Peter Groche

Abstract

Tube hydroforming (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. Often roll‐formed, non‐heat treated tubular materials made of steel with longitudinally oriented welding lines are used in tube hydroforming. Different production processes involve a change of the material properties from the initial flat sheet to the hydroformable tube. Testing methods such as tensile tests and conventional forming limit diagrams do not accurately reflect the state of stress and strain conditions seen in the tubular blank during the hydroforming process. Thus, inaccuracies in FEA predictions and design failures occur. Test methods were developed to characterize the relevant geometrical and mechanical properties of tubular semi‐finished products.

Induction Weld Seam Characterization of Continuously Roll Formed TRIP690 Tubes

“…The roll forming process is followed by a seam welding station, in which the tubular section is closed using high-frequency induction, laser or tungsten inert gas (TIG) welding processed. A final calibration of the cross-sectional geometry is then conducted, followed by cutting of the tube [12,13]. In addition to the consistency of the wall thickness in the finished tube product, the quality of the weld seam is of critical importance for the subsequent pre-bending and hydroforming process which these tubes will undergo.…”

“…In addition to the consistency of the wall thickness in the finished tube product, the quality of the weld seam is of critical importance for the subsequent pre-bending and hydroforming process which these tubes will undergo. Although they do not specify the welding process used, Groche et al [12] showed that continuous roll forming resulted in a weld seam thickness that is greater than the average cross-sectional thickness of the tube due to the force applied to the edges of the sheet during welding. This results in base metal failure when the tubes were subject to free-expansion bulge tests.…”