Multilayered tube and manufacturing method thereof based on high pressure tube hydroforming

A method of manufacturing a multilayered tube, comprising:

• preparing an outer tube, an inner tube having an outer diameter of 95˜98% of an inner diameter of the outer tube, a second inner tube having an outer diameter of 95˜98% of an inner diameter of the inner tube, and dies with a shaping void having a diameter of 100.20˜100.30% of an outer diameter of the outer tube;
• mounting the outer tube on the shaping void, with the inner tube and the second inner tube inserted into the outer tube;
• plastically expanding the second inner tube to be brought into contact with the inner tube and to force the inner tube to be brought into contact with the outer tube by an expanding force of the second inner tube by injecting a fluid into the second inner tube until a pressure of the fluid reaches a first forming pressure inside the second inner tube;
• elastically expanding the outer tube to be brought into contact with the shaping void by increasing the pressure of the fluid until the pressure of the fluid reaches a second forming pressure inside the second inner tube;
• and
• elastically recovering the outer tube to allow the outer tube, the inner tube and the second inner tube to be coupled to one another by removing the fluid from the second inner tube,
• wherein the first forming pressure is in the range of 10˜20% of the sum of yield strengths of the inner tube and the second inner tube, and
• wherein the second forming pressure is in the range of 10˜20% of the sum of the yield strengths of the second inner tube, the inner tube and the outer tube, and is maintained for 2˜3 seconds.