## 3 Experimental Results and Analysis
Theoretically, if the deformation of the workpiece is not taken into account, the maximum value of axial force should occur between the characteristic points B-C (Figure 2), i.e., the main cutting edge enters into the workpiece completely, and the top edge is not yet drilled out of the position; however, from the axial force waveform in Figure 3, the maximum value of the axial force is obviously lagging behind that at the points B However, from the axial force waveform in Figure 3, the maximum value of axial force is obviously lagging behind the point B-C, and at the theoretical characteristic points B and C, the axial force is in the state of steady increase, which indicates that the top edge of the drill bit is not drilled to the bottom surface of the workpiece, which is mainly caused by the fact that under the action of the axial force, the overall cambering deformation of the workpiece lags behind the relative position of the drill bit and the workpiece. In addition, AF1410 high-strength steel is a high-strength plastic material with poor thermal conductivity. Under the action of axial force and drilling temperature, not only does the overall convex deformation occur during the drilling process, but also a large local plastic deformation occurs when the drill tip is about to drill out of the bottom surface of the workpiece, resulting in the formation of a complete conical cap whose inner surface coincides with the rotating cone surface of the drill tip as shown in Figure 4. Due to the high strength of AF1410 high-strength steel, the drill caps and edge profiles formed during thin-walled drilling are significantly different from the exit profiles of titanium alloy drilling reported in Reference [26]. This also results in distinct characteristics of the drilling axial force compared to titanium alloy drilling. Based on the analysis of the characteristics of axial force and deformation changes during the drilling process of high-strength steel thin-wall panels, the schematic diagram of workpiece deformation during the drilling process is shown in Figure 5.  
In Figure 5, a is the top edge of the drill bit just contacting the upper surface of the workpiece; a-b is the stage of elastic deformation of the lower convexity of the workpiece; at this stage, although the top edge of the drill bit exerts a large extrusion friction on the workpiece, it is not drilled into the workpiece, and the main body manifests itself as the lower convexity elastic deformation of the workpiece, and the axial force grows linearly, and the elastic deformation and the elastic resistance of the workpiece in the position of b reach the maximum; b-c is the stage of the drill bit drilling into the workpiece, and at this stage, the lower convex elastic deformation of the workpiece is basically in a stable state, under the support of elastic resistance, the drill bit gradually drills into the workpiece, and the axial force increases with the increase in the drilling length of the main cutting edge; d is the stage of local deformation under the tip of the drill bit, and the center of the drill bit cracks after the top edge of the tip is pushed out from the bottom of the workpiece; e is the stage of the local plastic shaped of the workpiece under the main cutting edge of the drill bit, which gradually forms the drilling cap, and the axial force first starts to increase rapidly and reaches its maximum. The axial force at this stage first starts to increase rapidly, reaches the maximum value, and then decreases rapidly. f is the intersection of the main and secondary cutting edges of the drill bit drilling to the bottom surface of the workpiece, and the drill cap is separated from the bottom surface of the workpiece by fracture, and the axial force decreases to zero. From Figure 4, the morphology of the drill cap can be seen.