An innovative PVC mandrel for controlling the cross-sectional deformation of double-ridged rectangular tube in rotary draw bending

In order to control the cross-sectional deformation of double-ridged rectangular tube (DRRT) in rotary draw bending (RDB), a PVC mandrel just supporting the back of ridge grooves was introduced. The characteristics of cross-sectional deformation of DRRT and its evolution with the new PVC mandrel were revealed numerically by comparing with that with the mandrel-core die. In order to evaluate the application scope of the new PVC mandrel, the cross-sectional deformation for different specifications of DRRT in RDB were also researched. The results show that: (1) the flange sagging Delta h, space deformation between ridges Delta d, and width deformation of inner ridge groove Delta w by using the new PVC mandrel can be better controlled than that by using the mandrel-core die. But the width deformation of the outer ridge groove Delta W gets a little larger; (2) by using the new PVC mandrel, the maxima of absolute values of Delta h and Delta w and the maximum of Delta W all increase firstly with the process of bending and then change little when the bending angle is larger than 60A degrees, which are consistent with the variation of the peak value of tangent stress on the flange, while the maximum of absolute value of Delta d increases continuously. (3) For small-sized DRRT, its cross-sectional deformation can be well controlled by using the new PVC mandrel. However, with the increase of dimension of DRRT, the cross-sectional deformation of DRRT increases obviously, and its distribution is extremely non-homogeneous.