Investigating The Rear-jamming Of TC4 Super-heavy-wall Tubes In Cross Piercing

The composition of TC4 titanium alloy is Ti-6Al-4V which is a typicalα+βduplex titanium alloy.It has been widely used in petroleum,marine and aerospace industries owing to its good mechanical properties and corrosion resistance.In the manufacturing industry,a large number of titanium alloy thick wall tubes are required to be used as the billet of ring and complex shape parts,especially for those tubes with bimodal microstructures,which diameter thickness ratio is less than 5:1.And the TC4super-heavy-wall seamless tubes with dual microstructures are mainly deformed by extrusion.Although the bimodal microstructure can be obtained by extrusion process,but the rate of material utilization is lower than piercing process,and it may cause serious environmental pollution.However there is still have some problems in piercing process of TC4 titanium alloy such as the phenomenon of rear-jamming and the Widmanstatten microstructures.Based on the above issues,the relationship between rear-jamming and inside diameter expansion using different technology parameters was studied in greater details by finite element simulation technology.And the TC4super-heavy-wall seamless tubes with bimodal microstructures were obtained by piercing process in this paper.The main research contents are as follows:By analyzing the specimen of the TC4 heavy-wall tube,it was found that the phenomenon of rear-jamming is related to the insufficient inside diameter expansion during the process and the diameter reduced at the tail of tube.Therefore,maintaining the proper amount of internal expansion during the piercing process is the key to avoid the phenomenon of rear-jamming.A rigid-plastic finite element model of the TC4 thick-wall tube in cross piercing process was established.The experiment of single factor was carried out to analyze the influence of main process parameters on the inside expansion rate during steady state deformation,including the diameter reduction ratio,feed angle,and diameter reduction ratio before the plug.The results of simulation shows that the inside expansion rapidly increases with the increase in maximum diameter reduction ratio,?.When the range of?is between 10%to 12%,feed angleβis between 12 to 18 degrees and plug diameter reduction ratio?_dq is between 5%to 7%,the inside expansion ratio in steady-state deformation zone can increase to more than 6%,thus solving the problem of rear-jamming effectively.By means of orthogonal experiment design,the parameters range of initial determination was optimized.The optimization criterion includes three aspects:dimensional accuracy,deformation uniformity and microstructure control.These were considered as good technology parameters,including feed angle of 15 degrees,diameter reduction ratio before the plug of 7%and maximum diameter reduction ratio of 11%.The experiment of cross piercing process was carried out by using the optimized process parameters.No rear-jamming phenomenon occurs during the process.The ratio of diameter to thickness is 3.75 and the microstructure of tube obtained by piercing process is uniform.The research of this paper has made some progress in the production of TC4super-heavy-wall tube which is obtained by cross piercing.It provides theoretical and technical support for the cross piercing of super-heavy-wall tube of titanium alloy,which has important significance for industrial production.