Simulation And Experiment Research On Process Of Superplastic Forming/diffusion Bonding For Multi-sheet Structure Of TC4

Superplastic forming / diffusion bonding(SPF / DB)is one of the main process methods for the manufacturing of large and complex thin titanium alloy structures in aerospace industry. The titanium multi-sheet structures made by this process which break through the traditional sheet manufacturing methods are light and rigid in design, the process can shorten the manufacturing cycle and reduce the cost. The titanium alloy multi-sheet structures made by SPF / DB process have been widely used in aerospace fields abroad and the economic benefits are significant. Compared with developed countries, the manufacturing process level and the application of titanium alloy multi-sheet structures SPF/DB technology have not been so advanced in china at present. Main process defects: The outer sheet of three-sheet structure often appears"groove", the improper process control can result in DB inadequate because of large DB area in four-sheet structure. Using CAD/CAE to optimize the structure has become one of the most important research on SPF / DB process in aerospace fields. According to above process defects, following works are done during the research on TC4 multi-sheet structure SPF / DB process.First ,the ratio of initial outer sheet thickness to inner sheet thickness r₁(r₁=t_outer/t_inner),the ratio of DB width to outer sheet thickness r₂(r₂=b/t_outer) are two important structural parameters that influence the groove of the three-sheet structure. The die structure and gas system are designed according to three-sheet SPF / DB, SPF/DB process is simulated in Marc and simulation is applied to analyze the influence of r₁ and r₂ on the groove defect. Finally, based on simulation, the three-sheet SPF/DB process experiment of TC4 is carried out by DB first and then SPF, the DB ratio is high, thickness distribution is uniform, no"groove"in outer-sheet. The results show that it is useful to reduce the outer-sheet defect when structure satisfies in TC4 three-sheet SPF/DB process. Best DB parameters: temperature 900℃, DB pressure 2³.5MPa, keeping pressure time 3600s; Best SPF parameters: temperature 900℃, strain rate 0.00098s^-1, forming time 2000s, keeping pressure 2.5MPa.The SPF/DB process of four-sheet structue that is often carried out by SPF and DB at the same time has the characteristic of multi-sheet,large deformation of inner-sheet and large DB area. Therefore, the input gas and vacuum system are complex. The four-sheet structure is designed according to four-sheet SPF/DB process, The TC4 SPF/DB process is simulated by MARC and simulation is applied to analyze the process and thickness distribution.