Sheet Metal Bending
Sheet metal bending refers to the process of changing the angle of a sheet or plate. It involves bending the sheet into shapes such as V-shapes or U-shapes. Generally, there are two methods for sheet metal bending: one is mold bending, which is used for complex structures, small volumes, and large-scale production of sheet metal structures; the other is press brake bending, which is used for processing larger-sized structures or sheet metal structures with lower production volumes. These two bending methods have their own principles, characteristics, and applicability.
1. Commonly Used Bending Dies
To prolong the lifespan of the dies, it is preferable to design parts with rounded corners.
Excessively small bending heights are not conducive to forming even with the use of bending dies. Generally, the bending height L should be greater than or equal to 3t (including the thickness of the material).
Processing methods for steps
For Z-shaped steps with lower heights in sheet metal, manufacturers often use simple dies for punching presses or hydraulic presses. If the production volume is not large, step bending can also be done using segmented dies on a press brake. However, the height H of the step should not be too high and should generally be within the range of (0 to 1.0)t. If the height is within the range of (1.0 to 4.0)t, the use of molds with loading and unloading structures should be considered based on the actual situation.
The height of this type of die step can be adjusted by adding shims. Therefore, the height H is adjustable, but it has a drawback: it is difficult to ensure the length L dimension and the perpendicularity of the vertical edge. If the height H dimension is large, bending on a press brake should be considered.
Press brakes can be classified into conventional press brakes and CNC press brakes. Due to the high precision requirements and irregular bending shapes in communication equipment sheet metal bending, CNC press brakes are generally used. The basic principle is to use the bending punch (upper die) and V-shaped groove (lower die) of the press brake to bend and form the sheet metal components.
Advantages: Convenient clamping, precise positioning, and fast processing speed.
Disadvantages: Lower pressure, suitable for simple forming, and lower efficiency.
Basic forming principle.
Sheet Metal Bending
During the processing, the selection of bending tools is mainly based on the shape of the workpiece. Generally, manufacturers offer a variety of bending tool shapes, especially highly specialized ones. To accommodate various complex bending requirements, customized bending tools of different shapes and specifications are made.
The lower die is typically a V=6t (t is the material thickness) die.
There are many factors that affect the bending process, including the radius of the upper die arc, material, material thickness, lower die strength, and the size of the lower die opening. To meet product requirements and ensure the safe use of press brakes, manufacturers have standardized the series of bending tools. It is important to have a general understanding of the existing bending tool series during the structural design process.
Basic principles of bending sequence:
(1) Perform bending from the inside to the outside.
(2) Perform bending from small to large.
(3) Bend special shapes first, then bend general shapes.
(4) The preceding process should not have any impact or interference on the subsequent processes.
2. Bending Radius
When sheet metal is bent, a bending radius is required at the bending point. The bending radius should not be too large or too small; it should be appropriately selected. A too small bending radius can cause cracking at the bend, while a too large bending radius can result in springback.
The preferred bending radii (inner radii) for different materials and thicknesses are shown in the table below.
The data in the table are preferred values for reference purposes only. In practice, the corner radius of bending tools from manufacturers is usually 0.3, while a small number of bending tools have a corner radius of 0.5.
For ordinary low-carbon steel plates, rust-resistant aluminum plates, brass plates, copper plates, etc., an inner corner radius of 0.2 is acceptable. However, for some high-carbon steel, hard aluminum, and super-hard aluminum, this bending radius can lead to bending fractures or cracking at the outer corner.
3. Springback
Springback angle Δα = b - a
Where:
b - Actual angle of the workpiece after springback.
a - Angle of the die.
Size of springback angle
The springback angle for single-angle 90° free bending is shown in the table below.
Factors influencing springback and measures to reduce springback:
(1) Mechanical properties of the material: The size of the springback angle is directly proportional to the yield point of the material and inversely proportional to the elastic modulus E. For sheet metal parts with high precision requirements, low-carbon steel should be chosen to minimize springback, avoiding high-carbon steel and stainless steel.
(2) The larger the relative bending radius r/t, the smaller the degree of deformation and the larger the springback angle Δα. This is an important concept in sheet metal bending. Within the limits of material properties, smaller bending radii should be selected to improve accuracy. It is especially important to avoid designing large arcs, as they present challenges in production and quality control.
Sheet metal bending refers to the process of changing the angle of a sheet or plate. It involves bending the sheet into shapes such as V-shapes or U-shapes. Generally, there are two methods for sheet metal bending: one is mold bending, which is used for complex structures, small volumes, and large-scale production of sheet metal structures; the other is press brake bending, which is used for processing larger-sized structures or sheet metal structures with lower production volumes. These two bending methods have their own principles, characteristics, and applicability.
1. Commonly Used Bending Dies
To prolong the lifespan of the dies, it is preferable to design parts with rounded corners.
Excessively small bending heights are not conducive to forming even with the use of bending dies. Generally, the bending height L should be greater than or equal to 3t (including the thickness of the material).
Processing methods for steps
For Z-shaped steps with lower heights in sheet metal, manufacturers often use simple dies for punching presses or hydraulic presses. If the production volume is not large, step bending can also be done using segmented dies on a press brake. However, the height H of the step should not be too high and should generally be within the range of (0 to 1.0)t. If the height is within the range of (1.0 to 4.0)t, the use of molds with loading and unloading structures should be considered based on the actual situation.
The height of this type of die step can be adjusted by adding shims. Therefore, the height H is adjustable, but it has a drawback: it is difficult to ensure the length L dimension and the perpendicularity of the vertical edge. If the height H dimension is large, bending on a press brake should be considered.
Press brakes can be classified into conventional press brakes and CNC press brakes. Due to the high precision requirements and irregular bending shapes in communication equipment sheet metal bending, CNC press brakes are generally used. The basic principle is to use the bending punch (upper die) and V-shaped groove (lower die) of the press brake to bend and form the sheet metal components.
Advantages: Convenient clamping, precise positioning, and fast processing speed.
Disadvantages: Lower pressure, suitable for simple forming, and lower efficiency.
Basic forming principle.
Sheet Metal Bending
During the processing, the selection of bending tools is mainly based on the shape of the workpiece. Generally, manufacturers offer a variety of bending tool shapes, especially highly specialized ones. To accommodate various complex bending requirements, customized bending tools of different shapes and specifications are made.
The lower die is typically a V=6t (t is the material thickness) die.
There are many factors that affect the bending process, including the radius of the upper die arc, material, material thickness, lower die strength, and the size of the lower die opening. To meet product requirements and ensure the safe use of press brakes, manufacturers have standardized the series of bending tools. It is important to have a general understanding of the existing bending tool series during the structural design process.
Basic principles of bending sequence:
(1) Perform bending from the inside to the outside.
(2) Perform bending from small to large.
(3) Bend special shapes first, then bend general shapes.
(4) The preceding process should not have any impact or interference on the subsequent processes.
2. Bending Radius
When sheet metal is bent, a bending radius is required at the bending point. The bending radius should not be too large or too small; it should be appropriately selected. A too small bending radius can cause cracking at the bend, while a too large bending radius can result in springback.
The preferred bending radii (inner radii) for different materials and thicknesses are shown in the table below.
The data in the table are preferred values for reference purposes only. In practice, the corner radius of bending tools from manufacturers is usually 0.3, while a small number of bending tools have a corner radius of 0.5.
For ordinary low-carbon steel plates, rust-resistant aluminum plates, brass plates, copper plates, etc., an inner corner radius of 0.2 is acceptable. However, for some high-carbon steel, hard aluminum, and super-hard aluminum, this bending radius can lead to bending fractures or cracking at the outer corner.
3. Springback
Springback angle Δα = b - a
Where:
b - Actual angle of the workpiece after springback.
a - Angle of the die.
Size of springback angle
The springback angle for single-angle 90° free bending is shown in the table below.
Factors influencing springback and measures to reduce springback:
(1) Mechanical properties of the material: The size of the springback angle is directly proportional to the yield point of the material and inversely proportional to the elastic modulus E. For sheet metal parts with high precision requirements, low-carbon steel should be chosen to minimize springback, avoiding high-carbon steel and stainless steel.
(2) The larger the relative bending radius r/t, the smaller the degree of deformation and the larger the springback angle Δα. This is an important concept in sheet metal bending. Within the limits of material properties, smaller bending radii should be selected to improve accuracy. It is especially important to avoid designing large arcs, as they present challenges in production and quality control.
