The rocket nozzle is one of the core components to ensure the safe flight of rockets. To overcome the problems of multi-step forming, the occurrence of defects, and severe plastic deformation in traditional technology, a novel forming method named tube upsetting-bulging (TUBG) is put forward. With the support of internal pressure, a tube is deformed with an upsetting and bulging process at the same time. The tube is thickened at the small end and thinned at the large end. A nozzle with sharply varying diameters can be obtained. A theoretical model of TUBG that considers wrinkles and rupture is built. The influence factors of internal pressure during TUBG are discussed. Experiments and simulation works are conducted to analyze the plastic deformation process of TUBG. Results show that mechanical properties and geometrical parameters have an obvious influence on critical internal pressure. The proposed theoretical model can be used to predict a forming zone without wrinkles, rupture, and severe strain values. A well-formed nozzle can be obtained using the predicted forming zone, which verifies the correctness of the theoretical analysis. It can be found that TUBG is a novel potential method to fabricate rocket nozzles with high efficiency and quality without defects.
Keywords: critical pressure; plastic deformation; rocket nozzle; tube upsetting-bulging.