Tubing benders come in many sizes

Tubing benders come in many sizes, for use in everything from heavy construction to auto building to home landscaping. They range from a 16-ton hydraulic pipe bender to a handheld bender for small-gauge copper and aluminum tubing. All of them, however, use one of four basic methods. Ram bending is the cheapest and easiest method. Tube benders are restrained at two ends and a ram deforms the pipe in the middle. This is suitable for light gauge tubing only. Rotary draw bending is the most commonly used method, and maintains the diameter of the pipe without deformation. In this method, the tube is drawn through a stationary counter-bending die onto a forming die of a specified radius. These tube bending machines are used in the formation of exhaust pipes, process pipes, and any aluminum or stainless steel application where interior deformation can’t be tolerated. Bending is similar to rotary draw bending, except that the interior of the tube is supported by a flexible mandrel. The mandrel bends with the tube, ensuring that the interior diameter is not deformed. Ring roll bender is used for bending pipes and tubes with a large diameter. There are three rollers, two on the bottom and one on the top. As the pipe is rolled through, the top roller exerts a downward pressure, bending the pipe. The pressure of the top roller can be adjusted manually or hydraulically, and either two or all three rollers can be powered. This method is used to make drum barrels, awnings, and other circular shapes.

For a tube bending, two things happen to metal. The outside wall is reduced in thickness due to the stretching of the material and the inside wall becomes thicker due to the compressing of the material. The material actually is formed approximately about the centerline of the tube. The material that forms the outside of the bend has further to travel and therefore is stretched; the inside of the bend has less distance to travel and is compressed.
When the ratio of the tube diameter to wall thickness is small enough, the tube can be bent on a relatively small radius. Excessive flattening or wrinkling of the bend should not occur. The outside and inside of the bend tend to pull towards the centerline of the tube. Two factors that help prevent this from happening are a grooved bend die, which supports the tube along the centerline and the natural strength of the tube.