Press Brake

# Metal Sheet Bending Force: Bending Pieces Design

Today we learn about the calculation method of sheet bending force. Or you can directly use the calculation formula of bending force on our website.

#### Expansion calculation principle

The outer layer of the sheet material is subjected to tensile stress during the bending process, and the inner layer is subjected to compressible stress.

From tension to compression, there is a transition layer that is neither tension nor pressure-the neutral layer. The length of the neutral layer during the bending process It remains the same as before bending, so the neutral layer is the basis for calculating the expanded length of the bent part. The position of the neutral layer is related to the degree of deformation.

When the bending radius is larger and the bending angle is smaller, the degree of deformation is smaller and neutral The position of the layer is close to the center of the thickness of the sheet. When the bending radius becomes smaller and the bending angle increases, the degree of deformation increases, and the position of the neutral layer gradually moves to the inner side of the bending center. The distance is represented by λ

#### Calculation method

Basic formula for expansion
Unfolded length=in-material +in-material+compensation amount
1.1
R=0, bending angle θ=90°(T<1.2, excluding 1.2mm)
L=(A-T)+(B-T)+K=A+B-2T+0.4T
Take from the above formula: λ=T/4K=λπ/2=T/4π/2=0.4T

R=0,θ=90°(T≧1.2, including 1.2mm)
L=(A-T)+(B-T)+K=A+B-2T+0.5T
Take from the above formula: λ=T/3K=λπ/2=T/3π/2 =0.5T

R≠0θ=90°
L=(A-T-R)+(B-T-R)+(R+λ)π/2(=A+B-2T-2R+(R+T/3)π/2)
When R≧5T时 λ=T/2 1T≦R<5T λ=T/30<R<T λ=T/4

#### Z-fold

Please refer to the superior for the calculation method, and the following principles can be referred to in the actual calculation:

(1) When C≧5, it is generally divided into two moldings and calculated according to two 90° bends. (The strength of the bending punch should be considered)
(2) L=A-T+C+B+2K [K=λ*α (when α=90 degrees, α=π/2, λ=T/3 as above)]
(3) When 3T: L=A-T+C+B+K
(4) When C≦3T, : L=A-T+C+B+K/2

When C≦3T :
L=A-T+C+B+D+K

#### Calculation of bending force

If we want to bend a relatively large and thick plate, we must first understand the required bending tonnage force.

Then we can calculate the tonnage required for bending (it is recommended that the required pressure for the bending of the workpiece be within 80% of the rated tonnage of the equipment), and through calculation we can also determine the tonnage equipment required for the bending, and the mold V groove is reasonable The choice also has an effect on the bending force.

Bending pressure calculation formula: P=650SS*L/V

P=Bending pressure (unit: kN)

S=plate thickness (unit: mm)

L=Length of sheet material (unit: m)

V=Lower die slot (unit: mm, generally 8-10 times the plate thickness)

Remarks: The pressure during bending of stainless steel can be calculated according to the following standards, 304 stainless steel = carbon steel * 1.5 times, 201 stainless steel = carbon steel * 2 times

#### Bending of bending workpieces

Under normal circumstances, there are two methods for bending sheet metal: one method is die bending, which is used for sheet metal structures with complex structures, small volumes, and mass-processed; the other is bending with a bending machine.

It is suitable for processing sheet metal structures with relatively large structure size or not too large output. At present, the company’s products are mainly processed by bending machines.

#### Bending Tool bending

Commonly used bending molds, as shown in Figure 1-1:
In order to extend the life of the mold, round corners should be used as much as possible when designing parts.

#### Press Brake machine bending

There are two types of bending machines: ordinary bending machines and CNC press brake.

The precision requirements are high, and the sheet metal bending with irregular bending shapes is generally bent with a CNC bending machine.

The basic principle is to use the bending knife (upper mold) and V-shaped groove (lower mold) of the bending machine. Bending and forming sheet metal parts.

Advantages: convenient clamping, accurate positioning, fast processing speed;
Disadvantages: The pressure is small, only simple forming can be processed, and the efficiency is low.

#### Principles of bending workpieces

1)  Bend from the inside to the outside;
2)  Bend from small to large;
3)  First bend the special shape, and then bend the general shape;
4)  The former process does not affect or interfere with the subsequent process after forming.