Study On Uneven Deformation Behavior And Formability Of Ta18 High Strength Titanium Tube In Numerical Control Bending

TA18 high strength titanium tube has many advantages,such as small density,high specific strength,corrosion resistance,creep resistance and other properties,that has been widely used in aerospace,automobile and other fields.But it is difficult to deform and the forming precision is low during numerical control(NC)bending process of TA18 high strength titanium tube.Therefore,it is urgently needed to develop the NC bending precision forming technology for TA18 high strength titanium tube.So,taking?6.35 mm × t0.4064 mm specification of the TA18 high strength titanium tube as object,the TA18 high strength titanium tube uneven deformation behavior and forming limit were studied systemically and deeply during NC bending by numerical simulation method.The research results were obtained as follows.Based on the numerical simulation software of ABAQUS,the finite element model of TA18 high strength titanium tube NC bending was established,and the key technology problems of the model were solved.The reasonable mass factor and mesh size are obtained.The stability of the model is verified by the energy of the model,and the reliability of the model is verified by the experimental results in the literature.The foundation is laid for the research of TA18 high strength titanium tube uneven deformation behavior and forming limit in NC bending.The stress / strain behaviors of TA18 high strength titanium tube in NC bending were studied deeply,the results show that: the tangential stress / strain of tube increase rapidly in the initial stage of bending.With the increase of the bending angle,the maximum value of tangential compressive and tangential tensile stresses is situated nearly the bending plane.When the bending angle reaches 45 °,the maximum tangential tensile stress and the maximum tangential compressive stress have no obvious change.The tube NC bending reaches a stable plastic deformation stage,and the tangential tensile stress is less than the tangential compressive stress.The distribution of tangential strain is similar to that of tangential stress.After mandrel retracting,the tangential stress occurs certain unloading.After springback,the tangential stress is further unloaded.The tangential stress on the outside of tube appears to reversely load,while the mandrel retracting and springback have little effects on tangential strain.The mandrel must be configured,and the suitable mandrel type is hemispherical mandrel for the specification of ? 6.35 mm × t0.4064 mm TA18 high strength titanium tube in NC bending.When the bending angle ? is less than 45°,the maximum value of cross section deformation ratio,wall thinning ratio and wall thickening ratio increase with the increase of ?.The cross section deformation ratio curve is similar to the parabola.When ? is greater than 45 °,with the increase of bending angle,the maximum value of cross section deformation ratio,wall thinning ratio and wall thickening ratio change little,and that of curves show platform characteristics.Increasing the bending radius can reduce cross section deformation ratio,wall thinning ratio and wall thickening ratio.In the condition of the same tube diameter,reducing wall thickness can increase cross section deformation ratio,wall thinning ratio and wall thickening ratio.In the condition of the same wall thickness,increasing tube diameter can increase cross section deformation ratio,wall thinning ratio and wall thickening ratio.When tube diameter and wall thickness proportionally increase,the cross section deformation ratio and wall thickening ratio increase,the wall thinning ratio decreases.While when the size of diameter and wall thickness are too small,the wrinkling phenomenon will occur.The cross section deformation ratio decreases with the decrease of mandrel / tube clearance,bending die / tube clearance and pressure die / tube clearance.Reducing bending die / tube clearance,pressure die / tube clearance or increasing clearance between mandrel and tube can reduce the wall thinning ratio.The wall thickening ratio decreases with bending die/ tube clearance and mandrel / tube clearance decreasing or the pressure die / tube clearance increasing.The clearance and friction of wiper die / tube have little effects on cross section deformation ratio and wall thickness change ratio.Reducing mandrel / tube friction coefficient and bending die/ tube friction coefficient or increasing pressure / tube friction coefficient can reduce the cross section deformation ratio and wall thinning ratio.Increasing the friction coefficient of mandrel / tube and bending die / tube or decreasing the pressure / tube friction coefficient can reduce wall thickening ratio.When the boosting velocity is less than V0(tangential speed of bending die),with the decrease of the boosting speed,cross section deformation ratio and wall thinning ratio increase,wall thickening ratio decreases.Conversely,when the boosting velocity is greater than or equal to V0,with the increase of the boosting speed,cross section deformation ratio and wall thinning ratio decrease,wall thickening ratio increases.Increasing the extension of the mandrel can reduce the cross section deformation ratio and increase the wall thinning ratio,while the extension of the mandrel has little effect on the wall thickening ratio.With the increase of elastic modulus or with the decrease of ratio of width and thickness,the cross section deformation ratio decreases,wall thickness change ratio increases.With the increase of hardening exponent,the cross section deformation ratio decreases,wall thinning ratio and wall thickening ratio change little;the yield strength has little effect on cross section deformation ratio,wall thinning ratio and wall thickening ratio.when the bending angle is 180°,the minimum relative bending radius R/D equals to 2.5 for the specifications of the ?6.35 mm × t0.4064 mm TA18 titanium tube in NC bending.