Design And Performance Study Of Bimetallic Tube Drawing Process

With the increasingly severe industrial environment and the changing global climate,tube applications are facing more severe service conditions and more complex load conditions.Every year,the global energy waste caused by tube damage accounts for a huge part of the energy loss,causing serious economic losses.With the mature development of industrial technology,metal tubes are required to meet the needs of actual working conditions with a variety of performance characteristics and low cost.Bimetal tube with unique structural advantages,its performance characteristics to meet today’s industrial needs,more and more attention in research and development.In this paper,the Cu/304 stainless steel bimetal tube was prepared by drawing forming technology.The composite mechanism of the base tube and the liner in the drawing process was explored.The tooling design was carried out.The finite element simulation of the forming process was carried out by DEFORM-3D.The stress and deformation law of the base tube and the liner in the forming process were analyzed.On this basis,the optimal process parameters were determined by orthogonal experiment design.Combined with the forming experiment,the bonding interface was characterized and the bonding performance was tested by optical microscope(OM)and X-ray diffractometer(XRD).The main research contents and conclusions are as follows:Based on the theoretical basis of elastic-plastic mechanics and the forming characteristics of the bimetallic tube drawing,the forming process of the bimetallic tube is simplified to an axisymmetric model analysis.During the drawing and forming process of the metal tube,the base tube must be plastically deformed,and the liner tube must be elastically deformed or plastically deformed.According to the elastic recovery of the base tube and the liner,the criterion for drawing and forming the bimetallic composite tube was obtained,and the composite mechanism of the drawing and forming bimetallic tube was revealed.According to the composite determination coefficient of the drawn bimetallic composite tube,the lining tube can be in the elastic deformation state or plastic deformation state to achieve preliminary composite.Combined with the characteristics of the drawing technology,it is determined that the Cu/304 stainless steel bimetallic tube is formed by 2-pass drawing,the elongation coefficient of the first pass is 1.48,and the elongation coefficient of the second pass is 1.56.By means of DEFORM-3D finite element simulation software,the deformation characteristics of the drawn bimetallic tube were explored,and it was found that the stress was transmitted from the base tube to the liner tube and a sudden change occurred at the interface.On this basis,four bimetallic tubes of Cu/Cu,Cu/304,304/Cu,and 304/Al are studied.Through comparison,it is found that the materials of the base tube and the liner are different,and the stress transferred from the base tube to the liner is the trend of its increase and decrease at the interface is also different.The higher the yield strength of a material,the more resistant it is to deformation.At the same time,the forming laws of Cu/304 stainless steel bimetal tube with different wall thicknesses of the base tube and liner were studied,and it was found that when the wall thickness ratio was 5:2～6:1,the Cu tube and 304 stainless steel tube could achieve drawing compound.Using DEFORM-3D finite element simulation software to analyze the three principal stresses and three principal strains of the drawn Cu/304 stainless steel bimetallic tube,it is found that the Cu tube is formed by lining during the forming process,and the 304 stainless steel tube is formed by empty drawing Forming,the Cu tube in the axial direction is tensile stress,the 304 stainless steel tube is compressive stress,and the two tubes in the radial and circumferential directions are compressive stress.The deformation mainly occurs in the Cu tube layer,and the 304 stainless steel tube has almost no deformation.During the drawing and forming of the bimetallic tube,the plastic deformation of the base tube and the liner are closely combined,and the greater the radial stress on the outer surface of the liner at the bonding interface,the tighter the bond.An experimental study on drawing and forming of Cu/304 stainless steel bimetallic tube was carried out through orthogonal experimental design.Based on the evaluation criteria,the range analysis method determined that the optimal forming process parameters were the drawing speed of 10mm/s,the die angle of 9°,The unilateral gap between the base tube and the liner is 0.2 mm,and the friction coefficient between the base tube and the mold is 0.15.The gap between the base tube and the liner has the most influence,followed by the die angle,then the friction coefficient between the base tube and the die,and finally the drawing speed.Two passes of Cu/304 stainless steel bimetallic tubes were prepared based on the optimal process parameters.The bonding interface was characterized by optical microscope(OM)and X-ray diffraction(XRD)and the bonding properties were tested.The results showed that:1 pass The interface between the tubes is smooth and there is no gap,and two metals are bonded in the second pass;the radial residual contact stress between the tubes in the first pass is between 70 and 90MPa;the radial residual contact stress between the two tubes is 210 Between～230MPa,the bonding performance of 2 passes is better than that of 1 pass.