In order to obtain a bent pipe with an improved shape and a smaller bending radius by the pipe bending method using a floating expanding plug, first an r-plug expected to remove redundant shear deformation at the entry was used, and then an oval plug expected to reduce cross-sectional flattening was used, and the diameter of the pipe was further pre-reducted. (1) Use of the r-plug decreases the bending radius limit, the wall thickness difference and the roughness of the inner and outer bent surfaces. (2) Use of the oval plug can reduce cross-sectional flattening for small bending radiuses. (3) Use of the pre-reduced pipe enables the realization of a bent pipe with its original diameter and wall thickness, along with a smaller bending radius limit and wall thickness difference.
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