# The Impact of Drilling Parameters on Drilling Temperature in High-Strength Steel Thin-Walled Parts
## 2 Experimental Condition
### Characteristics of the Workpiece Bottom-Surface Temperature Field During Thin-Wall Drilling  
The temperature field variation on the bottom surface of the workpiece during the drilling process is shown in Figure 6, where the curve plot shows the temperature distribution along the radial direction of the workpiece; point 0 in the plot is the centre of the drilled hole, from which it can be seen that the highest temperatures of the temperature field on the bottom surface of the workpiece occurred at the centre of the drilled hole before the drill bit drilled out the drill cap and fractured it. In order to highlight the temperature field and line temperature map changes due to drilling, based on the size of the temperature field spread area, Figures 6, 7 and 9 show a screenshot of the temperature field symmetrically located at the centre of the drill hole with a length \(\times\) width of 23 mm \(\times\) 23 mm. Since the layer to be machined below the intersection point of the main and secondary cutting edges is thicker before the drill reaches point C', and the elastic recovery of the workpiece during the drilling process is small, in order to facilitate the calculation, the screenshot of point C' in the temperature field diagram in this paper is taken as the position recorded in the temperature field diagram without considering the rebound of the drill after drilling into the workpiece. This position is intercepted at the time of the axial stroke of the drill, which is equal to the thickness of the workpiece, by taking the actual start point when drilling into the workpiece surface at point A' as the starting point. The previous drilling process of high-strength steel, in combination with thin-walled plate deformation and characteristic point analysis, can be seen in Figure 6. The top edge of the drill bit is able to contact the upper surface of the workpiece until the drill bit is drilled into the workpiece; the elasticity of the workpiece leads to convex deformation, and the top edge of the upper surface of the workpiece leads to extrusion friction. The top edge of the drill bit has a small diameter; thus, linear velocity is small, the initial generation of the cutting heat is relatively small, and the tip of the drill bit is farther away from the bottom surface of the workpiece, meaning that less heat is transferred to the bottom surface. As a result, the temperature of the bottom surface of the workpiece is relatively low. Because of the small diameter of the top edge of the drill, the linear velocity is small, the cutting heat generated is reduced at the beginning, and the tip of the drill is far away from the bottom surface of the workpiece. Moreover, the heat transferred to the bottom surface is reduced; thus, the temperature of the bottom surface of the workpiece is lower, and the temperature only increases slightly in the corresponding range of the diameter of the top edge. The change in the temperature gradient is very small, as shown in Figure 6a. Under the feed rate of the drill, the axial force of the top edge of the drill increases when placed against the workpiece, and the heat generated by the extrusion and friction of the top edge increases, forming a circular maximum temperature zone within the radius of the top edge, which is about 83 \({}^{\circ}\)C; the heat is transmitted along the radial direction to form an annular temperature field distribution, as shown in Figure 6b. After the drill starts drilling into the workpiece, with the drilling and feeding of the drill, the drill tip gradually approaches the bottom surface of the workpiece, the temperature of the bottom surface of the workpiece increases. At the same time, the heat is transmitted along the radial direction, and the temperature field has an obvious circular gradient distribution; the change in the temperature field of the bottom surface of the workpiece at this stage is shown in Figure 6c-f.