Study On Mechanism Of The Mannesmann Effect In TC4 Cross Piercing

In cross piercing,the transverse compression force in the axial symmetry direction is caused by the billet during the repeated rotation and compression.The phenomenon that the core is induced by the tensile stress to form porosity and cavity is called the Mannesmann effect.Making more use of Mannesmann effect can refrain piercing resistance,improve the life of plug,decrease the increase of deformation temperature of the billet and obtain ideal microstructure during cross piercing.At present,most of the research on the Mannesmann effect was discussed with the continuous casting billet of carbon steel,there were few studied on the Mannesmann effect of TC4 alloy.In this paper,the method of experiment with finite element simulation is used to study the Mannesmann effect of the cone-type roll piercing of TC4 alloy,the main research content and analysis are as follows:The tensile stress of Mannesmann effect are observed in TC4 alloy and 45 steel rotating cross forging experiment and rolling block experiment,but there is no obvious crack and hole cavity.The centre of the workpiece is subjected to two tension stress.The tensile stress of the 45 steel is more obvious along the axial,but the tensile stress of the TC4 alloy is more obvious along the circumferential direction.The finite element model of the cone-type cross piercing was establelished to analyze the change law of the Mannesmann effect of different rolls and materials.When used cone-type,the Mannesmann effect is more intense.The maximum principal stress in the centre of the tube is 1.03 times the barrel-type,and the tensile stress distribution is larger.The TC4 alloy is 1.25 times of the 45 steel,and the maximum principal stress peak is appeared about at maximum diameter reduction 7.5 %.The effects of feed angle,maximum diameter reduction,cross angle and rolling speed on the Mannesmann effect of TC4 alloy were discussed.With the increase of them,Mannesmann effect showed the trend of increasing first and then decreasing.The process parameters were optimized and analyzed from two aspects of deformation uniformity and temperature control.The optimum technological parameters are as follows: feed angle 12 degree,maximum diameter reduction 12 %,cross angle 15 degrees,rotating speed 70 rpm.The perforation test of tapered roll with different length of TC4 alloy was carried out by developed cross piercing mill with the optimum process parameters.The quality of the inner and outer wall of the tube was better,the cracks and the hole cavity were not found,and the microstructure were ideal.The resistance of plug is small,and it can be reused again.The research content of this paper makes up the blank of the study on the mechanism of TC4 alloy Mannesmann effect.It provides theoretical basis and technical support for the oblique rolling of titanium alloy thick wall tube,which has important guiding significance for practical production.