Research On Hydroforming Technology For Branch Tube Of Complex Sheet Metal In Aviation Field

The branch tube was one of the main typical parts in aircraft structures,and the quality of these parts affected the surface quality and flight safety of the entire aircraft.At present,this kind of parts was mainly formed by falling compression process,but this process has large amount of noise pollution and the forming quality was difficult to control.In addition,after falling compression process,the surface and interior grains of the parts were seriously damaged and extensive manual trimming was required,which can not meet the fatigue life requirements of high-performance fighters aircraft,and it had been expressly prohibited or restricted by European and American and other international aviation powers.The hydroforming technology had the characteristics of high forming limit,small springback and good surface quality.It was one of the main directions to realize flexible medium forming of aviation sheet metal.In order to change the traditional manufacturing process and realize the high quality and efficient forming of aviation branch tube parts,this paper focused on the hydroforming technology of aviation branch tube.Firstly,this paper selects the typical branch tube of aviation complex sheet metal parts as the research object.Combining with domestic and foreign scholars research methods and results of plank charging technology,the method of controlling variable was put forward through finite element numerical simulation and process test,the influence of the geometric shape,blank holder force and liquid chamber pressure on the quality of hydroforming of branch tube was investigated.The optimal process parameters were optimized to solve the problem of wrinkling and rupturing in the process of hydroforming of branch tube.Secondly,branch tube was given parts of structure,size and shape forming requirement,the falling pressing and the existing hydroforming process can not meet the forming requirements of branch tube,the dimension and surface quality of parts can not be guaranteed,meanwhile the qualified rate of parts was very low.The fundamental reason was that the process parameters obtained by the process trial-and-error method were not the optimal parameters of part forming.The influence of blank geometry,blank holder force and liquid chamber pressure on the hydroforming quality of branch tube which were studied by finiting element numerical simulation.The optimization of process parameters was completed to solve the forming problems in the production of branch tube.Thirdly,hydroforming process window and expression form for branch tube were studied.It was pointed out that there exists certain formable region(process window)of liquid chamber pressure and blank holder force,and theoretical analysis and calculation were carried out.Meanwhile,the key technological parameters of hydroforming,such as liquid chamber pressure,blank holder force,drawing force and fillet radius of male and female dies were analyzed theoretically,and the key technological parameters were calculated theoretically,which provide data for subsequent numerical simulation research.Then,the effects of blank geometry,blank holder force and liquid chamber pressure on the forming law of the bifurcated tube were studied by finite element numerical simulation.The geometric shape,blank holder force and liquid pressure equivalent stress,equivalent strain and wall thickness distribution were simulated and compared.It was concluded that the branch tube of hydroforming numerical simulation of the optimal process parameters,and verified the branch tube of hydroforming process parameters on the accuracy of the theoretical analysis and calculation.Finally,several groups of different process parameters were set up for the process test,and the branch tube specimens were detected and analyzed.The experimental parts under the optimal process parameters of finite element numerical simulation were studied and analyzed,and the differences between the test results and numerical simulation results were compared and analyzed.The experimental results showed that the thickness variation of the branch tube was consistent with the strain variation of the numerical simulation,which verified the correctness of the numerical simulation method.The optimal process parameters of hydroforming of branch tube were obtained as follows: blank geometry IV,blank holder force 30 T and liquid chamber pressure 8MPa.