Bending of Sheet Metal
Bending of sheet metal refers to the process of changing the angle of a sheet or workpiece, such as bending it into V-shape or U-shape. Generally, there are two methods for sheet metal bending: one is mold bending, used for complex structures, small volumes, and mass production of sheet metal structures; the other is bending machine bending, 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 advisable to incorporate rounded corners in the part design.
A too small bending height, even with the use of bending dies, is not conducive to forming. Generally, the bending height L should be ≥3t (including the thickness of the material).
Processing of Steps
For Z-shaped steps with relatively low height, manufacturers often use simple dies on punching presses or hydraulic presses for processing. If the production volume is not large, segmental dies can be used on bending machines as well. However, the height H should not be too high, generally ranging from (0 to 1.0)t. If the height is between (1.0 to 4.0)t, the use of loading and unloading structures for the dies should be considered based on the actual situation.
The height of this type of die step can be adjusted by adding shims, so the height H is adjustable. However, there is a drawback: it is difficult to guarantee the length dimension L and the perpendicularity of the vertical edge. If the height H dimension is large, bending on a bending machine should be considered.
Bending machines can be divided into conventional bending machines and CNC bending machines. Due to the high precision requirements and irregular bending shapes of communication equipment sheet metal bending, CNC bending machines are generally used. The basic principle is to use the bending blade (upper die) and the V-shaped groove (lower die) of the bending machine to bend and shape the sheet metal parts.
Advantages: Convenient clamping, accurate positioning, and fast processing speed.
Disadvantages: Low pressure, can only process simple forms, and lower efficiency.
Basic Principles of Forming
During the processing, the selection of the bending blade is mainly based on the shape requirements of the workpiece. Generally, manufacturers offer a variety of shapes for bending blades, especially highly specialized manufacturers who customize bending blades of various shapes and specifications to process complex bends.
The lower die is usually 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 size of the lower die opening. To meet the product requirements and ensure the safe use of the bending machine, manufacturers have standardized the series of bending blade dies. It is necessary for us to have a rough understanding of the existing bending blade dies during the structural design process.
Basic Principles of Bending Sequence:
(1) Bend from the inside to the outside.
(2) Bend from small to large.
(3) Bend special shapes first, then general shapes.
(4) The previous process should not affect or interfere with the subsequent processes after forming.
2. Bending Radius
When bending sheet metal, there should be a bending radius at the bending point. The bending radius should not be too large or too small and should be selected appropriately. A too small bending radius can cause cracking at the bend, while a too large bending radius makes the bend prone to rebound.
In practice, the rounded corners of manufacturers' bending blades are usually 0.3, and a small number of bending blades have a rounded corner of 0.5.
For ordinary low-carbon steel plates, rust-resistant aluminum plates, brass plates, bronze plates, etc., a 0.2 internal rounded corner is acceptable. However, for some high-carbon steel, hard aluminum, and super-hard aluminum, this bending radius can cause bending fractures or external rounded corner cracking.
3. Bending Springback
Springback angle Δα = b - a
Where b is the actual angle of the workpiece after springback,
and a is the angle of the die.
Factors influencing springback and measures to reduce springback:
(1) The magnitude 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 as much as possible to reduce springback, avoiding high-carbon steel and stainless steel, among others.
(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. For sheet metal bending, within the limits of material properties, smaller bending radii should be chosen to improve precision. It is particularly important to avoid designing large arcs, as they present greater difficulties in production and quality control.
What are the key points of sheet metal bending?
Sheet metal bending involves several key points that are important to understand. Here are the main ones:
1. Material Selection: The choice of material plays a crucial role in the bending process. Different materials have varying characteristics, such as ductility and elasticity, which affect how they respond to bending forces. Understanding the properties of the material is essential for achieving accurate and precise bends.
2. Bending Tools: Bending tools, such as dies and blades, are used to shape the sheet metal. The selection of the appropriate bending tools depends on factors like the complexity of the bend, the material thickness, and the desired bend angle. Different tools have different shapes and specifications to accommodate various bending requirements.
3. Bending Sequence: The order in which bends are made is important to ensure proper forming and avoid interference between subsequent bends. Generally, bends should be made from the inside to the outside and from small to large. Special shapes should be bent first, followed by general shapes.
4. Bending Radius: The bending radius refers to the curvature of the bend. It is important to choose an appropriate bending radius to prevent cracking or excessive springback. The bending radius should be selected based on the material type, thickness, and other factors to achieve the desired bend without compromising the integrity of the sheet metal.
5. Springback: Springback is the tendency of the material to return to its original shape after bending. It is caused by the elastic properties of the material. Understanding springback and its potential impact on the final shape of the bent part is crucial for achieving accurate dimensions and angles. Techniques such as overbending or adjusting the bending angle can be employed to compensate for springback.
6. Tooling Design: The design of bending tools, such as dies, should consider factors like the material thickness, bend angle, and desired precision. The shape and dimensions of the tools should be optimized to minimize distortion, improve accuracy, and reduce the risk of defects during the bending process.
7. Process Control: Controlling the bending process involves factors like the applied force, tool positioning, and speed. Proper process control ensures consistent and repeatable bends, reducing variations and improving overall quality.
By understanding these key points, sheet metal fabricators can optimize their bending processes, minimize errors, and produce high-quality bent parts that meet the desired specifications.
