CNC hydraulic press brake is mainly used for bending processing of workpieces. It is composed of a frame, slide, working table, hydraulic cylinder, hydraulic proportional servo system, position detection system, CNC system, and electrical system. The press brake can maintain the synchronization of the slide's position (parallel to the working table) at the conditions of idle speed, working speed, and return speed, and achieve high-precision positioning at the end of the stroke. Therefore, it is widely used in industries such as automotive, shipbuilding, containers, construction machinery, building structures, lamp posts, and power poles for component bending.
In the following, we will analyze the hydraulic system of the CNC hydraulic press brake, sort out the possible causes of faults such as no pressure during the working stroke, and introduce the working principle and troubleshooting of the filling valve.
1. Fault Description
When the CNC hydraulic press brake is in operation, under the control of the CNC system and hydraulic servo system, the slide completes one stroke through six stages: rapid descent, deceleration descent, material pressing and holding, pressure release, rapid ascent, and stop at the top dead center. For the convenience of analysis, this article combines the six stages into three stages: rapid advance, working stroke, and rapid return (retraction).
The fault phenomenon that occurs in the operation of the press brake is that the slide can descend rapidly, but there is obviously insufficient pressure when pressing the material, resulting in the inability to complete the bending operation.
2. Overview of the Hydraulic System
Hydraulic System Principle:
1 - Filling Valve 2 - Proportional Servo Valve 3 - Relief Valve 4 - Insert Valve 15 - Proportional Relief Valve 6 - Insert Valve 27 - Oil Filter 8 - Hydraulic Pump
(1) Rapid Descent (Rapid Advance) of the Slide
When 4Y5 (cross) and 4Y3 are energized, the oil in the lower chamber of the hydraulic cylinder quickly returns to the oil tank through the insert valve 1 and the proportional servo valve, losing the oil pressure required to support the slide. The self-weight of the slide drives the piston to descend rapidly, and a negative pressure is formed in the upper chamber of the hydraulic cylinder, "sucking open" the filling valve. A large amount of oil enters the upper chamber of the hydraulic cylinder through the filling valve from the oil tank, and the slide rapidly moves downward.
(2) Pressure Application during the Working Stroke
When the slide descends to the transition point, 4Y3 is de-energized, and the insert valve is closed, causing pressure to be generated in the lower chamber of the hydraulic cylinder through the relief valve, preventing the slide from freely falling. At this time, 1Y1 is energized, establishing system pressure for the proportional relief valve, and 1Y2 is energized, closing the filling valve. Oil enters the upper chamber of the hydraulic cylinder through the proportional servo valve, forcing the slide to move downward and completing the material pressing action.
(3) Rapid Return (Retraction) of the Slide
When 4Y3 is energized, insert valve 1 opens, and 4Y5 is energized (direct passage). At this time, the oil output by the oil pump enters the lower chamber of the hydraulic cylinder through the proportional servo valve and insert valve 1. Meanwhile, 1Y1 remains energized, and the proportional relief valve continues to establish pressure. At the same time, 1Y2 is de-energized, and the filling valve opens under the control of the oil pressure in the control oil circuit. The oil in the upper chamber of the hydraulic cylinder rapidly returns to the oil tank through the filling valve (in large quantities), and the slide completes the rapid return action.
3. Fault Analysis and Troubleshooting
Based on the fault phenomenon, analyzing the hydraulic system diagram reveals the following possible causes of the press brake's lack of pressure during the working stroke.
Possible Causes of the Fault:
1) The solenoid of the proportional relief valve in the pressure control valve group, 1Y1, is not energized, causing the proportional relief valve to function as an ordinary relief valve, unable to establish sufficient pressure in the system.
2) The taper hole of the insert valve 2 in the pressure control valve group is worn or the seal is damaged, causing the valve port to remain open, resulting in oil flowing through the insert valve directly back to the oil tank, resulting in no pressure in the system.
3) The filling valve cannot close properly, the spool is damaged, or the seal is ineffective. The upper chamber of the hydraulic cylinder is in communication with the oil tank through the cavity of the filling valve. During the working stroke of the press brake, oil directly returns to the oil tank from the upper chamber of the hydraulic cylinder through the filling valve, resulting in insufficient pressure.
Through a step-by-step troubleshooting process, the fault points are eliminated as follows.
Troubleshooting Steps:
1) Check if the solenoid of the proportional relief valve in the pressure control valve group is energized. Check the proportional relief valve while the press brake is in the working stroke state. If the indicator light of 1Y1 is on and the proportional relief valve functions normally, the fault of the proportional relief valve can be ruled out.
2) Check the insert valve 2 in the pressure control valve group. Disassemble the insert valve 2, check the wear of the taper hole, and clean the spool before reinstalling it. If the press brake still lacks pressure during the working stroke, the fault of the insert valve can be temporarily ruled out.
3) Check the control oil circuit solenoid directional valve of the filling valve. When the press brake is in the working stroke, the solenoid directional valve is in the closed state, and the command to close the filling valve is normal, indicating no abnormalities in the solenoid directional valve.
4) Check the filling valve. Disassemble the filling valve and find that the locking bolt at the end of the filling valve is loose and detached, the pilot spool is damaged, causing the pilot valve port to remain open, and the filling valve cannot close properly. At this point, the cause of the fault is discovered.
In the following, we will analyze the hydraulic system of the CNC hydraulic press brake, sort out the possible causes of faults such as no pressure during the working stroke, and introduce the working principle and troubleshooting of the filling valve.
1. Fault Description
When the CNC hydraulic press brake is in operation, under the control of the CNC system and hydraulic servo system, the slide completes one stroke through six stages: rapid descent, deceleration descent, material pressing and holding, pressure release, rapid ascent, and stop at the top dead center. For the convenience of analysis, this article combines the six stages into three stages: rapid advance, working stroke, and rapid return (retraction).
The fault phenomenon that occurs in the operation of the press brake is that the slide can descend rapidly, but there is obviously insufficient pressure when pressing the material, resulting in the inability to complete the bending operation.
2. Overview of the Hydraulic System
Hydraulic System Principle:
1 - Filling Valve 2 - Proportional Servo Valve 3 - Relief Valve 4 - Insert Valve 15 - Proportional Relief Valve 6 - Insert Valve 27 - Oil Filter 8 - Hydraulic Pump
(1) Rapid Descent (Rapid Advance) of the Slide
When 4Y5 (cross) and 4Y3 are energized, the oil in the lower chamber of the hydraulic cylinder quickly returns to the oil tank through the insert valve 1 and the proportional servo valve, losing the oil pressure required to support the slide. The self-weight of the slide drives the piston to descend rapidly, and a negative pressure is formed in the upper chamber of the hydraulic cylinder, "sucking open" the filling valve. A large amount of oil enters the upper chamber of the hydraulic cylinder through the filling valve from the oil tank, and the slide rapidly moves downward.
(2) Pressure Application during the Working Stroke
When the slide descends to the transition point, 4Y3 is de-energized, and the insert valve is closed, causing pressure to be generated in the lower chamber of the hydraulic cylinder through the relief valve, preventing the slide from freely falling. At this time, 1Y1 is energized, establishing system pressure for the proportional relief valve, and 1Y2 is energized, closing the filling valve. Oil enters the upper chamber of the hydraulic cylinder through the proportional servo valve, forcing the slide to move downward and completing the material pressing action.
(3) Rapid Return (Retraction) of the Slide
When 4Y3 is energized, insert valve 1 opens, and 4Y5 is energized (direct passage). At this time, the oil output by the oil pump enters the lower chamber of the hydraulic cylinder through the proportional servo valve and insert valve 1. Meanwhile, 1Y1 remains energized, and the proportional relief valve continues to establish pressure. At the same time, 1Y2 is de-energized, and the filling valve opens under the control of the oil pressure in the control oil circuit. The oil in the upper chamber of the hydraulic cylinder rapidly returns to the oil tank through the filling valve (in large quantities), and the slide completes the rapid return action.
3. Fault Analysis and Troubleshooting
Based on the fault phenomenon, analyzing the hydraulic system diagram reveals the following possible causes of the press brake's lack of pressure during the working stroke.
Possible Causes of the Fault:
1) The solenoid of the proportional relief valve in the pressure control valve group, 1Y1, is not energized, causing the proportional relief valve to function as an ordinary relief valve, unable to establish sufficient pressure in the system.
2) The taper hole of the insert valve 2 in the pressure control valve group is worn or the seal is damaged, causing the valve port to remain open, resulting in oil flowing through the insert valve directly back to the oil tank, resulting in no pressure in the system.
3) The filling valve cannot close properly, the spool is damaged, or the seal is ineffective. The upper chamber of the hydraulic cylinder is in communication with the oil tank through the cavity of the filling valve. During the working stroke of the press brake, oil directly returns to the oil tank from the upper chamber of the hydraulic cylinder through the filling valve, resulting in insufficient pressure.
Through a step-by-step troubleshooting process, the fault points are eliminated as follows.
Troubleshooting Steps:
1) Check if the solenoid of the proportional relief valve in the pressure control valve group is energized. Check the proportional relief valve while the press brake is in the working stroke state. If the indicator light of 1Y1 is on and the proportional relief valve functions normally, the fault of the proportional relief valve can be ruled out.
2) Check the insert valve 2 in the pressure control valve group. Disassemble the insert valve 2, check the wear of the taper hole, and clean the spool before reinstalling it. If the press brake still lacks pressure during the working stroke, the fault of the insert valve can be temporarily ruled out.
3) Check the control oil circuit solenoid directional valve of the filling valve. When the press brake is in the working stroke, the solenoid directional valve is in the closed state, and the command to close the filling valve is normal, indicating no abnormalities in the solenoid directional valve.
4) Check the filling valve. Disassemble the filling valve and find that the locking bolt at the end of the filling valve is loose and detached, the pilot spool is damaged, causing the pilot valve port to remain open, and the filling valve cannot close properly. At this point, the cause of the fault is discovered.
