How to improve the bending accuracy of the bending machine
Bending accuracy is critical to high-quality metal parts to ensure that thedimensions meet the design specifications. In industries such as aerospace ormedical device manufacturing, tight tolerances mean that even small deviationscan cause problems.
Bending accuracy affects economic benefits. Inaccurate bends waste material,lead to costly rework and delays, increase production time and labor costs, andreduce customer satisfaction. Poor accuracy can weaken the integrity of thestructure or misalign the assembly, leading to warranty claims and damagedreputation.
Maintaining stable bending accuracy is essential in press brake operation.Accurate bending optimizes resources, reduces waste and increases profitability,so manufacturers must perfect their processes.
Errors that lead to failure of bending accuracy of press brakes have avariety of reasons, including mechanical problems with the metal sheet bendingmachine, as well as external factors such as bending tools, material thicknessand human operator error.
In this article, we will explore the various factors that affect accuratebending and provide solutions for some common situations encountered.
1. Machine factors
There are several factors that affect the bending accuracy of press brakes.These factors include
Straightness of the slider opening
The clamping opening of the slider is straight in both the Y and Xdirections. Repositioning accuracy and arbitrary positioning accuracy of theleft and right sliders. The opening accuracy of the slider in the Y and Xdirections is critical to the bending accuracy. If the slider opening is notstraight, it will cause deviations in the bending angle and position.
Gap between the slider and the frame rail
The gap between the plunger of the bending machine and the linear guide ofthe frame should be reasonable. The proper gap between the slider and the framerail ensures the stability of the slider during movement, thereby improving thebending accuracy of the bending machine.
Verticality and inclination of the frame
Verticality and inclination of the frame. The verticality and inclination ofthe frame affect the distribution of the bending force during the bendingprocess, thereby ensuring the bending accuracy of the finished product.
Experimental data (as shown below) show that a 0.1° tilt of the frame alongthe Y axis will reduce the uniformity of the bending force by 5%, resulting in amaximum bending angle deviation of 0.5°. This is due to the uneven force on theslider cylinder, which causes the bending force distribution to shift.
| Frametilt angle (Y axis direction) | Bendingforce is evenly distributed | Bendingangle deviation |
| 0° | 99.50% | <0.1° |
| 0.05° | 97.20% | 0.2°- 0.3° |
| 0.1° | 94.80% | 0.3°- 0.5° |
Connection between cylinder and slide
The connection between cylinder and slide must be consistent to ensure evendistribution of bending force during bending in the press brake.
Mechanical precision
Precise calibration of slides, dies, hydraulics and backgauges is essential.Regular calibration ensures that these components work within specifiedtolerances.
There are other factors that affect the bending of precision press brakes,such as the strength and accuracy of the frame and slide, the repositioningaccuracy of the back gauge system in both X and R directions, the correctadjustment of the computer system, the adjustment of the hydraulic system, andthe matching between the hydraulic system and the computer adjustment.
2. Tool factors
a.. Accuracy of upper and lower dies:
The accuracy of upper and lower dies is crucial. Deformation, damage, wearand other problems of the die will affect all aspects of metal bending. Oncediscovered, they should be reported and corrected in time. Therefore, regularinspection and maintenance are necessary.
b. Die alignment:
The misalignment between the upper and lower dies will cause deviations inthe bending size. Make sure that the tool is properly aligned when setting thetool.
After the left and right position of the back gauge moves, the distancebetween the lower die and the back gauge will change. This can be measured witha vernier caliper and adjusted using the back gauge screw.
The accuracy and compatibility of the lower die compensation device shouldmatch the design of the frame. The upper die fixture should be highlyaccurate.
c. V-die opening size:
The opening size of the V-die is inversely proportional to the bendingpressure. When the sheet length and thickness are fixed, the larger the opening,the less pressure is required. Therefore, when processing sheets of differentthicknesses, the appropriate V-die opening size should be used.
When processing with a single-sided load, such as at one end of the bendingmachine, the bending pressure may be affected, which may damage the machine.This is strictly prohibited. When assembling the die, the middle part of themachine should always be stressed.
d. Tool selection:
It is crucial to select the appropriate die opening width and punch profileaccording to the material and bending radius. In the metal forming andmanufacturing industry, incorrect dies can cause angle deviations and surfacedefects.
Selecting the appropriate bending tools and dies is a meticulous process thatrequires a deep understanding of both the equipment and the processedmaterials.
3. Sheet metal factors
The straightness of the metal sheet reference surface must be checked. Ensurethat the metal sheet is evenly stressed. Check the sheet metal for consistentthickness.
During the bending process, if the parallelism between the workpiece and thelower die is insufficient, it will cause the workpiece to spring back after theupper die is pressed, affecting the bend size.
Springback is the phenomenon that the material tries to return to itsoriginal shape after being bent. Tensile strength, thickness, tooling and thetype of press brake all affect springback. Effectively predicting and evaluatingspringback is essential for handling tight bends and thick, high-strengthmaterials.
Material properties and thickness affect the bend angle, so each workpiecemust be properly inspected and spot-checked before bending.
Below are the detailed properties of the material:
Yield Strength: Yield strength is the maximum stress that a material canwithstand before it begins to deform permanently. Knowing the yield strengthhelps determine the maximum force that can be applied during the bending processto avoid damaging the material.
Modulus of Elasticity: The modulus of elasticity indicates the stiffness ofthe material and determines the amount of deformation under a given stress.Knowing the modulus of elasticity helps predict the amount of springback afterbending.
Material Thickness: The thickness of the material has a great impact on thebending process. Thicker materials require more force to bend and require alarger bend radius to avoid cracking or deformation.
Ductility: Ductility refers to the ability of a material to undergo plasticdeformation without breaking. Materials with high ductility are easier to bendand are less likely to crack or tear during the bending process.
Surface condition: The condition of the metal surface (including coating ortreatment) will affect the bending effect. Thorough cleaning to removeimpurities is also key to preventing defects.
4. Bending operation factors
a. Consistency of operator actions:
Check whether the left and right forces when the bending machine operatorpushes the material to bend are consistent. Inconsistent bending force willcause deviations in the bending size.
b. Adjust system data:
When using the system, make sure to adjust the system data error correctly.Insufficient bending angle in one time will affect the secondary bending size.Accumulated bending errors will increase the error of the workpiece contoursize.
The pressure required for bending varies with the length and thickness of theworkpiece, and the length and thickness of the plate are proportional to therequired pressure.
When the length and thickness of the workpiece change, it is important toadjust the bending capacity accordingly.
5. Environmental factors
In addition to equipment, molds and process parameters, environmental factorswill also have a certain impact on bending accuracy. Among them, the impact oftemperature and humidity is the most significant.
Temperature
Temperature changes will affect material properties such as yield strengthand elastic modulus. Increased temperature will reduce yield strength andelastic modulus and increase springback. Uneven temperature will cause thermalexpansion, resulting in deformation of the workpiece. To achieve precisebending, the workshop temperature should be kept constant or adjusted accordingto changes.
Humidity
Humidity will affect the surface of the material. In a high humidityenvironment, the metal will absorb moisture, form rust, and affect friction andbending accuracy. This is critical for materials with high surface qualityrequirements such as aluminum alloys and stainless steel.
6. Methods for achieving high bending accuracy
To achieve high bending accuracy in press brake operations, it is necessaryto combine advanced equipment, precise tools, proper material handling andoptimized process parameters. Each element plays a vital role in ensuring thatthe bends are accurate, consistent and meet design specifications.
a. Use a high-precision bending machine
Modern bending machines are equipped with advanced control systems such asCNC (computer numerical control) technology, which achieves excellent bendingaccuracy by minimizing human error and automating complex calculations. Featuressuch as real-time angle measurement systems and automatic top angle adjustmentcompensate for deviations in the mold or workpiece, ensuring consistent bendingperformance.
Hydraulic and electric bending machines in particular have features thatimprove accuracy, including programmable slide positioning and speed control.These features allow the operation to be fine-tuned to ensure accurate bends onmultiple parts. In addition, machines equipped with servo-electric drives canprovide excellent repeatability due to the precise control of slidemovement.
b. Tool selection and maintenance
The selection and condition of the bending machine tooling directly affectsthe quality of the bend. Key considerations include
Tool geometry: Selecting dies and punches with radii and angles that matchthe material type ensures optimal force distribution during the bending process.Using incorrect dies can result in unexpected deformation or inaccurateangles.
Material quality: High-strength tool materials, such as hardened toolsteel, resist wear and maintain stable performance over the long term.
Regular maintenance: Ensuring that tool surfaces are free of damage, wearor contaminants prevents errors during the bending process. Regularly inspectingtools for even minor defects and replacing worn parts is essential tomaintaining accuracy over the long term.
c. Accurate material preparation
The uniformity of the feed has a great influence on the bending result.Irregularities such as varying material thickness, surface imperfections, orinconsistent mechanical properties can cause variations in the desired bendangle. To ensure consistency
Confirm material thickness and hardness before bending. If thickness isuneven or hardness is too high, the process needs to be adjusted.
Deburr and clean metal surfaces to remove contaminants that could interferewith tooling or cause inconsistencies.
Standardize material batches to minimize variability and promotepredictable bending behavior.
d. Material Springback Compensation
Springback, the tendency of metal to partially recover its original shapeafter being bent, is a common challenge in achieving precise angle accuracy.Measures to combat springback include the following:
Overbending: Intentionally overbending during operation to account forelastic recovery.
Bottom bending or coining: In these methods, sufficient force is applied tothe workpiece to deform it beyond the elastic limit, thereby minimizingspringback.
Adjustments for specific materials: Different metals have differentspringback characteristics. Advanced press brakes equipped with a materiallibrary can automatically calculate the appropriate compensation angle based onthe selected material.
e. Implementing precision backgauges
Backgauges are important components for controlling workpiece positioning,especially in mass production where consistency is critical. High-precisionbackgauges, usually controlled by CNC systems, help:
Precise alignment of the workpiece with the die and punch.
Consistent placement of the material during repeated bends.
In multi-stage bending operations, rapid adjustments can be made todifferent workpiece geometries.
f. Optimizing process configuration
Proper configuration of process parameters is critical to achieving precisebends. Key factors to consider include
Bending force: Adjust tonnage based on material type, thickness, and toolcharacteristics to ensure consistent force is applied.
Bending speed: For thicker or stronger materials, slower bending speeds arebetter for maintaining accuracy, while faster speeds may causeinconsistencies.
Sequence planning: Complex parts with multiple bends require a carefullyplanned sequence to avoid interference and maintain alignment at each step.
g. Operator training and skill development
Even with advanced equipment, operator expertise remains critical toachieving high bending accuracy. Operators who undergo regular training arebetter able to
Identify potential sources of inaccuracy, such as misaligned tools orimproper material setup.
Dynamically adjust press brake settings based on observed deviations.
Maintain consistency in inspection procedures during and after productionto verify part quality.
Investing in ongoing operator education, especially in how to handle newtechnologies and challenges, ensures a skilled workforce that can maintainprecise bending standards.
h. Quality control and monitoring
Strong quality control measures throughout the bending process help detectand correct errors early. These measures include
Statistical process control (SPC): Analyzing long-term production data toidentify trends and deviations helps optimize processes and eliminate sources ofinconsistency.
Online angle measurement system: Real-time monitoring tools installed on thebending machine ensure that the bend reaches the specified angle beforereleasing the workpiece.
Dimensional inspection: Use precision instruments such as calipers,coordinate measuring machines or laser measurement systems to verify dimensionsand angles.
7. Frequently Asked Questions
a. How often should a press brake be maintained for optimal accuracy?
Maintain the accuracy of your press brake with a systematic maintenanceschedule.
Daily: Clean and inspect for loose or damaged parts.
Weekly: Lubricate and inspect for leaks.
Monthly: Clean hydraulic components and inspect air filters.
After the first 2,000 hours, change hydraulic oil every 4,000-6,000 hours.Inspect all systems every six months to one year. Regular calibration ensuresaccurate bending. This routine prevents downtime and extends the life of themachine.
b. What are the common problems that affect press brake accuracy?
Press brake accuracy issues include inconsistent materials, worn tools,misaligned alignment, improper calibration, machine errors, inaccuratebackgauges, and inappropriate bending methods.
Solve these problems by ensuring consistent material properties, maintainingtools, performing machine calibrations, using CNC backgauges, and selectingappropriate bending methods. Make real-time adjustments to the CNC system andmaintain an appropriate schedule to reduce the occurrence of problems.
c. What is the ideal tolerance level for bending accuracy of a pressbrake?
The tolerance level of a press brake depends on the application and industryrequirements. Generally speaking, for most precision projects, an angulardeviation of ±0.5° and a dimensional deviation of ±0.1 mm are acceptable. Inaerospace or medical device manufacturing, tolerances are typically tighter,less than ±0.25°.
To achieve these goals, advanced CNC systems, precision tooling, and qualityassurance are required. Manufacturers must evaluate specifications, materialproperties, and constraints to determine the appropriate tolerances.
To improve the bending accuracy of a press brake, many factors need to beconsidered. In addition to adjusting the components of the press brake, ensuringthe accuracy and repeatability of the die, and performing correct bendingcompensation, attention should also be paid to the daily maintenance and care ofthe press brake.
This will help extend its service life and maintain efficient and accuratebending. There are four bending technologies for sheet metal bending: airbending, bottom bending, coin bending, and three-point bending.
Investing in a high-quality press brake is another effective way to ensure aproductive bending operation in metal manufacturing. JUGAO CNC MACHINE is atrusted bending machine manufacturer with over two decades of expertise in thesheet metal industry.
In addition to modern bending machines such as hydraulic bending machines,CNC bending machines, we also offer other machinery such as laser cuttingmachines, plate bending machines, tube bending machines, and more.
Please visit our bending machine product page for more information or visitour contact us page for detailed product and pricing information.
