Tools and products for bending and end forming tube and pipe

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Tube bending guide

Defects while tube bending

When bending the pipes there is a few adverse phenomena, which have an effect on the resulting shape of the bent parts.  Using appropriate tools we can avoid these defects and reduce their acceptable values.

Basic defects in tube bending:


Flattening of the cross-section of the tube

Flattening of the cross-section of the pipes is cause by the distribution forces through the bend and can be greatly reduced by using the appropriate inner insert (mandrel) and setting them up properly.
The flattening can be monitored by using the coefficient of ovalness: EQUATION

Crinkling of the walls of the tubes on the inner side of the bend.

This is where the stability of the walls is lost on the inner radius of the bend due to pressing forces caused during bending.  Reduction or limitation of wrinkling can be achieved by using the right insert (mandrel) and the appropriate wiper die and properly setting them up.

Thinning of the walls of the tubes on the outer side of the bend.

The thinning of the walls on the outer side of the radius of the bend and the strengthening of the outer radius of the bend due to the distribution of the forces during the bend. It's not completely possible to reduce the thinning of the walls, but through a bad choice of tools and their being badly set up can lead to increased thinning of the walls.

It is very effective to reduce the thinning of the walls with a so-called Booster, which is essentially just extra pressure, which pushes on the tube in the direction of the bend and reduces the tensile force on the inner diameter of the bend.

There are many other factors which can lead to the thinning of the walls during a bend. The parameters of the tube bending are crucial (OD, CLR, WT), but there is also a significant impact from the tools and how they are set up; the materials of the tube; the equipment used etc.
The calculation of the thickness of the walls on the outer radius of the bending depends on many relationships. But in essence all are only theoretical and neglect external influences. An example of one of them is below: EQUATION


Springbuck during bending

One common defect is the change in the radius of the bend and the change in the angle of the bend after the end of a bend due to springback.
It is necessary of course to differentiate ANGULAR SPRINGBACK from RADIAL GROWTH.

Angular springback

This is springback of the tube in the direction of the bend, when it is necessary to carry out bending with a greater angle of bend than is necessary (so-called overbending), or the real effect of springback of the deformation is reduced when the tube returns back.

Radial growth

This is about the growth of the radius of the bend over the radius that the tool has from the effect of the springback defect. There was a significant increase occurs primarily in large relative radius bends ( "D of bend") and during the bending high-stiffness materials.  In these cases it is necessary to reduce the radius of the tools so that they have the required shape after bending.