| 摘要 |
PURPOSE:To improve production efficiency and to reduce cost by forming three bulging projections to a pipe material and using one thereof for engaging an upper pipe and the remaining two as apertures to accept the top end of a seat stay. CONSTITUTION:Working fluid 11 is fed by an oil feed pump 13 through an oil introducing hole running the center of pistons 15, 15a into the pipe material in segmental dies 20 to fill the inside of said dies. Both ends of the pipe material are tightly adhered and sealed at the same instant when both ends are pressed by the pistons 15, 15a. The oil pressure is increased by the effect of a high- pressure pump 14 so that the pipe material bulges and projects from the inside toward the recessed parts of the dies 20. The pipe material is thus bulged. A collar 22 is fixed by welding, etc. to the formed seat lug and is further slit including the seat lug body. The middle part between the bulging projections 4 and 5 for the seat stay (to be used as the housing and accepting ports to accept the top end of the seat stay) is slit as well.
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