Thickness Improvement and Calibration Pressure Reduction of Stepped Tubular Components Using Axial Hydro-pressing Method

Abstract

A new tube axial hydro-pressing method was proposed to solve the problems of high forming pressure and severely uneven wall thickness distribution of traditional tube hydroforming methods to form stepped tubular components. The forming pressure of the traditional hydroforming and the tube axial hydro-pressing method is studied theoretically, the mechanical model of the fillet area is established, and the forming pressure calculation formula is given. Based on this, an investigation of the tube axial hydro-pressing method is carried out by numerical simulation and experimental methods, and compared with the traditional tube hydroforming method. The key to the tube axial hydro-pressing method is to precisely control the relationship between the protrusion height and the axial feed, which is achieved by precisely controlling the feeding pressure and the axial displacement. Therefore, the constant pressure device in the experiment was used to eliminate the influence of the pressure rise caused by the volume compression on its cooperation relationship, to achieve accurate control of the loading path, eliminate wrinkles and flash defects. A qualified workpiece is successfully manufactured when the internal pressure is 18.0 MPa and the feed on each side is 15.0 mm. The forming pressure is reduced by 88.0%, and the feed is increased by 6.5%, which reduces the wall thickness reduction by 9.0%. The wall thickness difference of the workpiece can be controlled within 7.0%. The tube axial hydro-pressing method is suitable for forming stepped tubular components, which can achieve more replenishment at lower pressures, thereby effectively improving the uniformity of wall thickness and significantly reducing the forming pressure.