## Effect of Process Parameters on Forming Load
### Effects of Roller Feed Ratio on Forming Load  
The effect of the roller feed ratio on the spinning force is shown in Figure 9. Under the condition of constant mandrel rotational speed, increasing the roller feed ratio will lead to an increase of the strain rate and the amount of metal formed in the same time, so the spinning force also increases. This is because the mechanism of plastic deformation is complicated; it requires a certain amount of time to complete. The effect of the roller feed ratio \(f\) is highly significant when considering the influence of the single factor variation on the spinning force maximum.  
In general, when the rotary feed ratio is 0.6 mm/r, the spinning force in the shear spinning stage is similar to that in the conventional spinning stage; when the rotary feed ratio is 1.0 mm/r, the spinning force changes steadily; when the rotary feed ratio is 1.4 mm/r, the spinning pressure increases as a whole, and the average spinning force difference between the shear spinning and conventional spinning is the largest.  
At the start of the spinning stage of shear spinning, the spinning pressure rises steadily when the rotary speed is 200 r/min and 320 r/min, but there is an obvious peak at 450 r/min, due to the rapid change of the metal stress and strain and the impact on the roller. During the transition from shear spinning to conventional spinning, when the feed rate is 0.6 mm/r, the roller contacts with the sheet again. When the mandrel speed is 200 r/min, the lower rotary speed cannot provide enough friction force to rotate the roller, resulting in poor feed and metal flow obstruction, which makes the spinning force fluctuate greatly; when the feed rate is 1.4 mm/r, the rotary speed of the mandrel is low, and the roller can only feed repeatedly once during a circle. The sheet metal thins excessively, so fluctuation also appears.  
As shown in Figure 10, when the gap deviation rate is 2.5% and the rotary speed is 320 r/min, the spinning force in the power spinning stage increases with the increase of the roller feed ratio, and the fluctuation amplitude increases. In the conventional spinning stage, the spinning force instead decreases, and the amplitude of fluctuations decreases. When the clearance deviation rate is 2.5% and the rotary speed is 450 r/min, the spinning pressure in the power spinning stage increases with the increase of the roller feed ratio. In the initial contact stage between the roller and the blank, the material involved in deformation increases and the material flow rate decreases because of the large feed ratio. In addition, the material deformation resistance and the roller feed resistance on different cross-sectional areas are both different, causing a large fluctuation of the spinning force. Therefore, the wall thickness uniformity of the formed conical part reduces, which causes an adverse effect on the stable operation of the spinning machine. In the conventional spinning stage, the extreme value and the change trend of the spinning force are both the same, but the fluctuation of the spinning force is small when the roller feed ratio is 1.4 mm/r, which proves that the roller feed ratio matches the mandrel rotational speed.  
Figure 9: The change of the spinning force when \(\omega\) is the same: (**a**) \(\omega\) = 200 r/min; (**b**) \(\omega\) = 320 r/min; and (**c**) \(\omega\) = 450 r/min.