# An Accuracy-Efficiency-Power Consumption Hybrid Optimization Method for CNC Milling Process
## 4 Results and Discussions
### Power Consumption Analysis without Cutting Load
From the results, the power consumption tends to increase with feedrate increase, but a feedrate of 1500 mm/min, 3000 mm/min, and 6000 mm/min showed lower power consumption. Therefore, these three feedrates can be considered to obtain lower power consumption without decrease machining efficiency. Figure 8 shows the power consumption of Y-axis motor downward direction. It is seen the power consumption at a feedrate of 200 mm/min and 500 mm/min is greater than the feedrate of 1000 to  
Figure 6: Curve of average X-axis motor feedrate vs. power consumption w/o cutting load. Figure 7: Relationship between Y-axis motor (up direction) feedrate vs. power consumption w/o cutting load. is decreased. When the feedrate range is 2500 to 3500 mm/min, the power consumption rate increases about 0.002 kW per 500 mm/min. When the feedrate is 4000 mm/min and 4500 mm/min, the power consumption is reduced, but at a feedrate range of 4500 to 6000 mm/min the power consumption rate increase is about 0.003 kW per 500 mm/min. It can be seen that the overall power consumption tends to increase with the increasing feedrate, but at a feedrate of 2000 mm/min, 2500 mm/min, 4000 mm/min, and 4500 mm/min the power consumption is lower. These feedrates can be considered as the machining parameter to obtain lower power consumption without production efficiency loss. Figure 10: Curve of average Y-axis motor (down direction) feedrate vs. power consumption w/o cutting load. Figure 9: Curve of average Y-axis motor (up direction) feedrate vs. power consumption w/o cutting load. Since the power consumption at a feedrate of 5500 mm/min has a larger difference, it will be excluded from the average calculation analysis. Figure 12 shows the average calculation result, and the regression equation of each section can be obtained as follow: Equation (11) for a feedrate of 500 mm/min to 2000 mm/min, Equation (12) for a feedrate of 2000 to 4500 mm/min, Equation (13) for a feedrate of 4500 to 6000 mm/min. \[y=-0.0014x^{2}+0.0078x-0.0029 \tag{3}\]0  
\[y=-0.0014x^{2}+0.0078x-0.0029 \tag{3}\]1  
\[y=-0.0014x^{2}+0.0078x-0.0029 \tag{3}\]2  
As seen in Figure 12, when the feedrate is 500 mm/min, the power consumption is 0.004 kW. If the feedrate is increased to 1500 mm/min, the power consumption is 0.005 kW. When the feedrate increases to 3000 mm/min, the power consumption is 0.006 kW. If in the beginning, the machining used a feedrate of 500 mm/min, the power consumption is 0.004 kW per second, so for an hour  
\[y=-0.0014x^{2}+0.0078x-0.0029 \tag{3}\]3 Relationship between \(Z\)-axis motor feedrate vs. power consumption w/o cutting load. \[y=-0.0014x^{2}+0.0078x-0.0029 \tag{3}\]4 Curve of average \(Z\)-axis motor feedrate vs. power consumption w/o cutting load. the power consumption 0.004 kW/sec X 3,600 sec/hr = 14.4 kWh. When the machining feedrate is 1500 mm/min for which the machining efficiency increases three times, the power consumption is 0.005 kW/sec X 3,600 sec/hr = 18 kWh. When the machining feedrate is 3000 mm/min for which the machining efficiency increase six times, the power consumption is 0.006 kW/sec X 3,600 sec/hr = 21.6 kWh. If we assume for a feedrate of 500 mm/min, the machining time needed is half an hour, the power consumption is 0.5 hr X 14.4 kWh = 7.2 kWh. If we use the feedrate of 1500 mm/min, the machining time needed is 10 min, then the power consumption is 3 kWh. Hence, compared to a feedrate of 500 mm/min, the power saving is 4.2 kWh and also the machining time is three times faster.