摘要:
An aluminum plate (13) is first plastic-deformed (FIG. 3D) in such a way as to envelop a foaming-agent compact (14), which is not foamed yet. Then, terminals of the aluminum plate (13) are integrally seam-welded (FIG. 3E) to thereby obtain a closed section structure (23). Subsequently, the foaming-agent compact (14) contained in the closed section structure (23) is foamed by being heated to foaming temperature thereof. Consequently, a pipe-like frame filled with a foam (27) is obtained.