What is Sheet Metal Bending?

Putting angular bends in sheet metal not only allows the creation of complex shapes – it can also dramatically enhance its strength and rigidity, as can be observed in angle iron and similar components. Bending sheet metal comes with some important benefits when compared with welding or casting, for example:

• Versatility: Capable of producing a wide range of shapes and components.
• Cost-effectiveness: Many bending methods offer high repeatability, reducing production costs.
• Strength retention: Properly executed bends do not compromise the material’s structural integrity.
• Efficiency: Modern presses and CNC systems provide high precision and throughput, essential for large-scale manufacturing.
• Consistency: When done by hand, welding depends largely on the skill of the welder, which can lead to inconsistent quality along the length of the join. A good quality piece of sheet metal will have its own internal consistency pre- and post-bend.

The act of putting a straight bend in metal sheeting can be achieved in a number of ways. The choice will depend on factors such as the thickness of the metal, the type of metal, availability of machinery, budget, whether a V-shape or a curve is desired, and the radius of the bend. Below are the commonest means of bending sheet metal.

Hydraulic bending machines

Hydraulic press brakes are integral to modern sheet metal bending. Their advanced technology makes them suitable for highly precise bending tasks. Used extensively for applications requiring meticulous control and accuracy, hydraulic press brakes function by using hydraulic fluid to exert force. Their ability to provide consistent pressure results in uniform bends, crucial for high-quality production.

Pneumatic bending

Pneumatic press brakes use compressed air to generate force for bending operations. Ideal for applications requiring less pressure than hydraulic bending, these systems are efficient for bending smaller metal parts. The simplicity of pneumatic systems makes them cost-effective and easier to maintain, though they are limited by the lower pressure output compared to hydraulic systems.

Electric bending

Electric bending machines use servos to deliver high torque movement directly to the punch. There are numerous benefits to this. They provide fast and instant power, available the moment the machine is activated, which means faster throughput. They can also operate with greater precision, thanks to the way the servos operate. Fewer moving parts, such as pumps and pistons, results in easier maintenance. And as they are either off or on, there’s no backup state where fluids need to be kept pressurised, which can make them more efficient. 

Computer numerically controlled (CNC) bending

CNC press brakes stand out for their precision and versatility. These machines can bend sheet metal from a few millimetres to several metres in length, enabling the production of both small-scale and large-scale components. The precision of CNC bending stems from the automated control systems that control the bending precisely, reducing human error and increasing production efficiency.

Mechanical bending machines

Mechanical press brakes are valued for their speed and accuracy. The mechanical design provides rapid cycle times, making them suitable for high-production runs. However, mechanical press brakes are less user-friendly compared to CNC models and generally lack the safety features and ease of use found in modern systems.

Here are the commonest means of metal bending in the industrial setting.

Air bending

Air bending is characterised by minimal contact between the workpiece and the equipment, engaging only the very tip of the punch and the die shoulders. The punch does not fully penetrate the V-die, allowing the material to bend under less force. That’s where the name comes from – there’s still a gap (air) between the edges of the punch and those of the V-die when the machine has finished its stroke. This technique is widely adopted due to its flexibility and reduced need for different dies. However, the accuracy of air bending depends on precise control of the punch.

Bottom bending

With bottom bending, the material is pressed against the V-die completely, although like air bending, only the tip of the punch presses against the sheet metal. This results in greater accuracy and reduced springback. Although it requires higher tonnage than air bending, bottom bending offers superior precision and repeatability, making it suitable for applications where consistency matters.

Coining

Coining involves pressing the punch and the material into the die with enough force to press the metal firmly between the die and the punch – no air gaps. This method produces minimal springback and exceptional accuracy. Coining demands significantly more tonnage compared to other bending methods but offers unparalleled control over the bend angle and consistency.

Folding

The folding process secures the workpiece with clamps and bends it by moving a beam along the sheet. This technique can manage large sheet sizes and allows for multiple bends, achieving complex geometries such as channels or tubes. The limited risk of surface damage and the ability to produce repetitive folds make folding a valuable method for specific large-scale applications.

Wiping

Wiping bends the metal by holding the workpiece between a pad and a die while a flange slides down to create the bend. This method ensures even force distribution across the workpiece, maintaining high precision and minimising surface damage. However, it is a costlier technique and cannot bend sharper than 90 degrees. It also requires specific tooling for curved shapes.

Joggling

Joggling is a method used for creating Z-shaped bends (with any angles from acute to obtuse) in sheet metal. This technique is particularly useful for producing patterns along the length of a workpiece, such as on overlapping cladding panels. It can also be used on small pieces such as brackets. Despite potential surface deterioration, joggling is valued for its versatility, low production costs and minimal springback.

Rolling

Rolling involves feeding sheet metal between paired rollers to form tubes, cones or large radius bends. Repeated passes are usually needed to achieve the desired curvature, making it especially suited for large workpieces in the construction industry. Rolling machines provide consistent results for long, continuous bends.

Rotary bending

Rotary bending uses a mandrel inside the tube to achieve precise bends up to 180 degrees. This method is highly versatile, accommodating multiple bends in a single run with limited springback. Despite its complexity and potential for surface deterioration, rotary bending is preferred for creating complex, highly accurate pipe and tube shapes.

Hot bending

As the name suggests, hot bending relies on the softening effect of heating metal to make it more pliable. The heating will be just part of the process – there will still be a punch and die, rollers or any of the other means of bending mentioned above. However, because of the extra pliability, there can be a reduction in tonnage compared with cold metal bending.

These are the main parameters that determine which machine and technique are used for a given bend in a certain type of sheet metal.

Springback

Springback is a prominent factor in metal bending. It is the effect of metal partially returning to its original shape after bending thanks to its “memory”. It necessitates overbending or employing methods like coining to mitigate its effects.

Bend radius

The bend radius is the inside radius of the bend. It is essential to select an appropriate bend radius to avoid cracking or deforming the material. The minimum bend radius depends on the material’s thickness and type. Generally, a larger bend radius is preferred to maintain the material’s integrity, reduce stress, and improve the bending process’s overall quality. However, a sharper bend will produce a neater finish, and might be necessary for engineering purposes.

Bend allowance

This is a critical measurement that considers the stretch and compression of metal. In short, a certain length of the metal sheet will be required to make the curve or angle itself, and this must be calculated precisely if the final piece is not to be too long or too short. The bend radius will need to be known to calculate the bend allowance.

You can hit the ground running by digesting a few tips before you do your first bend.

• Material and thickness: Always consider the thickness of the material to determine the appropriate bending method and required force. The material itself will also matter, as different metals have different characteristics under the stress of bending.
• Tooling selection: Use appropriate dies and punches to achieve the desired accuracy and reduce wear. While some tools can be taken off the shelf, others will need to be fabricated to achieve specific bends, especially with complex shapes and joggling.
• Pre-bend testing: Conduct sample bends to adjust equipment settings and achieve the desired outcomes before full-scale production.
• Consider springback: A 135 degree bend might require a tighter bend of (for example) 130 degrees to accommodate its relaxation after being bent. Testing should help to give consistent results.

Most metals can be bent with good results. The benefits of the commonest ones are listed here:

• Steel: Particularly galvanised and stainless steel, due to their robustness and versatility.
• Aluminium: Valued for its light weight and corrosion resistance, it’s suitable for both decorative and structural applications.
• Copper: Offering excellent malleability and conductivity, copper is ideal for specialty applications like electrical components. It’s also a beautiful architectural metal for cladding or indoor features.
• Brass: Combining strength with aesthetic appeal, it is frequently used in decorative applications, particularly where the patina of copper is not wanted. 
• Titanium: Known for its strength and lightweight properties, titanium is commonly used in aerospace and high-performance applications. It comes at a price, though.

Sheet metal bending is a cornerstone of manufacturing and construction, offering various methods to suit specific applications. Understanding the nuances of each technique and the considerations involved ensures optimal results. At Greengate we offer a range of metal bending services so speak to our experts about your sheet metal fabrication needs – we understand the properties and capabilities of all metals in common use, and can ensure your specifications are met precisely.