The friction between the tube and the tools at the point of bend. Drag has the undesirable effect of retarding the free flow of the tubing material as it drawn forward around the bend die and so becomes plastic at the point of bend. This retardation of the flow exacerbates the inherent compression of the intrados and elongation of the extrados, and so must be minimized. Drag, however, is also inherent to the rotary-draw bending process and cannot be completely eliminated, but low direct pressure and a forward mandrel setting do keep drag to a minimum.
FREE Tube-Bending Guide Download:
A complete guide to the principles of the 4-Step set-up for tube-bending tools
This is a printable handbook showing how to implement in four standardized steps the “forward mandrel” set-up for rotary-draw tube-bending machines and establish process control over the so-called black art. The procedure is based upon the guiding principle that the tools make the bend and takes advantage of the inserted design of modern mandrel tooling.