Effects of Various Factors on Formability of Press Bending of Tube Using Movable Rolls

The press bending of a tube using movable rolls is a process in which the distance between the rolls at the support points is small in the initial stage of bending, and the rolls move outward along the punch as the punch is lowered, bending the tube. In this process, the rolls always require a force in the inward direction during the bending process, and this load is called the required roll load. Although this process has a buckling resistance superior to that of conventional 3-point bending, there is a slight dimensional error in the bent radius and slight flattening occurs at the center of the bend after processing. The effects of various factors on the required roll load, the slight dimensional error in the bent radius, and the flattening ratio were investigated using the finite element method. The following conclusions were obtained. The required roll load increases with decreasing n-value, increasing wall thickness, and decreasing friction coefficient μ. Although the effects of n and r-values on the slight dimensional error and flatness after bending are small, the slight dimensional error and flatness increase with decreasing friction coefficient μ. However, the effect is smaller than that in conventional 3-point bending.