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The telescopic tube screw, which can provide an adjustable length feature, has been widely used in many applications that allow for a secure and perfect fit. This study investigates an innovative hydroforming process for producing a telescopic tube screw with internal thread on the outer tube and outer thread on the inner tube. First, the outer tubes, with internal thread, are hydroformed. Thereafter, one hydroformed outer tube is half-sectioned and concentrically combined with the inner tube. Following this, the concentric tubes are expanded by using a hydroforming process so that external thread is formed on the inner tube. The small gap between inner and outer tubes that is created by the difference in elastic recoveries allows them to rotate about one another to ensure smooth operation of the screw and sleeve mechanism. The investigation is supported by finite element analysis to determine the optimum thread shape. The structural strength of tube screw is experimentally estimated by lateral three-point bending test. The superior structural strength of the tube screws strongly confirms the reliability and applicability of the telescopic tube screws manufactured in this study. [ABSTRACT FROM AUTHOR]

Tube hydroforming is a metal forming technology that uses internal pressure and the axial feeding force to fabricate products with complicated cross-sectional geometries. In this study, an advanced sealing system is proposed to prevent leakage during the hydroforming process. The advanced sealing system is composed of a die spring, cylindrical sleeve and punch with end fillet. The improved sealing effect originates from the increased contact because of the axial force of the punch and reaction force of the spring caused by the punch. When the proposed sealing system is used, the circumference of the tube end becomes more tightly sealed by the axial pressure between the punch and sleeve, and the axial pressure increases with increasing axial feeding. The effects of the advanced sealing system on the effectiveness of the contact between the tube end and punch were further analyzed with finite element method. The feasibility of the proposed sealing system is experimentally confirmed by hydroforming a non-axisymmetric complicated part. [ABSTRACT FROM AUTHOR]