| 摘要 |
PROBLEM TO BE SOLVED: To provide a sub-muffler which can be manufactured at a high yield.SOLUTION: A manufacturing method of sub-mufflers (1, 201) includes a square cylindrical body forming process (S3), preliminary forming processes (S5, S26), and contracted-diameter forming processes (S7, 27). In the square cylindrical body forming process (S3), a plate material (70) is bent, and a square cylindrical body (720) having a rectangular cross section shape is formed. In the preliminary forming processes (S5, S26), end parts (724, 725) of the square cylindrical bodies (72, 720) are preliminarily formed, and cross section shapes of the end parts of the square cylindrical bodies (72, 720) are formed into circular shapes. In the contracted-diameter forming processes (S7, 27), the end parts (724, 725) of the square cylindrical bodies (72, 720) are contracted in diameters. |
