinder may be loose, causing shaking at the bottom dead center, uneven height, inaccurate bending angles, and noise during bending.

11. The ram has no return action or the return is very slow.

1. Whether there is any reversing action in the electromagnetic proportional reversing valve and whether it is damaged.

2. Whether the system has built up pressure or the return pressure is too low.

3. One of the filling valves may be stuck or not completely opened.

4. After the slow descent valve receives power, closing the filling valve will prevent rapid return.

5. CNC system: the programming angle may be too small, unable to reach the bottom dead center of the bending programming.

6. Adjustment of CNC system parameters.

7. Grating scale damage or cable problems.

8. Check whether the system pressure is building slowly.

12. The ram vibrates or shakes during the return

1. The return pressure may be too high or too low.

2. System parameters or PLC and DM02 modules.

3. Whether the coil of the proportional valve has any deviation.

13. The ram moves down (to the top dead center).

1. Adjustment of back pressure valve.

2. Leakage of back pressure valve or rapid descent valve.

3. Oil leakage between the upper and lower chambers of the cylinder.

4. Proportional valve deviation.

5. The supporting stability performance of the sealing ring is not enough, and when it deforms, the ram moves down.

6. To determine the cause of the downward movement, remove the proportional valve and observe whether oil comes out of the oil outlet at the lower chamber.

14. Large bending angle error.

1. Check whether the compensation cylinder has a large deflection and cannot completely return to the zero position.

2. Check whether the quick clamp wedge is loose.

3. Check whether there is any change in the bottom dead center during each bending.

4. Check whether the installation of the crowning unit is standard, whether the screw holes are flush.

5. Changes in the plate itself (thickness, material, stress).

6. Whether the grating scale is loose.

7. Inaccurate positioning accuracy: whether the zero offset value of the proportional valve is appropriate, and whether it can reach the bottom dead center for positioning, which prevents the return.

15. Large bending straightness error.

1. Check whether the compensation cylinder has an appropriate deflection to compensate.

2. Check whether the quick clamp wedge is loose.

3. Check whether the horizontal and vertical mold fitting surfaces on the ram are deformed.

4. Check whether the upper and lower molds are deformed.

5. Changes in the plate itself (thickness, material, stress).

6. Check whether the lower worktable (neutral plate) is deformed.

16. Hydraulic oil leak or hydraulic hose rupture.

1. Check whether the hydraulic hose installation meets the requirements (extension length, pipe diameter, wall thickness, clamping sleeve, nut over-tightening or loose, bending radius, etc.).

2. Check whether the hydraulic hose has any impact or vibration.

3. Check whether the pipeline interferes with other objects and collides with them.

4. The pipeline may not have a pipe clamp for fixation.

17. Precautions for installation and maintenance of hydraulic systems:

1. The paint-sealed valves must not be disassembled or adjusted by themselves.

2. After the valve is cleaned and works normally, new oil must be replaced immediately and the oil tank should be cleaned.

3. The oil pump must not be subjected to any hitting or impact during installation, and it must be pre-filled with oil before the oil pump is tested.

4. When installing each valve, only its valve body can be moved, and it must not touch any solenoid valve.

18. Common analysis of faults in rear material stop.

1. The rear material stop cannot move:

Check if the driver has an alarm

Check the limit switches of each axis

Check the reliability of connectors

2. Driver alarm

3. X and R-axis operation is unstable with shaking

4. Changes in positioning accuracy:

Mechanical problems (check for looseness or impact)

Electrical issues (one-way positioning, parameter adjustments)

Check if the clamping wheel or screw connecting nut is loose.

5. Overload alarm: check if the ball screw can rotate smoothly, possible damage to steel balls.

6. R-axis driver alarm 16 → bad gas spring

7. Z1, Z2 axis alarm 22 → replace the encoder cable

8. Alarm 38 → loose connection in the wiring

9. Servo motor makes noise: gain settings too high.

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