# Study of Copper/Aluminum Bimetallic Tube Rotary Ring Spinning Composite Forming Characteristics
## 4 Results and Discussion
### Study of Rotary Ring Spinning Process Parameters
#### 4.2.3 Angle of Attack of the Rotary Ring  
The angle of attack of the rotary ring is the angle between the formed contact surface of the rotary ring and the tube and the axial direction of the spindle, as shown in Figure 11. The single factor control method was used to simulate the rotary ring spinning forming by taking 12\({}^{\circ}\), 15\({}^{\circ}\), 18\({}^{\circ}\), 21\({}^{\circ}\) and 24\({}^{\circ}\) as the angle of attack, and the other process parameters were kept unchanged, with a press amount of 0.3 and feed ratio of 0.4 mm/r.  
Figure 12 shows the simulation results of thickness after rotary ring spinning with different angles of attack. It can be seen that as the angle of attack of the rotary ring decreases, the wall thickness of the basic tube becomes smaller, and the thickness of the cover tube becomes larger. As the angle of attack of the rotary ring decreases, the area of contact between the rotary ring and the cover tube increases, which leads to the convergence of forces on the basic and cover tubes. Furthermore, since copper is stronger than aluminum, along with the reduced angle of attack of the rotary ring, the thinning of the basic tube increases, the thickness is reduced, and the thinning of the cover tube decreases; thus, the wall thickness becomes larger.  
Figure 9: Variation of average thickness and ratio of thinning rate after rotary ring spinning with different feed ratios.  
Figure 13 shows the distribution of three-way strain in the basic and cover tubes after rotary ring spinning at different angles of attack. It can be found that the radial strain of the two tubes is less affected by the angle of attack of the rotating ring, and with decreased angle of attack, axial and tangential strains increase by 12.45 and 27.84%, respectively, with the increase being larger for the cover tube than the basic tube. The analysis shows that as the angle of attack decreases, the area of contact between the rotary ring and the tube increases, and the volume of the tube involved in deformation increases at the same time; in turn, the axial and tangential strains of the tube will increase by a certain amount. In addition, during the spinning process, smaller angles of attack lead to an increase in the  
Figure 11: Diagram of angle of attack of rotary ring.  
Figure 10: Three-way strain distribution for basic and cover tubes with different feed ratios.  
applied load on the tube, which causes more metal to flow to the undeformed area, leading to an expansion of the actual thickness of the cover tube involved in spinning; this then leads to a greater increase in the equivalent strain of the cover tube than the basic tube.  
From the above, it can be seen that a smaller angle of attack helps the plastic deformation of the metal, but a too small angle of attack is not conducive to biting into the tube. The radial compressive strain and axial tensile strain contribute to the plastic flow of the metal material [22]; when the axial flow rate of the metal is less than the feeding speed of the tube, it will lead to a certain accumulation of metal in front of the axial feeding direction of the rotary ring, which will greatly reduce the forming quality of the composite tube.  
Figure 12: Simulated results of thickness after rotary ring spinning with different angles of attacks: (a) cover tube; (b) basic tube.  
Figure 13: Three-way strain distribution for basic and cover tubes at different angles of attacks of rotary ring.