Sub-muffler and manufacturing method of sub-muffler

Abstract

A manufacturing method of a sub-muffler ( 1, 201 ) includes a tubular body shaping step (S 3 ), a central part spinning machining step (S 5 , S 7 , S 26 , S 27 ), and a diameter reduction machining step (S 8 , S 28 ). In the tubular body shaping step (S 3 ), a cylindrical body ( 2, 202 ) is formed by rolling a plate material ( 70 ). In the central part spinning machining step (S 5 , S 7 , S 26 , S 27 ), the cross-sectional shape of a central part ( 20, 220 ) of the cylindrical body ( 2, 202 ) is machined into a rectangular shape by performing a spinning machining in which a rotating roller ( 88 ) is moved along a rectangular trajectory (T 3 , T 6 ) while pressing the rotating roller ( 88 ) onto the central part ( 20, 220 ) of the cylindrical body ( 2, 208 ). In the diameter reduction machining step (S 8 , S 28 ), the diameter of an end ( 80, 81, 280, 281 ) of the cylindrical body ( 2, 208 ) is reduced.

What is claimed is: 
     
         1 . A manufacturing method of a sub-muffler comprising:
 a tubular body shaping step of rolling a plate material, and thereby forming a cylindrical body;   a central part spinning machining step of performing a rectangular spinning machining in which a rotating roller is moved along a rectangular trajectory while pressing the rotating roller onto a central part of the cylindrical body, and thereby machining the central part so that a cross-sectional shape of the central part becomes a rectangular shape; and   a diameter reducing step of reducing a diameter of an end of the cylindrical body.   
     
     
         2 . The manufacturing method of a sub-muffler according to  claim 1 , wherein in the diameter reducing step, the diameter of the end of the cylindrical body is reduced by performing a circular spinning machining in which the rotating roller is moved along a circular trajectory while pressing the rotating roller onto the end of the cylindrical body. 
     
     
         3 . The manufacturing method of a sub-muffler according to  claim 1 , wherein in the central part spinning machining step, the central part is machined so that the cross-sectional shape of the central part becomes a rectangular shape by performing the rectangular spinning step after performing a circular spinning machining in which the rotating roller is moved along a circular trajectory while pressing the rotating roller onto the central part of the cylindrical body. 
     
     
         4 . The manufacturing method of a sub-muffler according to any one of  claims 1 , wherein in the central part spinning machining step, the trajectory of the rotating roller is gradually changed from the cross-sectional shape of the central part of the cylindrical body into a rectangular shape. 
     
     
         5 . A sub-muffler manufactured by using a manufacturing method of a sub-muffler according to any one of  claims 1 .