Basic Research On Equidistant Expansion Forming Process Of Continuous Extrusion Of U-shaped Strip

With the development of electronics,information and automobile industries,the demand for copper and copper alloy strip,especially high-precision copper strip,is growing,while the traditional processing methods have problems such as high energy consumption,high oxygen content and low material utilization.Continuous extrusion process makes full use of friction and deformation energy,which is an advanced processing technology with high efficiency and energy saving.This technology can obtain copper electromagnets,busbars,and strips after continuous extrusion in one forming,which has been widely used and has produced significant economic and social benefits.However,with the increase of continuous extrusion expansion ratio,the unevenness of the cross-sectional organization and properties of flat copper strip blanks is significant,and it is difficult to manufacture high-precision copper strip after reaching the expansion forming limit.For this reason,this paper uses a U-shaped copper continuous extrusion isometric expansion forming + flattening of the process program.The use of continuous extrusion isometric expansion forming U-shaped copper,metal expansion forming flow distance is more uniform,after flattening the slab has a more uniform organization.Therefore,it is of great significance for manufacturing high-precision copper sheet and strip.In this dissertation,based on TLJ630 continuous extrusion machine,the mechanical model of equidistant expansion forming of continuous extrusion of U-shaped copper material is established by using the upper-bound approach,and the influence law of chamber expansion angle,extrusion channel length,outer radius of U-shaped strip,outer radius of die entrance and other chamber structure parameters on unit extrusion pressure of chamber entrance was studied.The ultimate load of unit extrusion pressure of chamber entrance was determined.When the unit extrusion pressure of the chamber entrance reaches limit load 1050 MPa,the limit flattening width of U-shaped copper is 634 mm.Based on the upper-bound approach,the temperature model of continuous extrusion of U-shaped copper strip are established.The temperatures of initial pressing zone,rigid moving zone,rectangular deformation zone,expansion zone and extrusion zone are determined,and the influence of rotational speed of extrusion wheel on the temperature of each deformation zone is analyzed.The finite element model of equidistant expansion forming of continuous extrusion of Ushaped copper strip was established by DEFORM-3D software.The effect of process parameters such as width-to-thickness ratio,chamber expansion angle,height of chamber entrance and rotational speed of extrusion wheel on the temperature,SDV(mean squared difference of flow velocity)and torque of extrusion wheel on continuous extrusion process of U-shaped copper strip was investigated by numerical simulation.The results show that: with the increase of width-thickness ratio,chamber expansion angle and e rotational speed of extrusion wheel,the temperature of metal at the block will increase,the temperature difference between the upper and lower part of the die exit will become larger,the SDV value will become larger,and the uniformity of the product will decrease;the torque of extrusion wheel increases with the increase of width-thickness ratio and decreases with the increase of rotational speed of extrusion wheel and chamber expansion angle;with the increase of height of chamber entrance,the temperature of metal at the block first decreases and then increases,torque of extrusion wheel first increases and then decreases,and the SDV value does not differ greatly.The microstructure evolution law of continuous extrusion equidistant expansion forming process of U-shaped copper strip was elucidated,and the micromechanism of equidistant expansion forming of continuous extrusion of U-shaped copper strip under large expansion ratio condition.The as-cast organization of the billet is flattened in the initial pressing zone,and in the upsetting zone and the right-angle deformation zone,the organization starts to undergo dynamic recrystallization under high temperature and violent shear deformation,and fine isometric crystals are gradually formed,with the smallest average grain size of only about 20 μm at the chamber entrance.In the expansion zone affected by high temperature grain growth occurs,to the extrusion zone grain size further growth,U-shaped copper products is the average size of 65.6 μm isometric crystals,straight edge section area is smaller than the arc section grain size.Studied the process parameters on the U-shaped copper continuous extrusion microstructure of the influence of the law,the results show that: with the chamber expansion angle,extrusion wheel speed,U-shaped copper width increases,the average grain size of the product increases,the billet in the die exit temperature difference increases,the degree of uniformity of the microstructure of the product will be reduced.Based on the response surface method,a regression model is established with the radius of the outer circle of the U-shaped copper material,the chamber expansion angle,and the extrusion wheel speed as the design variables,and the SDV value and the torque of extrusion wheel as the response targets,and the optimal process plan is determined.The results show that the U-shaped copper material manufactured by continuous extrusion isometric expansion forming process has higher width dimension,lower extrusion wheel torque,and more uniform microstructure than the flat strip manufactured by traditional continuous extrusion process.