## 3 Experimental Results and Analysis
Points A, B, C, D, and E correspond to the theoretical drilling characteristic points shown in Figure 2.  
As can be seen from Figure 3, from the beginning of drilling to the axial force decreasing to 0 (Figure 3, A-E), the actual drilling time lagged about 0.63 s compared with the theoretical drilling time without considering the deformation of the thin-walled plate (Figure 2, A-D), which indicates that the thin-walled plate had undergone overall convex deformation under the action of axial force during the drilling process, so that the time from the contact of the drill bit with the workpiece's upper surface to the intersection of the drill bit main and vice cutting edges drilling to the bottom of the workpiece was increased. Figure 3: Variation in axial force during drilling of a thin-walled AF1410 high-strength steel. (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). Figure 2: Schematic diagram of the characteristic stages of the thin-walled plate drilling process. From the curve of axial force with drilling time in Figure 3, the change in axial force during the drilling process can be divided into four stages in general: In the first stage (corresponding to the straight line segment between point A and point P in the figure), the axial force rises in a straight line with a large slope, and the axial force is mainly caused by elastic deformation resistance of the workpiece, which lasts significantly longer than the difference between actual and theoretical drilling time (0.63 s). The axial force is mainly caused by the elastic deformation resistance of the workpiece, and the duration (1.19 s) is significantly larger than the difference between the actual drilling and theoretical drilling time (0.63 s). In the second stage, the axial force shows a curved increase at the initial stage and basically increases linearly at the later stage; when the elastic resistance of the workpiece increases to a certain value in the first stage, the drill starts to drill into the workpiece, and at the initial stage, the main cutting edge has just cut into the workpiece, and the axial force is mainly caused by the extrusion of the top cutting edge; at the later stage, with the drill drilling, the role of the top cutting edge stabilizes, and the length of the main cutting edge involved in the cutting increases gradually, and the axial force increases approximately and linearly at a relatively small slope. In the second stage, the increase in axial force after drilling is smaller than the elastic resistance generated in the first stage, and it can be assumed that this stage is mainly dominated by the drilling of the drill bit, and at the same time, due to the production of a certain amount of elastic recovery of the thin-walled plate, the actual drilling thickness is greater than the feed amount, which is one of the reasons why the difference between the actual drilling and the theoretical drilling time is less than the duration of the overall convex deformation at the early stage of the drilling process. In the third stage (between points M-Q in the figure), the axial force increases rapidly with a large slope to the maximum value of the whole drilling process. In the fourth stage, the axial force decreases rapidly after reaching the maximum value. The variation characteristics of the axial force during the drilling of thin-walled AF1410 high-strength steel plates are completely different from those of the brittle SiCP/Al composite material, which experiences a sudden drop in axial force when the drill bit is about to exit the bottom surface of the workpiece [27].