| With the development of the aerospace,naval,and energy industries,the size of structural components in products has increased,the shape has become more and more complex,and the strength of the materials used has increased.Which have brought new challenges to plastic forming.As a result,the tonnage of the equipment is insufficient and the non-uniformity of deformation increases.Among them,large-scale structural parts for aviation are mainly made of high-strength titanium alloys.The conventional forming methods have many defects of the forgings,such as large forming loads,non-uniform deformation,and poor stability of the microstructure and mechanical properties.Therefore,the research on the method of less-loading and near-uniform forming has become the key technology to improve the quality and stability of aircrafts.In this paper,a type of large-scale disk component for aviation is taken as the object of study,the research on the forging deformation mechanism and forming defects of the forgings under two conventional forming methods is carried out.Based on this,a new method to achieve the less-loading forming and near-uniform forming is proposed,it is hollow divided flow forming process.Based on the forming process,the influence of the diameter of the center hole,the soft wrapping process and various process parameters on the forming load and the uniformity of the forging deformation are studied,and the optimum process parameters of the forging are obtained.The main points of the thesis are as follows:?1?A series of hot compression experiments which were tested on Gleeble-3500test machine was performed at a temperature of 730-880°C and a strain rate of0.001-1s-1 to study the hot deformation features of Ti55531 alloy,and the true stress-strain curves under different deformation conditions were obtained.Based on the regression analysis of the experimental data,the constitutive models for the deformation of Ti55531 alloy in the two-phase region and single-phase region were established respectively,which laid the theoretical foundation for the later numerical simulation analysis.?2?Based on the material characteristics and structural features of the large-scale disk component,the deformation mechanism under two conventional forming methods was studied,and two conventional forging methods were found to have defects of large forming load and non-uniform deformation,which are caused by factors such as large size of forgings,large deformation resistance of materials and unreasonable forging process.According to the analysis results,a new process that achieves less-loading forming and near-uniform forming is proposed,namely,hollow divided flow forming;?3?The hollow divided flow forming process and the soft wrapping process were applied to the forming of the large-scale disk component.The deformation mechanism of the forming process was studied,and the influence of the diameter of the center hole,the soft wrapping process and various process parameters on the forming load and the uniformity of the forging deformation were studied.When the diameter of center hole is?150mm,the mold preheating temperature is 350-450°C,the friction coefficient is0.2-0.4,and the press speed is 5mm/s,the forming load and deformation uniformity has a good match relationship.The load is 70,300 tons,and the effective deformation area of the forging accounts for more than 80%,and the small deformation and the large deformation are mainly distributed in the surface and the inner hole areas,which can be removed by the subsequent machining.The goal of less-loading and near-uniform forming is achieved;?4?The hollow divided flow forming process and the optimized process parameters were applied to guide the actual production.The production results showed that the microstructure and properties of forgings could meet the application requirements. |
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