## 3 Experimental Results and Analysis
### Influence of Cutting Speed (Spindle Speed) on Axial Force and Deformation in Drilling  
Under the conditions of feed \(f=0.025\) mm/r and dry cutting, the cutting speed \(v=12.6\)-\(37.7\) m/min (spindle speed \(n=500\)-\(1500\) r/min) was varied to study the effect of cutting speed on the axial force of drilling. The waveforms of axial force with time at different cutting speeds (rpm) are shown in Figure 6.  
As can be seen from Figure 6, the axial force of drilling thin-walled plates of AF1410 high-strength steel at different drilling speeds generally exhibits the same change characteristics as those described before. Among them, in the range of higher cutting speed \(v=25.1\)-\(37.7\) m/min (\(n=1000\)-\(1500\) r/min), the axial force waveform graphs have higher similarity, and there is an obvious rapid increase in the process of drill cap formation in the late stage of drilling; while in the range of lower cutting speed \(v=12.6\)-\(18.8\) m/min (\(n=500\)-\(750\) r/min), the axial force in the increase in axial force in the process of drilling cap formation is more gentle, and the lower the speed, the more gentle. From the time of generation of the maximum axial force, at the cutting speed \(v=25.1\)-\(37.7\) m/min (\(n=1000\)-\(1500\) r/min), the generation of the maximum axial force is closer to the intersection point of the main and secondary cutting edges where the bottom surface of the workpiece is to be drilled out; and at the low cutting speed range of \(v=12.6\)-\(18.8\) m/min (\(n=500\)-\(750\) r/min), the generation of the maximum axial force slightly deviates from the theoretical position of the top edge of the drill bit where the  
Figure 6: Waveform of axial force variation with time under different drilling speed conditions. (**a**) \(v=12.6\) m/min (\(n=500\) r/min). (**b**) \(v=18.8\) m/min (\(n=750\) r/min). (**c**) \(v=25.1\) m/min (\(n=1000\) r/min). (**d**) \(v=31.4\) m/min (\(n=1250\) r/min). (**e**) \(v=37.7\) m/min (\(n=1500\) r/min). (A–E correspond to the several characteristic stages of the drilling process defined for Figure 2; the red line indicates the axial cutting force, and the blue line corresponds to the other three characteristic moments during the cutting process.) bottom surface of the workpiece is to be drilled out. In the low cutting speed range of \(v\) = 126-18 m/min (\(n\) = 500-750 r/min), the maximum axial force is slightly deviated from the theoretical position of the top edge of the drill bit to drill out the bottom surface of the workpiece, and considering the effect of convex deformation of the workpiece at the initial stage of drilling, the maximum axial force occurs at the position of the top edge of the drill bit when the drill bit is actually about to be drilled out, which indicates that the maximum axial force occurs due to different reasons at different cutting speeds. This change in axial force with cutting speed is characterized by the temperature of the bottom of the workpiece corresponding to the drill tip during the formation of the drill cap. Figure 7 shows the morphology of the drill cap formed at different cutting speeds and the temperature field at the time of maximum axial force. From the color of the drill cap and the temperature field of the bottom surface of the workpiece, it can be seen that the temperature of the bottom surface of the drill cap increases greatly with the increase in the cutting speed. Due to the increase in temperature in the process of cap formation at higher cutting speed, the yield strength of AF1410 high-strength steel decreases with the increase in temperature [28], the bottom material of the workpiece corresponding to the drill tip is more prone to thermoplastic deformation, and the cap formation is dominated by the rotational extrusion of the drill tip on the bottom material of the workpiece, so that the thickness and width of the machined layer of the  
Figure 7: Drill cap morphology and bottom surface temperature field of thin-walled drilled holes in AF1410 high-strength steel at different cutting speeds.