On Key Technology Of Impact Hydroforming Process Of Titanium Alloy Part

Titanium alloy materials have been widely used in the aerospace field because of their superior comprehensive properties.For the development of lightweight in this field,processing of light alloy titanium alloys with poor plasticity has become an urgent problem to be solved.The strain rate range of impact hydroforming is 1×10³-1×10⁴s^-1.This technology combines the advantages of hydraulic forming and high strain rate forming,and can significantly improve the forming performance of low plasticity light alloy at room temperature.In this paper,the key technology of impact hydroforming for TC4 titanium alloy hemispherical parts is studied by combining experimental research and simulation analysis.The mechanical properties of TC4 titanium alloy under high strain rate and quasi-static conditions were obtained by uniaxial tensile test and Split Hopkinson Tensile Bar test.By designing and developing quasi static hydraulic experimental platform and high strain rate impact hydroforming equipment,quasi static hydraulic pressure forming and high strain rate impact hydroforming test research were studied,the influence law of height of TC4 titanium alloy hemispherical parts were obtained under different technological parameters and technological scheme.The forming height limit of TC4 titanium alloy under the condition of high strain rate is obtained,which proves that the impact hydroforming technology can significantly improve the plastic forming ability of TC4 titanium alloy.The main conclusions of this paper are as follows:(1)Testing of material properties of TC4 titanium alloy sheet under quasi-static and high strain rate conditions.The thickness of TC4 titanium alloy sheet is 1.2mm.Unidirectional tensile test and Split Hopkinson Tensile Bar are performed on the samples at 0°(RD),45°,90°(TD)directions to the rolling.The mechanical property parameters and stress-strain curves of TC4 titanium alloy sheet with strain rate of 1×10^-1s^-1 were obtained by uniaxial tensile test.A Hopkinson bar with diameter d=20mm was used to carry out dynamic tensile tests,and the stress-strain curve of TC4 titanium alloy sheet with strain rate in the range of 1×10³-4.8×10³s^-1 was obtained.The experimental results show that the strength and plasticity of TC4 titanium alloy increase with the increase of strain rate,and the elongation of TC4 titanium alloy at high strain rate is 1.25 times of that at quasi-static condition.The Johnson-Cook(J-C)constitutive model of TC4 titanium alloy was obtained by fitting:?=(1064.8+1245.2g^1.04)?1+0.16ln?(?)??.(2)Experimental study on hydroforming of TC4 titanium alloy hemispherical parts.A quasi-static hydroforming finite element simulation model was established for the hemispherical part of aerospace gas storage tank front cover with an inner diameter of SR=50mm and the simulation analysis was carried out.A hydraulic forming process experimental platform was built for,carrying out hydroforming experimental research.The equivalent stress,equivalent plastic strain and the thinning rate distribution of TC4 titanium alloy hemispherical parts during forming process are obtained by simulation analyzes the influence of different process parameters such as the liquid pressure,blank-holder force and the height of the blank diameter to the forming height curve,the accuracy of the simulation result is verified by hydroforming experiments,the maximum forming height of quasi static hydraulic forming parts is H=24.01mm.(3)Simulation and analysis of impact hydroforming for TC4 titanium alloy hemispherical parts.Based on the process characteristics of impact hydroforming,a fluid-solid coupling simulation model of impact hydroforming was established.The equivalent stress and equivalent plastic strain and the liquid pressure contours distribution obtained by simulation analysis forming the process of hemispherical parts impact hydroforming of the TC4 titanium alloy,the effect of different process parameter such as impact velocity,diameter of blank holder force and sheet metal parts forming height to component forming height were studied.The results show that the forming height of TC4 titanium alloy hemispherical parts is obviously by impact velocity and blank holding force.(4)Experimental study on impact hydroforming of TC4 titanium alloy hemispherical part.Developing impact hydraulic forming experimental equipment,and establishing impact hydroforming experimental research platform,carry out different experimental schemes of impact hydroforming experimental research.The influences of impact velocity,blank holder force and sheet diameter on the forming height of parts and the changing curves of parts height under different process parameters were obtained.The sheet diameter D=155mm,the blank holder force p=7.69k N,the impact velocity V=43m/s,and the maximum forming height H=27.31mm were adopted in the forming experiment scheme of"single die single impact".The forming experiment scheme of"single die multi impact"is adopted,the impact speed is V=46m/s,the impact is carried out three times,and the parts have the maximum forming height H_max?=30.26mm.(5)By comparing the impact hydroforming experiment and simulation results,it is found that the forming height curves of parts under different process parameters are consistent,which verifies the accuracy of the impact hydroforming simulation results.It shows that the forming height of parts increases with the increase of impact velocity.With the increase of blank holder force,the forming height of parts decreases.Parts height unchanged by changing sheet diameter.Comparing the experimental results of impact hydroforming and hydroforming,it is found that the forming limit of parts can be increased by 14%by using the"single die single impact"forming process compared with the quasi-static forming process.Compared with the quasi-static forming process,the forming limit of the part is increased by 26% by adopting the"single die multi impact"forming process.