Patent ID: 9579705
Date: 2017-02-28
CPC Classifications: B21C,B21D,F16L,Y10T

Claim:
1. A method of manufacturing a double water pipe using hydroforming, the method comprising: inserting an inner pipe into an outer pipe made of steel, the inner pipe being made of a corrosion resistant material selected from among stainless steel, titanium and aluminum, and having a smaller outer diameter than an inner diameter of the outer pipe; enlarging opposite ends of the inner pipe, with the inner pipe inserted into the outer pipe; welding the enlarged opposite ends of the inner pipe to the outer pipe; placing the outer pipe on a die unit and sealing opposite ends of the die unit with sealing members, each seal member having a through-hole connected to a fluid supply unit for supplying a fluid to the inner pipe; supplying the fluid to the inner pipe to perform plastic expansion of the inner pipe and elastic expansion of the outer pipe; discharging the fluid from the inner pipe to allow frictional coupling between the inner pipe and the outer pipe through elastic restoration of the outer pipe; and cutting opposite ends of the double water pipe to remove the welded enlarged opposite ends after discharging the fluid from the inner pipe, wherein each of an inner surface of the outer pipe and an outer surface of the inner pipe includes a rough surface which maintains the frictional coupling of the outer pipe with the inner pipe.