Sheet metal bending is a foundational fabrication process that uses specialized equipment like press brakes and rollers to create precise angular shapes in metal. This process offers significant advantages over welding and riveting—namely faster production, lower costs, and the ability to form complete parts from a single piece of material. Whether you’re designing automotive components, industrial equipment, or consumer products, understanding when and how to use bending will help you optimize your designs for manufacturability while achieving the strength, accuracy, and cost-effectiveness your project demands.

• Bending employs specialized equipment (like a press brake, rollers, or a CNC machine) to create precise bends in sheet metal.
• Bending can create sheet metal more quickly and at a lower cost, compared to methods like welding and riveting.
• Sheet metal bending is ideal for smaller production runs that don’t exceed thousands of units.
• The material’s tolerance, the equipment’s tonnage, and whether heat is applied by other processes (such as welding) all determine whether bending is a suitable option.

• What is Sheet Metal Bending?
• Types of Sheet Metal Bending
• When to Use Sheet Metal Bending in Fabrication
• Sheet Metal Bending Compared to Other Fabrication Processes
• Materials Suitable for Bending
• Design Considerations for Sheet Metal Bending
• In Summary
• FAQ Section

CNC sheet metal bending is an automated process that allows engineers to produce a wide variety of part geometries without tooling, at fast lead times, and with high levels of repeatability. Bending is especially useful for low- and-medium volume production, where the reduced quantities (several hundred to several thousand per lot) don’t justify the creation of costly and difficult-to-maintain stamping tools.

Bending sheet metal gives engineers the ability to create different shapes and designs in the material. In some cases, it can also create a whole part from a single piece of metal, which can be far more efficient than joining pieces together with hardware or welding, while creating a stronger and more durable result.

This Komaspec guide provides you with an overview of the main sheet metal bending processes, the advantages and disadvantages of each, basic design considerations, and advice for selecting materials.  This guide, along with our other articles exploring the subject, will provide you with a thorough understanding of how sheet metal parts are made so you’re better equipped to discuss your products with manufacturers. 

There are two basic methods for bending sheet metal:

• Brake press bending
• Rolling

There are also other techniques that can be employed when bends can’t be achieved through these simple means, but they are far less common.

Air Bending

Air bending is the most common press brake method. It involves using a punching tool to press the material against a V-shaped bottom die. To create a bend, the press pushes the tool downwards a set distance, bending the material into the bottom die, but not completely flush against it.

This method gets its name from the gap that is left between the part being bent and the die it is pressed against (since the partial bend still allows air to flow through when the metal is pressed). 

Bottom Bending

Bottom bending uses the same equipment as air bending. But instead of leaving gaps, the punch tool presses the material flat against the bottom of the die.

Bottom bending creates more accurate angles with less springback compared to air bending. However, each bend radius will require a different bottom die, use more machine pressure, and take longer to execute.

For a full breakdown of both methods, check out our guide here: Bottom Bending Vs Air Bending.

Once the rolling is complete, the bottom roller can be adjusted downwards to release the sheet metal. Most rolling machines also allow operators to open the top end yoke (as seen in figure).

When using rolling to produce a cylinder, a pre-bend operation may be required to ensure that each end of the cylinder meets after the rolling is complete.

Advantages of Sheet Metal Bending

Speed of Manufacture

Since less tooling is required, bending can produce sheet metal parts very quickly. This is especially the case with automated equipment, which can run 24/7 with only a handful of personnel to monitor production.

Accuracy

With careful planning during the design stage, sheet metal parts can be manufactured to a high level of accuracy. Advancements in fabrication techniques and equipment have made it possible to achieve accuracy levels of ±0.05 mm in some cases. Not only is bending accurate to begin with, but that accuracy can be repeated consistently throughout a production run, particularly when using CNC bending machines.

Reduced Post-Processing

Other fabrication processes require post-processing before a part is complete. Heat used in welding, for example, can cause dimensional distortion in a sheet metal part, requiring straightening before it can be used. Weld splatter might also need to be removed, which is a time-consuming and labor-intensive task. With bending, the parts are ready to go as soon as they’ve gone through the equipment.

Disadvantages of Sheet Metal Bending

Thickness Limitations

A rule of thumb in sheet metal bending is that thicker materials have a higher bend radiuse. As a result, tight bends are usually better performed on thinner sections of sheet metal rather than thicker ones.

This can mean that some complex parts can become limited to lightweight materials, suitable for low-load or no-load applications. Thicker materials can also bulge outward post-bend, crack if it is too rigid, or require a higher tonnage (and more expensive) press.

Need for Consistent Thickness

Because it’s optimal to produce parts from one piece of material, it’s better if the thickness of separate flanges on a part does not change. This means that it may be necessary to design a part so it has the same thickness throughout.

Cost of Manufacturing

Sheet metal bending is most competitively priced for low- to medium-volume production runs. When volume increases beyond 100s or 1,000s of units, stamping is generally considered a more cost-effective alternative, depending on part geometry and other design specifications. This is because CNC bending requires components to be processed one bend at a time, while multiple bends can be produced at the same time through progressive stamping. In those cases, even roboticized bending can’t compete with the cost of high-volume stamping.

While machine-assisted bending can reduce labor costs, they can still be fairly labor intensive in some cases. Some specialist bending projects may also require custom tooling, and while it costs significantly less than custom stamping tooling, it is still an additional expense.

Production Issues

In some cases, bending will leave indentations or scratches in the material, due to the pressure exerted through the narrow bending tool.

Fractures can also occur if hard metals are bent parallel to the direction the sheet metal has been rolled in during production.

Holes, slots, and other features located close to the bend can also become distorted during bending.

Finally, bends need to be in a position on the sheet metal that allows enough material to fit into the equipment without slipping.

Sheet Metal Bending Compared to Other Fabrication Processes (“Sheet Metal Fabrication”)

Most engineering materials are available in sheet form, and thus can be bent to some degree. There are, however, processing limitations with certain materials due to their different inherent properties.

Sheet metal is available in sizes ranging from gauge 50 (0.03mm) to gauge 1 (7.62mm). Bending with a brake press can be performed with all these thickness gauges and higher.

The thickness of materials is still widely referred to as gauges, despite many now being referred to in millimeters. One exception is aluminum, which is often still defined in all three dimensions by imperial measurements (feet and inches), with a gauge to denote its thickness.

For the best information on the materials available, refer to our standard materials page.

Each type of metal has its own unique characteristics. The following table outlines some of the factors you should consider when choosing materials.

Sheet Metal Materials (“Sheet Metal Standard Options in China”)

Mild Steel

The most commonly used material in the world, mild steel (also known as carbon steel) is available in both hot and cold rolled variants. Both offer excellent cold working performance, with high ductility.

The biggest downside to mild steel is the need for a rust-proof coating. Galvanized steel counters this issue by coming with a hard-wearing zinc coating that protects against moisture.

Aluminum

First used for aircraft production, aluminum alloys are now used in a vast range of applications. Because aluminum combines very well with other elements, it can offer a number of different properties.

The most commonly used aluminum alloys for sheet metal applications are the 1000 series alloys, particularly 1060 aluminum, which have high workability and low weight. These metals can be bent to tight radii without cracking, which can be a vital feature when manufacturing complex parts.

For general guidelines to material suitability for CNC bending, see the table below:

Material Properties (“How Material Properties Impact Air Bending Precision and Tolerances”)

Stainless Steel

Commonly used in the food and medical industries, stainless steel is an alloy of mild steel that contains at least 10.5% chromium. This gives the material corrosion resistance, with some grades excelling at resistance to acids, alkalis, and other chemicals.

Commonly used grades of stainless steel are 301 (for superior flexibility), 304 (for general use), and 316 (for greater strength and corrosion resistance).

Parts that will be subject to bending should be designed with the characteristics and limitations of the bending process in mind.

Bend Radius

When a material is formed into a bend, its outer surface is stretched and the inner surface is compressed. The result is a part with a rounded corner at the bent edge on both the inside and outside.

The bend radius is a measurement of the curvature of the inside bend edge. The potential radius will depend on the properties of the material, its condition, and the tooling geometry.

It’s good practice to ensure that all bends on a particular part are equal in radius because this greatly simplifies tooling set up, reducing cost.

Bend Length

The bend length required will usually depend on the design specifications of a sheet metal part. Bending machines, however, all have maximum widths according to their physical size and configuration. The standard sheet and press brake sizes go up to 2m, so if your parts are longer than this, it’s best to seek guidance.

Bend to Bend Distance

The size and shape of the tooling impose a physical limit on how close bends can be from one another. Bends without sufficient distance on the same side of a sheet will interfere with the tooling, while close bends on opposing sides will often be impossible to reach because of the bottom tool.

This commonly occurs when bending U-shaped sections where the upright flanges are longer than the horizontal section. In some cases, extra deep tooling can be used to avoid these problems. Supplementary processes like welding or bolting can also help you get the correct geometry.

Hole to Edge Distance

Materials stretch during bending, which causes internal stresses that are evenly distributed across the part. If a hole or slot is made too close to a bend, these stresses will be focused on that area, potentially causing deformation.

Springback

Metals tend to return slightly towards their original shape after bending, a phenomenon known as springback.

Several factors affect the amount of springback a part will exhibit:

• Materials with higher tensile strength have more springback
• A sharp bend radius usually produces less springback
• Wider die openings result in more springback
• The larger the bend radius relative to the material thickness, the greater the springback

In practice, springback generally only amounts to 1-2° of difference. This can usually be compensated for by adding a slightly greater bend so the springback causes the part to have the desired shape, which may be sufficient if a high level of accuracy isn’t required. When it is, using a newer CNC bending machine with built-in sensors to automatically compensate for material variability can ensure a more precise and consistent output.

Fabricators often use the K-factor to calculate springback and better understand how to compensate and achieve tighter tolerances when needed.

Processing Tolerances

As with any fabrication process, there are tolerances on dimensional accuracy. These often arise due to variations in sheet metal composition, thickness and processing. These variations should be considered when designing part to ensure the right bending methods and materials are used.

CNC control has reduced variation, and most tolerances can be achieved with modern press brake machines. It can, however, still be a pertinent issue, particularly when designing complex or precision parts.

Here are some rules of thumb:

•    You can’t typically achieve a true 90° corner
•    Corners will have a radius
•    Bend angles have a standard tolerance of ± 1°
•    Bend length tolerances are typically ±0.20 mm per bend (0.010”)

Consulting an experienced sheet metal fabricator can help you better understand tolerances in sheet metal bending processes.

Tonnage

As mentioned above, each press has a maximum tonnage capacity. It may be worth checking to make sure it will be able to perform the bends you need. If you’re not sure the tonnage will be sufficient, reach out to your manufacturer for advice before committing to a design.

Heat Affected Zones (HAZ)

Processes such as laser and plasma cutting create heat affected zones in metal. These can sometimes cause issues during bending, such as inconsistent shapes near holes and edges or cracking due to the increased surface hardness from cutting. If your parts will need other processes that create heat, be sure to take these issues into consideration.

For even more information, check out our sheet metal design guide.

CNC Sheet Metal Bending - Process Tolerances and Techniques

Minimum Distance Guidelines for Features Relative to Bends

Sheet metal bending has distinct advantages over alternative sheet metal fabrication processes, including higher output, lower cost, and greater flexibility in design. It also removes many of the difficulties associated with welding, riveting, and other assembly techniques. With modern technology and careful consideration during the design process, bending can create sheet metal parts that are stronger, lighter, and quicker to produce than those made with traditional fabrication methods.

What is sheet metal bending?

Bending is one of the most common sheet metal fabrication techniques. Bending utilizes specialized machinery to deform metal into an angular shape. This allows the creation of a wide variety of part geometries and is particularly versatile when performed alongside cutting. The most commonly used method for each process is brake press bending and CNC laser cutting.

What is sheet metal bending used for?

Sheet metal typically refers to materials under 3mm thick, but bending can be performed on materials far in excess of this, up to 8mm or more depending on the tonnage and material yield strength of the press being used. The process is very flexible and can accommodate a range of materials and thicknesses.

Bending is used to make a vast array of different parts that are used in every industry, including automotive, transport, domestic appliances, furniture, and industrial equipment.

What are the advantages of sheet metal bending?

Some of the major advantages of sheet metal bending include the speed of manufacture, its high accuracy levels, the reduced need for post processing, lower part weight, lower cost, the reduction or elimination of tooling, and reducing the number of parts produced during manufacture.

What are the disadvantages of sheet metal bending?

The downsides of sheet metal bending include limitations on how thick the materials can be, the need for consistent material thickness, the extra tolerance (roughly ±0.2mm per bend), and the cost of manufacturing for certain types of parts.

The specific downsides will differ from one bending method to another. CNC bending will require relief cuts to be added to the part in order to prevent material deformation or “mushrooming” due to the bending process. Stamping will have lower cost and higher precision, but require custom tooling. Rolling is typically a more manual process and can only produce limited types of bends.

What are some of the bending methods?

Sheet metal bending methods include air bending (in which the material is partially pressed into a V-shaped die), bottom bending (where the material is pressed fully against the die), and rolling (where the material is passed through cylinders to create a rounded bend).

Which materials are suitable for bending?

Most engineering materials are available in sheet form, meaning they can be bent to some extent. However, there are limitations depending on the bending process and the material’s properties. In general, the harder the material, the greater the risk for cracking or deformation.

How should a part be designed for bending?

Parts that will be made using bending equipment should be designed from the outset with the limitations and characteristics of the process in mind. You will have to consider the bend radius, hole to edge distance, bend to bend distance, springback, and processing tolerances.

Tolerances Guidelines for Sheet Metal Fabrication