# Prediction of Manufacturing Quality of Holes Based on a BP Neural Network
## 2 The Plan of Hole Manufacturing
### The Process of Hole Manufacturing  
In order to ensure the reliability of the experimental data, the CFRP materials before the experiment were carefully cut using special diamond cutters to ensure that there were no original defects. All experiments were conducted under the following conditions: (1) the integrity of the diamond layer on the drilling tool surface was checked; (2) the CNC machine was verified to be in good working condition; (3) the stack material was clamped by the C-clip without gaps and reliably positioned by the view. The structure parameters and materials of the tool have a great influence on the quality of holes. Therefore, before the experimental analysis of the stack material, the drilling effects of four kinds of cutting tools, including a three-pointed two-edge drill, double-edge drill, reamer drill, and octahedral composite drill, were firstly compared on the CFRP material to check the quality of hole-making. The four types of drilling tools are shown in Table 1. The hole diameter was 4.8 mm, the average hole-making distance was 12 mm, and the count was 20. A total of 20 holes with one cutter was the basic requirement. For the \(140\times 140\) mm T300 CFRP with 3 mm thickness, basic experimental research was performed on the CNC machines. The corresponding drilling effect diagrams are shown in Figure 3.  
Figure 1: The manufacturing schematic. Figure 2: The manufacturing device. It can be seen that the tearing defect in Figure 3a was significant, and the carbon fiber showed obvious tearing defects surrounding the hole. In Figure 3b,c, there were also carbon fiber burrs, but the tearing defect in the hole edge was not obvious. As a result, the effect of the octahedral composite drill was the best as shown in Figure 3d, and the quality of hole exit of all 20 holes met the requirements. Thus, the octahedral composite drill was chosen to manufacture all holes for further study. In order to improve manufacturing quality of holes, cushion plates with 3 mm thickness made of pine, Al5051 sheet, and acrylonitrile butadiene styrene(ABS) plastic plate were selected for pre-experiments based on the previous experimental results. After that, the hole quality was compared. The experimental results are shown in Figure 4. It can be found that the ABS plastic cushion plate had the best effect on hole-making. Thus, the ABS plastic cushion plate with 3 mm thickness was used for all holes in further experimental studies with the CFRP at the bottom of the stacks. In this paper, the stack materials composed of T300 CFRP (thickness 3 mm) and 7050-T7 (thickness 2 mm) Al alloy were studied. The main defects for holes of CFRP were burrs, delamination, and tearing. The hole-making defects of CFRP were the main research object, and experimental research and prediction analysis were carried out. Four parameters of feed rate (0.005-0.06 mm/r), spindle speed (2000-9000 r/min), drilling diameter (3-8 mm), and cushion plate were taken as the input layer parameters to study the effect of manufacturing holes. Four stack types (CFRP/Al, Al/CFRP, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Drill Bit** & **Appearance Picture** & **Drill Bit** & **Appearance Picture** \\ \hline Three-pointed two-edged drill & & Reamer drill \\ Double-edged drill & & Octahedral composite drill \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Four types of drilling tool (\(\Phi\)4.8 mm). Figure 4: The appearance of the hole exit using three types of cushion plates: (**a**) pine; (**b**) Al5051; (**c**) ABS plastic. Figure 3: The appearance of the hole exit using the four types of tools: (**a**) three-pointed two-edged drill; (**b**) double-edged drill; (**c**) reamer drill; (**d**) octahedral composite drill. Al/CFRP/Al, and CFRP/Al/CFRP) were studied. The 140 \(\times\) 140 mm area in the middle of the support block was the hole-making area of the stack material. The average hole-making distance was 20 mm and the count was 20.