1. What is bending?

Bending steel is the process of permanently transforming a flat steel member into a curve or angle. In steel processing, bending creates a permanent deformation of the material.

2. What is the difference between roll forming, roll bending and press braking?

Three differently designed machines are used to obtain the required shape of an originally flat plate. Roll forming results in an open or closed section. Roll bending gives a circular section, truncated cone section or a shape with variable radius. Press braking creates a linear deformation. 

Roll forming

Roll bending

Press braking

3. What material properties are important for bending forming?

Materials with high plasticity are better for forming. High plasticity means that the material more easily withstands sustainable deformation. The material’s ductility is also an important property. Good ductility means that a material can undergo a change of physical form without losing its mechanical properties.

4. How thick and hard material is it possible to bend?

What is most important when understanding the maximum hardness or maximum thickness, is the ability to be plastically (permanently) deformed without cracking. This property often goes by the name of ductility.

5. What is the set-up for bending?

The basic principle for bending is that you need a force for influencing a permanent deformation in the material, and a support for the steel. For press braking, terms commonly used are punch and die. 

7. How is BendCalc used to calculate and simulate bending?

Carefully fill in the plate and machine parameters as requested by the app SSAB BendCalc, run it and it will provide a set of recommendations to apply. To get the best result, adjust the process or parameters if needed. 

8. What bending force is necessary?

The SSAB BendCalc mobile app can be used to calculate all parameters needed for a successful bending operation. 

9. What kind of bending dies are common?

The most common dies are V-dies and U-dies, see pictures.

10. What is air bending and bottom bending?

In bottom bending, the bending angle is limited by the plate touching the die bottom. In air bending, the plate bendability sets the limit.

Air bending (left) and bottom bending (right).

11. What is bend allowance?

Bending will somewhat increase the original length of the workpiece, perpendicular to the bending line. Bend allowance is the extra material required to accommodate the bend in the material. 

12. What is springback in bending?

During the bending operation, the workpiece will be deformed elastically and plastically. When the bending force is released, the elastic deformation will be reversed to zero, thus decreasing the bending angle. The press brake operator must overbend to the bending angle, which is angularly past the required bent angle, thereby compensating for the springback angle. 

13. What is the bending neutral axis?

During bending, the material will be stretched on one side and be compressed on the other. This means at a point between the sides, the deformation will be zero. This is the neutral axis.

14. What is a bend angle?

The purpose of bending a plate is to obtain an angle between the parts on either side of the bending line. This is the bend angle.

15. Which parameters affect the final bend angle?

Provided the available bending force is sufficient and the machine dimensions are compatible with the size of the workpiece, it is up to the operator to run the punch such that the desired bend angle is obtained after release of the load. 

The final bend angle depends on:

  • Material mechanical properties
  • Material thickness 
  • Bending tool setup
  • Punch radius
  • Die depth and width
  • Available bending force
  • Working temperature
 

16. Which parameters affect the bend radius?

Machine geometry and settings as well as workpiece properties do have an influence. The punch radius is the dominating parameter. “Trial and error” is the way to get the required bending result. 

The bending radius depends on parameters such as:

  • Bending angle
  • Material thickness
  • Material mechanical properties
  • Top punch radius
  • Bending force
  • Bottom die opening
  • Operating temperature
  • Friction between tool and workpiece.

17. How narrow can I bend?

It depends on how ductile the material is. A very ductile steel workpiece can be folded like a piece of paper, whereas a brittle one may crack at minor bend angles.

18. How can I bend with a very small bending radius?

The minimum punch radii recommended for SSAB steel grades are based on a large number of tests and can be found in our Bending brochure and SSAB BendCalc. Using a smaller radius than recommended will increase the risk for cracking.

19. How are the stresses after bending?

Tensile and compressive residual stresses are present in the vicinity of the bending line and balance each other. 

20. How can I bend close to the plate edge parallel to the bending line?

Use the SSAB BendCalc to calculate the recommended minimum distance. Too short a distance can cause the workpiece to slip and result in serious physical harm. Safety must always come first. 

The information in this report is only applicable to SSAB’s products and should not be applied to any other products than original SSAB products. 

This report provides general results and recommendations for SSAB steel products. This report is subject to SSAB’s Terms of Use. It shall be the user's responsibility to verify that the information contained herein is correct and is suitable to be used for the particular purpose and application of the user. The report is intended to be used by professional users only who possess adequate expertise, qualification and knowledge for the safe and correct use of the results and recommendations in this report. This report is provided “as is”. The use of the report is at user’s own discretion and risk and that users will be solely responsible for any use of this report. SSAB disclaims any liability for the content or potential errors of this report, including but not limited to warranties and condition of merchantability or fitness for a particular purpose or suitability for individual applications. SSAB shall not be liable for any kind of direct or indirect damages and/or costs related to or arising therefrom, whether special, incidental, consequential or directly or indirectly related to the use of, or the inability to use, the report or the content, information or results included therein.