Research On Finite Element Simulation Of Diffusion Welding Of Titanium Alloy Injector Based On Micro-Hole Welding Models

The laminate injector consists of several layers of thin plates with precision holes.It is one of the key structures of liquid rocket engine combustion chamber.It has been widely used in spacecraft,missile and other fields.However,diffusion welding is adopted in the manufacturing process of the injector,and the local welding deformation is easy to occur.Therefore,the manufacturing difficulty is larger and the yield is lower.It is difficult to guide the process optimization theoretically because of the complicated influence factors and change rules of welding deformation.And it is difficult to meet the development schedule requirements of each model because of the long period of process test.In this paper,the diffusion welding interface micro-hole welding model and finite element simulation technology are used.Theoretical calculation and simulation of diffusion welding of injector are carried out to explore the mechanism of deformation after welding.It provides theoretical basis for solving the manufacturing problem of laminate injector.Based on four theoretical models of plastic deformation,surface source,interface source and creep,the model was established.In view of the changing behavior of diffusion welding interface,the calculation formula of micro-hole welding model is deduced and modified comprehensively.The computational flow of the model and the representation of the results are also designed.By comparing the calculated data of this model with the existing experimental data,the error is found to be small.It shows that the model has certain predict ive ability.This model is used to calculate and analyze the interface welding of TC4 titanium alloy diffusion welding.The influence of different theories in the model on micro-hole bonding was studied.The influence mechanism of technological parameters on weld rate is also analyzed.Based on the micro-hole welding model,the finite element simulation method of diffusing welding in injector was studied.The whole structure and welding process curve of the model are established.The welding critical point is defined and the change hypothesis of welding interface before and after the critical point is proposed.Based on the assumption,the necessary conditions such as contact relation and mechanical constraint are established.So the simulation method can reflect the change of welding interface and the whole structure.Based on the structure characteristics of the injector,the evaluation method of the deformation after diffusion welding is proposed.It includes thickness variation,hole center deviation,hole radius variation,etc.By using the proposed method,the creep change law of welding process is simulated.The results show that the creep strain is mainly concentrated on the inner wall and around the hole and near the diffusion welding interface.The influence of process parameters and geometry structure on the deformation is analyzed by using the micro-hole welding model and the finite element simulation method of diffuser welding.The influencing factors include welding pressure,welding temperature,initial size of mold hole,initial position of mold hole,initial center distance of mold hole,etc.The results show that the influence of welding pressure and temperature on deformation and creep is more significant.The influence of geometric structure on the thickness and hole radiu s is not obvious,but different geometric factors have different influence on the center distance of the hole.The linear regression model was used to fit all the influencing factors involved,and the quantitative analysis results were obtained.The diffusion welding test was carried out with TA2 as the welding material,and the finite element model corresponding to the test was established.The comparison between the experimental results and the simulation results shows that the relative error is small,which shows the effectiveness of the simulation method to some extent.In addition,a diffusion welding prediction system is developed based on micro-hole welding model.The system can predict the time required to complete the diffusion welding,the influence of different theories in the model on the bonding rate at the interface,and the data of the bonding rate changing with the welding time.It makes the research of diffused welding deformation more convenient.