Bending
PDF brochure (You need ACROBAT READER - download program)
This chapter is dedicated to free bending including curling technology. The result of bending depends on a number of factors which have been divided into the following three chapters: plate, tools, procedure.
Steel quality
Higher strength requires greater bending springing-back force.
The stronger and harder the metal,
Surface
Our recommendation applies to blasted plate with anti-corrosion paint. Non-blasted material can be bent to relatively smaller radii. The material's bendability can indirectly lead to surface defects and rusting on the side of the material, which will be subjected to tensile stress. In critical cases it will be necessary to correct these defects by grinding.
Edges
Flame-cut or sheared edges must be rid of irregularities caused by flame-cutting and ground.
Thickness (t)
A rule applies that thinner material can be bent to smaller radii.
Direction of rolling
Material bent to smaller radii should be bent almost perpendicularly to the direction of rolling.
Bending length
If the length of the material is less then ten-times the material thickness, it can be bent to a smaller radius that the values shown in the table.
Stamping angle (R)
When bending HARDOX and WELDOX plates, the most important parameter is the correct stamping radius (see picture).
With softer steels (up to WELDOX 500 inclusive), we recommend to bend the material using a stamping radius equal to or smaller than the required radius of the bend.
For harder steels we recommend to bend the material using a stamping radius equal to or greater than the required radius of the bend.
The following table shows minimum stamping radius at which the material being bent to 90 degrees does not break yet.
Width of the stamping die slot (W)
The table above shows recommended minimum widths of the stamping die slot required to spring-back the material. Increasing this width will reduce the bending force and forcing-off, at the expense of greater springing-back of the material.
The opening angle has to be sufficiently small to allow adequate folding (see Fig. and Table ). When roller-bending, the springing-back will be much greater than the values stated in the table.
Friction
The stamping die edges must be clean and undamaged. The force necessary to bend the material can be reduced by using as the stamping die edges rotating circular rods, or by lubricating the die edges. This will reduce the risk of breaking.
Bending angle
The values recommended in Table 1 apply to bending to a 90° angle. If the angle is smaller, we can use a stamping die of a smaller radius than the recommended values in the table.
The bending angle has less effect on the required force and springing-back of the material than the width of the stamping die slot and the steel quality.
Bending force (P)
The required bending force can be estimated using the formula below. The force is in tons (1 ton = 10 kN) with a ±20% accuracy, under the condition that all dimensions are in mm. The symbols used are shown in Fig. 1. The value of the material's tensile strength Rm can be obtained from Table 4.
If the stamping die radius used to bend the material is much greater than the radius shown in Table 1, the required force might be greater that the value derived from the above formula, unless you increase the width of the stamping die slot accordingly.
Example 1:
A bending press is capable of bending only 20 mm thick steel plate EN 10025 (S355), (11 523 by STN) using a stamping die with a 150 mm wide slot. If we use the same die and the bending length is identical, how thick HARDOX 400 material will the press be able to bent?
The bending force should be identical. Changed will be only the material thickness (t) and tensile strength (Rm). If we substitute the values to the formula and simplify the equation, we get:
202 x 550 = t2 x 1250
The HARDOX material thickness (t) will be 13.3 mm.
Thus the W/t ratio for the HARDOX material will be 150/13.3 =11.3, which according to Table 1 is adequate.
Example 2:
In order to make a 2000 mm long cantilever, the material has to be bent. We have two options:
(a) use a10 mm thick EN 10025 (5355) material (11 523 by STN) of standard tensile strength 550 N/mm2, or
(b) a 7 mm thick WELDOX 700 material of standard tensile strength 860 N/mm2
In either case the available stamping die with a 100 mm wide slot will be used. What force will be necessary for the two steels?
For 11523:
tons
For WELDOX 700:
tons
The material thickness has more effect as its strength, therefore the force necessary to bend WELDOX will be in this case smaller.
This chapter is dedicated to free bending including curling technology. The result of bending depends on a number of factors which have been divided into the following three chapters: plate, tools, procedure.
| Fig. 1 Bending perpendicularly to the direction of rolling | Material ID is always stamped perpendicularly to the direction of rolling |
| Bending axis | |
| Grind off all defects. Grind off also all cutting edges. | |
| Direction of rolling | |
| To prevent the stamping die from getting damaged, edges of the die slot should have the same hardness as the material
being bent. A simple method how to guarantee this is to mill grooves in the die edges and insert in them for instance greased circular rods made tool steel. The die edge radius (r) should be at least equal to half the material thickness (t). The die slot must allow the material to back-spring. If for instance we want to bend HARDOX 500 to a 90°C angle, then the angle of the die slot should not be greater than 70°C (see Table 1). |
Material
Steel quality
Higher strength requires greater bending springing-back force.
The stronger and harder the metal,
- the greater force is required to bend it,
- the greater the material springing-back will be,
- the greater the stamping angle necessary to bend the material,
- the greater the width of the stamping die slot necessary to bend the material
Surface
Our recommendation applies to blasted plate with anti-corrosion paint. Non-blasted material can be bent to relatively smaller radii. The material's bendability can indirectly lead to surface defects and rusting on the side of the material, which will be subjected to tensile stress. In critical cases it will be necessary to correct these defects by grinding.
Edges
Flame-cut or sheared edges must be rid of irregularities caused by flame-cutting and ground.
Thickness (t)
A rule applies that thinner material can be bent to smaller radii.
Direction of rolling
Material bent to smaller radii should be bent almost perpendicularly to the direction of rolling.
Bending length
If the length of the material is less then ten-times the material thickness, it can be bent to a smaller radius that the values shown in the table.
Tools
Stamping angle (R)
When bending HARDOX and WELDOX plates, the most important parameter is the correct stamping radius (see picture).
With softer steels (up to WELDOX 500 inclusive), we recommend to bend the material using a stamping radius equal to or smaller than the required radius of the bend.
For harder steels we recommend to bend the material using a stamping radius equal to or greater than the required radius of the bend.
The following table shows minimum stamping radius at which the material being bent to 90 degrees does not break yet.
| Minimum recommended stamping radius (R), slot width (W) for material thickness (t) and bending to 90° in the direction of rolling and in the direction perpendicular, with the corresponding material springing-back value. | ||||||
| Thickness | Perpendicular | In direction | Perpendicular | In direction | Springing-back | |
| */ when bending HARDOX 450, HARDOX 500 and WELDOX 1100 material, it is necessary to proceed very carefully. These materials have a high strength and bending them requires a considerable force. If the material breaks, pieces will fly off in the direction of bending. Therefore during bending operations the operator or any other person may not stand in front of the machine, but rather at the side of it. | ||||||
Width of the stamping die slot (W)
The table above shows recommended minimum widths of the stamping die slot required to spring-back the material. Increasing this width will reduce the bending force and forcing-off, at the expense of greater springing-back of the material.
The opening angle has to be sufficiently small to allow adequate folding (see Fig. and Table ). When roller-bending, the springing-back will be much greater than the values stated in the table.
Bending procedure
Friction
The stamping die edges must be clean and undamaged. The force necessary to bend the material can be reduced by using as the stamping die edges rotating circular rods, or by lubricating the die edges. This will reduce the risk of breaking.
Bending angle
The values recommended in Table 1 apply to bending to a 90° angle. If the angle is smaller, we can use a stamping die of a smaller radius than the recommended values in the table.
The bending angle has less effect on the required force and springing-back of the material than the width of the stamping die slot and the steel quality.
Bending force (P)
The required bending force can be estimated using the formula below. The force is in tons (1 ton = 10 kN) with a ±20% accuracy, under the condition that all dimensions are in mm. The symbols used are shown in Fig. 1. The value of the material's tensile strength Rm can be obtained from Table 4.
If the stamping die radius used to bend the material is much greater than the radius shown in Table 1, the required force might be greater that the value derived from the above formula, unless you increase the width of the stamping die slot accordingly.
Example 1:
A bending press is capable of bending only 20 mm thick steel plate EN 10025 (S355), (11 523 by STN) using a stamping die with a 150 mm wide slot. If we use the same die and the bending length is identical, how thick HARDOX 400 material will the press be able to bent?
The bending force should be identical. Changed will be only the material thickness (t) and tensile strength (Rm). If we substitute the values to the formula and simplify the equation, we get:
202 x 550 = t2 x 1250
The HARDOX material thickness (t) will be 13.3 mm.
Thus the W/t ratio for the HARDOX material will be 150/13.3 =11.3, which according to Table 1 is adequate.
Example 2:
In order to make a 2000 mm long cantilever, the material has to be bent. We have two options:
(a) use a10 mm thick EN 10025 (5355) material (11 523 by STN) of standard tensile strength 550 N/mm2, or
(b) a 7 mm thick WELDOX 700 material of standard tensile strength 860 N/mm2
In either case the available stamping die with a 100 mm wide slot will be used. What force will be necessary for the two steels?
For 11523:
tonsFor WELDOX 700:
tonsThe material thickness has more effect as its strength, therefore the force necessary to bend WELDOX will be in this case smaller.
| Material thickness [mm] | Table 2 The table shows material thickness, at which an identical bending force is required per metre of length of the bend, with a width of the die slot (W) shown in the table |
|
| Bending force per metre [tons] - with width of the die slot (W) [mm] |
| Table 4 Mechanical properties |
|||
| Tensile strength Rm | Elongation A 5 | Hardness | |