Method for manufacturing curved hollow pipe

Abstract

[Problem] A method for manufacturing a bent hollow pipe is provided, in which even when a three-dimensionally bent pipe is formed, a gap, an uneven thickness, and the like would not occur at contact portions at the ends of both of the flange portions when press work is finished, and thus a pipe having the high quality contact portions can be formed. [Solution] In a method for manufacturing a bent hollow pipe, a material W, which is to be processed and which is a flat plate extending a first plane formed by a first direction and a second direction perpendicular to the first direction, is pressed in a stepwise manner using a plurality of forming dies from a third direction perpendicular to the first plane, so that two sides of a second plane formed by the second direction and the third direction of the material W are brought into contact with each other, and the bent hollow pipe is made to be bent and extend in a three dimensional manner that is bent in the first plane and in the second plane. The method includes a step in which a push out portionis formed that is pushed out onto the material W in the third direction and that is bent and extends within a third plane formed by the first direction and the third direction in a press work, and extension portionsare formed to extend away from each other at both sides which sandwich the push out portionof the material W, and flange portionsare formed that are bent, in a direction opposite to a push out direction of the push out portion, at ends of the extension portions, a step in which while bending is maintained between the extension portionsand the flange portions, a bent portionsbetween the push out portionand the extension portionsare bent in the opposite directions, so that the both of the flange portionsare formed in a direction in which the both of the flange portionsface each other, a step in which the both of the flange portionsof a three-dimensionally bent portion P that is bent in the first plane and in the second plane are bent and brought closer to each other as compared with both of the flange portionsin a portion other than the three-dimensionally bent portion P, and a step of bringing ends of the flange portionsinto contact with each other.