Effect of Pipe Bending by Rotary Tube Bending Process on Durability of Frame Structure

Automobile frames, particularly trellis frame structures, are engineered for superior dynamic performance, with stiffness being a paramount consideration¹. These frames frequently utilize welded tubes, a manufacturing process made more complex by the necessity of bending tubes to precise angles to meet packaging and assembly requirements². This bending, however, induces residual stresses that can substantially compromise the frame's durability³. This investigation employs a detailed finite element simulation to analyse the structural deformation and residual stresses that arise during the bending of Cold Electric Welded (CEW) annealed round pipes⁴. A comprehensive 3D mechanical model, incorporating realistic tooling and contact interactions, was developed to accurately simulate shape change, ovality, and wall thickness redistribution during the bending process⁵. CEW pipes, unlike their Electric Resistance Welded (ERW) counterparts, possess minimal initial forming stresses, and the annealing process ensures they are stress-free prior to bending, facilitating a more controlled analysis of their deformation⁶. The simulation results reveal significant geometric alterations in the bent region, including changes in ovality and wall thickness, which are heavily influenced by the bend radius and angle⁷. The residual stress analysis indicates a combination of tensile and compressive stresses that could jeopardize the pipe's structural integrity⁸. Furthermore, deformation in the bend zone can lead to welding issues such as uneven fit-up, altered section modulus, and irregular weld profiles, all of which can diminish weld joint performance⁹. To address these challenges, a conservative approach was adopted in our fatigue analysis using FE-Safe, applying the lower bound of weld material properties to account for potential weld imperfections stemming from bending¹⁰. These simulation outcomes are critical for evaluating the fatigue life of weld joints and comprehending how bending affects the pipe's long-term performance¹¹. Ultimately, this research aims to enhance the reliability and efficiency of piping systems, especially in trellis structures, by improving the accuracy of fatigue simulations¹². The insights gleaned will aid in optimizing bending processes, refining weld joint designs, and supporting the development of robust tubular structures for demanding applications¹³.