Model-driven multi-step hot metal gas forming of irregular tubular aluminum components : physically based simulation and experimental validation

Abstract

Hot metal gas forming (HMGF) is a cutting-edge technology to integrally form hollow complex tubular parts. However, components with spatially curved centerlines and variable cross-sections are difficult to form directly from straight tubular workpieces without fracture. Therefore, a multi-step hot metal gas forming (HMGF) method, which includes CNC bending, pre-forming, and hot metal gas forming, is proposed and validated in this study, together with a newly developed physically based constitutive model implemented within a finite element framework to capture microstructural and mechanical inheritance across steps. First, representative segments were formed and simulated using a four-step hot metal gas forming (HMGF) route across forming temperatures, internal pressures, and pressurization rates. The results indicate that the forming parameters have coupled effects on corner filling and thickness uniformity, revealing inherent trade-offs among temperature, pressure, and pressurization rate. An optimal combination of process parameters was identified, enabling accurate forming of the full-scale component without macroscopic defects at an initial diameter of 142 mm. Full-scale trials at initial diameters of 140 mm and 145 mm likewise confirmed accurate prediction of defects and grain-size evolution, demonstrating robust and geometry-independent predictability of both forming defects and microstructural evolution. This study advances a general methodology for parameter optimization and defect suppression in industrial production of complex tubular components.