Bending of thin-walled tubing to a prescribed bend radius is typically performed by bending it around a mandrel of the desired bend radius, corrected for spring back. By eliminating the mandrel, costly setup time would be reduced, permitting multiple change of radius during a production run, and even intermixing different products on the same line. The principal challenge is to avoid buckling, as the mandrel and shoe are generally shaped to enclose the tube while bending. Without the shaped mandrel, buckling will likely occur sooner, that is, at larger bend radii. A test apparatus has been built for arborless bending. It has been used to determine the limits of bend radius, wall thickness, material properties, etc. on buckling. Key to the process is a set of moveable clamps, which grip the tube and rotate to produce the bend. A complex control system moves the clamps radially to maintain pure bending, without superimposing tension or compression. A series of tests were performed to document the safe region of operation to avoid buckling. Charts have been created to assist the operator, as well as the design engineer, in determining the minimum bend radius. Similar tests will be required for each additional tube size, thickness, material, etc.



College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering



Date Submitted


Document Type





Daniel Miller, pure bending, tube bending, buckling, failure boundary