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Metal Bending: Basics, Cold vs Hot, 6 Types, and Tips

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What is metal bending?

Bending is one of the most common metal fabrication operations. Also known as press braking(plate bending), or plate rolling, it is a process by which metal can be deformed when applying force to the subject at room temperature(cold bending), which causes it to bend at an angle and form the anticipated shape, which often results in it being in a ‘O’, a ‘V’ or a ‘U’ shape, this process is called cold bending(What is cold bending?).

Bending and Rolling Metal

Bending steel plates is defined as deforming steel around a straight axis. We use force to manipulate steel until it reaches a desired angle or shape. The difference between bending versus rolling depends on the radius. For larger radii, we call it plate rolling, and for smaller radii, we use to call it plate bending.

What is the process of bending?

In doing cold bending, a press brake(bending machine) tool or plate rolling machine is usually employed to bend the sheet/plate metal.
Commonly used equipment includes plate rolling machines, box, and pan brakes, brake presses, and other specialized machine presses.

Hot Bending vs Cold Bending

They are two metal bending methods cold and hot(induction) bending.

Cold bending methods often rely on sheer physical force to help bring the pipe to its final shape while hot bending methods use careful heating to reduce the force required. Each method has unique benefits and will determine the degree of bending possible and the final shape of the metal profiles(sheet/plate, pipe, beam, and others).

How many types of metal bending?

cone rolling machine
Roll bending: cone rolling machine

There are different varieties of bending used to achieve different bends in different ways. Three of these bending methods (air bending, bottoming, and coining) use a press brake, while the others such as folding, wiping, rolling bending, and rotary bending use assorted machinery to create the desired bends.

7 types of metal bending

  1. Air bending: Air bending is the most common type of bending used in sheet metal shops today. It is the process of forming materials by pressing a punch into the material, thereby forcing it into a bottom V-die to be mounted on the press.
  2. Bottom bending: Bottoming is a bending process in which sheet metal is pressed against a bottom die featuring a V shape, bottoming only uses a V-shaped die.
  3. Coin bending is a bending process in which the punch and the workpiece bottom are on the die. This produces a controlled angle, which leads to little spring back. There is more tonnage required for this type of bending than in air bending and bottom bending.
  4. Fold bending: Changes the shape of sheet metal parts by cold forming along straight lines, simultaneously over the entire length. The bending process is carried out simultaneously along the entire length of the bending line and it is a manufacturing process for the machining of sheet metal, i.e. thin, semi-finished metal products. Folding is used to produce profiles, more precisely, folded profiles.
  5. Wipe bending: In wiping, the longest end of the sheet is clamped, then the tool moves up and down, bending the sheet around the bend profile. Though faster than folding, wiping has a higher risk of producing scratches or otherwise damaging the sheet, because the tool is moving over the sheet surface. The risk increases if sharp angles are produced.
  6. Roll bending: The roll bending process induces a curve into bar or plate workpieces. There should be a proper pre-punching allowance.
  7. Rotary bending: Rotary bending is similar to wiping but the top die is made of a freely rotating cylinder with the final formed shape cut into it and a matching bottom die. On contact with the sheet, the roll contacts two points and it rotates as the forming process bends the sheet.

Benefits of 7 type metal bending

  1. Air bending is the most preferred type of metal bending due to its benefits – such as less need for the punch tip to be pushed past the surface of the metal and less weight required for bending.
  2. The advantages of bottom bending include better accuracy and fewer spring-backs, while the disadvantages are that a different tool is usually needed for each bend angle, sheet thickness, and material.
  3. Advantages of coin bending are that, in order to produce outstanding results, accuracy is essential and that is exactly what the coining method can provide. Along with being accurate, repeating the results is also an easy task when it comes to using this technique. Spring back is also less common when using coining, meaning that the metal is less likely to return to its original state.
  4. Large sheets can be handled in the fold bending process, making the operation easily automated. There is little risk of surface damage to the sheet.
  5. The main advantages to wipe bending are repeatability and that it requires less skill to perform the bend.
  6. The roll bending can make larger radii, this method allows us to make a cylindrical product, or even, with the right kind of control over the rollers, cones.
  7. For precision work, rotary draw bending dominates the tube bending landscape, especially for those applications involving tight radii—sometimes down to a CLR that’s just 0.7 times the tube OD (or as tube processors call it, less than 1×D).

5 Tips for Metal Sheet Bending

Bending steel plates can seem complex. However, with some tips, it can be easy. Below are some tips that can help you with the process.

  • Spring back: When bending a sheet, the material must be bent beyond its required angle. This is because sheet metal possesses a high-bending ability that allows it to spring back to its original position. Hence, an allocation must be made for such occurrence by bending the material slightly above the desired position.
  • Malleable enough: Bending into a sharp corner would crack the sheet metal. Therefore, you should avoid this as much as possible. It would be best if you considered the steel metal gauge, as not every material would be malleable enough to withstand bends into sharp corners.
  • Use bending machines: Always use bending machines where applicable as it provides support and guarantees cleaner sheet metal bending and continuous pattern across bent sheets.
  • Position holes: Process position holes should be created on bending parts to guarantee the sheet metal’s precise positioning in the die. This would eliminate the sheet metal moving during the bending process and ensure precise results across multiple sheet metals.
  • Bend allowance: Accounting for bend allowance is important in knowing how to bend sheet metal. This would guarantee more precise numbers ensuring accuracy in finished products.

Works Cited