Sheet metal bending
Bending is the forming of sheet metal by application of force, which exerts pressure on a certain length of material either at a certain point or linear as an evenly distributed weight. This applied force is also called the bending moment. The force of the bending moment determines the degree of deformation. Bending of sheet metals can be done with press brakes, roll bending machines and embossing/coining machines.
To use the example of a press brake, where the upper tool will be pressed onto the sheet metal with a certain force (F1). The contact points of the die counter the press force from above with the same force (F2), but in the opposite direction, to create a sum of the forces. The combination of two equally strong forces that are parallel aligned but work in opposite directions build a force pair. The effect of this pair of forces must be strong enough to deform the sheet metal permanently and retain the desired shape after the force application has subsided.
Knowledge of the static load capacity of the various materials is a prerequisite for achieving this goal. Each material has a different load capacity and reacts differently to the application of force. But all metals have the common property of being able to be deformed elastically and plastically. However, these phases occur at different stress levels depending on the material type and thickness. For more information, please read our article about the Stress Strain Diagram to gain further insight into this issue.
In order to bend sheet metal permanently, enough force has to be applied to the metal so that the material specific range of elastic deformation is exceeded (Yield point). As long as this point has not been reached, the sheet metal will just return to its original shape.
But as soon as the maximum point of elastic deformation has been exceeded, a shift in the crystalline structure of the metal takes place and the crystals change their position in the micro-structure. This plastic deformation cannot be reversed and a sheet of metal would be permanently bent from the time of this load application.
Our company uses folding and rolling processes for bending sheet metal. Our machines are computer-controlled and can easily be adapted to the materials to be bent.
Important facts when bending metal
There are several factors that go into the calculation of the necessary press force:
What is the material to be bent?
This is an important question when bending sheet metal, as every material has its own individual load capacity with regard to yield point and tensile strength. The alloy composition of the material is important as well, since the addition of alloying elements can significantly affect the mechanical strength of a material.
Material Yield Point Tensile Strength AlMg1 135 N/mm² 100–155 N/mm² X5CrNi18-10 360 N/mm² 500–700 N/mm² S 235 235 N/mm² 340–470 N/mm² S 355 355 N/mm² 490–630 N/mm²
The value of the yield point has to be exceeded in order to permanently deform the material, otherwise the metal will spring back to its original shape. Only a load larger than the yield point will cause a permanent plastic deformation. It is very important to make sure the tensile strength of the material is not exceeded, since this would damage the material.
The bending length is very important when determining the press force. This can be best explained with an example. In order to bend an S235 sheet of metal with a thickness of 10 mm, the press force needed on a die with an 80 mm opening will be 131.35 t. The press force increases proportionally with the bending length and is 1,050.80 t at a maximum bending length of 16 m.
Our dictionary also contains a practical calculation tool, which you can use to calculate the press force.
In our operation the customer can specify at what angle the sheet metal is supposed to be bent. Metals can be bent easily with machines, but will spring back a little after folding the edges. In our practical application this means that the sheet metal has to be bent – more than specified – so that the dimensions are still stable within the specified range after it springs back. We have no problem bending metal at a certain angle. By entering the material, the bending length and material thickness, the machine calculates all settings for the bending process.
To produce work pieces with different radii, we have a great selection of different tools for the sizes of bending radii. Especially for thicker materials larger bending radii are necessary so that the material will not tear or no creases appear. There is a more detailed article about the topic of Minimum bending radii available in our sheet metal-Wiki.