Press brake bending is one of the important procedures in the sheet metal processing industry.
It involves forming sheet metal into the desired profile by applying force to the workpiece.
This process is generally performed using a press brake - a mechanical processing tool that is mainly used for sheet metal bending and forming.
Bending is a common process used for manufacturing parts and workpieces in various industrious fields. It can deal with small parts as well as large workpieces.
Due to the different thickness, hardness of the sheet metals, and different shapes of anticipated profiles.
Therefore, we need press brakes with different tonnage and pressure to bend sheet metals.
Bending stretches and compresses sheet metal. External force only changes the shape of the metal plate.
The length of the outer part of the sheet metal will be elongated, while the inner part will be compressed and the length will be shortened.
However, the length of the neutral axis remains unchanged.
The ductility of sheet metal allows its shape to change while other parameters, such as volume and thickness, remain constant.
In some cases, bending may alter the external characteristics of the sheet metal.
Additionally, bending can change the moment of inertia of workpieces.
The tonnage of press brakes is determined by the driving source, which can be mechanical press drive, hydraulic press drive, pneumatic press drive, or servo press drive.
Furthermore, it's also necessary to match punches (upper dies) and dies (lower molds) with different heights, shapes, and V-opening sizes.
Generally, bending dies are made of gray cast iron or low-carbon steel.
However, the materials of punches and dies vary from hardwood to carbide according to the workpiece.
The sheet metal is placed properly on the bottom die, and the punch is lowered on the die through the power of the ram.
The bending process involves repeating the bending stroke several times to achieve the desired profiles.
The metal plate will rebound slightly after bending.
To ensure that the predetermined bending radius and bending angle remain unchanged, the bending radius should be set to a value greater than the predetermined bending radius during operation.
As a result, the final bending angle will become smaller.
Types of Press Brake Bending
There are different types of sheet metal bending methods, based on the relationship between the end tool position and the material thickness.
These methods also differ in the method of plastic deformation of the plate.
Although the bending techniques are different, the tooling and configurations are basically the same.
Bending methods are also determined by the material, size, and thickness of sheet metals.
The bending dimension, bending radius, bending angle, bending curvature, and bending position in the workpiece are also essential for the bending methods.
V bending is one of the most common types of sheet metal bending methods.
It requires a V-shaped punch and die.
During the bending process, the metal plate is placed on the V-shaped die, and the punch presses the metal plate into the V-shaped die under the action of pressure.
The bending angle of the metal plate is determined by the pressure point of the punch.
The angles and shapes of the dies include acute angle, obtuse angle, right angle, etc.
V-bending can be subdivided into air bending, bottoming, and coining.
Air Bending
Air bending is also called partial bending because the workpiece is not in full contact with the die.
In air bending, the sheet metal is only connected with the shoulder of the die and the tip of the punch.
The punch is pressed onto the plate and passes through the top of the die into the V-shaped die opening, but does not contact the surface of the V-shaped opening.
Therefore, the distance between the punch and the sidewall of the die must be greater than the thickness of the metal plate.
Air bending is the bending method with the least contact with sheet metal.
The equipment only needs to contact the sheet metal at three points, namely, the punch, punch tip, and die shoulder.
Therefore, the relationship between the bending angle and the tooling angle is not very significant.
The depth of the punch pressing into the V-shaped opening is the important factor that affects the bending angle.
The greater the pressing depth of the punch, the sharper the bending angle.
The bottom die and punch used in air bending do not need to have the same radius, as the bending radius is determined by the elasticity of the sheet metal.
Air bending is the most widely used bending method due to its many advantages.
Because the punch tip does not need to be pushed past the surface of the metal, it requires less bending force or tonnage.
Moreover, it does not require too many tools and the operation is simple and flexible.
However, air bending also has some disadvantages. It will result in a certain degree of springback after bending.
Therefore, during bending, the actual bending angle should be sharper than the preset bending angle to achieve the final bending angle.
In addition, in air bending, because the metal plate and die are not in full contact, ensuring bending accuracy is difficult.
Also, it is challenging to maintain a highly accurate stroke depth.
Bottoming
Bottoming is also known as bottom pressing, bottom bending, or bottom striking. Like air bending, bottom bending also requires a punch and die.
In bottom bending, the punch presses the metal plate to the bottom of the die, so the angle of the die determines the final bending angle of the metal plate.
The release of the punch will cause the sheet metal to spring back and contact the die.
Excessive bending helps to reduce springback. Using more force will also reduce the springback effect and provide better accuracy.
The difference between air bending and bottom bending is in the radius. The radius of the die determines the inner radius of the bending sheet metal.
The width of the "V" shaped opening is usually 6 to 18 times the thickness of the sheet plate.
In bottom bending, because the angle of the die is fixed, the bending accuracy is higher, and the springback is smaller.
However, a larger tonnage of force is required. Moreover, each bending angle, plate thickness, and material requires a separate die
Coining
Coining is also a widely used bending method. The word “coining” comes from coin making.
In the United States, in order to print Lincoln's profile on a coin, a large tonnage machine is used to compress the coin to obtain the same image as that on the mold.
In coining, its punch and metal plate are at the bottom of the die.
The force produced by the punch is 5 to 8 times that of air bending. In this way, the sheet metal will hardly spring back.
The bending accuracy of coining is extremely high and the bending radius is small. Therefore, its cost for manufacturing is also very high.
However, in this bending process, the press brake and tooling are easy to be damaged by friction.
Moreover, more toolings need to be equipped. Basically, each plate thickness needs different punches and dies. Also consider the angle, radius, and die opening.
What Needs To Be Considered When Bending a Metal Using a Press Brake?
Types of the Bending Materials
Before sheet metal bending, we must first make sure which materials are good for bending.
Some metal materials have good ductility, and these kinds of metals are more suitable for bending, while some metals are less malleable or brittle, and are easy to be damaged or broken during bending.
Materials like mild steel, annealed alloy steel, 5052 aluminum, copper, etc. are malleable and easy to bend, while some materials, such as brass, 6061 aluminum, and bronze, are difficult to bend and more likely to crack.
Bending Springback
In the bending process, the sheet metal inner surface will be compressed and the outer surface will be stretched.
Because the metal plate has a good bendability, the compressed surface will produce a certain springback after the load is relieved.
As a result, over-bend is necessary when bending.
The bending radius affects the springback of the plate. The larger the bending radius, the greater the springback.
Using a sharp punch can reduce springback. Because the sharp punch has a small inner radius.
Bend Allowance
Bend allowance is a critical factor to consider when calculating the length of material required for a bending operation.
It refers to the length of the neutral axis between the two bend lines, and it can vary depending on the thickness, material, and bending angle of the workpiece.
To calculate the bend allowance, you need to take into account the material's tensile strength, elongation, and thickness, as well as the bend radius and angle.
Once you have determined the bend allowance, you add it to the total flat length of the material to obtain the required material length for the desired workpiece.
It's essential to ensure that the bend allowance is accurate because even a slight miscalculation can lead to errors in the final workpiece's dimensions and shape.
By taking into account the bend allowance, you can achieve more precise and consistent results in your bending operations.
Conclusion
Air bending, bottoming, and coining are very effective and common bending methods.
You need to determine which bending method to use according to the material, thickness, length, ductility and complexity of the workpiece.
You can also consult our sales who can recommend the most suitable and intelligent press brake for you.
ADH produces all kinds of CNC press brakes, NC press brakes, and even all kinds of large press brakes.
ADH is a professional sheet metal machine manufacturer that can provide you with a comprehensive range of sheet metal processing solutions.
