Table of Contents

During the operation of the press brake, you will encounter various bending problems. And each of the problems may be caused by different reasons. In this article, we will analyze 56 press brake bending problems that you may have.

We not only put forward the causes but also solutions to help you troubleshoot.

Press Brake Troubleshooting

The main motor of the press brake cannot be started

The main motor of the press brake cannot be started

Causes:

  • The start circuit of main motor failure, such as: not release emergency stop button, cable wiring loose, 24V control power;
  • The relevant components of the main motor’s start part failure, such as thermal relays, circuit breakers, overload protection or damage of AC contactors;
  • Power problems;

Solutions:

  • Check whether the emergency stop the main motor’s start the circuit is not released, loose wiring, 24V control power;
  • Check whether the components of the main motor’s starting circuit part of are overload protection, if yes, then analyze the reasons, check whether the components damaged;
  • Check whether the three-phase power is normal;

 

The press brake ram cannot be quickly down

press brake ram cannot be quickly down

Causes:

  • The ram rail tuning too tight;
  • Backgauge axis is not in place;
  • The ram is not at the top dead center position;
  • Footswitch signals did not enter the module;
  • The malfunction of the proportional servo valve;

Solutions:

  • Check whether the ram rail is appropriate;
  • Check whether there is a cursor of the X-axis actual position on the controller, or to check whether the backgauge programming value and the actual value is consistent in the manual interface;
  • The Y-axis state should be “1” on the controller, if it is “6”, check the actual coordinates of the Y axis, the value should be less than the difference between the Y-axis and return;
  • According to electrical schematics, check whether the input signals of the foot switch are normal;
  • Check whether the proportional servo valve feedback is normal;

 

The press brake ram cannot bend or bend speed is very slow

Causes:

  • The ram is not at the speed conversion point;
  • The set of the parameters of Y-axis bending is not good;
  • The pressure is not enough, such as programming, machine tool parameter settings, hydraulic;

Solutions:

  • Check whether the Y-axis state from “2” to “3”, Y-axis actual value should be greater than the speed conversion point value, if not need to adjust the parameters of the fast forward part;
  • Re-adjust part of the parameters the Y-axis bending;
  • Check whether the programming operation is not right, or parameter settings are wrong, or hydraulic problems; can use pressure gauge, multimeter to detect the main pressure and proportional pressure valve signal, and then check whether the proportional pressure valve, the main valve is stuck and then check the filter and oil, and finally check the pump and its coupling;

 

The ram can not return during the bending process

Causes:

  • Cannot return without load, maybe the parameter’s problem or hydraulic failure;
  • Can not return during bending, the workpiece angle does not meet the set value;
  • Can not return during bending, the workpiece angle has exceeded the set value;

Solutions:

  • Debugging the parameters of Y-axis, bending parameters should be based on actual debugging, part of the gain is too small, the ram cannot bend or not bend well, too much ram will shake, the parameters should be adjusted during the action the ram do not shake or a little bit more of the gain. Or the bias settings of the left and right valve are not good in diagnostic procedures. If too small Y-axis cannot be in place, if too large Y-axis cannot unload; If it is the hydraulic failure, need to check the main pressure, check whether the PV valve S5 has been in the power position;
  • Probably the gain set of Y-axis parameter is too small, can increase properly, or pressure is not enough, analyze the reason why the pressure is not enough. It is because of the program or signal, hydraulics; programming reasons include mold selection, plate thickness, materials, workpiece length, bending method, etc.; hydraulic reasons include: hydraulic pump leakage, the proportional pressure valve is contaminated or damaged, the filter is blocked, whether the oil has been polluted;
  • Mainly the programming and operating reasons, check the program and the workpiece;

 

The ram moving is not good

Causes:

  • The tightness of the ram rail is not appropriate;
  • Ram lock nut loose;
  • Machine parameters need to be adjusted;
  • The gain, zero points on the amplifier of proportional servo valve need to adjust;
  • The back pressure valve pressure is not correct or the two sides are the imbalance. Back pressure setting is too small, the ram will slowly decline, and will shake during working process; two sides back pressure is imbalance, the ram will twist during running;

Solutions:

  • Re-adjust the guide clearance;
  • Re-locking, if the lock nut and screw are too loose, need to be replaced;
  • If there is a reference curve, should be adjusted according to the reference curve;
  • Only BOSCH, REXROTH valve can be adjustable, but need to be cautious;
  • Use pressure gauges to adjust the pressure of the back pressure valve, and make the two sides consistent;

 

The main motor automatically stops, heat relay, circuit breaker protection

Causes:

  • The proportional pressure valve, the main valve was stuck, the machine has been in the state of pressure-adding;
  • Filter plug blocked, the oil movement is not smooth, the pump pressure has been high;
  • The use of oil for too long has been contaminated;
  • Ooor oil quality;
  • Circuit breakers, thermal succession problems, fail to reach the rated current;
  • The failure of pressure output controlled by the system, and send the wrong signal, so that the proportional pressure valve worked all the time;

Solutions:

  • Cleaning the proportional pressure valve, the main valve;
  • Replace the filter and check the pollution degree of the oil;
  • I3, immediately replace the oil filter;
  • Replaced with the recommended oil;
  • Replace the circuit breaker, overheat switch;
  • Check the system output;

 

Hydraulic valve is stuck

Hydraulic valve is stuck

Causes:

  • The use of oil for too long has been contaminated;
  • Poor quality of oil;
  • The rubber skin at the mouth of the oil tank aging;

Solutions:

  • Replace oil on time;
  • Replace the recommended oil;
  • Replace oil-resistant rubber sheet;

 

Press brake cylinder decline

Press brake cylinder decline

Causes:

  • Back pressure valve, the lift valve is dirty or damaged;
  • Back pressure is small;
  • Glyd lap strain, wear;
  • Cylinder inner wall damaged;
  • If the ram stopped at any position and slowly decline, if 5 minutes down less than 0.50mm, then it’s normal, this phenomenon is mainly caused by hydraulic oil characteristics;

Solutions:

  • Cleaning back pressure valve, lift the valve, if damage replaced;
  • Re-adjust the pressure on the back pressure valve according to the standard;
  • Replace the Glyd ring, and check the strain and wear causes of Gglyd ring,;
  • Generally due to oil pollution, replace the cylinder, sealing ring;
  • No need to deal with;

When pressing the die of the press brake, the height on both sides is inconsistent

Press Brake Crowing

Causes:

  • Back pressure on both sides is inconsistent, back pressure setting may be high;

Solutions:

  • Adjust the back pressure to the specified value, to maintain consistency;

 

The ram is waiting too long at the speed transition point

Causes:

  • The tank suction port leak;
  • Filling valve failure, such as the poor installation leads to the stuck of the valve core, or spring tension is not enough;
  • The set of Y-axis parameters is not good;

Solutions:

  • Check the sealing of the rubber sheet, re-install the cover here;
  • Check the filling valve installation, check the running of the valve core, check the spring tension;
  • Adjust the Y axis parameters;

 

The length and bending angles of the workpiece changes too much

Causes:

  • Machine inertia parameter setting is not appropriate;
  • sheet material;

Solutions:

  • Re-adjust the machine inertia parameters;
  • Check the sheet material;

 

When the workpiece has a multi-way bend, the size of cumulative error has too large errors

Causes:

  • The workpiece has too much bending steps, resulting in a large accumulation error;
  • Unreasonable bending order;

Solutions:

  • Fine adjust the accuracy of each bend so that the angle as far as possible in the negative difference, the size as accurate as possible;
  • Adjust the bending sequence if possible;

 

The automatically calculated pressure from the press brake controller is greater than the die impedance

Causes:

  • The selection of lower die during programming mode is unreasonable;
  • The set of mold impedance is not correct;
  • The programming bending method is chosen wrong;
  • The machine constant parameters are modified, such as material parameters, unit selection;

Solutions:

  • Should select the press brake toolings according to the relationship between the plate thickness and V slot width of lower die;
  • The correct set of mold impedance;
  • Check the program;
  • Check the machine tool constant parameters;

 

When programming large circular arc bending, the system is calculated to be slow or dead

Causes:

  • The programmed value of the X value exceeds the maximum value of the X-axis in the parameter;

Solutions:

  • Check the program;

 

The press brake hydraulic oil temperature is too high

Causes:

  • Hydraulic failure, such as the filter is blocked, oil pollution, deterioration, etc;
  • Long hours work under high pressure;

Solutions:

  • Check the filter, oil, if necessary, replacement;
  • Check the reasons for long hours of high-pressure work, is the actual needs, or other reasons;

 

The angles of the fabricated workpiece are not accurate

Fig. 6 Long parts bending and crowning

Causes:

  • If the error is very large, it may be programming error, ram connection loosening, grating ruler failure;
  • if small error, you can correct the parameters in the controller, after the amendment can work stably, then is it normal;
  • Unstable angle, often change, may be caused by the ram loose, grating ruler failure, metal materials;

Solutions:

  • Check the running procedures, focusing on inspection whether the mold, material, thickness, the length of the workpiece, bending mode in the procedures is consistent with the actual operation; whether ram connection is loose, the grating connection is firm;
  • The small error may be caused by a variety of reasons, such as the thickness of the programmed material and the actual use of the thickness has a little difference; material uniformity, mold wear, and operation reasons;
  • Check the Y-axis re-positioning accuracy, check whether the ram connection, the grating connection is normal, if normal, it is likely caused by the plate materials;

 

The fabricated workpiece size is not accurate

Causes:

  • The size of instability, often change, may be caused by the press brake machine power supply, servo drive, servo motor encoder and related cables, systems, screw mechanical connection, timing belt (wheel) factors;
  • The size of the deviation, but stable, and most caused by the parallelism, straightness of backgauge beam, and parallelism, vertical degree of the back stopper;
  • When positioning by the bending edge, if the bend angle is greater than 90 degrees, resulting in small positioning distance;

Solutions:

  • Check the backgauge axis repeat positioning accuracy, generally, less than 0.02mm, if differentiate too much, need to check the possible factors, if caused by the servo drive, servo motor encoder, controller, best to deal with by the press brake manufacturer;
  • First, check the parallelism and straightness of the beam, and then check the parallelism, vertical degree of the back stopper;
  • If positioning by the bending edge, try to make this bend not greater than 90 degrees;

The workpiece deforms at the bending position after bending

Causes:

The reason for deformation is mainly because of fast bending speed while the hand did not keep up with the bending deformation of the workpiece.

Solutions:

Reduce bending speed. The hands move simultaneously with the workpiece.

 

The bending angle of the long workpiece is not consistent

Causes:

  • The Material thickness is not consistent, one end is thick and the other end is thin.
  • The height of the punch is inconsistent. One end is higher than the other one.
  • The middle block is not at the same level.

Solutions:

  • Give feedback to the laser cutting dept. and make sure attentions are paid to materials selection.
  • Replace press brake punch.
  • Adjust the middle block.

 

Sometimes the workpiece will be deformed during Z-bending

Causes:

During the bending process, the rear end of the workpiece moves up in the curve and hit against the back finger and then get stuck. After the bending, it will be deformed.

Solutions:

Adopt the rear-pulling function of the back stopper.

 

The edge of the square hole in the middle of the sheet metal is very close to the bending line which makes the workpiece can’t be bent completely.

Causes:

The size from the edge of the workpiece to the bending line is smaller than half of the V-opening of the die, which makes it not possible to be bent.

Solutions:

  • Grind the material to the bending line.
  • Press the bending line first and then bend it.

 

There is the hole on the workpiece and it is very close to the bending line. The hole will be deformed if bend directly.

Solutions:

  • Press the line first and then bend.
  • Cut out one line at the bending position with laser cutter so as to avoid material pulling.
  • If the production is in the small batch and also need good finishing, the laser cutting machine should be used for hole making and then bending. At last, do the whole expansion process.

The small bending size makes it hard for positioning and the punch is easily press the back finger

Causes:

The bending size is in the range of the distance from the centerline of the V-opening of the die to the edge of the workpiece, which makes in unable to do positioning if install the die normally. If install it in reverse, the punch will press the back finger.

Solutions:

  • Install the die in reverse. Add one gasket in front of the back stopper to make the back stopper retreat to avoid the punch.
  • If the size of the other end is correct, the positioning can also be done there. Remember to install the die in reverse.

 

The bending flange is not straight and the size is unstable

Causes:

  • Press line and pre-bending are not been considered during the design process.
  • The press force is not enough
  • The angular wear of convex and concave die is asymmetrical or the bending force is uneven
  • Height is too small

Solutions:

  • Design press line or pre-bending process
  • Increase press force
  • Even clearance of the convex and concave die, round angle polishing
  • The height must not be less than the minimum limit size

 

External surface abrasion of the workpiece after bending

Causes:

  • The surface of the material is not smooth
  • The bending radius of the punch is too small
  • Bending clearance is too small

Solutions:

  • Improve the smoothness of convex and concave dies
  • Increase the bending radius of the punch
  • Adjust bending clearance

There are cracks in the bending angle

crack at the bending section

Causes:

  • The bending radius is too small
  • The material grain is parallel to the bending line
  • One side of the burr of the work blank facing outside
  • Poor metal plasticity

Solutions:

  • Increase the bending radius of the punch
  • Change the blanking arrangement
  • The burrs were changed to round corners in the parts
  • Annealing or use soft materials

Bending causes hole deformation

Causes:

When bending with elastic pressure and positioning with holes, the outside of the elbow is pulled due to friction between the concave die surface and the outside surface of the parts, resulting in deformation of the positioning hole.

Solutions:

  • Adopt shape bending
  • Increase the pressure of ejector plate
  • Add some hard spot or grain of the ejector plate in order to increase the friction force to prevent the parts from sliding during bending.

The curved surface is been squeezed thinner

Causes:

  • The round angle of the concave die is too small
  • The gap between the convex and concave dies is too small

Solutions:

  • Increase the radius of the concave die
  • Correct the gap between convex and concave dies

The end face of the workpiece is bulging or uneven

Causes:

When bending, the outer surface of the material is pulled in the circular direction to produce contraction deformation, and the inner surface is pressed in the circular direction to produce elongation deformation, so the flexural end surface is bulging along the bending direction.

Solutions:

  • The punch shall be under sufficient pressure in the final stage of stamping
  • Make the concave die radius corresponding to the outside corner of the parts
  • Additional process improvement

The bottom of the concave piece is uneven

Causes:

The material itself is uneven

The contact area between the top plate and material is small or the material ejection force is insufficient

No need for the ejection device in the concave die

Solutions:

  • Leveling materials
  • Adjust the ejection device to increase ejector force
  • Add ejector device or calibration
  • Add reshaping procedure

Axis dislocation of two holes opposed to each other after bending

Causes:

The material bounces back and changes the bending angle so that the center line is misaligned.

Solutions:

  • Add calibration procedure
  • Improve bending die structure to reduce material resilience

The precision of the hole position cannot be guaranteed after bending

Causes:

  • The expansion size of the parts is wrong
  • The material spring back
  • Positioning instability

Solutions:

  • Calculate the blank size accurately
  • Add calibration procedure or improve bending die forming structure
  • Change technique methods or add technique positioning process

The curved line is not parallel to the center of the two holes

Causes:

When the bending height is less than the minimum bending limit height, the bending part will expand.

Solutions:

  • Increase the height of the bending parts
  • Improve the bending technique

The bent part has a bow deflection in the width direction

Causes:

Torsion and deflection are produced because of the inconsistency of the drawing depth and shrinkage in the width direction of the component.

Solutions:

  • Increase bending pressure
  • Add calibration procedure
  • Ensure that the material grain direction and bending direction have a certain angle

The parts with cut notch bend down

Causes:

The cut notch opens the two straight edges to the left and right, causing a deflection at the bottom of the piece.

Solutions:

  • Improve component structure
  • The amount of technological bend allowance is increased at the incision to make the incision connected and then cut off after bending

The workpiece deformed after bending

Causes:

The deformation is mainly due to the speed of the bending machine, and the hand did not keep up with the speed of the machine.

Solutions:

Reduce the speed of the bending machine, the hand-held workpiece has the same speed as the operation of the machine.

For the longer workpiece, there will be a big angle and a small one at two ends

Causes:

  • Material thickness is inconsistent, one end thick one end thin.
  • Mold wear uneven, different height at both ends.
  • The middle block is not balanced, not at the same level.

Solutions:

  • Feedback to the laser or NCT, let it pay attention to the material selection.
  • Change the punch die
  • Adjust the middle block.

When bending Z shape by CNC bending machine, some parts will be deformed

Causes:

This is mainly due to the workpiece bending up movement, hit the back stopper and was squeezed which lead to the deformation.

Solutions:

Pull-back the back gauge.

Bending size is small, bad positioning, the mold is easy to press the back gauge

Causes:

The bottom die cannot be positioned during the distance from the V center line to the edge of the die.

Solutions:

Install the mold in another way around. Add one gasket (no more than 3t) before the back gauge, so that the back gauge can avoid the upper mold.

If the other end size ≧ 3 can also make the other end stay and install the lower mold in another way around.

A too large gap between ram and guide rail, make an abnormal sound.

Causes:

This type of malfunction is due to the long use of rails, increased gap caused by wear.

Solutions:

It is necessary to check the degree of wear of the guide plate, to determine whether to replace the rail plate depending on the degree of wear, re-adjust the gap to meet the requirements.

Transmission failure of the back gauge.

Transmission failure of the back gauge

Causes:

The back-gauge transmission fails because the drive shaft is disengaged from the timing belt of the timing pulley or the belt is slipping.

Solutions:

This malfunction requires reassembling the chain and timing belt, then check the electrical section.

Parallel misalignment too much between the cross-beam guide rail of back gauge and the mold center line.

Solutions:

Such failure needs to release the “X” axis synchronous belt, re-adjust to the parallelism tolerance range, reinstall the synchronous belt.

Cylinder and ram connection loosening, causing bending angle not accurate or the machine cannot find the reference point.

Solutions:

This type of fault requires re-checking the tightened ram and the cylinder connection nut.

The hydraulic system without pressure.

Solutions:

  • Check whether the proportional relief valve solenoid coil is power on. If the electromagnetic coil voltage meets the requirements. For the above reasons, please check the relevant electrical parts.
  • Check whether the cartridge valve is stuck or the main spool is stuck as well as damp hole clogging. If this is the reason, please remove the relief valve and clean it.
  • three-phase power phase modulation, resulting in motor reversal.

Ram speed turns to slow from fast, pause too long.

Solutions:

  • Check whether the tank oil surface is too low, the filling mouth was not flooded. When fast forward the cylinder chamber filled with liquid and air which leads to the insufficient filling. For the above reasons, the tank oil can be added to the filling tank 5mm above the filling mouth until it been completely flooded.
  • Check whether fast forward speed is too fast, causing insufficient filling. For the reasons described above, you can reduce the fast forward speed by modifying the system parameters.
  • Check whether the filling valve is completely open if it is because of oil pollution so that the valve spool activity is not flexible and stuck issue lead to insufficient oil filling. Need to clean the filling valve and re-install it, make the spool flexible.

Ram returns normal, fast forward normal, manual cannot slow down, bending weak.

Solutions:

  • Check whether the reversing valve, which controls the oil circuit, is working properly. If so, it causes the filling valve is not closed, so that the upper chamber and the tank filling port connected, cannot build pressure. The reason why the valve does not work properly is that it is not energized or stuck.
  • Check whether the filling valve is stuck, if so, please clean the filling valve, reinstalled, so that the spool flexible.

The ram return speed is too slow.

Causes:

The malfunction like high return pressure is mainly because the filling valve is not open. This phenomenon is just contrary to the logical of above malfunction 3.

Solutions:

This can be handled by referring to the solution of the malfunction 3.

After starting the pump of CNC bending machine, low voltage disconnect switch.

Solutions:

The following checks are required for such failures:

  • Check the lack of power supply phenomenon.
  • Check whether the high-pressure filter blockage, resulting in pump motor current is too large.
  • Check whether the low-voltage switch is set too small.

After start the CNC press brakes, the reference point cannot be found during the return.

Solutions:

  • Due to the reading head connection parts of grating ruler get loose, cause the reading head cannot coincide with the reference point of the grating ruler in return stroke. At this time, the cylinder has run out of the stroke, the pump is working in the overload state. If this is the case, you need to press the red stop button of the CNC system, stop the reference point, reconnect the connector to correct the grating ruler, and then enter the manual mode, manually let the ram down, make the ram re-enter the manual or semi-automatic mode when coincide with lower die. Again, back to the reference point and remedy of the trouble.
  • After the last operation of the press brakes, because the operator did not shut down the press brake machine strictly in accordance with the operation rule – Before power off the CNC press brakes, the ram stops at the top dead center position, and in the next boot, the ram is not manually down, place at the overlap position of upper and lower mold, and carry out the reference point operation, causing the operation cannot find the reference point. If this is the case, you need to switch the system to manual mode, manual mode will adjust the ram down to the overlap position of the upper and lower mold, and then enter the semi-automatic or automatic mode, re-find the reference point.

For DNC60 or DNC600 CNC bending machine, CNC system did not display, gray-white programming key indicator light flashing.

Causes:

This malfunction is mainly because the controller operator did not timely and effectively clear the original not used product program during the product programming operation, and directly modify the program of last product. After repeated several times causing the system filled with the buffer memory program which makes the system program cannot run properly.

Solutions:

First, disconnect the main motor power, press the “+ +” “- -” key on the keyboard at the same time, then turn the power on to make the system into the initial state.

Then, you will need to clear the project before you input: “1” indicates that the item is cleared, after entering the password “817”, press the enter key to confirm, the screen will prompt you “has been executed”. At this time, the required empty content has been completed.

“count is not accurate” of CNC bending machine grating ruler cause bending angle error.

Causes:

This kind of malfunction mainly reflects the cumulative increase of “Y1” “Y2” axis repositioning accuracy error increase the workpiece angle error after bending, and the angular error increases in the previous base. The main reason is the grating ruler feedback signal count leaks out of the pulse.

Solutions:

Need to remove the grating ruler, clean and prepare a good job of dust and vibration measures. Redesign and re-install it to the reasonable level for those irrational installations. For the damaged grating ruler, need to return to the manufacturer repair or replacement.

After the product is programmed, the safe distance alarmed for back gauge “X” axis and “R” axis.

Causes:

This type of malfunction is mainly because the setting of upper/lower mold safe distance as well as the X-axis R-axis limit position contradicts the programmed position. For the sake of safety, the system prompts the alarm and will not run, also can’t be operated.

Solutions:

You need to re-program the product or modify the product or modify the parameters of the mold to meet the requirements, that is, the alarm can be removed before the operation.

Back gauge X-axis and R-axis, an error occurs in the drive motor

Solutions:

This type of failure need to first open the CNC bending machine electric box, check the driver display alarm code, check out the cause of the alarm according to the prompt alarm code with reference of the user manual.

There are two common alarms:

16 # alarm, suggesting that the drive motor overload. We can check whether the transmission of X-axis Y-axis drive is flexible, resistance and whether the X-axis and R-axis have reached the mechanical limit. If so, to solve mechanical problems.

22 # alarm, suggesting that the encoder feedback signal alarm, maybe “joint” poor contact, unsoldering or disconnection and signal interference, etc., need to check one by one.

Y1, Y2 computer display location does not match the actual location.

Causes:

This type of failure is mainly due to changes in the original reference point of NC bending machine are not accurate.

Solutions:

To reinitialize the reference point.

X-axis R-axis controller positioning does not match the actual positioning.

Causes:

This type of malfunction is mainly because the position of X-axis and R-axis under power-off state has been changed. At this point, the computer still remembers the location before the shutdown, resulting in X-axis R-axis actual position changes.

Solutions:

The position of the X-axis R-axis needs to be reinitialized.

Y1 axis and Y2 axis position deviation exceed the allowed synchronization deviation distance, the ram cannot move up and down.

Causes:

This type of failure is mainly because before we shut down the press brake machine, the ram is not placed in the upper and lower mold contact position and power off, at this time due to the fall of punch, the real position at both ends of Y1, Y2 axis exceeds the limit. It is necessary to adjust the actual position of the Y1 axis Y2 axis at both ends. The controller should display the current value of the position. Then the press brakes can be operated normally.

Solutions:

Increase the data in the controller of CNC press brake machine for 5mm on the original basis, then enter into manual mode, manual down, the system will automatically correct the location and return to normal work.