Rotary Tube Flaring with Relieved Punch

In this paper, we propose rotary tube flaring with a relieved punch to achieve high formability and productivity. The punch, which has grooves as relief, is pressed into a rotated tube to flare the tube end. The effects of the contact area between the punch and the tube and feed rate on formability were investigated by experiments and finite element analysis. The contact area was controlled by changing the relief size of the punch, and the contact angle was defined as the size of the contact area. As a result, the flaring limit of the proposed method was higher than that of conventional press forming, which was obtained by using the relieved punch with an optimum contact angle. The maximum flaring ratio was 1.12 in the proposed method. When the contact angle was very small, cracks easily occurred at the flared tube end. When the contact angle was very large, buckling easily occurred. When the feed rate was increased, the tube wall thickness increased at the flared portion, and buckling easily occurred owing to the large axial load.