Effect Of Blank And Lubrication On Hot Back Extrusion Forming Of High Pressure Gas Cylinders

High-pressure cylinders can hold various energy gases with low production cost,high production efficiency and convenient movement.With the rapid development of clean energy,the demand for high-pressure cylinders is growing rapidly.However,due to the high pressure,flammability,explosiveness and toxicity of the gas contained in the cylinder,and the repeated filling and moving of the cylinder,the quality requirement of the cylinder is very strict.Currently used in the industry is the drawing of seamless steel cylinders.The reverse extrusion process is a front-end process of the drawing process in the drawing forming process,and the quality of the formed part will have a great influence on the subsequent drawing forming process,and even on the quality of the final cylinder forming part.In the reverse extrusion process,there are many factors that affect the quality of the formed part.This paper mainly studies the influence of the inclination of the blank end face and the axial offset of the blank and the uneven lubrication on the quality of the formed part.Using 34CrMo4 steel as high-pressure cylinder material,through its true stress-strain curve at high temperature,the hot working maps of 34CrMo4 steel in the temperature range of 950?¹150?and the strain rate range of 0.1s^-14.5s^-1 were established to determine the safe working area of the material.According to the actual situation of industrial processing,four simulation models of billet end inclination,two simulation models of billet axis offset and four simulation models of uneven lubrication of punch and concave dies are established.The simulation calculations were carried out for each model by means of DEFORM-3D finite element simulation software.The variation law of metal flow velocity,forming lug and punch displacement during the forming process of each model was analyzed.Based on the measurement of the wall thickness difference and lugs of the formed parts,the variation law of the wall thickness difference and lugs of the formed parts under various simulation models is summarized..The results show that the greater the inclination angle of the blank end face,the greater the influence on the quality of the formed part;the inclination of the upper end of the blank only has the least influence on the quality of the formed part;the greater the offset distance of the blank axis,the greater the influence on the quality of the formed part;If the offset of the blank axis is too large and the inclination angle of the blank end face istoo large,the blank will be repositioned under the action of the punch,and the influence law of the quality of the formed part will change.The uneven lubrication of the die affects the quality of the formed part.Obviously,the uneven lubrication of the punch is not significant to the quality of the formed part;the uneven lubrication at the bottom of the die has little effect on the formed part,and the uneven lubrication of the side wall has obvious influence on the formed part;the larger the uneven lubrication range of the mold,the more uniform The difference in the quality of the molded part is greater.The uneven lubrication of the mold has little effect on the wall thickness difference of the formed part,and has a great influence on the lug of the formed part.