Influences of inner pressure and tube thickness on process responses of hydroforming copper tubes without axial force

Abstract

Tube hydroforming is a metal forming technique which has attracted the attention of several industries because of its ability to produce complex parts with high strength and low weight in low expense and time. In this process, a piece of tube attains the shape of the die under the pressure of inner fluid and exerted axial force. This process is able to produce a unified part in a single-step process. In order to achieve these advantages and an appropriate process, it is necessary to select convenient process and part parameters. Therefore, the present research focused on the effects of two important tube hydroforming process parameters, inner pressure and tube thickness, on process responses during the hydroforming of copper tubes without axial force. In the analytical investigation, the relationships for calculating pressures in three steps of tube hydroforming, i.e. yield pressure, ultimate plastic pressure, and calibration pressure, were developed. By using the derived pressures from these relationships, finite element investigations using a dynamic explicit code and experimental tests using tube hydroforming experimental facilities were performed. These investigations were accomplished on seamless copper tubes of four different thicknesses (0.5, 0.63, 0.9, and 1,mm) under different pressures. The results of these investigations showed that by increasing inner pressure, the thickness strain, bulging height, and von Mises equivalent plastic stress increase along with the length of the part. Also, higher tube thickness results in both higher required forming pressures in all forming steps and more capacity of enduring thickness strain and equivalent plastic stress. The results of these three different investigations showed good agreement with each other.