METHOD FOR MANUFACTURING HOLLOW HYDRO-FORMED PRODUCT using MULTI-TUBE ASSEMBLY

Abstract

A method for manufacturing a hollow hydro-formed product using a multi-tube assembly is provided, which comprises the steps of: (a) stably placing a multi-tube assembly in a Die, the hollow inner tube having fluid channel holes radially formed therethrough; (b) injecting fluid into the inner periphery of the inner tube; (c) applying fluid pressure to the inner periphery of the outer tube by the fluid while the fluid is discharged through the fluid channel holes of the inner tube; and (d) obtaining a formed product having an intended outer peripheral shape completed according to diameter-enlargement and plastic deformation of the outer tube. The inner periphery of the outer tube is pressed and hydro-formed by discharging the fluid through the fluid channel holes of the inner tube formed through the inner tube of the multi-tube assembly.

1 . A method for manufacturing a hollow hydroformed product using a multi-tube assembly, the method comprising the steps of:
 (a) loading a multi-tube assembly into a die, the multi-tube assembly including a hollow outer tube and a hollow inner tube inserted into the hollow outer tube, the hollow inner tube having a plurality of fluid channel holes radially formed on the inner peripheral surface thereof;   (b) injecting fluid into the inner tube so as to be supplied to the inner periphery of the inner tube;   (c) applying a hydraulic pressure of the fluid to the inner periphery of the outer tube while the fluid flows out of the inner tube through the fluid channel holes of the inner tube; and   (d) subjecting the outer tube to bulging and plastic deformation to obtain a finally formed product having a desired outer peripheral shape.   
     
     
         2 . The method according to  claim 1 , wherein the inner tube is implemented as a multi-layered tube configured such that at least two hollow tubes are inserted into the outer tube, each of the hollow tubes having a plurality of flow channel holes formed thereon so as to fluidically communicate each other. 
     
     
         3 . The method according to  claim 1 , wherein the outer tube and the inner tube are made of heterogeneous materials. 
     
     
         4 . The method according to  claim 1 , wherein the flow rate of the fluid injected into the inner tube in step (b) is maintained to be equal to that of the fluid flowing out of the inner tube through the fluid channel holes of the inner tube in step (c) so that only the outer tube is plastic-deformed. 
     
     
         5 . The method according to  claim 1 , wherein the flow rate of the fluid injected into the inner tube in step (b) is determined within a range in which a pressure difference caused by a difference in the flow rate of the fluid supplied to the inner periphery and the outer periphery of the inner tube is less than a yield stress of the inner tube so that only the outer tube is plastic-deformed.