A method of manufacturing a fuel tank includes: an introducing process in which a molten resin sheet formed with a tank body is introduced in a forming mold; a shaping process in which a movable member abuts against the molten resin sheet to form a molten resin projection projected in a thickness direction of the molten resin sheet; an arranging process in which the molten resin projection is inserted in an attachment hole provided in an attachment part, and the attachment part is arranged on the molten resin sheet; and a machining process in which the molten resin projection is pressurized by a pressurizing member, so as to bulge out a portion of the molten resin projection to an outer peripheral side.

A method of manufacturing a fuel tank includes: an introducing process in which a molten resin sheet formed with a tank body is introduced in a forming mold; a shaping process in which a movable member abuts against the molten resin sheet to form a molten resin projection projected in a thickness direction of the molten resin sheet; an arranging process in which the molten resin projection is inserted in an attachment hole provided in an attachment part, and the attachment part is arranged on the molten resin sheet; and a machining process in which the molten resin projection is pressurized by a pressurizing member, so as to bulge out a portion of the molten resin projection to an outer peripheral side.

Disclosed herein are methods and systems for the preparation of a co-injection molded multilayer plastic article. Some methods include co-extruding a combined polymeric stream having an interior core stream encased by an inner stream and an outer stream. One or more pulses in a thickness of the interior core stream create portions of an edge of the outer flow stream flowing along different streamlines. A first portion of an outer edge of the interior core stream flows beyond a second portion of the outer edge thereby forming one or more cohesion members that physically interlock the interior layer with the inner layer, with the outer layer or with both. Some embodiments reduce or eliminate a need for addition of an adhesive in the composite stream to prevent delamination of layers of the resulting multilayer plastic article. In some embodiments, cohesion members may be employed to produce a desired cosmetic effect in a resulting article.