Abstract: A molding manufacturing method includes: preparing a molding body including a molding main body made of thermoplastic material and a decorative layer higher than the molding main body in hardness and melt temperature; setting the molding body in a fixed die; heating and softening an end portion of the molding body while maintaining the decorative layer softer than the molding main body, by irradiating an infrared ray onto a back surface of the molding main body corresponding to the end portion; and press forming the end portion of the molding body by applying a movable punch onto the fixed die while the end portion of the molding body is in a softened state to bend the end portion of the molding body to obtain an end cover portion having a predetermined shape.

Abstract: An exhaust manifold has a plurality of double pipes, each of which includes an inner pipe and an outer pipe, and a collecting pipe to which each of the double pipes is connected. The outer peripheral portion of the outer pipe is secured to the collecting pipe, and a thermal insulating layer of air, which is formed as a closed space so that substantially no exhaust gas will penetrate it, is disposed on an inner peripheral side of the portion at which the outer periphery of the outer pipe is secured to the collecting pipe. Owing to the presence of the thermal insulating layer, heat is not transmitted to the welded joint directly via the inner and outer pipes.