Study On Wall Thinning Of TA2/T2 Titanium-copper Bimetallic Composite Tube In Rotary Draw Bending

In recent years,in order to meet the requirements of industrial lightweight and low-cost,bimetallic composite tube are often used in piping systems to replace single-layer tube,which not only meets its comprehensive performance requirements,but also reduces the cost of metal materials.The copper-the base bimetallic composite tube uses copper and its alloys with corrosion resistance,good thermal and electrical properties,and strong plasticity as the base tube,and uses light-weight aluminum or titanium as the covered tube.Combining the advantages of the base tube and the covered tube,it is often used in heating and corrosive liquids and pipeline transportation.The based on the ABAQUS finite element simulation platform,this paper studies the wall thickness reduction mechanism of TA2/T2 titanium-copper bimetallic composite tube of specification during rotary draw bending process.The main research contents and conclusions are as follows:(1)A predictive model for the wall thickness reduction of TA2/T2 titanium-copper bimetallic composite tube in rotary draw bending has been established.In the ABAQUS finite element software,the geometric assembly model,material model,friction contact model and clamping force of the clamping die are established.The optimized mesh size is 1.5mm and the optimized quality magnification factor is 2000.Considering the delamination defects,the Coulomb friction model is selected as the interface contact model between the covered tube and the base tube of the composite tube.The accuracy of the optimized finite element model has been significantly improved.The average forecast errors of the wall thickness reduction rate of the covered tube and the base tube are 13.76%and 13.83%respectively,which are both lower than 15%.The average forecast error of the cross section distortion rate of the covered tube and the base tube are 19.44%and 15.94%respectively,which are both lower than 20%.Therefore,the established finite element model can effectively predict the wall thickness reduction of the composite tube in rotary draw bending.(2)The influence of forming parameters on the wall thickness reduction of TA2/T2titanium-copper bimetallic composite tube was studied,and it was found that:(1)The bending radius R has the same influence on the wall thickness reduction of the covered tube and the base tube.When the bending radius R³85mm(relative bending radius R/D=2.5),the wall thickness distribution of the composite tube tends to be uniform.The initial wall thicknesst₀has a smaller effect on the thickness reduction of the base tube than that of the covered tube,and the wall thickness reduction firstly decreases and then increases.(2)Filling with the elastic mandrel can get a good flexible support effect,but the suppression effect on the wall thickness reduction is not good.With the increase of the number of cores N and the extension of the mandrel e,the wall thickness reduction rate of the covered tube and the base tube gradually increases.(3)With the increase of the friction coefficient of the mandrel-core?_m and the wiper die?_w,the wall thickness reduction rate of the composite tube gradually increases.With the increase of the friction coefficient of the pressure die?_p,the thickness reduction rate of the composite tube does not change regularly,but the overall trend is decreasing.With the increase of the friction coefficient of the bending die?_b,the change rule of the wall thickness reduction rate of the composite tube firstly decreases and then increases,showing a"funnel"shape.(4)With the increase of the boost speedV_p and the clamping force of the clamping dieF_c,the wall thickness reduction rate of the covered tube and the base tube decreases and tends to a stable value.With the increase of the bending speedw,the wall thickness reduction of the covered tube firstly increases and then tends to a certain stable value,while the base tube firstly decreases and then tends to a certain stable value.(3)The influence of the bending radius R,initial wall thicknesst₀ and the mandrel-core filling on the damage and cracking of the composite tube was explored,and it was found that:(1)During the bending process,the covered tube are more susceptible to the bending radius R to cause cracking than the base tube.As the bending radius R increases,the covered tube and the base tube of the composite tube are less likely to be cracked.With the increase of the initial wall thicknesst₀,the maximum damage value of the covered tube and the base tube of the composite tube decreases firstly and then increases.(2)Under the filling without mandrel and rigid mandrel filling,the covered tube and the base tube did not crack.With the increase of the number of cores N,the maximum damage value of the covered tube gradually decreases and tends to a stable value,as the extension of the mandrel e increases,the maximum damage value of the composite tube firstly decreases and then increases,while the base tube gradually increases.(3)The easy cracking positions of the composite tube is mainly distributed in the middle and back sections of the bending,and the easy cracking area of overlying tubes is relatively large.(4)In order to meet the engineering requirements of the composite tube(the maximum wall thickness reduction rate?_max(?)10%),without cracking,delamination and serious cross section distortion defects,the bending radius R³102mm(the relative bending radius R/D=3)should be selected.At the bending radius R=102mm,the best value range of other forming parameters:the initial wall thicknesst₀ is 3?5mm,the number of cores N is 1?3,the extension of the mandrel e is 3?7mm,the friction coefficient of the mandrel-core?_m is 0.02?0.1,the friction coefficient of the pressure die?_p is 0.1?0.34,the friction coefficient of the wiper die?_w is 0.18?0.34,the friction coefficient of the bending die?_b is 0.14?0.22,the boost speedV_pis R??1.4R?mm/s,the bending speed?is 0.25?0.75rad/s,and the clamping forceF_c of the clamping die is 30?60MPa.Combining with the optimal value range of forming parameters,it is that design the orthogonal test of the wall thickness reduction of the composite tube,and obtain the best combination of the various process parameters with the smallest wall thickness reduction rate and significance of forming parameters.