Relation Between Roll Shape And Rear-jamming In TC4 Heavy-wall Tube Cross Piercing

TC4 alloy is a kind of α+β type biphase titanium alloy,which has excellent comprehensive performance and is widely used in aviation,aerospace,ship and energy industries.Due to the large deformation resistance and the strong work hardening of TC4 alloys,it is easy to crack during the plastic deformation process,so titanium alloy seamless pipes are difficult to produce.Compared with extrusion and other progress,cross piercing has the advantages of low consumption of metal and mold,low processing cost,and is used in the production of TC4 alloy billet.However,at present,when cross piercing produces a thick-walled tube of TC4 alloy,rear-jamming phenomenon frequently occurs,and the temperature rise is so severe that the microstructures unsatisfactory.This paper analyzes the reasons for the rear-jamming phenomenon during the process of cross piercing and designs a new type of spiral roller.The reasonable perforation technology system was discussed and the thick-walled tube of the TC4 alloy with duplex microstructures was successfully prepared.The main research and analysis as follows:Combined with the theory and test of cross piercing,the main reason of the rear-jamming phenomenon of TC4 alloy was the lack of internal expansion and a new design method of spiral roller is presented by using the space geometry of the cross piercing.The effect of roll shape on piercing process was studied by means of finite element method,and the roller type suitable for the perforation of TC4 thick wall tube was optimized.The shape of the roll is: the cone-type roller with arc type mother-line.The effect of feed angel,diameter reduction rate,and diameter reduction ratio before the plug on the prevention of rear-jamming capacity and internal expansion ratio was analyzed by a single factor variable.The results show that the internal expansion ratio increases with the rise of feed angel and diameter reduction rate.When the feed angel is between 9°~15°,the diameter reduction rate is between 8%~12%,and the diameter reduction ratio before the plug is between 5%~7%,the use of the spiral roller can effectively prevent the occurrence of rear-jamming phenomenon.The three-factor orthogonal experiment was used to analyze the establishment of piercing process,the strain field and the temperature field distribution.The optimum technological parameters for the spiral type roller piercing were obtained as follows:feed angel was 15°,diameter reduction rate was 8%,diameter reduction ratio before the plug was 7%.The TC4 thick-wall tube cross piercing test was conducted with the self-developed Φ60mm spiral roller rolling piercing mill under the best process parameters.The tube with dimensions of Φ47.0mm×12.5mm×223mm was obtained with a diameter-to-thickness ratio of 3.76,which satisfies the thick-wall diameter requirement.The radial and axial structures of the tube are evenly distributed and both are duplex microstructures.The tube was subjected to a tensile test.Under constant strain rate,the yield strength of the capillary after rolling was 467.9MPa,and the tensile strength was 893.4MPa.The research of this paper makes up the blank of TC4 super-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.