Research On The Key Technology Of Die Forging For Large Aircraft Hub

The hub is the main load-bearing component of the aircraft.It bears the impact load and static pressure of the aircraft during the take-off and landing stages,which is related to the flight safety.The service conditions of hub are very harsh,so the structure is complex,and the quality requirements are high.Due to the insufficient capacity of China's aviation manufacturing industry and the technical blockade of the United States and other Western countries,China does not yet have the ability to independently produce the hub of aircraft.This thesis focus on the characteristics of complex shape of the hub forgings,high surface quality requirements,difficulty in precision forging,inhomogeneous microstructure and coarse crystals in the forming process of domestic large aircraft hub.The forming process and microstructure evolution of hub were studied by isothermal heat compression experiment,finite element numerical simulation and actual trial production.The main work and conclusions are as follows:(1)The isothermal hot compression simulator Gleeble3500 was used to heat-compress the as-cast 2014 aluminum alloy at a deformation temperature of 375?-450?and the rate of 0.01s^-1-10s^-1.The effect of temperature and deformation rate on flow stress was analyzed by the true stress-strain curve.The results show that the whole deformation interval of 2014 aluminum alloy consists of work hardening,dynamic recovery and dynamic recrystallization mechanism.the material has lower rheological stress at high deformation temperature and low deformation rate,and higher stress at high strain rate at low deformation temperature.based on the Arrhenius constitutive equation and regression analysis of the true stress-strain data,the 2014 aluminum alloy constitutive relation expressed by Z parameters is established.The material model of finite element numerical simulation is provided,which lays a theoretical foundation for numerical simulation analysis of forgings(2)Designed the hub forming scheme and die structure,the forming process parameters,die structure were optimized.The shape of the forging is complex,so forming scheme consists of dummying,pre-forming and final-forming.Then the forming parameters and structure of die were optimized by analyzing the effect of these on forging defects and macro quality.The results show that the forming load decreases with the increase of forging temperature,friction coefficient and forming speed.The temperature change of forging is mainly affected by the preheating temperature of forging.(3)The critical strain model,recrystallization volume percentage model and grain size model of the 2014 aluminum alloy were obtained based on the true strain stress data and sample grain size statistics.The microstructure evolution model(JMAK)of the2014 as-cast aluminum alloy was established.(4)Based on the grain size distribution of the original billet,the microstructure evolution in different forming stage were simulated and analyzed.The result showed that the key process of grain refinement is dummying and it can cause large deformation and grain refinement of metal.Therefore,the effect of process parameters on microstructure was studied based on dummying,the forming parameters were further optimized to create conditions for grain size refinement and uniform distribution at the final-forming.(5)Deformation and temperature were coupled to analyze the entire forming process,and the forming experiments were carried out.The test results show that both the dummying and final-forming stages,the folding defects and filling defects were occurred at forgings.The reasons of defect were analyzed by numerical simulation,and the difference between actual boundary conditions and ideal conditions and unreasonable distribution of deformation are the main reasons of defect.(6)The forming process were optimized according to the defects found in the initial test and the optimized scheme is used for the new test again.The test results showed that no defects occurred during the forming,the microstructure and mechanical properties meet the design requirements.It realized the first manufacturing of large aircraft wheels in China.