## 3 Experimental Results and Analysis  
Characteristics of Axial Force Changes and Workpiece Deformation Mechanism During Drilling of Thin-Walled Plates of AF1410 High-Tensile Steel  
When the thickness of the workpiece is greater than the height of the drill tip, the drilling process can be divided into several characteristic stages as shown in Figure 2 if the deformation of the thin-walled plate during the drilling process is not considered. In the figure, A is the top edge of the drill just touching the upper surface of the workpiece, B is the intersection point of the main and secondary cutting edges of the drill drilling to the upper surface of the workpiece, C is the top edge of the drill drilling to the bottom surface of the workpiece, D is the intersection point of the main and secondary cutting edges of the drill drilling to the bottom surface of the workpiece, and E is the point at which the drill \begin{table}
\begin{tabular}{l c} \hline \hline
**Physical Property Index** & **Numerical Value** \\ \hline Density \(\rho\) (kg/m\({}^{3}\)) & 7860 \\ \hline Modulus of elasticity (GPa) & 203 \\ \hline Yield strength \(\sigma_{0,2}\) (MPa) & 1580 \\ \hline Thermal conductivity (W/mK) & 27.8 \\ \hline Specific heat capacity (J\(\cdot\)Kg\({}^{-1}\)K\({}^{-1}\)) & 490 \\ \hline Poisson’s ratio \(\mu\) & 0.29 \\ \hline Tensile strength \(\sigma\) (MPa) & 1700 \\ \hline Melting temperature (K) & 1623\(-\)1695 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Material physical properties of AF1410 steel [6]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Overhanging Dimensions of Workpiece** & **Feedrate** & **Cutting Feed(m/min)/** \\
**Length \(\times\) Width \(\times\) Thickness (mm)** & **(mm/r)** & **Spindle Speed (r/min)** \\ \hline \hline \multirow{4}{*}{\(70\times 70\times 1.5\)} & \multirow{4}{*}{0.025} & 12.6/(500) \\  & & 18.8/(750) \\  & & 25.1/(1000) \\  & & 31.4/(1250) \\  & & 37.7/(1500) \\ \hline \hline \multirow{4}{*}{\(70\times 70\times 1.5\)} & 0.01 & \\  & 0.025 & \\ \cline{1-1}  & 0.05 & 18.8/(750) \\ \cline{1-1}  & 0.075 & \\ \cline{1-1}  & 0.1 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental plan. drills out the bottom surface of the workpiece completely, and the axial force is zero. If the friction between the drill bit and the hole wall is not taken into account, the axial force is theoretically 0 when the drill bit is in the position of the D point. If the deformation of the workpiece in the drilling process is not considered, the axial traveling of the drill from state A to state B is the height of the drill tip; the axial traveling from state B to state C is the difference between the thickness of the workpiece and the height of the drill tip; the axial traveling from state C to state D is the height of the drill tip. The theoretical drilling time for each characteristic stage of the drilling process is calculated as follows:  
\[\Delta t_{i}=\frac{60h_{i}}{f\cdot n}, \tag{1}\]  
where \(h_{i}\) is the theoretical stroke of the drill at a certain stage, in mm;\(f\) is the feed, in mm/\(r\); \(n\) is the spindle speed, in r/min; and \(\Delta t_{i}\) is the theoretical drilling time, in \(s\). Drilling experiments were carried out on the center of a thin-walled plate of AF1410 high-tensile steel under the cutting speed \(v\) = 25.1 m/min (rotational speed \(n\) = 1000 r/min), feed \(f\) = 0.025 mm/\(\tau\), workpiece overhang size (length \(\times\) width \(\times\) thickness) of 70 mm \(\times\) 70 mm \(\times\) 1.5 mm, and dry cutting conditions, and the variation in axial force with time is shown in Figure 3, and the points labeled in the figures.