MULTI-LAYER TUBE USING HIGH-PRESSURE TUBE-HYDROFORMING AND MANUFACTURING METHOD THEREOF

摘要

The present invention comprises: a step for preparing a mold including an outer tube, an inner tube having a diameter of 95~98% of the diameter of the outer tube, and a molding groove having a diameter of 100.20~100.30% of the diameter of the outer tube; a step for inserting the inner tube into the outer tube and settling the tubes in the molding groove; a first molding step for expanding the inner tube to bring the inner tube into contact with the outer tube by injecting fluid into the inner tube to the first molding pressure; a second molding step for elastically expanding the outer tube to bring the outer tube into contact with the inner groove by increasing the hydraulic pressure of the inner tube to the second molding pressure; and an elasticity restoring step for bonding the outer tube and inner tube by restoring the elasticity of the outer tube through the removal of the fluid injected into the inner tube. The first molding pressure of the first molding step ranges within10~20% of the yield strength of the inner tube. The second molding pressure of the second molding step ranges within 10~20% of the sum of the yield strengths of the inner and outer tubes and is maintained for 2~3 seconds.