Numerical Simulation And Experimental Study On The Forming Of Copper Bar By Continuous Extrusion Based On TLJ250 Machine

The market demand of copper bar especially high precision copper bar,which is used for processing dynamic or static guide rod in high or ultra-high pressure vacuum switch,contactors for high voltage or ultra high voltage appliance controllers and heavy traffic conductor devices,is becoming more and more vigorous.The traditional processing technology of copper bar has 9?12 processes,longer production cycle,higher energy consumption,lower discontinuous production efficiency and pollutes environment.While the continuous extrusion technology can realize the forming and continuous production from billets to products through only one process,so studying the forming law of copper bar by continuous extrusion technology is helpful to solve the problem of forming copper bar in actual production,and provides guidance for producing compact and well-behaved copper bars.In this paper,pure copper is used as the studying object,the continuous extrusion process of copper bar is simulated and analyzed by Deform-3D software based on TLJ250 continuous extrusion machine,and analyzes the effect of different process parameters on the forming of copper bar by continuous extrusion technology.And also studies the law of delamination defect distribution and the effect of process parameters on the copper bar products through the continuous extrusion process experiment.The numerical simulation results and experimental results show that:During the whole continuous extrusion forming of copper bar,there are 2 effective-stress peaks of billets,one is appear in clamping zone which reaches 175MPa,the other is appear in upsetting deformation zone which reaches 200MPa.The temperature of billets is becoming higher from groove deformation zone to right-angle bending zone,the maximum temperature reaches 418? in right-angle bending zone and reaches 550? in extending extrusion zone.Area expansion ratio(?=2.25?4?6.25):In extending extrusion zone,stratified flow with symmetry axis in longitudinal symmetry.When the area expansion ratio is 4,the longitudinal velocity curve is the smoothest and the velocity at calibrating strap is the most uniform,the compactness of copper products is better,there are only a few delamination defect in the near surface of copper bar.delamination defect mainly appear near the bottom side of the product's cross-section and distribute continuously along the length of the copper bar.Extrusion wheel angular velocity(n=10rpm?7rpm?4rpm):The flow velocity,deformation rate and deformation temperature of the metal decrease with the decrease of extrusion wheel angular velocity.When the wheel angular velocity is 4rpm,the longitudinal velocity curve is the smoothest,both the velocity and temperature at calibrating strap is the most uniform,the compactness of copper products is better and the delamination defect appearing near the bottom side of product's cross-section is less.Average grain size and stratified defect quantity decrease with the decrease of extrusion wheel angular velocity.Structures of tooling mould:Increasing the extended channel length or decreasing the die angle can improve the uniformity of flow velocity at calibrating strap.The change of tooling mould structure has no obvious effect on improving the stratified defect in optimized process conditions(when the area expansion ratio is 4,the wheel angular velocity is 4rpm).The results of research show that:The copper bar product,which is extruded under this process condition the wheel angular velocity is 4rpm,the extended channel length is 10mm,the area expansion ratio is 4(n=4rpm,L=10mm,?=4),has the least delamination defect.The thickness of the least delamination defect is only 0.2mm,the length of the least delamination defect is 3mm.