## 3 Experimental Results and Analysis
### Influence of Cutting Speed (Spindle Speed) on Axial Force and Deformation in Drilling
(**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). workpiece corresponding to the main cutting edge below the main cutting edge under the process of cap formation increase, and the increase in the axial force is mainly caused by the rotational extrusion of the drill tip on the bottom material of the workpiece, and the axial force increases in the intersection point of the main and secondary cutting edges close to the bottom surface of the workpiece. The increase in axial force is mainly caused by the rotational extrusion of the drill tip on the workpiece material at its bottom, and the axial force reaches the maximum when the intersection point of the main and vice cutting edges is close to the bottom surface of the workpiece, and the workpiece machining layer corresponding to the workpiece below the main cutting edge undergoes the overall outward plastic deformation, and then it decreases rapidly with the plastic yielding. When the cutting speed is low, during the formation of the drill cap, the temperature of the material on the bottom surface of the workpiece corresponding to the drill tip is low, and the hardness and stiffness are large, so that the bearing capacity of the axial drilling force during the formation of the drill cap is large, and the thickness and width of the plastic deformation of the whole outward turning of the main and vice cutting edges are small when the main cutting edge is about to be drilled out of the bottom surface of the workpiece, at this time, the axial force is also small, and the largest axial force occurs in the early stage of the formation of the drill cap, and the top cutting edge of the drill bit is about to be drilled out of the bottom surface of the workpiece. The maximum axial force occurs at the early stage of cap formation, when the top edge of the drill bit is about to drill out the bottom surface of the workpiece. From the photo of the morphology of the drill cap, when the cutting speed is lower, the rupture opening in the center of the drill cap is larger, and with the increase in cutting speed, the drilling temperature rises, the material softens, the plasticity increases, the cracks at the top of the drill cap become smaller, and the drill cap tends to be complete. Different cutting speeds under the formation of the characteristics of the drill cap directly affect the formation of edge defects in the workpiece; if the cutting speed is higher, the main cutting edge below the corresponding workpiece processing layer occurs as a whole when the thickness of the plastic deformation of the flap is greater; the edge of the plastic deformation caused by the crimping and other defects is greater. When the cutting speed is lower, the edge of the main cutting edge by the drill cutting edge cutting is completed, and the edge is more flat, as shown in Figure 8.  
The effect of cutting speed on the maximum axial force during drilling and the maximum value of axial force at the initial stage of linear variation in axial force during cutting is shown in Figure 9.  
As can be seen from Figure 9, the maximum values of the axial force at the stage of linear change at the early stage of drilling do not differ much, and the cutting speed has less influence on it.