One aspect of the present disclosure is a manufacturing device by which the bent pipe is obtained by bending a double pipe. The device includes inner and intermediate core metals, a bending mold, and a controller. The controller executes: a first bending process in which first and second pipes are bent by the bending mold in a first direction in a first area of the double pipe where the inner and intermediate core metals are placed; a second bending process in which the first and second pipes are bent, after the first bending process, by the bending mold in a second direction in a second area of the double pipe where the inner and intermediate core metals are placed; and a first bending-back process in which the second pipe is bent, after the first bending process, in a direction opposite to the first direction in the first area.

One aspect of the present disclosure is a manufacturing device for a bent pipe by which the bent pipe is obtained by bending a double pipe. The manufacturing device for a bent pipe includes an inner core metal, an intermediate core metal, a bending mold, and a controller. The controller executes a first bending process, a second bending process, and a re-bending process. In the first bending process, a first pipe and a second pipe are bend in a first direction in a first area. In the second bending process, the first pipe and the second pipe are bent in a second direction in a second area. The second area has more distance from a coupling portion than the first area does. In the re-bending process, the second pipe is bent in the same direction as the second direction in the second area.

One aspect of the present disclosure is a manufacturing device for a bent pipe by which the bent pipe is obtained by bending a double pipe. The manufacturing device for a bent pipe includes an inner core metal, an intermediate core metal, a bending mold, and a controller. The controller executes a first bending process, a second bending process, and a re-bending process. In the first bending process, a first pipe and a second pipe are bend in a first direction in a first area. In the second bending process, the first pipe and the second pipe are bent in a second direction in a second area. The second area has more distance from a coupling portion than the first area does. In the re-bending process, the second pipe is bent in the same direction as the second direction in the second area.

A mandrel 10 for producing a thin-walled bent tube having a bending portion with high strength and a small radius of curvature by rotary draw bending without either cracks in an outside of bend or winkles and buckling in an inside of bend occurring includes a shank 14, a connection mechanism 15 and a mandrel ball 16. In a cross-section orthogonal to an axial direction of the mandrel ball 16 at a central position in the axial direction of the mandrel ball 16, the mandrel ball 16 has a first position 19 and a second position 20 at which a first straight line m that passes through a mandrel ball center 17 meets an outer periphery 21 of the mandrel ball. Further, a ratio (L.sub.1/L.sub.2) between a dimension L.sub.1 from the mandrel ball center 17 to the first position 19 and a dimension L.sub.2 from the mandrel ball center 17 to the second position 20 is in a range of 0.915 to 0.976.

A mandrel 10 for producing a thin-walled bent tube having a bending portion with high strength and a small radius of curvature by rotary draw bending without either cracks in an outside of bend or winkles and buckling in an inside of bend occurring includes a shank 14, a connection mechanism 15 and a mandrel ball 16. In a cross-section orthogonal to an axial direction of the mandrel ball 16 at a central position in the axial direction of the mandrel ball 16, the mandrel ball 16 has a first position 19 and a second position 20 at which a first straight line m that passes through a mandrel ball center 17 meets an outer periphery 21 of the mandrel ball. Further, a ratio (L.sub.1/L.sub.2) between a dimension L.sub.1 from the mandrel ball center 17 to the first position 19 and a dimension L.sub.2 from the mandrel ball center 17 to the second position 20 is in a range of 0.915 to 0.976.

A mandrel 10 for producing a thin-walled bent tube having a bending portion with high strength and a small radius of curvature by rotary draw bending without either cracks in an outside of bend or winkles and buckling in an inside of bend occurring includes a shank 14, a connection mechanism 15 and a mandrel ball 16. In a cross-section orthogonal to an axial direction of the mandrel ball 16 at a central position in the axial direction of the mandrel ball 16, the mandrel ball 16 has a first position 19 and a second position 20 at which a first straight line m that passes through a mandrel ball center 17 meets an outer periphery 21 of the mandrel ball. Further, a ratio (L.sub.1/L.sub.2) between a dimension L.sub.1 from the mandrel ball center 17 to the first position 19 and a dimension L.sub.2 from the mandrel ball center 17 to the second position 20 is in a range of 0.915 to 0.976.

A mandrel 10 for producing a thin-walled bent tube having a bending portion with high strength and a small radius of curvature by rotary draw bending without either cracks in an outside of bend or winkles and buckling in an inside of bend occurring includes a shank 14, a connection mechanism 15 and a mandrel ball 16. In a cross-section orthogonal to an axial direction of the mandrel ball 16 at a central position in the axial direction of the mandrel ball 16, the mandrel ball 16 has a first position 19 and a second position 20 at which a first straight line m that passes through a mandrel ball center 17 meets an outer periphery 21 of the mandrel ball. Further, a ratio (L.sub.1/L.sub.2) between a dimension L.sub.1 from the mandrel ball center 17 to the first position 19 and a dimension L.sub.2 from the mandrel ball center 17 to the second position 20 is in a range of 0.915 to 0.976.

A round metal pipe 1 including a bend portion 10 is configured such that on an axial direction cross-section of the bend portion 10, an outer half portion 11b of a peripheral wall portion 11 of the bend portion 10 has an outwardly projecting, non-circular arc shape in which a central portion in a y direction, which is orthogonal to a bend radius direction x of the bend portion 10, forms an outermost peripheral portion 13, and a distance Lb from respective intermediate portions 15 between the outermost peripheral portion 13 and a pair of proximal end portions 14 of the outer half portion 11b to a pipe center O is shorter than a distance La from the outermost peripheral portion 13 to the pipe center O. Thus, advantages such as suppressing reductions in the sectional area and minimum inside width of the bend portion 10 and reducing flow path resistance can be obtained, and the round metal pipe 1 can be manufactured easily and appropriately.

A mandrel 10 for producing a thin-walled bent tube having a bending portion with high strength and a small radius of curvature by rotary draw bending without either cracks in an outside of bend or winkles and buckling in an inside of bend occurring includes a shank 14, a connection mechanism 15 and a mandrel ball 16. In a cross-section orthogonal to an axial direction of the mandrel ball 16 at a central position in the axial direction of the mandrel ball 16, the mandrel ball 16 has a first position 19 and a second position 20 at which a first straight line m that passes through a mandrel ball center 17 meets an outer periphery 21 of the mandrel ball. Further, a ratio (L.sub.1/L.sub.2) between a dimension L.sub.1 from the mandrel ball center 17 to the first position 19 and a dimension L.sub.2 from the mandrel ball center 17 to the second position 20 is in a range of 0.915 to 0.976.

A mandrel 10 for producing a thin-walled bent tube having a bending portion with high strength and a small radius of curvature by rotary draw bending without either cracks in an outside of bend or winkles and buckling in an inside of bend occurring includes a shank 14, a connection mechanism 15 and a mandrel ball 16. In a cross-section orthogonal to an axial direction of the mandrel ball 16 at a central position in the axial direction of the mandrel ball 16, the mandrel ball 16 has a first position 19 and a second position 20 at which a first straight line m that passes through a mandrel ball center 17 meets an outer periphery 21 of the mandrel ball. Further, a ratio (L.sub.1/L.sub.2) between a dimension L.sub.1 from the mandrel ball center 17 to the first position 19 and a dimension L.sub.2 from the mandrel ball center 17 to the second position 20 is in a range of 0.915 to 0.976.