# Study of Copper/Aluminum Bimetallic Tube Rotary Ring Spinning Composite Forming Characteristics
## 4 Results and Discussion
### Study of Rotary Ring Spinning Process Parameters
#### 4.2.1 Press Amount  
In the process of bimetallic tube rotary ring spinning, the press amount directly reflects the degree of thinning of the composite tube, so it has a large impact on the thickness variation of the bimetallic composite tube and the three-way strain distribution; therefore, in this paper we adopted the single-factor control method to analyze the influence law of the press amount on the forming quality. The press amount was taken as 0.1, 0.2, 0.3, 0.4, and 0.5 mm, and the other process parameters were kept unchanged, with a feed ratio of 0.4 mm/r and an angle of attack of the rotary ring of 18\({}^{\circ}\).  
Figure 5 shows the simulated and experimental results of thickness after rotary ring spinning with different press amounts. It can be seen that the corresponding thicknesses in the simulation and the experiment are basically the same. Considering the deformation of the rotary ring in the experiment, the non-uniform distribution of surface roughness, and other objective factors, there will be some deviation between the simulation and experiment, but it does not affect the accuracy of the model. The wall thickness of both the cover tube and the basic tube decreases as the press amount increases.  
Figure 4: Distribution of radial equivalent stress during the rotary ring spinning of a bimetallic tube.  
Figure 6 shows the ratio of the thinning rate of the cover and basic tubes after rotary ring spinning with different press amounts; it can be seen that the ratio trends toward 1 as the press amount increases. Since the wall thickness of both tubes is the same, it is known from the principle of volume invariance that when the ratio of the thinning rate of the tubes is closer to 1, the harmonization of the distortion between the two will be better. Therefore, an increased press amount will promote the coordination of the deformation of the basic cover tube somewhat. As can be seen in Figure 6, the experimental data are within 8% error of the simulated data for the range of process parameters studied, thus verifying the accuracy of the model.  
Figure 7 shows the simulated distribution of equivalent strain after rotary ring spinning with different press amounts. It can be seen that with an increased press amount, the equivalent strain of the bimetallic tube also increases, the difference in axial deformation between the basic and cover tube gradually decreases, and the deformation becomes more coordinated.  
Figure 5: Simulated and experimental results of thickness after rotary ring spinning with different press amounts: (**a**) cover tube; (**b**) basic tube.  
Figure 6: Ratio of thinning rate of cover and basic tubes after rotary ring spinning.  
Figure 8 shows the three-way strain distribution for the basic tube and cover tube with different press amounts. As can be seen in the Figure 8, the three-way strain is greater on the cover tube than the basic tube, and increases as the press amount increases. The strain distribution in the radial, axial, and tangential directions shows that the radial strain is the largest, followed by the axial, and the tangential is the smallest. This is because as the rotary ring spinning process proceeds, the metal buildup will have a detrimental effect on the axial flow of the metal, and the axial strain of the basic cover tube will be reduced compared to the radial strain, ultimately resulting in an increasing difference between the two.