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Sheet metal bending process: Cold and hot bending, press, roll, and stretch bending

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C channel bending machine

Know What Materials Are Good For Bending

Some materials are more malleable than others. That means that some will bend, whereas others will weaken and crack. For less malleable materials, it might be practical to heat up the workpiece to reduce the risk of cracking.

Here are some common materials that you might run into in sheet form and some information on how easy they are to bend without cracking.

Mild SteelThis is very malleable, and you should be able to bend it cold without problem
Spring SteelVery bendable when fully annealed. You’ll need to heat treat it again to get it to perform like spring steel once it’s formed in the shape you want. If you try to bend it when it’s hardened, it’ll probably snap.
Annealed Alloy SteelWildly variable, unless you know the exact alloy. 4140 is usually pretty malleable,  In general, you’ll always want it to be annealed if you’re planning on bending it or else it’ll crack.
6061 AluminumMiserable to bend, cracking is very common and cold bending will always weaken the metal. Proper bending can be done with annealing the aluminum first, although it’s not an ideal candidate for formed parts.
5052 AluminumHighly formable, and one of the best kinds of aluminum to bend. Typically cracking or fatiguing is not an issue unless it needs to be unbent and reworked, but that’s pretty common of almost any malleable metal.
CopperSuper malleable, very easy to bend.
BrassFormability will be affected by how much zinc there is in the alloy – the higher the zinc, the less malleable to brass. For simple bends in sheet metal it’s usually not a problem, but for something more complicated you may need to use heat to soften it up.
BronzeGenerally stiffer and more likely to crack. Use heat to improve formability.
TitaniumThis is strong stuff, so you’ll need to be careful not to break your tools. To avoid cracking it, use a larger internal bend radius that you would for other metals. It also has a low modulus of elasticity, so you’ll need to overbend it considerably so it springs back in the shape you want.

Don’t Bend to a Sharp Internal Corner

If you bend to a sharp inside corner with sheet metal, you’ll be adding a ton of internal stresses. Even on malleable materials, you can end up cracking the metal at the bend, or weakening it to the point where it’ll break with minimal force.

The solution is to have a radius on the tool that you’ll be using to bend the metal. This will prevent cracking or weak spots.

Rule of thumb for most materials

The inside bend radius should be equal to the thickness of the material that you’re forming.

In other words, if you’re bending 1/8″ sheet, use a tool with a 1/8″ radius to form the inside of the bend. If you’re bending 0.020″ thick material, use a 0.020″ radius.

However: For most applications with stainless steel or aluminum, you can get away with a zero radius bend on anything under 0.050″ thick. It just won’t really be at maximum strength.

Minimum Bend Radius for Maximum Strength – Aerospace Standard


Aluminum0.0120.0160.0200.0250.0320.0360.0400.0450.0500.0630.0710.0800.0900.1000.1120.1250.1600.190
2024-0 & W0.0600.0600.0600.0600.0600.0600.0900.1900.1200.1200.1600.1900.2200.3100.360
2024-T30.0600.0600.0600.0900.0900.1200.1600.2200.2500.3100.3800.4400.6200.7501.000
2024-T360.0600.0900.0900.0900.1200.1600.1900.2500.3100.3800.4400.5000.7501.0001.250
3003-00.0600.0600.0600.0600.0600.0600.0600.0600.0900.0900.0900.1200.1200.1600.190
3003-H140.0600.0600.0600.0600.0600.0900.0900.1200.1200.1600.1900.2200.3100.3800.440
5052-00.0600.0600.0600.0600.0600.0600.0600.0900.0900.0900.1200.1200.1600.1900.220
6061-0 & W0.0600.0600.0600.0600.0600.0600.0600.0900.0900.0900.1200.1200.1600.1900.220
6061-T4 & T60.0600.0600.0600.0600.0600.0600.0900.0900.1200.1200.1600.1900.2200.3100.380
7075-0 & W0.0600.0600.0600.0600.0900.0900.1200.1600.1900.2200.2500.3100.3800.5000.620
7075-T60.0600.0900.1200.1200.1600.2200.2500.3100.4100.4400.5000.6900.8701.0001.250
7178-0 & W0.0600.0600.0600.0600.0900.0900.1200.1900.2200.2500.3100.3800.5000.750
7178-T60.0600.0900.1600.1900.2200.3100.3800.5000.5600.6200.6200.7501.0001.250
Stainless
302 Annealed0.0600.0600.0600.0600.0600.0600.0900.0900.0900.0900.1200.1200.1600.1900.2200.250
347-1A0.0600.0600.0600.0900.0900.0600.0600.0900.0900.0900.1200.1200.1600.1900.2200.250
1/4 Hard Cres0.0600.0600.0600.0600.0600.0900.0900.0900.1200.1200.1600.1900.2200.2500.3100.380
1/2 Hard Cres0.0600.0600.0600.0900.0900.1200.1200.1200.1600.1600.2500.2500.3100.3800.5000.620
Full Hard Cres0.0600.0600.0900.1200.1200.1600.1600.0900.2200.2500.3100.3800.4400.5000.6200.870

Bending forming

Definition

A stamping process for bending metal sheets, pipes, and profiles into workpieces with a certain curvature, shape, and size.

Application

Bending forming is widely used in the manufacture of high-pressure vessels, boiler drums, boiler tubes, steel plates and ribs of ship hulls, various utensils, instrument components, and cabinet inserts.

Bending deformation

When the material is bent, the stress state of each part in the deformation zone is different.

The part that does not deform in the middle of the cross-section is called the neutral layer.

  • Metals other than the neutral layer are subjected to tensile stress, resulting in elongation and deformation.
  • The metal within the neutral layer is subjected to compressive stress, resulting in compression deformation.

Since the stress and strain directions of the metals on both sides of the neutral layer are opposite, when the load is removed, the directions of elastic deformation and recovery of the metals on both sides of the neutral layer are opposite, causing different degrees of rebound.

Although the bending deformation is limited to a local area of ​​the material, the rebound effect will affect the accuracy of the bending part. There are many influencing factors of spring-back, and these factors are difficult to control. The accuracy of bending parts caused by spring-back has always been the key to bending production.

What is the difference between cold bending and hot bending?

According to the physical process characteristics, the bending of the workpiece is divided into two types: cold bending and hot bending.

So what are the cold bending and hot bending, press bending, roll bending, and stretch bending in the profile bending processing industry?

Definition of Cold bending

Bending at room temperature is called cold bending, which is often done by special bending machines.

Definition of Hot bending

When the cross-section of the workpiece is large and the radius is small, it needs to be bent under heating, which is called hot bending, which is often completed by intermediate frequency pipe bending equipment.

Cold bending

  • Most special-shaped materials are processed by cold bending.
  • According to the characteristics of the processing technology, the cold bending of the workpiece is divided into press bending, roll bending, and stretch bending.

Stretch bending

Stretch bending is to pull the deformation point of the profile after changing the extension of the profile, and drawing the arc by the template. The process methods include template rolling, tension adjustment, extension calculation, rebound calculation, stretching speed, boom angle, single-arm bending, and double arms are bent.

Press bending

Press bending is the most commonly used bending method.

Most of the equipment used are general mechanical presses or hydraulic presses, but also special bending presses.

Roll bending

Commonly used roll bending equipment is plate bending machine and profile bending machine.

The three-roller bending machine is based on the principle of three points to determine a circle and continuously bends the slab.

The three-roller plate bending machine has two driving rollers (fixed) and a pressing roller (adjustable). The relative distance between the pressing roller and the driving roller can be changed by adjusting the upper and lower positions of the pressing roller.

When bending, the plate is placed between the driving roller and the pressing roller, and the driving roller rotates in the forward and reverses directions to make the plate reciprocate. By adjusting the pressing roller to gradually press it down, the plate can be bent into a cylindrical surface with a required curvature, a conical surface, and a hyperboloid with a smaller curvature. One end of the pressing roller can be raised to facilitate the unloading of the workpiece.

There are also four-roller and multi-roller plate rolling machines. Four-roller plate rolling machines are used to roll thick plate cylinders. Multi-roller plate rolling machines with more than four rollers use multiple pairs of rollers to gradually bend the plates into complex shapes.

For bending parts that require high precision, large length and radius of curvature, and small transverse dimensions, they can be stretched and bent on a special stretch-bending machine. During stretching and bending, the entire plate thickness is subjected to tensile stress, so only elongation deformation occurs, and the deformation caused by spring-back after unloading is small, which is easy to ensure accuracy.

Profile bending machine

It is a kind of cold bending equipment for metal profiles and a commonly used bending machine for metal profiles.

Such as angle steel, channel steel, I-beam, metal square pipe, metal round pipe, and various metal special-shaped profiles.

The shapes that can be processed are round, arc, ellipse, parabola, and so on. Can be divided into vertical and horizontal, easy to operate, low cost, and suitable for cold bending forming of small and medium-sized materials.

Cold bending application

Stretch bending

Aluminum doors and windows, automobile luggage racks, automobile high-speed rail structural parts, elevator handrails, yacht structural parts, bathroom stainless steel pipes, etc., are widely used in high-speed trains, automobiles, ships, large buildings, and bridges, wind power generation, aviation, and other high-end fields.

Roll bending

They were used in the manufacture of circular flanges in automobiles, aerospace, rail transit elevators, conveyor guides, doors and windows, curtain walls, decoration engineering, ships, lighting, etc., and other industries.

Sheet Metal Terminology, Definitions & Phrases

Assembling

Binding metal with adhesives and bending in the form of a crimped seam through the process of welding.

Band saw

A tool with hardened blades that feeds sheet metal to ensure even cutting.

Base metal

Metal to be welded or cut.

Bend allowance

The length of flat sheet metal is required to make a bend of a specific angle and radius.

Chop saws

A tool that has an abrasive disc specifically designed for cutting sheet metal.

Corner relief

A technique involving the removal of a circular section from sheet metal to meet the design intent by accounting for material stretch while modeling.

Cut solid

Removing solid sections of material from the sheet metal wall.

Develop

The length of flat sheet metal is required to make a bend.

Die-cutting

The process that cuts metal pieces without the formation of chips or the use of burning, or melting; is known as shearing.

Extruded wall

A solid structure of sheet metal that extends from an edge into space.

Fab shops

Abbreviation of fabrication shops.

Form die

Device used for cutting out or stamping material.

Form tool

A tool used as a cast or mold to manipulate the shape of sheet metal.

Fully formed

Attaining a definite structure as intended.

Notch

A cut in the surface or edge of sheet metal.

Relief point

The point from where a sheet metal wall is sheared or torn, especially along seams.

Saw cut

Toothed cut.

Sheet metal

Metal formed into thin, flat pieces. Can be cut and bent to endless shapes and sizes.

Stamping

Using a tool to cut or emboss sheet metal.

Welding

The main focus of fabrication. The use of a torch or electric arc to join together metal pieces.

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