Sheet metal bending is one of the most popular forming processes we use in creating sheet metal parts. It is a simple and cost-effective process for achieving all sorts of basic and complex part geometries.
Sheet metal bending is a very attractive option for both prototyping and low-volume production runs. It can produce highly precise sheet metal fabrication parts with no part variations and little to no tooling costs.
In this guide, we’ll run through all you need to know before choosing sheet metal bending for your part’s production. We’ll go through the various types of bending methods and their advantages, and we’ll also give you some design tips.
What is Sheet Metal Bending?
Sheet metal bending is the process of changing a piece of sheet metal’s geometry by applying force to it. The applied force deforms the metal permanently along a straight axis to a given angle or shape, resulting in a new part geometry.
You can create several types of shapes using this process. Here are some of them:
V-Bends:These are bends with a sharp “Vee” angle achieved with a punch and a die.
U-Bends: These are bends with a semi-circular U-shaped profile.
Channel bends:These are bends with a rectangular profile.
Types of Sheet Metal Bending Processes
There are several methods and processes you can use in bending sheet metal. You can use these different processes to create various shapes and geometries from sheet metal.
Here are some of the more popular sheet metal bending processes:
√ Press Brake
The press brake is the most common machine for bending and forming sheet metal. It comprises an upper tool known as the punch and a lower die.
To bend the sheet metal, the machinist places it between the punch and the die. The machine lowers the punch into the sheet metal and presses it into the die, creating the required geometry.
This machine can create several bend shapes like U-bends, V-bends, etc. It all depends on the die’s shape and the process used.
The three main press brake processes are; Air bending, Bottoming, and Coining.
In this process, the punch doesn’t force the sheet metal completely into the die during bending. When the machine lowers the punch into the sheet metal, the sheet metal doesn’t touch the die walls.
This method isn’t very accurate, and the metal is prone to spring back after bending. However, it is simpler, less costly, and doesn’t require complicated tooling or dies.
In Bottoming, the punch presses the sheet metal against the die with significantly more pressure. This way, the sheet metal is deformed to the exact shape and angle of the die.
In this version of Vee bending, the sheet metal touches the sides of the die. However, there is still a bit of space between the bottom of the die and the bend.
Coining uses the most pressure out of all the press brake procedures. It forces the metal into the die with incredible force to ensure it conforms exactly to the die’s shape.
After coining, there is no space left between the die and the metal. The sheet metal touches both the bottom and sides of the die.
Coining produces incredibly precise parts that have zeros spring back. However, due to the incredible pressure and precise tooling needed, it can be very expensive.
Wiping is a process of bending the edges of metal sheets into a given profile. The process involves clamping the longest end of the sheet.
The bottom part of the clamp has the required bend profile on its edge. After clamping, a tool moves over the unclamped end of the sheet and bends it over the bend profile on the clamp.
It is a fast process ideal for creating folds that aren’t sharp. However, the workpiece can be scratched or damaged as the tool moves over its surface.
√ Roll Bending
Roll bending is a process for creating curved geometries from straight pieces of sheet metal. Different shapes like cones, tubes, and rolls can be created using this method.
It uses a series of extrusion rollers to bend the material to the required radius or shape.
√ Rotary Bending
The rotary bending process is similar to the wiping process. They both have bottom dies cut to the required bend profile.
However, rotary bending utilizes a rotating, cylindrical punch instead of a punch going up and down. This cylinder has the desired bend angle cut out of it.
So, when the cylinder rotates, it bends the overhanging part of the sheet metal over the die’s bend profile.
Rotary bending is a great process for creating acute bend angles (<90°). Also, it doesn’t damage the workpiece’s surface, so it’s suitable for finished or delicate surfaces.
Advantages of Sheet Metal Bending
Sheet metal bending has many advantages as a manufacturing process. Here are some of them:
Requires little to no new tooling. Standard punches and dies are available for creating simple bends.
Very cost-effective for creating highly precise parts. Engineers can choose between using bottoming and coining where high accuracy is required.
Lead and setup times are short, making it ideal for low and medium-volume production.
Minimal post-processing is required, especially when compared with processes like welding.
Factors To Consider When Bending Sheet Metal
Before starting a production run with sheet metal bending, many factors must be considered. The engineer has to weigh these factors carefully and make certain decisions as they can affect the project’s success.
These factors include:
√ Material Malleability (Workability)
The ductility or workability of the material determines how easily you can bend the material. It also influences factors like the minimum bend radius and angles possible.
If you bend the metal past these angles and radii, you can experience cracking or failure along the bend seam.
Some highly malleable materials include:
1050, 1100, 1060 Aluminum
430 Stainless steel
√ Spring Back
Spring back refers to when the sheet metal tries to return to its original shape after bending. This usually happens with materials that have high tensile strength.
To avoid this, engineers usually bend the material past the required bend angle to compensate for spring back. Alternatively, they can use processes like bottoming or coining to get the material to retain its bent shape.
The tonnage refers to the capacity of the metal bending machine. It’s important to know the machine’s maximum pressure, bend length, bend radius, etc.
Knowing this enables the production engineer to design the manufacturing process accordingly.
√ Bend Allowance
Bending sheet metal deforms it plastically. This leads to an increase in the length of sheet metal, especially around the bend.
The bend allowance is a value engineers calculate to compensate for this length increase. This way, the final part will still be accurate and fit the required dimensions.
Sheet metal bending can create highly precise parts, but it still has some limitations. Here are some of the tolerances achievable with this process:
Sheet metal bending can’t create a true 90° corner. All corners have a radius, no matter how small.
Bend Angle: ±1°
Bending Length: ±0.0024mm (0.010”)
Tips on Designing Bends in Sheet Metal
For a seamless manufacturing process and a great final product, here are some tips for designing sheet metal bends you should follow:
The bend radius should at least be equal to the material’s thickness. Any less can lead to part distortions and cracking.
Make sure all your bends have the same direction, if possible. This will reduce the time spent repositioning the metal during manufacturing.
Use a uniform bend radius throughout the part.
Keep a suitable clearance between the bend and other features. Having them too close to a bend can lead to their deformation.
Here are suitable clearances for some features (T = metal thickness):
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