Pseudo-bulk forming of thin-walled hollow components based on the self-consistency of internal pressure and shell deformation

• Pseudo-bulk forming method was proposed to simplify process control in the manufacture of thin-walled hollow components. • Tube forming was converted to quasi-bulk deformation problem via self-consistency of forming pressure and shell deformation. • Excessive thinning of shell thickness and inward buckling could be prevented in the proposed forming method. • Self-consistent variation of forming pressure was combined with friction-assisted effect to clarify the-forming mechanism. Instable metal flow easily occurs during the forming of thin-walled hollow components due to inappropriate control of forming load in conventional forming processes, thereby leading to forming failure. Accordingly, a Pseudo-Bulk Forming (PBF) method was proposed in this work, aiming at achieving the self-consistency of internal pressure and tubular blank’s deformation in a simple and stable way. In this process, Low-Melting-Point Alloy (LMPA) was solidified inside of tubular blank to constitute a composite rod and deformed simultaneously under compression. Then forming of thin-walled hollow component was converted to pseudo-bulk plastic deformation of a composite rod. PBF of a rectangular tube was taken as an example to study the loading conditions, stress state, and deformation behavior of tubular blank during this process experimentally and numerically. The results showed that PBF exhibited the advantages in preventing excessive thinning of shell thickness in hydroforming and inward buckling during roll-forming. The strong stability of LMPA’s plastic flow stress, which was caused by its low strain hardening behavior, could induce self-adaptive inner pressure on tubular blank, thereby resulting in the balanced metal flow in sidewall and corner regions. Besides, due to tangential friction generated by LMPA at LMPA/tubular blank interface and along metal flow direction, circumferential metal flow towards the corner region could be enhanced, and thereby leading to the conversion of stress states from tension-tension to tension–compression. The risk of fracture was then reduced and forming stability was improved in the case of forming structures with sharp corners.