Tools and products for bending and end forming tube and pipe

Comprehensive range of services in the development, design and manufacture of tools, including customer support and advice

Tube bending guide

The basic parameters for tube bending

OD - outer diameter of tube
WT - wall thickness
CLR - Centre line radius

Using these parameters we can judge the difficulty of the bend and with other parameters of the tube we can then suggest the best set of tools for a given application.

Wall Factor (WF) - the relative thickness of the wall, this is the relationship of the outside diameter and the thickness of the walls of the tubes. The resulting value then determines whether it is a thin-walled or a thick-walled tube. Generally we can say that tubes with a relative WT below 10 are considered to be strong walled (thick walled) and conversely with a relative WT higher than 40 are thin walled.

Wall Factor (WF) = the outside diameter OD / thickness of the walls WT.

Note: In some literature on the subject there is the inverted ratio calculation:
Relative wall thickness = wall thickness / external bend radius, however, it is really the same thing reversed.

"D" of bend - or so-called relative bend radius, this parameter determines the character of the bend, whether it is a bend on a large radius bend or bend on a small bend radius.

"D" of bend = Central line radius CLR / Outer diameter of tube OD

Difficulty of bending then depends on both parameters at the same time.

The practical demonstration of this calculation of both these characteristics and their effect on the choice of tool you can find in the part Choice of tools, later on in this guide.

Other parameters are linked directly with the shape bent part and they also affect the difficulty bending and the selection of the appropriate tools.

DOB (Degree of bend) - the angle of bend between straight parts of the tube
DBB (distance between bends) - this is a straight distance between bends

For more complex components containing many bends in different planes, there are so-called X,Y,Z coordinates of the tubes, which together with the Centre Line Radius CLR simply define both the parameters used above times and DBB for all bends.