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Static pressure dies do not move during the bending process, rather, the tube simply drags through the pressure die during the bend.
Traveling pressure dies, also called follower pressure dies, can reduce galling and marking of the tube by alleviating some drag during bending. By traveling at bend speed it can also reduce wall thinning on the out side of the tube. Some benders are equipped with boost or pressure die assist. By adding pressure at or faster than bend speed, material can actually be added to the outside of the tube.
Elliptical Tube Grooves for Bending Without Mandrels
Elliptical bending is not for every situation. It is a very specific solution which depends on tube O.D., (Outside Diameter) wall thickness, C.L.R. (Center Line Radius), and material and product specs. Bending with an elliptical shaped tube groove can eliminate the need for a mandrel, but comes with some cost. Because it actually reshapes and resizes the shape of the tube, a lot of the machines ability is used up in working the tube. Therefore, a machine's elliptical capacity is only 5/8 of its round capacity. To see if bending without a mandrel is applicable, you’ll need to know some formulas.
To find the Difficulty Factor (DF):
Tube O.D. divided by Wall = Wall Factor
C.L.R. divided by Tube O.D. = Degree Of Bend
Wall Factor divided by Degree Of Bend = Difficulty Factor.
Once you know the difficulty factor, you can evalutate the elliptical feasibllity per your material type and/or configurator data.
For more extensive information see our Nonmandrel Bending article. Because these factors, as well as the type of tube material affect the process, Tube Bending Concepts can customize shape geometry per your application, producing predicable results.
Square and rectangle tubing is usually bent using leaf tooling. Without leaf tooling, the vertically expanded tube will lock into the bend die. Once the leaf (or plate) is removed, the tube is free to be extracted. Single leaf tooling has one plate. For highly cosmetic parts, double leaf tooling provides very little marking.
To save time and effort, reach adjusted PRESSURE DIES eliminate excessive movements to the bolsters during set up. This allows significantly reduced set up time.