Research On Influence Of Temperature Uniformity On Hot Backword Extrusion Of High-pressure Gas Cylinder

With the rapid development of the world economy,especially the electronic industry and the gas industry,a strong demand for high-pressure cylinders is increasing all over the world,bringing a fast-growing Market of high-pressure cylinders.Suffering from high working pressure with thin wall thickness,gas cylinders get extensive attention on its security.So the quality requirement is very strict during producing process of gas cylinders.In drawing forming method for seamless gas cylinder,the backword extrusion process is in front of the drawing process,and the quality of cup shaped workpiece from the former process has a direct impact on molding in the latter process.This paper mainly studies the influence of the uneven temperature of the blank on the quality of the cup shaped workpiece from the backword extrusion process.34CrMo4 steel is selected as the research material and the real stress-strain curve at high temperature is obtained through unidirectional compression test.The Z parameter model of peak stress in high temperature of 34CrMo4 steel is established according to the experiments data.By analyzing the influencing factors of the backword extrusion process,finite element models are established and three cases of uneven temperature for blank are designed according to actual working conditions.The process of backword extrusion for the blank of uneven temperature is analyzed with the help of DEFORM-3D finite element simulation software.The distribution of blank temperature,the flow velocity,and the force of the punch in the process of deformation were studied,and also the size of the backword extruded cup shaped workpiece were measured.Results show that the initial uneven temperature of blank will lead to lug and uneven wall thickness for cup shaped workpiece.When the difference between the maximum and the lowest temperatures of the billet changes,the difference between the lug and the maximum wall thickness difference also changes.The higher the temperature difference,the greater the lug as well as the maximum wall thickness difference.The lug and the maximum wall thickness difference also be affected by friction coefficient,extrusion speed and the ratio of height to diameter of the blank when the blank exists uneven temperature.