Friction Coefficient Determination Of The TC4 Titanium Alloy During Hot Forming By Ring Upsetting

The glass lubricating coating has been widely used in hot forming processes such as high temperature precision forging of TC4 titanium alloy,to resist high temperature oxidation and reduce friction resistance of plastic flow.In order to study the plastic flow forming law of TC4 titanium alloy,it is necessary to accurately measure the friction coefficient in the hot forming process of TC4 titanium alloy,and the ring upsetting method is one of the most common methods to determine the contact friction coefficient in the metal plastic deformation process.In order to determine the friction coefficient of TC4 titanium alloy ring during upsetting deformation under different lubrication conditions,three kinds of TC4 titanium alloy ring upsetting samples with different lubrication treatment were made.Three kinds of ring upsetting friction coefficient calibration curves were obtained by theoretical analysis and finite element numerical simulation.The friction coefficient of TC4 titanium alloy during hot forming process was measured by using the results of ring upsetting and the friction coefficient calibration curve.The specific research process and results are as follows:(1)The glass powder of lubricating coating was prepared with 44.0%SiO₂,25.0%B₂O₃,10.0%Na₂O,7.5%Ca O,6.8%Mg O,5.0%TiO₂ and 1.7%Al₂O₃.Two kinds of glass lubricating coatings with thickness about 0.20-0.30 mm were prepared on the surface of TC4 titanium alloy ring samples by dip coating method with lab-prepared glass powder and purchased Ti-1 glass coating slurry,respectively.The uncoated ring sample and two kinds of samples with glass lubricating coating were heated to 950?,and the upsetting experiment was completed under the conditions of die temperature 400?and uppseting speed 5 mm/s.(2)After theoretical analysis of ring upsetting process,improving traditional DEFORM-3D finite element model and completing numerical simulation,Three kinds of friction coefficient calibration curves of TC4 titanium alloy ring upsetting were obtained by theoretical analysis,traditional finite element model and improved finite element model numerical simulation.The difference and dispersion of three calibration curves were compared and analyzed.The results show that,the calibration curve of theoretical analysis is independent to the technological parameters of ring upsetting,and has great deviation from the actual working condition of upsetting deformation.There are obvious differences in the three kinds of friction coefficient calibration curves of ring upsetting;The dispersion of the improved model calibration curve>the traditional model calibration curve>the dispersion of the theoretical analysis calibration curve,It is easier to accurately determine the friction coefficient of TC4 titanium alloy ring upsetting by using the improved model calibration curve.(3)The effects of billet temperature,die temperature,upsetting speed and thermal conductivity on the friction coefficient calibration curve were analyzed by orthogonal finite element numerical simulation.The results show that the influence of upsetting speed>billet temperature>heat conductivity>the influence of die temperature.(4)According to the upsetting experiment results and the improved model calibration curves,the dry friction coefficient of the uncoated samples was 0.64,and the friction coefficients of lab-prepared glass coating and Ti-1 glass coating were 0.23and 0.20 respectively.However,the friction coefficient of this ring upsetting experiment can not be determined by theoretical analysis calibration curve and traditional model calibration curve.The improved model friction coefficient calibration curve has fully considered the influence of forming process parameters,which is closer to the actual process of TC4 titanium alloy hot forming.The accuracy and reliability of the numerical simulation results of the improved model has been verified by ring upsetting experiment.