Solving the Springback Enigma: 7 Proven Methods to Achieve Perfect Bends

You can effectively prevent springback by using the right tools and methods in bending. Quality is crucial because springback can lead to costly errors and material waste. Advanced press brake tooling, like those from Nanjing Metal, assists you in achieving perfect bends by providing:

1. High-precision press brakes with CNC technology, which help minimize mistakes.
2. Real-time angle measurement systems that automatically adjust settings.
3. Built-in springback compensation techniques, such as over-bending.

Preventing springback ensures that your metal parts fit correctly every time.

Key Takeaways

• Springback happens when metal tries to go back to its old shape after you bend it. Knowing this helps you make better bends.
• Using good press brake tooling helps you make fewer mistakes. It also makes your bends more accurate.
• Overbending is a good way to fix springback. Bend the metal a little more than you need to get the right angle.
• Material properties like yield strength and thickness change how much springback you get. Pick your materials carefully for better results.
• Changing the bend radius can help lower springback. Smaller radii usually mean less springback.
• CNC compensation systems make changes while you bend. This helps keep your bends accurate and lowers mistakes.
• Keeping your press brake tooling in good shape helps it work the same every time. This also helps stop springback problems.
• Test and change your bending settings, like force and speed, to control springback better. This can also make your parts higher quality.

Preventing Springback: Fundamentals

What Is Springback

When you bend metal, it tries to go back. This is called springback. During sheet metal bending or metal stamping, metal stretches and bends. When you stop bending, the metal’s elasticity makes it move back a little. So, the final shape may not be what you wanted.

Springback happens because metals are elastic. The atoms move when you bend the metal. They want to go back when you stop. That is why stopping springback is important in bending.

Why Springback Matters

Springback can cause problems in metal stamping and sheet metal bending. If you do not control it, parts may not fit together. You might see gaps or holes that do not line up. Parts may not be the right size. This wastes material and time.

Tip: Engineers always think about springback when planning bends. Predicting and fixing springback helps you get the right size and avoid mistakes.

You must prevent springback to make sure your parts are correct. Dimensional accuracy is very important in automotive, aerospace, and electronics. If you ignore springback, your parts may not pass quality checks.

Key Factors

Many things change how much springback you see in sheet metal bending and metal stamping. Knowing these things helps you pick the best ways and tools to stop springback.

• Material Properties:
  Different metals act differently when you bend them. High-strength steels and metals with high yield strength have more springback. They bounce back more. The table below shows how some material properties affect springback:Material PropertyTypical Influence on SpringbackYield StrengthHigh yield strength increases springback a lot.Young’s ModulusHigh values make springback bigger.Strain Hardening ExponentChanges how the metal resists bending, affecting springback.Sheet ThicknessEvery 10% less thickness can make springback go up by 5-8%.Carbon ContentEvery 0.1% more carbon can raise springback by 5-8%.Grain SizeSmaller grains can make springback go up by 10-15%.Heat TreatmentCan lower springback by 20-30% by making yield strength lower.
• Bend Radius:
  The bend radius size changes springback a lot. A smaller bend radius means less springback. If you use a big bend radius, like eight times the thickness, you get more springback. Here is how different materials react:MaterialSpringback Range (degrees)304 stainless steel2 to 3Mild aluminum1.5 to 2Cold-rolled steel0.75 to 1.0Hot-rolled steel0.5 to 1.0Copper and brass0.00 to 0.5
• Die Clearance:
  The space between the punch and die is die clearance. It changes how much the metal bends and springs back. For mild steel, the best die clearance is about 12-13% per side. For stainless steel, you need over 25% per side. If the clearance is too big or too small, springback gets worse.
• Tooling Quality:
  Good press brake tooling helps control springback. Well-made and cared-for tools give steady results. Bad or old dies can cause more springback and wrong shapes. You can look at custom blades and advanced tooling options here to help your process.
• Other Causes:
  • Material elasticity: Metals that are more elastic have more springback.
  • Part geometry: Hard shapes with curves or sharp angles spring back more.
  • Stamping pressure: Not enough pressure makes springback worse.
  • Die characteristics: The design and condition of dies matter a lot.

Note: The size effect can change the springback angle by more than 7%. Even small changes in thickness or grain size can make a big difference.

If you know these key factors, you can work to stop springback in every sheet metal stamping or bending job. Using the right materials, changing your bend radius, setting good die clearance, and picking good press brake tooling all help you get accurate results.

Overbending Technique

How Overbending Works

When you bend metal, it wants to go back. This is called springback. Overbending helps stop this from happening. You bend the metal more than you need. After springback, the metal ends up at the right angle.

Overbending is easy and works well. Many shops use it for different metals and thicknesses. Overbending can cut springback almost in half. For example, a compensation algorithm can lower springback by 45%. If the first displacement is 20.1 mm, overbending can make it only 11.3 mm at the most important flange. This makes your parts fit better and saves time fixing mistakes.

Tip: Overbending works best when you know your material and use the right press brake tooling. Always check your work and change things if needed.

Calculating Overbend Angles

You need to figure out the right overbend angle for good results. There are a few steps to follow. Each step helps you control springback and make bending better.

Here is how you find the overbend angle:

1. Identify the Material Type:
   Different metals act differently. Aluminum, steel, and copper have different springback.
2. Measure the Thickness of the Material:
   Thicker metal has more springback. You must know the thickness before you start.
3. Check the Bend Radius:
   The bend radius should match the thickness. A small radius can crack brittle metals.
4. Set the Desired Bend Angle:
   Pick the angle you want for your finished part.
5. Estimate Springback Compensation:
   Use your experience, tables, or test bends to guess how much the metal will spring back.
6. Calculate the Overbend Angle:
   Use this formula:Overbend Angle = Desired Angle + Springback Compensation For example, if you want a 90° angle and expect 2° of springback, set your press brake to 92°.
7. Adjust Tooling and Machine Settings:
   The tooling and press brake machine change your results. Make sure you use the right setup for your metal.
8. Perform a Test Bend:
   Bend a sample piece and measure the angle. See if it matches your goal.
9. Fine-Tune as Needed:
   If the angle is wrong, change the overbend angle and try again.

Here is a quick checklist for your overbend calculation:

• Material type
• Material thickness
• Bend radius
• Bend angle
• Springback
• Tooling and machine features

Note: Always do a test bend before making lots of parts. This helps you find mistakes early and makes sure your parts are good.

If you follow these steps, you can control springback and get accurate bends every time. Overbending is a proven way to help you get the results you want.

Tooling Optimization for Springback Prevention

Special press brake tooling helps stop springback. Picking the right dies and punches lets you control how metal bends. Companies like Nanjing Metal have advanced press brake tooling. These tools help you get accurate results in sheet metal bending and metal stamping.

Die and Punch Selection

Common Die Types and Their Impact on Springback

The shape of your die changes how much metal springs back. Different die shapes help control elastic recovery and stop springback. The table below shows how die geometry affects your results:

You can add shapes or darts to the flange radius. This makes the part stronger and lowers springback. To reduce springback, try to make more of the part bend plastically. You can do this by adding reduction features to your part’s shape.

Punch Geometry Considerations

Punch shape also matters for springback prevention. For thin and thick sheet metals, use a punch nose radius bigger than four times the sheet thickness. This helps lower springback and gives better results. Smaller punch radii and tight clearances help with both thin and thick metals.

Making higher strain levels and even strain lowers springback. This gives you better results in finished parts. Always match your punch shape to your material and thickness for the best results in sheet metal bending and metal stamping.

Application Scenarios for Optimal Selection

Pick your die and punch based on metal type, thickness, and shape. For example:

• Use compensating dies if you expect high elastic recovery.
• Pick high-precision guides and punches for tight tolerance parts.
• Add darts or shapes to flanges for extra strength and less springback.
• Choose a punch nose radius bigger than four times the sheet thickness for most springback prevention.

Tooling Material and Design

Role of Advanced Materials (e.g., Carbide, Special Steels) in Reducing Springback

Tooling material affects how well you control springback. Advanced materials like carbide and special steels lower springback better than regular materials. The table below compares average springback angles for different materials and die sizes:

Using advanced tooling materials gives you better springback prevention. These materials last longer and keep their shape. This helps you stay accurate in sheet metal stamping and metal stamping.

Innovative Tooling Designs for Enhanced Accuracy

New tooling designs, like custom V-punches and gooseneck punches, give you more control. These designs help you adjust and align better. You can use custom tooling to fit your needs in sheet metal bending.

Maintenance Tips

Daily Inspection Checklist

Check your press brake tooling every day to keep it working well. This helps you keep springback prevention strong. Here is a simple checklist:

• Clean tools to remove dust, oil, and fingerprints.
• Look for wear or damage.
• Make sure all parts are lined up and tight.

Tip: Clean your press brake tools after every shift. Use a lint-free cloth and a metal-safe cleaner.

Routine Maintenance Procedures

Regular maintenance makes your press brake tooling last longer. It keeps your springback prevention working well. Follow these steps:

• Lubricate your tools every week or when needed.
• Use approved anti-corrosion lubricants.
• Keep shop humidity below 50% and make sure air moves well to stop rust.
• Calibrate and align your press brake often for accurate bending.
• Train workers to spot problems early and use equipment right.
• Make a maintenance schedule and follow it.
• Use technology for real-time checks and predictive analytics.

If you follow these tips, your press brake tooling stays in good shape. This helps you stop springback and get high-quality results in every sheet metal bending and metal stamping job.

Bottoming and Coining Methods

Bottoming Process

Principle of Bottoming

Bottoming is when you press sheet metal hard into the die. You use more force than air bending but less than coining. The punch pushes the metal until it touches the die sides. This changes the metal’s shape and helps stop springback.

There are ways to lower springback in bottoming. Arc bottoming uses the arc’s springback at the die’s bottom to fight side wall springback. Pinching die methods use a beaded punch to pinch the metal with round beads. This helps get rid of springback.

Bottoming is good if you want the same angle and less springback in your sheet metal bending jobs.

Steps in the Bottoming Process

Here are the steps for bottoming. First, put the sheet metal on the die. Next, line up the punch with the bend line. Lower the punch until the metal touches the die sides. Push hard enough to change the metal’s shape. Hold the pressure for a short time. Then let go and take out the bent part.

You must use the right force and die clearance. These things change how much springback you get after bending.

Advantages and Limitations of Bottoming

Bottoming has some good points. You get okay bend accuracy. Springback is less than with air bending. It works for thicker metal sheets.

But there are some limits. You may not get the best accuracy. Bottoming is better for thick sheets and simple shapes. If you need very tight sizes, you might want to use coining.

Suitable Applications for Bottoming

You can use bottoming for many things. It works for car parts that need strong bends. It is good for building parts that need okay accuracy. Use it for sheet metal stamping when you want to control springback. It is also good for thick sheet metal projects.

Bottoming helps you stop bending problems and get steady results in many sheet metal bending jobs.

Coining for Accuracy

Principle of Coining

Coining is a way to bend metal with high accuracy. You use a punch to press the metal deep into the die with a lot of force. This force changes the metal and squeezes the bend area. Coining almost stops springback and gives you a very exact bend.

Coining needs much more force than air bending or bottoming. The punch and die press the metal so hard that the bend angle stays just as you set it.

Steps in the Coining Process

Here are the steps for coining. Put the sheet metal on the die. Line up the punch with the bend line. Lower the punch and use a lot of force, five to ten times more than air bending. Press the metal into the die until the bend is fully made. Hold the pressure for a short time. Let go and take out the part.

Coining works best for thin metal and parts that need to be very exact.

Benefits of Coining for Springback Prevention

Coining has many good points.

You get almost no springback. The bend angles are very exact. You can stop most bending problems.

Coining is best when you need perfect bends and almost no springback in your sheet metal bending work.

When to Use Coining

Use coining when you work with thin sheet metal. Use it if you need high accuracy and tight sizes. It is good when you want almost no springback. Use it for parts in electronics, airplanes, or home appliances.

Coining helps you get perfect bends and stop bending problems in tough sheet metal bending jobs.

Process Parameter Adjustment

When you want to control the quality of your bends, you must pay close attention to your process parameters. Adjusting force, speed, and temperature can help you achieve the right shape and reduce errors in your sheet metal work.

Force and Speed Settings

Effect of Bending Force Magnitude

You need to set the right amount of force when you bend metal. If you use too little force, the metal may not bend enough. If you use too much, you can damage the part or the tooling. The correct force helps you get a clean bend and keeps the angle close to what you want. When you use the right force, you also help control springback. The metal stays in its new shape better, and you get more accurate results.

Influence of Bending Speed on Springback

Bending speed changes how the metal reacts. If you bend too fast, the metal may not have time to stretch and form well. If you bend too slow, the metal can cool down or lose heat, which changes how it bends. You need to match the speed to the type of metal you use.

• Softer metals like aluminum and copper work best at speeds of 8-10 mm/s. This speed lets the metal bend smoothly and reduces springback.
• Harder metals like stainless steel and high-strength steel need slower speeds, around 5-8 mm/s. This helps the metal bend evenly and keeps the angle steady.

Tip: Always check your machine settings before you start. The right speed helps you get the best bend and keeps your parts within tolerance.

Material-Specific Parameter Adjustments

Every metal acts differently when you bend it. You must adjust your force and speed for each type. For example, aluminum bends easily, so you can use less force and a faster speed. Stainless steel is harder, so you need more force and a slower speed. If you switch materials, always test a sample first. This helps you find the best settings and avoid mistakes.

Experimental Methods for Optimizing Force and Speed

You can use simple experiments to find the best force and speed for your job. Start with a test piece. Try different settings and measure the bend angle after each test. Write down your results. Look for the settings that give you the closest angle with the least springback. Repeat this process when you change materials or thickness. Over time, you will build a chart of the best settings for your shop.

Temperature Control

Role of Heating in Reducing Springback

Heating the metal before bending can make a big difference. When you heat the metal, it becomes softer and easier to bend. This lowers the yield strength and makes the metal more flexible. Heated metal bends with less force and shows less springback. You get a more accurate angle and a smoother bend.

Suitable Materials for Temperature-Assisted Bending

Not all metals need heating, but some benefit from it. Stainless steel and aluminum are two common metals that respond well to pre-heating. When you heat these metals, you make them easier to form. This helps you get better results, especially with tight bends or thick sheets.

Temperature Control Methods and Equipment

You can use different tools to heat your metal. Some shops use ovens or heat lamps to warm the whole sheet. Others use induction heaters for fast, local heating. You must watch the temperature closely. Too much heat can damage the metal. Too little heat may not help at all. Use a thermometer or a temperature sensor to check your work.

Safety and Process Considerations

Always think about safety when you use heat. Wear gloves and eye protection. Keep flammable items away from your work area. Make sure your equipment is in good shape. Never leave heated metal unattended. Plan your process so you can bend the metal while it is still hot. This helps you get the best results and keeps your shop safe.

Note: Heating can help you control springback, but you must use it carefully. Always follow safety rules and check your results.

Material and Orientation Control

Material Selection

Choosing Materials with Low Springback Tendency

You can control the quality of your bends by choosing the right sheet metal. Some materials show less springback than others. Mild steel is a popular choice because it bends easily and keeps its shape well. Stainless steel and aluminum are also common, but they need more attention during bending.

Here is a table that shows how different materials behave:

If you want less springback, mild steel is a reliable option. Stainless steel and aluminum need extra steps to get the right bend.

Comparing Common Sheet Metals (Aluminum, Mild Steel, Stainless Steel)

You see different results when you bend aluminum, mild steel, or stainless steel. Mild steel bends with less force and keeps its shape. Aluminum is light and easy to handle, but thin sheets can spring back more. Stainless steel is strong and resists rust, but it needs careful control to avoid errors.

• Mild steel works well for most jobs.
• Aluminum is best for lightweight parts.
• Stainless steel is strong and durable.

You should match the material to your project needs. Each metal has its own benefits and challenges.

Impact of Material Thickness and Yield Strength

Material thickness changes how much springback you see. Thicker sheets bend with less springback because they can stretch more before returning to their original shape. Thin sheets need more adjustments because they spring back easily.

• Thicker materials need more force and bend with less springback.
• Thinner materials bend with less force but show more springback.
• You may need extra roller passes for thin sheets to get the right angle.

Yield strength also matters. Metals with high yield strength resist bending and show more springback. You should check both thickness and yield strength before you start bending.

Tip: Always measure your material thickness and choose the right settings for your press brake. This helps you control springback and get accurate bends.

Adjusting Orientation

Understanding Grain Direction (Rolling Direction)

Sheet metal has a grain direction from the rolling process. Grain direction affects how the metal bends and stretches. If you bend along the grain, the metal may crack or tear. If you bend across the grain, the metal bends more smoothly.

Grain direction also changes springback. You need to know the grain direction before you start bending.

Effects of Bending Parallel vs. Perpendicular to Grain

Bending parallel to the grain makes the metal stronger but less flexible. You may see more cracks and higher springback. Bending perpendicular to the grain gives you better formability and less risk of defects.

You can also rotate the blank to a 45 or 90-degree angle. This helps the metal stretch evenly and lowers the chance of cracks. A case study showed that changing the blank orientation reduced cracking by 15%. This proves that grain direction matters in bending.

Best Practices for Orienting Blanks Before Bending

You should always check the grain direction before you bend. Here are some best practices:

• Mark the grain direction on each blank.
• Bend perpendicular to the grain for better results.
• Rotate blanks if you see cracks or defects.
• Test a sample piece before starting a big job.

Note: Proper blank orientation helps you avoid defects and control springback. You get smoother bends and stronger parts.

Advanced Springback Prevention Techniques

CNC Compensation

Principle of CNC Compensation

CNC compensation helps you bend metal very accurately. The CNC system checks the bend angle while you work. A laser device looks at the metal as it bends. It finds changes in thickness and springback. The system moves the slide block to fix the angle. This helps you get the bend you want every time.

Types of CNC Compensation Systems

There are two main types of CNC compensation systems:

• Closed-loop systems use feedback to make bends better. They check the angle and fix it during bending.
• Open-loop systems do not use feedback. They follow commands but do not fix mistakes.
• Tool offsets let you set each tool’s size. This makes changing tools easier.
• Error compensation fixes problems from tool wear or heat.

Closed-loop systems work best because they fix errors right away.

Steps for Implementing CNC Compensation

Here are steps to use CNC compensation:

1. Measure the bend angle after a test bend.
2. Put the compensation value into the CNC system.
3. Use angle compensation to change the settings.
4. Pick CNC press brakes with real-time angle checks.
5. The system finds springback and fixes the bend as you work.

This keeps your bends correct and lowers mistakes.

Benefits and Limitations of CNC Compensation

CNC compensation has many good points. You get accurate bends and fewer mistakes. The system works for different metals and thicknesses. You save time because you do not need to fix parts later. You also waste less material.

But CNC systems can be hard to learn. Your team needs training to use them well. Some systems cost more, but they help you get better bends.

Application Scenarios for CNC Compensation

Use CNC compensation when you need very accurate bends. It is good for car, airplane, and electronics parts. It works well for jobs with many bends or tight sizes. CNC compensation helps with metals that spring back a lot.

Tip: If you want better bends, think about getting CNC press brakes with compensation.

Simulation and Prediction Tools

Overview of Simulation Tools (e.g., FEA Software)

Simulation tools help you see how metal will bend. Finite Element Analysis (FEA) software models the bending process. You can test different metals and shapes before you start. FEA uses special math to show how metal will act.

How Simulation Predicts Springback

Simulation tools use metal models and properties to guess springback. For example, Voce hardening law and Barlat’s yield functions help get good results. The software checks things like Young’s modulus and hardening law. It uses special math to match real bending.

You can compare simulation results with test bends. This helps you see if your guesses are right.

Integrating Simulation Results into Production

You can use simulation results to set up your press brake. The software tells you the best force, speed, and angle for each metal. You can change your process before you bend real parts. This saves time and cuts waste.

Many shops use simulation to plan jobs and teach workers. You can also use it to try new metals or designs.

Advantages of Using Prediction Tools

Simulation tools have many good points:

• You can guess springback before you bend metal.
• You save metal and time by avoiding mistakes.
• You can test new designs quickly.
• You get better accuracy and fewer defects.

Simulation helps you plan better and get steady results.

Common Challenges and Solutions

You may have problems with simulation tools. Setting up the software can take time. You need good metal data for good guesses. Sometimes, results do not match real bends. You can fix these problems by updating your metal library and checking your process often.

Note: Always check your simulation results with test bends. This helps you keep your process working well.

Geometric Stiffeners

What Are Geometric Stiffeners

Geometric stiffeners are shapes added to metal parts. You can use ribs, beads, or flanges to make the part stronger. Stiffeners help metal keep its shape after bending.

How Stiffeners Reduce Springback

Stiffeners make the part stiffer. They fight elastic stress and help keep the shape you want. You see less springback when you use stiffeners.

Design Considerations for Stiffeners

Plan stiffeners carefully. Think about the part’s size and shape. Pick the right stiffener for your job. Make sure the design fits your process.

Examples of Stiffener Applications

Add ribs to car panels to keep them flat. Use beads in appliance parts for extra strength. Flanges work well in building pieces to hold their shape.

Limitations and Best Practices

Here is a table showing the good and bad points of geometric stiffeners:

You should balance the good points with the extra cost and work. Test your stiffener designs before making lots of parts.

Tip: Use geometric stiffeners when you need strong, accurate parts with less springback.

Preventing Sheet Metal Bending Defects: Best Practices

Post-Bend Correction

You can fix many bending problems after you bend the metal. These fixes help you get the right angle and shape, especially if springback causes trouble. Here are some ways to fix your bends:

• Overbending: Push the metal a little more so it stays at the right angle after it springs back.
• Widening the die angle: Change the die’s angle to match how the metal acts and lower springback.
• Smaller punch radius: Use a punch with a smaller tip to help control the bend.
• Geometric adjustment: Change the tool’s shape in the opposite way of the springback.
• Springback correction tables: Use charts that show how metals react, so you can set your angles before you bend.
• Custom scripts: Set up your press brake to make automatic changes for each bend.

Tip: Always look at your parts after you bend them. Small fixes can really help your part’s quality.

Quality Control

Quality control helps you make sure your parts are right and do not have bending problems. You should check every part after you bend it. Look for cracks, wrinkles, or wrong angles. Use tools like protractors or digital angle finders to check each bend.

You can make a checklist for your team:

• Check the bend angle and radius.
• Look for marks or cracks on the surface.
• Match the part to your drawing.
• Write down any problems and fix them fast.

Using good press brake tooling, like OEM/ODM tools, helps you keep your work steady. Custom tools fit your job and help stop mistakes.

Here is how OEM/ODM press brake tooling helps you bend without mistakes:

Sequence Bending

The order you bend each part is important. Sequence bending helps you stop common bending problems and makes your work easier. Plan your bends so each step helps the next one. Start with easy bends and do hard ones last.

• Bend big flanges first to keep the part steady.
• Make small or tight bends last so nothing gets in the way.
• Use supports or holders to keep the part still while you bend.
• Try your plan on a test piece before making lots of parts.

Note: Good planning and the right order help you stop springback and keep your parts right.

If you follow these best steps, you can stop sheet metal bending problems and make good parts every time.

You can make perfect bends by using good ways to control springback. When you check your tools and how you work, you find ways to lower springback and make your parts better. Good press brake tooling helps you get the same results every time and stops springback problems. If you need help with bending, talk to a sales engineer here.

FAQ

What is springback in sheet metal bending?

Springback is when metal tries to go back to its old shape after you bend it. This can make the angle of your part change. You need to control springback to get the right bend.

How can you reduce springback during bending?

You can lower springback by overbending the metal. Picking the right tools and changing machine settings also helps. Heating the metal or using bottoming and coining can help too. Always test your setup before making lots of parts.

Why does material type affect springback?

Different metals act in their own way. High-strength steel and aluminum usually have more springback. Mild steel has less. Always check the metal’s yield strength and thickness before you bend it.

What role does press brake tooling play in springback control?

Press brake tooling shapes the metal and helps control springback. Good quality tools give better bends. Picking the right die and punch helps you get the angle you want.

Can you fix springback after bending?

Yes, you can fix springback by making small changes. You might bend the part a little more or use other fixes after bending. Always check the angle and fix it if you need to.

Does grain direction matter for springback?

Yes, grain direction changes how metal bends and springs back. Bending across the grain gives less springback and fewer cracks. Always mark and check the grain direction before you bend.

How do CNC systems help with springback?

CNC systems check the bend angle as you work. They change the press brake settings to fix springback. This helps you get the right bend every time.

See Also

Choosing the Best Press Brake Tooling for Stainless Steel

European vs. American Style Press Brake Tooling: Which is Right for Your Shop?

Air Bending vs. Bottoming: Choosing the Right Press Brake Tooling for Your Project

The Ultimate Guide to Press Brake Dies: Choosing the Best Material to Prevent Wear

Press Brake Tooling Guide for Beginners: Choosing the Right V-Die Opening

How to calculate press brake bending force and tonnage