## 5 Experiments and Analysis  
To verify the machining history data-based optimization method proposed in this study, aircraft parts in Figure 14 were tested. The target material was 'AL7075'. End mills (D100, D25, D16, D16R3, D10) were used for shaping. In addition, a hole drill was adopted for machining the back of the material. In terms of a CNC machine tool, HYUNDAI WIA's KV75 DM was chosen. Table 1 shows the specifications and cutting conditions of each tool. The current sensor was a product of Seri2B Co. Ltd. Its model was 'zen-U2-100 Ab-245.' The accelerometer was a product of PCB Co. Ltd. Its model was 607A11. Optimization was applied to an end mill specially designed for shaping. To diagnose machining load and chatter, current and acceleration sensors stated in Table 2 were used.  
Figure 14: Machining shape and tool path.  
Figure 13: Machining history data-based optimization flowchart.  
The optimization input is shown in Table 3, assuming that the CNC machine has sufficient torque (feed per tooth not considered). The chatter occurring during machining is described in Table 4. Chatter avoidance RPM was calculated using Equation (5). However, a single standard spindle speed was chosen according to diverse chatter frequencies. Figures 15-18 show optimized feed rates by the CNC load meter. In these figures, red, blue, black lines indicate the original feed rate, the optimized feed rate, and the cutting load, respectively. As illustrated in these figures, feed rates were interpolated linearly depending on the machining load.  
Figures 19-22 show the machining load before/after optimization and feed rate changes. As shown in these figures, chatter was completely removed in D100 and D16 optimizations. When D25 or D16R3 was used, some chatters were found even after chatter removal. Table 4 confirms a decrease of up to 50% after optimization with machining time. Table 5 shows machining time before and after optimization.  
Figure 16: Feed rates of D25 optimization results. This figure was directly captured from the result screen of the MDT4 DE.  
Figure 17: Feed rate of D16 optimization results. This figure was directly captured from the result screen of the MDT4 DE.  
Figure 18: Feed rate of D16R3.0 optimization results. This figure was directly captured from the result screen of the MDT4 DE.  
Figure 15: Feed rates of D100 optimization results. This figure was directly captured from the result screen of the MDT4 DE.  
Figure 19: Machining load and feed rate before and after D100 optimization. This figure was directly captured from the result screen of the MDT4 DE. In this figure, comma is a notation to separate thousands. It does not mean a decimal point.  
Figure 21: Cont.  
Figure 20: Machining load and feed rate before and after D25 optimization This figure was directly captured from the result screen of the MDT4 DE. In this figure, comma is a notation to separate thousands. It does not mean a decimal point.  
Figure 21: Machining load and feed rate before and after D16R3.0 optimization. This figure was directly captured from the result screen of the MDT4 DE. In this figure, comma is a notation to separate thousands. It does not mean a decimal point.  
Figure 22: Machining load and feed rate before and after D16 optimization. This figure was directly captured from the result screen of the MDT4 DE. In this figure, comma is a notation to separate thousands. It does not mean a decimal point.