Mechanism analysis and engineering experiment of multi-directional pressing-forming complex large-size automobile axle housing

Bulging-pressing forming process is a novel method for manufacturing complex large-size automobile axle housing; however, the multi-directional pressing-forming mechanism is not clear, there is no definite method to determine the pressing mode and liquid pressure, and the cracks in engineering tests cannot be explained. Based on mechanical analysis, the pressing-forming mechanism of small corner in cross section was revealed, the formulas between the stress components and die pressing forces and liquid pressure were deduced. The coupling relationship between compressive stress σ_θ and shear stress τ_θn in small corner were derived; the approximate plastic condition and yield trajectory of small corner were given. The application criterion of pressing mode and the calculation formula of initial liquid pressure were determined. The effects of pressing mode and initial liquid pressure on multi-directional pressing-forming were revealed, and the range of pressing coefficient k_s and pressure coefficient n_f were determined by finite element (FE) simulations and engineering experiments carried out on a five-direction hydraulic press. The relational formula between stress τ_θn and the relative inner diameter of small corner was fitted by FE simulations, which is determined as the design method of small corner. The axle housing tube samples have good formability, the initial liquid pressure is much lower than traditional hydroforming, and the thickness distribution meets the service requirements of the designed product.