Experimental study on role of mandrel in thin-walled tube NC bending process with small bending radius

The mandrel (including flexible balls) is the key to improving the forming limit and forming precision in thin-walled tube NC bending process. In the study, one analytical model of mandrel (including mandrel shank and balls) has been developed and reference formulas have been deduced in order to select the mandrel parameters preliminarily, i.e. mandrel diameter d, mandrel extension e, number of balls n, balls thickness k, space length between balls p and nose radius r. The experiment has been carried out to verify the analytical model. Then the influence laws of mandrel parameters on wrinkling insatiability, wall thickness change and cross section distortion degree are investigated by experiment. The stepped retraction method is used to form the high difficult stainless steel tube with φ38 mm × 1 mm × 38 mm (1D).