Study On Cross-Section Distortion And Filling Of TA2/T2 Titanium-Copper Bimetallic Composite Tube In Rotory Draw Bending

With the economic development and the transformation and upgrading of traditional industries,bimetallic composite tube are used more and more frequently in modern industrial fields such as petroleum,electrical appliances,nuclear power,aviation,and ships.Therefore,it is urgent to study the numerical control of bimetallic composite tube bending technology.This article uses a combination of experimental research,numerical simulation and theoretical analysis,mainly taking 34×3×R102mm TA2/T2 titanium copper bimetallic composite tubes as the research object,The influence of the process parameters of the CNC bending and forming mold on the CNC bending deformation and the size effect of the composite tube are systematically studied.?1?In order to accurately simulate the forming process of TA2/T2 bimetallic composite round tube bending,Unidirectional tensile experiments were carried out using single-layer TA2 round tube/T2 round tube samples,basic mechanical performance parameters such as elastic modulus E,yield strength,strength limit,elongation,etc.were obtained,and establish a constitutive model of TA2/T2 bimetallic composite tube material,a power exponential function is used to describe the plastic stress-strain curve obtained by the sample.The accuracy of the finite element model is verified from the perspective of prediction of cross-sectional distortion,thereby verifying the reliability of the finite element model.Based on the built finite element model,the stress in the process of numerically controlled bending of the titanium-copper bimetal composite tube is studied The strain distribution law found that the circumferential strain is smaller than the tangential strain and the thickness strain.The increase and thinning of the wall thickness of the overlying tube are greater than that of the base tube.The distribution of the triaxial strain inside the composite tube is more regular than the outside.?3?When the mandrel extension is 3mm,11mm,15mm,the base-cladding section distortion rate is too large or bulging occurs,so it is most appropriate to select the mandrel extension 7mm;when the core head is not used,the section distortion is close to 5%.At the head,the base-cladding cross-sectional distortion is controlled within 2%.When using a rigid mandrel and an elastic mandrel,the cross-sectional distortion rate of the composite tube base tube and the cladding tube is controlled within 5%.Using the rigid mandrel,the maximum difference between the distortion rate of the base tube T2 and the cladding tube TA2 is 0.75%and the uneven change caused the phenomenon of cross-sectional distortion such as wrinkling and layering.The use of PVC elastic core mold can better suppress the defects of cross-sectional distortion of the composite tube.With the increase of the lateral thrust speed,the maximum cross-sectional distortion of the cladding decreases from 9.78%to 2.02%,and the maximum cross-sectional distortion of the base tube decreases from 10.06%to 1.66%.With the increase of lateral friction,the cross-sectional distortion rate of the composite tube cladding and base tube is slightly reduced.Due to the work hardening of the composite pipe bent at a large angle,it is more difficult to deform the rear part.Orthogonal experiments were carried out by selecting three factors:the boosting speed V_p,the friction coefficient of the compact and the composite tube?_p,the friction coefficient of the wrinkle and the composite tube?_w,and the friction coefficient of the core mold and the composite tube?_m.The results show that the optimal parameter combination is V_p=59.5mm/s,?_p=0.23,?_w=0.1,?_m=0.02,and the maximum deformation value??_hmax=0.7913%is smaller than all the results in the orthogonal table.?3?With the increase of D,the maximum cross-sectional distortion rate of the cladding tube increased from 6.06%to 7.24%,and the base tube increased from 7.45%to 8.84%.Carrying out simulation experiments at 1mm,1.5mm and 2mm,and it was found that the change in the wall thickness of the composite tube base tube is more significant than that of the cladding tube on the section distortion.Under the premise of D/t and _t/_?or unchanged,with the increase of D,The maximum cross-sectional distortion rate is reduced from 8.96%to 7.91%,and the base tube is reduced from 9.84%to 8.84%.The increase in wall thickness t has a more significant effect on cross-sectional distortion than the increase in diameter D.