Research of bending process in industry
Definition

  According to 8586 bending is the formation of parts in which sheets and straps are transformed into studs or circular pieces.
In bending, stress is applied in dough.

Application
   Bending is used in the process of sheet defor

mation for stud parts of profiles of sheets and tubes, parts of buildings, ships and equipment. In addition to the above parts, various rings are produced with the above method for many fields.
Bending process

Freehand

In free bending, the mold is made up of a matrix punch only to transfer power. The workpiece sits on two points. The punch does the bending motion. As such, an increase in bending occurs at the center.

Freelance bending is often used to track parts.

2- Closed bending

In closed bending the bending punch pushes the workpiece to the closed matrix. The process of forming is completed with a final multiplication pressure.

There are two types of V-shaped and U-shaped closed bends.

2-1 bending - V shape

Punch and matrix are made in V-shape.

This is done at the beginning of the free-form bending. By the way, the workpiece acquires a new bending radius during forming the workpiece.

2-2 U-shaped closed bending

In U-shaped bending, the final shape is obtained by the final multiplication action.

In order to prevent the arc from forming at the bottom of the piece, it is often used with a punch to the matrix.

3. Bending with rolling

Rolling bending is applied by bending moment with three rollers.

 The upper roller is oscillating to the angle r and the two lower rollers are height adjustable. Both rollers are movable. By adjusting the rollers, the diameter of the parts changes so that the smallest diameter is limited by the size of the bending roller and the largest diameter by the plasticity condition.

2-4 Bending deformation range

2.4.1 Stresses applied to the material

The stresses applied to the cross section vary.

 The inner fibers are suppressed along the bending arms.

                           Spreads perpendicular to the force.

The outer fibers are stretched along the bending arms.

                          It is suppressed in a perpendicular direction to the bending arms.

Neutral fibers have no longitudinal changes. These fibers are almost in the middle.

The actual position of the neutral fibers is shifted to a smaller radius. Also, depends on the thickness of the sheet s and the bending radius r.

2-4-2 Closed Mold Bending

In bending molds the arbitrary forms of -v and -u shape are obtained with the application of the ultimate multiplication force and large enough with perfect accuracy.

The smaller the radius of curvature ri (= radius of punch), the more precise the closed angle of the arms. However, the bending radius shall not be less than 0,6 s and, in the case of high strength, equal to the sheet thickness.

2-4-3 Bending with rolling

In bending by rolling the limit values, the bending radius is obtained from the elasticity. In the smallest bending radius the rolling dimensions are also effective on it.

Maximum bending radius to mm ri max

Modulus of elasticity to N / mm2 E

Resistance to N / mm2 Re

Sheet thickness in mm S

Minimum bending radius allowed to mm ri min

Sheet thickness in mm S

Sex coefficient according to Table 2-2 - C

The bending radius of ri must be greater than ri min.

For N / mm2E steel = 2,1.105

Table 2-2 sex coefficient C

C values

Sex

Hard work

Soft annealed

Bending line position relative to

Rolling direction

Bending line position relative to

Rolling direction

Along

Perpendicular

Along

Perpendicular

0.8

0.3

0.3

0.01

Al

2

1

0.3

0.01

Cu

0.8

0.4

0.3

0.01

CuZn 37 (Ms 63)

0.8

0.4

0.4

0.01

13th St

1

0.5

0.5

0.01

C15-C25

St37-St42

1.5

0.8

0.8

0.3

C35-C45

St50-St70

2-5 Spring return

In any bending process, the bouncing phenomenon occurs. Bouncy bounce means the deviation from the bending angle of the theory.

 The size of the spring return depends on:

1- Limitation of the sex of the bending piece

2- Type of bending (free bending or closed bending)

3. Bending radius: The smaller r is, the larger the bending deformation area and the smaller bending return.

result is:

The angle of the bending mold should be smaller than the angle of the piece.

Bending angle or radius coefficient

*

Angle back to degree

*

Sheet thickness in mm

The actual angle to the degree

Table 2-3 The spring angles β = f (ri, s) for St up to Rm = 400 N / mm2 and Ms up to Rm = 300 N / mm2

1

3

β to degree

2-4

0.8-1.9

0.1-0.7

S to mm

1.s-5.s

1.s-5.s

1.s-5.s

ri to mm

2-6 Determining the length of the raw piece l

The sum of the bent and straight parts L = L1 + Lb + L2

Width in mm Lb

Arch length in mm L1

Arm length in mm L2

Bending radius to mm ri

Sheet thickness in mm s

Correction factor - e

Bending angle to degree a

At state 90 = L can be written: