PURPOSE: To reduce the tube manufacturing cost by locating a smoothing plug fit the required inside diameter after the forming with a grooved plug and forming the tops of grooves with a smoothing plug.
CONSTITUTION: A tube stock 1A is reduced with a reducing tool 12. At that time, a inside grooved tube 1 is manufactured by locating a grooved plug 11 in a tube 1A, pressing the inner face of the tube 1 onto the grooved plug 11 with the reducing tool 12 and forming grooves 2 on the inner face of the tube 1. Then a smoothing plug 14 with a outside diameter d2 adapted to the required inside diameter is located after the forming process with the grooved plug 11. The tops of the grooves 2 are formed and unified the dimension of the inside diameter with the smoothing plug 14. Thus, the cost reduction is achieved.
MIYAUCHI TOKUO
KIMURA HISASHI
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