Tube bending can be one of the most complex industries there is. Here you will find a list of commonly used tube bending terms to help you get to grips with the basic concepts.
CCW (Counter clock wise or left-hand rotation)
On rotary draw tube bending machine the rotation of the bend arm swing.
CW (Clock wise or right-hand rotation)
On rotary draw tube bending machine the rotation of the bend arm swing.
CLH (Center line height)
Centre line height can be one of two things. 1/ the height of the centre of the tube groove from the floor and 2/ the height from the bottom of bend die to the centre of the tube groove on the die.
CLR (Centreline radius)
Radius around which the tube is to be bent, referencing the centreline of the tube.
Captive lip
Tooling in which the groove in the bend die and wiper die is deeper than half the diameter of the tube. Used only with interlock tools in high precision aerospace applications minimizes tool marks from the bend die in ultra thin wall applications.
Carbide coating
Surface treatment to bend die grip sections and clamp dies to help prevent tube slippage.
Compound tooling
Tooling that has very short DBB (distance between bends) requires that the bend die grip section and the clamp die have the previous bend machined into them. Tooling is expensive but more practical than short grip sections in high production applications.
DOB (Degree of bend)
Number of degrees a tube is to be bent.
“D” of bend
The centerline radius divided by tube or pipe outside diameter.
DBB (Distance between bends)
The distance between the tangent of one bend and the tangent of another bend.
Easy Way
When bending rectangular tube, if the tube stands vertically in the bend die, this is known as bending the “easy way”.
E-plane
Refers to the direction of bend for rectangular tubes. The tube stands vertically when placed into the bend die.
Galling
The transference of one material to another caused by high pressure and friction. Occurs when stainless steel is bent with a steel mandrel or wiper die; or when aluminum is bent with aluminum-bronze tools. Can be reduced by using better lubricants, alternate materials, or a slow arm rotation may help.
Gauge
When referring to pipe sometimes the wall thickness is defined by gauge rather than mm or inches. There are specific charts for this here.
Hard Way
When bending rectangular tube, if the tube stands horizontally in the bend die, this is known as bending the “hard way”
H-plane
Refers to the direction of bend for rectangular tubes. The tube lies horizontally when placed in the bend die.
Integral grip
If a bend die has a removable grip section; it is the straight portion of the groove between the grip and the tangent point.
ISR (Inside radius of bend)
Typically used when specifying radius to bend on rectangular and square tubes. ISR = CLR minus half of O.D.
Knurl
Most aggressive surface treatment to bend die grip section and clamp die to prevent slippage. Fine and coarse knurls are available. Does not deform or mark the tube the way serration does.
LRA (or YBC Method)
A method for describing tube shapes- length, rotation, and angle (LRA) or (YBC) methods. These are two names for the same system, which tells the bender how far forward to feed the tube, how many degrees to rotate it (if any), and how many degrees to bend it.
Pipe schedule
When referring to pipe, sometimes the wall thickness is defined by schedule rather than mm or inches. There are specific charts for this here.
POB (Plane of bend)
Refers to the amount of rotation between two bends. Specified in degrees.
Radial growth
After a tube is bent, it will spring back and the radius of the tube will grow. It will be larger than the bend die CLR. Radial growth is greatest with CLRs greater than three times the tube O.D. and when bending harder materials. Tooling can be designed to “compensate” for this if the springback properties are known.
Reverse interlock
Tooling that utilizes an interlocking design in which the wiper die, clamp die and the pressure die fit into the bend die. Used primarily for cosmetic or aerospace parts and high production bending.
Serration
Vertical groove surface treatment to bend die grip section and clamp die to prevent slippage. Usually used with grip section shorter than three times the tube O.D. Tube deformation and marks should be expected.
Springback
When a material is bent it has a tendency to want to return back to its original position. The amount that it does actually return is called springback. The springback amount will differ depending on the material being bent and the CLR on which it is bent.
Tube ID
Inside diameter of tube.
Tube OD
Outside diameter of tube.
Wall factor
Tube OD divided by wall thickness.
Wall
Wall thickness or gauge of tube or pipe.
Wiper Die
A wiper die is fitted into the rear of the bend former and traps the tube between it and the pressure die. The wiper die helps to prevent wrinkles occurring on the inside of the bend.
XYZ Method
A method for describing tube shapes. The simplest is based on geometric points in the Cartesian coordinate system. These are the X, Y, and Z axes of 3-D space.
