Investigation of the Influence of the Pre-Hydro-forming Processes and Development of Characterization Methods for the Testing of Steel Semi-Products for Hydro-forming

摘要

Tube Hydro-forming (THF) is a relatively new but established technology among metal tube forming processes. It is the technology of forming closed sections, hollow parts with different cross-sections by applying an internal hydraulic pressure and sometimes additional axial compressive loads to force a tubular blank to conform to the shape of a given die cavity. Material properties have a significant influence on the process stability, particularly in series production. Mainly tubular material with longitudinally oriented welding lines is used in tube hydro-forming. Different production processes and subsequent processes such as the dressing of tubular semi-products involve pre-strains and hardening effects. Therefore, the geometrical and material properties of the tubular semi-product differs from the ones of the virgin sheet material. A new test method was developed to characterize the important properties of the semi-finished product, such as flow pressure or maximum circumferential elongation during the hydro-forming process.