Rotary draw bending
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Definition
From http://www.thefabricator.com/TubePipeFabrication/TubePipeFabrication_Article.cfm?ID=1444
By definition, a rotary draw bend is formed by drawing the workpiece around a rotating bend former. The leading edge of the material to be bent is clamped to the bend forming die, while material rests between the forming die groove and the opposing force, commonly referred to as the counterbend or pressure die. The forming die rotates to the desired degree of bend, completing the process (see Figure 3). This bending process is less costly than some and far more expensive than others, so its suitability depends largely on not only your application and productivity requirements, but also on your budget.
Advantages
Compared to many other styles of standard bending, draw bending is a process that often more closely controls the material flow during bending. The reason is because it is drawing (or pulling) the material through a rotating bend die.
It does not have the potential twisting weakness of compression bending. It can create much smaller CLR (centerlne radius) bends than Push Bending.
Disadvantages
The disadvantage is that there is a limit on how large a radius can be. These disadvantages are addressed with Push Bending. Some rotary draw benders can be converted so they can both draw and push on the same bender. Typically the draw bend tooling is placed on the lower radius and the Push Bending tooling is placed on the upper radius.
As of April, 2008, CNC Bender software supports both types of bending on the same bender. See this page for more information on the version of CNC Bender that can handle Push Bending here: CNC Bender v11-20080424
