Study On Process And Numerical Simulation Of Ball Spinning Of Copper/Aluminum Composite Tube

Dissimilar metal composite tube has a combination of excellent properties which ordinary tube of metal and alloy does not have. The substrate tube has perfect performance of high strength or toughness, and meanwhile the covered tube has good wear resistance,corrosion resistance and other special properties. Combining two different tubes together, the dissimilar metal composite tube shows versatility on circumstances of transportation of oil and natural gas, health care, nuclear industry and other field. According to the type of interface bond, dissimilar metal composite tube can be divided into two categories, namely,metallurgical composite tube, of which interface is bonded by means of metallurgical method,and mechanical composite tube, of which interface is manufactured on the basis of mechanical processing. Compared with the metallurgical bonding composite tube, the mechanical bonding composite tube is characterized by simple processing and high efficiency,but it possesses lower interface bonding strength as well as narrower application field.Therefore a new manufacturing method with high efficiency and good product quality is needed to produce dissimilar metal composite tube. As a multipoint local forming technology,ball spinning belongs to power spinning, and it is generally used to manufacture high-precision thin-walled tube, so that it is an ideal processing technology for producing dissimilar metal composite tube. However, during the forming process, deformation of inner and outer tubes is reasonably complex, so systematically theoretical analysis is performed. In this paper, finite element method (FEM) simulation and experiment are combined to analyze the deformation law of dissimilar metal composite tube manufactured by ball spinning.Based on plastic mechanics, the upper bound method is applied to analyzing the compatible deformation of the inner and outer tubes of dissimilar metal during the whole ball spinning process respectively, building the admissible velocity fields, getting the strain rates using the small strain geometric equations, obtaining the plastic deformation law of the deformation zones of both inner and outer tubes according to the Saint-Venant Equations,where furthermore the power consumption of velocity discontinuity can be acquired according to the velocity discontinuity values, and simultaneously the deformation and friction power consumption of the deformation zone can be obtained. Consequently, the compatible deformation conditions of inner and outer tubes are gained during ball spinning.According to plastic yield theory, yield condition as well as stable metal flow of composite tube under ball spinning is proposed.Based on the theory of FEM, the DEFORM software is used to simulate and analyze the formability of copper-aluminum composite tubes of equal thickness during ball spinning.Analysis of deformation law during ball spinning is implemented on the basis of different parameters, including thickness reduction (0.2mm, 0.4mm and 0.6mm), feed ratio (0.4mm/r,0.6mm/r and 0.8mm/r), friction coefficient (0.4, 0.6 and 0.8), ball diameter (16mm, 18mm and 20mm) and combination sequence of inner and outer tubes. The results of FEM simulation show that increasing the thickness reduction contributes to plastic flow of inner and outer tubes, and enhancing the diameter of spinning ball results in stable metal flow on surface layer of composite tube, and raising the friction coefficient leads to compatible deformation of inner and outer tubes. Nevertheless, feed ratio seems to make a slight contribution to the values of stress and strain.Based on the experimental equipment designed independently, backward ball spinning is employed for manufacturing the two kinds of blanks of aluminum tube and copper tube in terms of different combination sequence. On the basis of different parameters, such as thickness reduction, ball diameter and feed ratio, the experiment of backward ball spinning is carried out so as to manufacture dissimilar copper-aluminum composite tube. The experimental results indicate that the incompatibility on interface is shown on the inner-aluminum and outer-copper composite tube (Cu-Al composite tube) as well as the outer-aluminum and inner-copper composite tube (Al-Cu composite tube) produced by ball spinning. Furthermore, compared with the Cu-Al composite tube, the Al-Cu composite tube is of bad compatibility owing to high yield strength of Cu tube. Consequently, the interface exhibits increasingly apparent incompatibility with the increase in the thickness reduction.However, increasing feed ratio as well as ball diameter contributes to plastic deformation of composite tube, but leads to bad interface quality.