# Construction of a Cutting-Tool Wear Prediction Model through Ensemble Learning
## 3 Approach Methods and Procedures
### Milling Experimental Setup  
This study aims to explore various assistance methods and process parameters for SKD11 milling. The investigation is divided into two phases. In the first phase of the milling experiment, the focus is on the analysis of cutting performance with no assistance, rotary ultrasonic assistance, dual-axis ultrasonic assistance, and a combination of rotary and dual-axis ultrasonic assistance (triple-axis ultrasonic). In the second phase, based on the results of the first phase analysis, a better assistance method is selected for the second phase of the milling experiment. The milling parameters are planned by using an L9 orthogonal array. During the experiment processes, observations and measurements are made for surface roughness, cutting forces, surface morphology, and cutting-tool wear. A series of result analyses and discussions are conducted. The first phase of the experiment aims to explore the effects of different ultrasonic-assisted methods, namely rotary, dual-axis, and triple-axis, on milling performance. In this phase, two sets of process parameters are planned, as shown in Table 1. These two sets of process parameters, with or without assisted methods, respectively, are all conducted in the experiment, and a total of 8 experiments are executed in this phase. Two factors with individually extreme levels were designated in this phase. The superior ultrasonic-assisted method obtained from the first phase is adopted in the second phase both in conjunction with and without locally laser preheating assistance, respectively. The process parameter planning for the milling experiment of SKD11 is shown in Table 2. Three factors were considered, and each factor had three levels in the 2 nd phase. The Taguchi orthogonal array was applied to design milling process parameter combinations, resulting in a total of 18 experiments, as shown in Table 3. Surface roughness and cutting-tool life serve as the objective function and constraint, respectively, and the optimal combination of process parameters was thus determined by the characteristics of smaller-the-better in the Taguchi method. Based on the optimal milling process parameters obtained and the superior hybrid-assisted method adopted, milling experiments were repeatedly performed to collect the data on cutting force and cutting-tool wear. Based on the results from the second phase of the milling experiments, the optimal process parameters were determined to be a spindle speed of 10,000 rpm, a feed rate of 1000 mm/min, and a radial depth-of-cut of 0.1 mm, along with a hybrid-assisted method of rotary ultrasonic combined with local laser preheating. The experiments for data collection were conducted with these process parameters and assisted configurations. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Set**} & **Spindle Speed,** & **Radial Depth of** & **Feed Rate,** & **Axial Depth of** \\  & **n (rpm)** & **Cut, a\({}_{\text{e}}\) (mm)** & **F (mm/min)** & **Cut, a\({}_{\text{p}}\) (mm)** \\ \hline
1 & 8000 & 0.1 & 1000 & 10 \\ \hline
2 & 8000 & 0.3 & 1500 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Process parameter planning for milling experiment of SKD11 in 1 st phase. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Milling Cutter Diameter, d (mm)**} & \multicolumn{1}{c}{\(\boldsymbol{\Phi}\)**6**} \\ \hline Axial depth of cut, a\({}_{\text{p}}\) (mm) & 10 \\ \hline Spindle speed, n (rpm) & 8000, 9000, 10,000 \\ \hline Radial depth of cut, a\({}_{\text{e}}\) (mm) & 0.1, 0.3, 0.5 \\ \hline Feed rate F, (mm/min) & 1000, 1500, 2000 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Process parameter planning for milling experiment of SKD11 in the 2 nd phase. Figure 2: Entire list of procedures executed in this study. Figures 3 and 4 show the milling experimental setup and a photo depicting equipment configurations.