Bi-cylindrical part formed by a combined spinning process

Bi-cylindrical parts are a type of cylindrical component featuring an inner boss shape, making them suitable as lightweight structural parts for aerospace and transportation applications. A shovel-conventional combined spinning process for the integrated formation of bi-cylindrical parts is proposed in this work, representing a significant advancement over traditional manufacturing methods that require multiple operations and joining processes. A mathematical model is developed to elucidate the relationship between the inner boss shape height, outer cylindrical part height, and shovel reduction ratio under different thickness conditions. Through numerical simulations and experimental methods, the deformation mechanisms and microstructural evolution during both processes are analyzed. Results demonstrate that as the shovel reduction ratio increased from 20 % to 40 %, the inner boss height increased significantly while the outer cylindrical part height decreased correspondingly. The shovel spinning process exhibits three distinct deformation stages (shovel-up, stable feed, and roller-closing) with the inner boss wall forming a knife-shaped top region, transitional middle region, and uniform straight wall bottom region. Microstructural analysis reveals distinct deformation mechanisms across different zones in shovel spinning, with grain size varying from 7.51 μm to 104.83 μm depending on local stress states. At 40 % shovel reduction ratio, dynamic recrystallization mechanisms significantly increase the proportion of high-angle grain boundaries to 51.6 % while reducing internal strain, resulting in substantial grain refinement and texture randomization. In contrast, multi-pass conventional spinning produces more uniformly refined grains with stable boundary distributions and lower strain heterogeneity, developing strong textures in critical regions. This combined spinning method represents a transformative approach to integrated manufacturing, enabling seamless weld-free fabrication of complex components with tailored microstructures, optimized mechanical properties, and superior structural integrity—eliminating traditional joining-related weaknesses while maintaining the dimensional accuracy and material continuity critical for high-performance applications.