Francis Pan is the Foreign Trade Manager of RAYMAX, with over 10 years of experience in sheet metal fabrication equipment and CNC machinery. He has worked closely with manufacturers worldwide on press brakes, fiber laser cutting machines, fiber laser welding machines, and practical production-oriented metal processing solutions.
Most common bending issues with press brakes are not caused by the machine’s inability to bend the material, but rather because the air bending process is highly susceptible to fluctuations in material properties, springback, ram penetration depth, repeatability of the back gauge, and crowning. This leads to problems such as angle inconsistency, length-wise angle inconsistency in long workpieces, dimensional drift, and cracking.
When encountering these issues, some operators instinctively resort to applying greater pressure, such as by selecting bottoming or coining. While this approach can indeed reduce springback and stabilize angles, it also brings challenges such as increased tonnage requirements, tooling damage, and surface defects.
Therefore, when encountering bending issues, adjustments should be made based on actual conditions. The correct approach is to first optimize the air bending parameters and, under specific conditions, then consider using bottoming or coining processes that offer higher forming strength.
30-second quick reference chart:
On-site issues
Most likely causes
Top priority inspection items
Continue optimizing air bending parameters or consider a process with higher forming strength
First piece angle is inaccurate
Incorrect setting of ram penetration depth or sheet thickness
Verify that the sheet thickness in the controller matches the actual sheet thickness
Continue optimizing air bending parameters
Excessive springback/angle opening
High material yield strength, improper V-die opening
Check the V-die opening width and angle compensation
Optimize air bending parameters first, then evaluate process upgrades if necessary
Uneven angles on the left and right sides of long parts
Machine table deformation, insufficient crowning
Check the crowning settings
Adjust the crowning value
Batch variation in flange dimensions
Unstable repeat positioning of the back gauge, slippage of workpieces
Check the clamping force of the back gauge fingers and the workpiece reference
Optimize air bending operations and back gauge maintenance
Cracking or whitening on the outer bend surface
Inner radius too small; bend line parallel to the grain direction
Check the V-die opening and the workpiece grain direction / rolling direction
Replace with a larger V-die and optimize air bending parameters
Surface indentations, adhesive galling, or scratches
Excessive tonnage; dirty tooling; rough lower die edges; improper method for flipping workpieces
Check the surface finish of the upper punch and lower die working surfaces and the V-die opening width
Optimize air bending parameters
Deformed hole positions
Hole edge too close to the bend line
Measure the distance from the hole edge to the bend line
Must be addressed during the process or design phase
Bend lines are not straight
Unstable workpiece positioning; insufficient support for long workpieces
Check the workpiece positioning reference and support status
Optimize air bending operations and support methods
Who is this article for?
Shop floor supervisors: Quickly identify the causes of batch production issues and reduce scrap rates.
Process engineers: Optimize bending processes and improve workpiece forming efficiency.
Press brake operators: Master troubleshooting methods for common issues to reduce trial bends and scrap.
Factory managers purchasing press brakes: Gain insight into the equipment’s true capabilities to make more informed investment decisions.
Why Air Bending Is More Sensitive
What is air bending?
The core principle of air bending is three-point contact, meaning the sheet metal comes into contact only with the tip of the upper punch and the shoulder areas on either side of the V-die opening. Therefore, the bending angle in air bending is primarily controlled by the ram penetration depth of the upper punch. When using the same set of tools, different bending angles can be achieved by adjusting the ram penetration depth. This provides high flexibility, significantly reducing tool change time and tool costs, making it the most commonly used bending method in modern sheet metal workshops.
However, because the material does not make full contact with the tool, springback is more difficult to control. Consequently, modern CNC press brakes often rely on angle compensation, crowning, and a material database to address issues of angle consistency.
Schematic diagram of three-point contact in air bending
Why is air bending more susceptible to springback and material variations?
Because air bending does not fully press the sheet into the bottom of the lower die, it is highly dependent on the material’s condition. Variations in material strength, sheet thickness, batch differences, springback variations, and inconsistent stress distribution between the center and ends of long workpieces, all these factors ultimately affect the consistency of the bending angle.
What is coining, and why is it more stable?
The principle of coining is to use powerful pressure to force the material completely into the lower die via the upper punch, causing plastic deformation. This minimizes material springback, resulting in more stable bending angles.
Why coining cannot be considered a universal solution
First, coining requires immense pressure, which means it demands very high tonnage, typically significantly higher than air bending, depending on the material, sheet thickness, V-die opening, target angle, and tooling geometry. Blindly using coining may exceed the load-bearing capacity of the equipment and tooling, leading to severe damage.
Second, under extreme pressure, tooling wear accelerates, significantly shortening the tooling’s service life.
Finally, high pressure increases the risk of indentations on the workpiece surface, which is unacceptable, especially for appearance-critical parts.
Therefore, not all bending angle issues require blindly increasing pressure; instead, one should first optimize air bending parameters based on actual conditions before considering processes that require higher forming forces. Related technical reading: Air Bending vs Bottom Bending vs Coining
Find the Cause Before Adjusting the Program
Material issues
Material issues primarily manifest as: batch-to-batch variations, improper grain direction, and surface condition effects.
Materials from different batches may exhibit slight variations in sheet thickness and yield strength, leading to inconsistent springback. If you continue to use the program and compensation parameters from the previous batch after switching to a new batch, this can easily cause angle inconsistency;
If the bending line is parallel to the sheet’s grain direction or rolling direction, it can easily cause cracking on the outer edge of the material during bending;
Additionally, some materials have protective films or coatings on their surfaces, which typically affect the friction between the material and the tooling, thereby impacting springback, angle, and dimensions.
Tooling Issues
The tooling issues typically manifest in three areas: poor tooling surface condition, mismatch between the upper punch and lower dies, and improper selection of the V-die opening.
If the tooling surface is dirty or worn, it can easily cause indentations or scratches on the workpiece surface;
Mismatch between the upper punch and lower dies, such as misalignment of angles or centerlines,can directly alter the forming results;
Improper selection of the V-die opening, such as choosing a V-die opening that is too small,requires higher tonnage, which may increase the risk of material cracking.
Equipment issues
Equipment issues primarily include: ram synchronization errors, unstable back gauge repeatability, insufficient crowning, and instability in the clamping system.
If the synchronization between the left and right rams is inconsistent, it will result in angle inconsistency on the left and right sides of the workpieces;
Unstable back gauge repeatability will cause dimensional drift in flanges during batch production;
If the deflection compensation value is set too low after the worktable and rams deform under load, it will result in angle inconsistency along the entire length of long workpieces;
An unstable clamping system can cause the tooling to loosen, thereby affecting angular accuracy.
Operational and programming issues
Operational and programming issues primarily include: incorrect parameter settings, improper positioning references, and insufficient workpiece support.
Errors in material type or tooling parameter settings cause the system to calculate an incorrect ram penetration depth, resulting in inaccurate angles;
Incorrect workpiece positioning references cause slippage during bending, leading to dimensional drift;
If long workpieces lack support from a sheet follower during bending, their own weight causes sagging, resulting in unstable angles;
Recommended troubleshooting sequence
When the above issues occur on-site, it is recommended to follow this troubleshooting sequence:
First, observe the symptoms to determine whether the issue is related to angle or dimensions → Then analyze whether the problem lies with the material, tooling, equipment, or operator → First, check the variables that are quickest and easiest to adjust, such as the tooling, program parameters, operating techniques, and back gauge → Finally, assess the machine itself
10 Common Press Brake Bending Problems
Issue 1: Excessive springback, causing the bend to open
On-site observation: The bend angle is correct during the bending process, but as soon as the ram lifts, the bend opens.
Most common cause: High material strength leads to significant springback; this is common in stainless steel and high-strength steel.
Why this is more prone to occur during air bending: Air bending does not fully press the material into the lower die. Insufficient plastic deformation of the material means stresses are not fully released, making springback more likely.
Priority corrective actions: First, verify the material type and sheet thickness. Then, check whether the V-die, program compensation values, and ram penetration depth are correct. If necessary, evaluate whether a more suitable upper punch angle or punch tip radius is required for the bend. However, note that replacing the punch with a sharper-angled one should not be treated as a universal solution. Related technical reading: How To Reduce Springback In Press Brake Bending
When to consider higher-strength forming processes: When the product requires extremely strict angle consistency, springback must be controlled within a very narrow range, and equipment and tooling load capacity permit it, you may evaluate whether to adopt bottoming or other higher-strength forming processes.
Schematic diagram of springback angle change
Issue 2: Angle too large or too small; first piece is off-target
On-site observation: After the first-piece trial bend, the actual angle is found to be larger or smaller than the target angle.
Most common cause: Incorrect material properties or thickness entered into the system, resulting in an incorrect calculation of the Y-axis pressing depth.
Why this is more prone to occur during air bending: In air bending, the angle is controlled by the pressing depth; a deeper press results in a smaller angle.
Priority corrective actions: Measure the sheet thickness with a vernier caliper and update the system parameters; verify that the tooling dimensions called by the system match the actual installed tooling dimensions.
Issue 3: Angle inconsistency on the left, center, and right of long workpieces
On-site observation: After bending a workpiece longer than 3 meters, it was found that the angle at the center was greater than the angles at both ends.
Most common cause: When a long workpiece is subjected to force, the ram and worktable undergo elastic deformation. If there is insufficient crowning, the actual pressing depth along the entire bending length of the long workpiece will be inconsistent, resulting in angle inconsistency on the left, center, and right.
Why this is more prone to occur during air bending: Due to deflection in the center of the worktable, the actual ram depth is shallower than the target depth, resulting in a larger angle at the center of the long workpiece.
Priority corrective actions: If a crowning system is available, adjust the crowning value to lift the center of the worktable upward, offsetting the deformation.
The left, center and right angles of the long workpiece are inconsistent
Issue 4: Unstable flange dimensions and dimensional drift in batch production
On-site observation: During batch production, flange dimensions were found to be unstable, with variations observed in the first, tenth, and fiftieth parts.
Most common cause: Unstable back gauge repeatability; unstable workpiece positioning, causing slippage during bending.
Why this is more prone to occur during air bending: Flange dimensions are often affected by changes in angle. If the workpieces are not positioned accurately during bending, angular deviations will occur, thereby affecting the batch consistency of flange dimensions.
Priority corrective actions: Check whether the back gauge fingers are loose; ensure that operators apply consistent force when pushing the material; inspect the workpiece positioning edges for burrs or debris.
Issue 5: Surface indentations, dents, or adhesive galling
On-site observation: Two indentations appear on the outer side of the workpiece’s bend line.
Most common cause: Excessive contact pressure between the workpieces and the V-die opening edges, an overly narrow V-die opening, or rough or material-contaminated V-die opening edges can all cause noticeable indentations on the outer side of the bend line; if metal debris or material adheres to the tooling surface, it may further cause pressure marks or adhesive galling on the workpiece surface.
Why this is more prone to occur during air bending: In conventional V-die air bending, the sheet metal naturally comes into contact with the edges on both sides of the V-die opening, so the formation of slight die marks on the surface is a common occurrence; However, when the V-die opening is too small, contact pressure is excessive, the edges of the lower die’s V-die are too sharp or have burrs, or material is adhering to the die, these minor marks may develop into noticeable indentations, dents, or adhesive galling.
Priority corrective actions: First, check whether the edges of the V-die opening are smooth and free of burrs or material buildup, and reselect an appropriate V-die opening based on material thickness. For workpieces with high aesthetic requirements, consider using a lower die with smoother V-die edges, a soft protective layer, or non-marking tooling.
Indentation on workpiece surface
Issue 6: Scratches on brushed sheets, mirror-finished sheets, and film-coated sheets
On-site observation: Visible scratches appear on the workpiece surface.
Most common cause: Dirty tooling, debris on the edges of the V-die opening, or dragging and friction between the workpieces and the tooling, support surfaces, or surrounding components during flipping, movement, or when long workpieces sag can all lead to surface scratches.
Priority Corrective Actions: Clean the tooling surface; apply a polyurethane protective film to the lower die; install sheet followers to prevent long workpieces from sagging.
Issue 7: Workpiece slippage, shifting, and misalignment
On-site Observation: The workpiece moves during bending, resulting in an inaccurate bend line.
Most common cause: Asymmetrical workpiece, edges too narrow, or the back gauge failing to fully support the workpiece.
Why this is more prone to occur during air bending: During the initial press-down, insufficient contact between the workpieces and the tooling results in inadequate support force.
Priority corrective actions: If the workpiece edges are too narrow, do not immediately switch to a narrower V-die. Instead, first recalculate based on the minimum flange length, sheet thickness, material strength, and machine tonnage. If necessary, select a smaller V-die or specialized tooling, but avoid blindly choosing an excessively narrow V-die to prevent angle instability, increased tonnage requirements, and risks to the tooling and equipment.
Issue 8: Cracking, whitening, and fracturing on the outer side
On-site observation: Cracks appear on the outer side of the bend line, or the material may even break completely.
Most common cause: The inside radius is too small; the bend line is parallel to the grain direction.
Why this is more prone to occur during air bending: If the V-die opening is too small, the outer layer of the material is prone to excessive stretching when bending high-hardness materials.
Priority corrective actions: Select a larger V-die opening; replace the upper punch with one of larger radius; adjust the material layout direction so that the bend line is perpendicular to the material’s grain direction or rolling direction.
Issue 9: Too close to holes, hole deformation, or edge tearing
On-site observation: Round holes near the bend line become elliptical, or the edges are torn and bulge outward.
Most common cause: The hole is too close to the bend line.
Priority corrective actions: When a hole is too close to the bend line, this issue should typically be addressed during the design or process planning phase rather than attempting to resolve it by selecting a smaller V-die. Priority solutions include: increasing the distance from the hole edge to the bend line; adding relief or a notch near the bend line; adjusting the process sequence if necessary; or using a specialized lower die that provides better support for the area surrounding the hole.
Deformation caused by holes being too close to the bending line
Issue 10: Warping, arcing, or uneven bend lines on long workpieces
On-site observation: After bending, the ends of a long workpiece lift up, causing the workpiece to bend into an arc shape.
Most common cause: Sagging of the long workpiece and uneven force distribution between the left and right sides.
Priority corrective actions: Use a sheet follower to provide stable, synchronized support for the workpiece.
When to Optimize Air Bending，and When to Change the Process？
Situations where further optimizing air bending is more cost-effective
Situation 1: Your workshop’s production model focuses primarily on high-mix, low-volume production;
Reason: Air bending does not require frequent tool changes, offering high flexibility and production efficiency.
Situation 2: Your precision requirements are not very high; standard precision is sufficient;
Reason: High-end controllers combined with air bending can meet standard precision requirements.
Situation 3: You wish to extend the service life of the machine and tooling.
Reason: Air bending requires lower tonnage and does not cause significant damage to the machine or tooling.
Scenarios where higher-strength forming processes should be seriously considered
Situation 1: Your workshop primarily runs single-product, high-volume production;
Reason: High-volume batch production demands extremely strict angle consistency.
Situation 2: Angle consistency requirements are very strict, and the equipment and tooling can handle the load;
Reason: High-forming-force processes reduce springback and improve stability, but they require higher tonnage and carry greater risks of surface damage.
Situation 3: Your customers are not sensitive to surface indentations;
Reason: Processes with higher forming forces are more likely to cause surface indentations, making them more suitable for structural parts or workpieces with low aesthetic requirements.
Important considerations
When bending angles are inconsistent, we cannot simply assume that increasing the tonnage will solve the problem. In fact, many air bending issues stem primarily from material variations, insufficient crowning, and poor repeatability, and cannot be completely resolved by blindly increasing pressure.
What equipment capabilities should you consider to truly minimize these issues?
Ram synchronization capability
This primarily depends on whether the left and right Y1/Y2 axes can maintain synchronization under actual load; their synchronization capability directly determines the consistency of the left and right angles.
Backgauge repeatability
This primarily depends on whether the back gauge can reliably return to the same position after continuous, repeated back-and-forth movements; it directly determines the accuracy of the flange edge dimensions.
Crowning capability
This primarily depends on whether the crowning system can effectively compensate based on workpiece conditions, offsetting elastic deformation caused by applied forces, thereby ensuring angle consistency along the entire length of long workpieces.
Program compensation and material database
This primarily depends on whether the program can correctly access the material database, angle compensation, and ram penetration depth calculations based on the input sheet thickness and angle. This significantly reduces the number of manual trial bends required.
clamping and tool change efficiency
This primarily assesses whether the clamping system can perform tool changes quickly and securely hold the tooling in place. It enhances production efficiency and ensures repeatability of tooling positioning, which is particularly important for high-mix, low-volume production.
Support solutions for long workpieces
These solutions prevent dragging, deformation, and angle drift caused by the sagging of long workpieces under their own weight. For elevator panels, decorative panels, and exterior components, an excellent support system effectively ensures angle consistency and surface quality.
Angle detection and closed-loop control
This capability enables real-time angle correction when material thickness, springback, or surface conditions change, which is crucial for workpieces requiring high consistency.
Protecting the workpiece surface and minimizing indentations and scratches is crucial for high-precision exterior components such as brushed panels, mirror-finished panels, laminated panels, and painted parts.
8 Questions to Ask Before Buying a Press Brake
To avoid selecting the wrong equipment, we recommend asking suppliers the following 8 questions before making a purchase:
① Given the specified material, sheet thickness, length, and V-die opening, what bending accuracy can this machine consistently achieve?
Note: Be sure to clarify the test conditions; do not rely solely on a vague precision figure.
② When bending workpieces 3 meters or longer, how is the consistency of the left, center, and right angles verified?
Note: Focus on whether the supplier truly understands crowning, ram synchronization, and actual load measurement.
③ How is the back gauge repeatability measured? Is it based on a single positioning or repeatability after continuous back-and-forth movement?
Note: The stability of flange dimensions depends crucially on the back gauge repeatability, not on single-positioning accuracy.
④ When bending visible parts, how do you prevent indentations and scratches?
Note: Focus on whether the supplier offers scratch-free tooling, protective coatings, support systems, and anti-scratch solutions.
⑤ Do you have proven experience in springback control for high-strength steel, stainless steel, and aluminum?
Note: Focus on whether the supplier truly understands material strength differences, V-die selection methods, and springback compensation logic.
⑥ Is the machine equipped with a crowning system? What type of compensation method is used? How are setup parameters set and adjusted?
Note: Focus on whether the equipment has a proven solution for maintaining angle consistency along the entire length when bending long workpieces.
⑦ Does the controller support angle compensation? Does it include a built-in program database and material database?
Note: These features directly impact the number of trial bends required and changeover efficiency.
⑧ Can you provide recommendations on tooling, press tonnage, support, and processes based on my drawings and operating conditions?
Note: This best demonstrates whether the supplier possesses genuine engineering service capabilities.
Conclusion
The real challenge in bending lies not in whether the target shape can be achieved, but in whether it can be produced consistently in large batches over the long term while maintaining a low scrap rate and a minimal number of trial bends.
When bending issues arise, we must first determine whether the cause lies in the material, the tooling, the equipment, or the operator, and then optimize the air bending parameters based on the actual situation. We should not immediately resort to processes requiring higher forming forces.
When actually procuring equipment, the key is to evaluate the machine’s consistency rather than focusing solely on its tonnage and maximum bending length.
If you are struggling with issues such as angle inconsistency, variations in the left, center, and right sections of long workpieces, surface indentations, or dimensional drift in batches, please send us details regarding your material type, sheet thickness, bending length, target angle, and drawing or sample requirements. Raymax will provide you with a professional process optimization solution based on the actual characteristics of your workpieces.
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FAQ
Because air bending offers high flexibility, requires no frequent tool changes, and demands the lowest press brake tonnage. In air bending, the sheet metal forms a three-point contact with the tip of the upper punch and the edges on both sides of the V-die opening. The angle is controlled by ram penetration depth, allowing a single set of tools to produce a variety of different angles. This makes it ideal for workshops with high-mix, low-volume operations and frequent changeovers.
Generally speaking, yes. Because coining utilizes extremely high pressure to press the sheet metal into the lower die, causing thorough plastic deformation with minimal springback, it ensures stable and consistent angle accuracy. However, coining requires very high tonnage and is more likely to accelerate tooling wear and leave indentations on the workpiece surface; therefore, it is generally suitable only for a limited number of high-standard, high-volume parts.
This is because different batches of material may exhibit slight variations in thickness, yield strength, rolling direction/grain direction, and surface condition, leading to inconsistent springback. If you continue using the program and compensation parameters from the previous batch after switching to a new batch, the resulting angles will be inconsistent. Therefore, the initial program settings cannot be treated as fixed values for all batches of material. After switching batches, it is best to first perform a small-batch verification and then adjust the compensation values based on actual conditions.
This is caused by deflection deformation generated when the machine is under load. When bending long workpieces, the middle sections of the ram and the table undergo a certain degree of elastic deformation under high loads, causing the actual ram depth to be shallower than the target depth. This results in the angle at the center of the long workpiece being greater than that at the ends. It is necessary to use a crowning system to lift the middle section of the table upward to offset this deformation.
First, ensure the material is positioned accurately and the tooling is clamped securely; then apply program compensation; and only then should you consider processes that require higher forming strength. Specific steps typically include: verifying the actual material and thickness, adjusting the lower die V-opening and the inside radius, setting angle compensation in the program, and standardizing the material database and program parameters. If issues persist after these steps, then we should evaluate bottoming or coining solutions.
Surface indentations are typically caused by pressure and contact, while surface scratches are usually caused by friction and dragging. Surface indentations typically occur along the edges of the V-die opening, generally due to excessive contact pressure, overly sharp edges on the V-die opening, or the use of higher forming strength processes. Surface scratches, on the other hand, are typically caused by dirty tooling, incorrect sheet flipping methods, insufficient support for long workpieces, or dragging against the floor.
If you have replaced or cleaned the tooling but still encounter angle inconsistency during bending, inconsistency in angles along the entire length of long workpieces, or dimensional drift in batches under the same program, you should look for the cause in the equipment or clamping system. Typically, check the following: whether Y1/Y2 axes are synchronized, whether the back gauge’s repeat positioning is consistent, whether crowning is properly applied, and whether the tooling is securely clamped.
When certain issues persistently affect batch stability, changeover efficiency, and consistency in long workpieces, it is time to consider upgrading the equipment. Common issues include: dimensional drift during continuous batch production; inconsistency in the left, center, and right sections of long workpieces; significant variations in results between different operators; increased number of trial bends; high scrap rates for surface parts; and the lack of a crowning system, closed-loop angle detection, rapid clamping system, or a sheet follower on the existing machine. Relying on the experience of senior technicians can remedy one or two pieces, but it is impossible to maintain repeatable consistency during long-term batch production.
In press brake operations, efficiency and consistency matter—especially when tool changes are frequent, affecting the stability of…
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