| 摘要 |
A manufacturing method of a sub-muffler includes a rectangular tubular body shaping step (S3), a preliminary shaping step (S5), and a diameter reduction shaping step (S7). In the rectangular tubular body shaping step (S3), a plate material is bent and a rectangular tubular body having a rectangular shape in cross section is thereby formed. In the preliminary shaping step (S5), ends of the rectangular tubular body are preliminarily formed and the end parts of the tubular body are thereby formed so that its cross-sectional shape becomes a circular shape. In the diameter reduction shaping step (S7), the diameters of the ends of the rectangular tubular body are reduced. |
