| 摘要 |
The process according to the invention includes a step of punching in which a punching machine, in addition to the normal cutting of the metal sheet, also executes punching of adjacent portions of the foldable limbs of the metal sheet for forming complementary tongue elements that are seam foldable to each other. Following is a folding step in which a bending machine carries out folding of said side limbs and, simultaneously, provides a seam folded engagement of said complementary tongue elements for mutual fixing of the adjacent limbs. (Fig. 1).
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