Abstract: In a method of bending a pipe material, in order to use an apparatus, such as a press, and prevent the pipe material from being made thin and cracks from being generated, one side of a cylindrical pipe material is firmly held by a first clamp and another side thereof is loosely held by a second clamp. The clamp is relatively moved downward with respect to the clamp. At this time, pressing force is applied to the pipe material in an axial direction from both ends thereof. The pipe material is plastically deformed by being guided by one quarter spherical surface of a first mandrel and one quarter spherical surface of a second mandrel, whereby two bent portions and an intermediate straight portion are formed.

Abstract: In order to manufacture a pipe having a plurality of flow channels, by minimizing die jigs and steps, and thus to permit facilitation of manufacture, reduction of cost, and improvement of accuracy, the method of manufacturing a pipe comprises the steps of holding a sheet material at a center portion in the width direction thereof from both surfaces thereof by core members composing a split structure, folding both sides in the width direction of the sheet material in opposite directions and causing the thus folded both sides of the sheet material to follow the shapes of the outer surfaces of the core members, thereby forming a substantially an S-shaped cross-section.