There are five typical methods of bending in the industry: roll bending, incremental bending, hot bending, rotary-draw bending, and induction bending. Each method has its advantages. Some methods are more commonly used in the steel construction industry, while others are more common in the automobile or manufacturing industries.
Roll bending (cold bending) is the typical method of curving steel for construction and is usually the most economical for rolling members with tighter radii. A steel member is placed in a machine and curved between three rolls. Cold bending may also be called “pyramid rolling” because of the three rolls’ pyramid arrangement. Bending occurs when the distance between these rolls is manipulated before each successive pass.
The 3-roll profile bending machine is the profile bending industry workhorse. The profile bending machine has three hydraulically driven rolls in a triangular configuration. In a typical horizontal configuration, viewed from overhead, material is fed between the two top rolls and single bottom roll until the end of the material touches the far roll. The distance between the middle of the far roll and the middle of the bottom roll is called the grip length, which provides leverage to induce the force needed to create the bending moment. The greater the grip length, the more leverage you have. The downside: In most cases, the material within that grip length needs to be scrapped, which is the reason most profile bending machine request material that is a little longer than what’s required.
Incremental bending/incremental step bending or gag pressing is usually used for cambering and curving to very large radii. Bending is achieved by applying point loads with a hydraulic ram or press at the member’s third point. It is a cold-bending method that uses hydraulic rams to apply bending forces at several discrete, closely-spaced locations along the member. Cross-sectional elements can be supported mechanically or hydraulically to reduce distortion during the bending operation, resulting in the potential for small-radius bends with minimal distortion.
Incremental sheet forming (ISF) is a highly flexible manufacturing process suitable for low volume and rapid prototype production of sheet metal parts. The name incremental forming is used for a variety of processes, all characterized by the fact that at any time only a small part of the product is actually being formed, and that area of local deformation is moving over the entire product. It is generally carried out by having a small steel punch drawing consecutive overlapping contours over the sheet with increasing depth, thus creating a part of some depth. Although ISF is generally very slow, it is of interest because no or only a simple and cheap tool is required, making the process ideal for small-series production.
Hot bending is where a structural member is heated directly and then bent. The heat source could be a direct flame or furnace. This application is used extensively in repair.
Rotary-draw bending is where the structural member is bent by rotating it around a die. The member is clamped into a form and then is drawn through the machine until the bend is formed. This method produces tight radii and is mainly used for complicated bends in the machine and parts industry.
- Ram or push bending, as the name implies, uses a ram to force the extruded metal piece on a bending die.
- Hydraulic rotary draw bending process, place extruded aluminum onto a bender and hold it in place with a stationary or sliding pressure die and clamping block. The round bending die, powered by hydraulics, is rotated up to 90 degrees, bending the extrusion as it rotates.
- Electric rotary draw bending uses the same process as the hydraulic method, but allows faster setup.
Induction bending uses an electric coil to heat a short section of a structural member, and then that member is drawn through a process similar to rotary-draw and cooled with water directly after. In some cases, this process can produce a smaller, tighter radius.
Induction bending is a very effective method of section bending because it is fast, accurate, and almost error-free. The induction bending process is performed by heating a certain point of the metal profiles, which can then be bent effortlessly. It does not require any filling material, and the result of bending tends to keep deformation to a minimum. Many induction bending machines also choose this type of bending because of its sufficient energy. The heating process is the most time-consuming element of the process, after the heating process is completed, bending does not require much time at all.