## 5 Result and Discussion
### Trepanning Incision Quality of Nomex Honeycomb Core
#### 5.2.2 The Influence of Process Parameters on Trepanning Incision Quality  
In order to further clarify the influence of process parameters on the quality of preanning incision on Nomex honeycomb core, it is necessary to put forward the evaluation parameter of preanning incision quality, and quantitatively study the influence of process parameters on the preanning incision quality. The incision with wavy features constitutes  
Figure 21: Comparison of preanning incision: (**a**) ultrasonic preanning incision; and (**b**) non-ultrasonic preanning incision. Figure 20: Typical preanning incision. the most part of the preanning incision and has a major impact on the final preanning quality of the honeycomb core. Therefore, the size of the wavy feature is selected as the characterization parameter, which can quantitatively evaluate the impact of the process parameters on the preanning quality. Since the wavy characteristics on the actual preanning incision have obvious peaks and troughs, and the smaller the distance between the peaks and troughs, the smaller the actual incision deviates from the designed straight incision, and the better the quality of the machined vertical surface. The distance between the wave peak and trough is determined as the characterization parameter to evaluate the quality of the preanning incision. The characterization parameter \(L_{PT}\) is shown in Figure 22.  
The statistical results of the \(L_{PT}\) values with or without ultrasonic vibration at different feed rates are shown in Figure 23. The \(L_{PT}\) of the ultrasonic preanning with a vibration amplitude of 20 \(\upmu\)m was reduced by 40% compared with non-ultrasonic preanning, and the \(L_{PT}\) of the ultrasonic preanning with a vibration amplitude of 10 \(\upmu\)m was reduced by 30% on average. Ultrasonic vibration significantly reduces the \(L_{PT}\) of preanning incision, improves the quality of the preanning incision of the Nomex honeycomb core, and the effectiveness is significant at a different feed rate. With the increase in feed rate from 1000 to 3000 mm/min, the \(L_{PT}\) of traditional non-ultrasonic preanning increases by 52%, the \(L_{PT}\) of ultrasonic preanning with a vibration amplitude of 10 \(\upmu\)m increases by 46%, and the \(L_{PT}\) of ultrasonic preanning with a vibration amplitude of 20 \(\upmu\)m increases by 38%. Compared with the traditional non-ultrasonic preanning, ultrasonic vibration suppresses the deterioration of preanning quality when the feed rate increases. Figure 23: The influence of the feed rate on the quality of preanning incision. Figure 22: Trepanning quality characterization parameters. The statistical results of the \(L_{PT}\) with or without ultrasonic vibration at different rotating speeds are shown in Figure 24. With the increase in rotating speed from 500 r/min to 1500 r/min, the \(L_{PT}\) of ultrasonic trepenning with vibration amplitude of 20 \(\upmu\)m decreases by 49%, the \(L_{PT}\) of the ultrasonic trepenning with a vibration amplitude of 10 \(\upmu\)m decreases by 55%, and the \(L_{PT}\) of traditional non-ultrasonic trepenning decreases by 50%. The \(L_{PT}\) of trepenning incision with or without ultrasonic vibration decreases similarly with the increase in rotating speed of tool. At different rotating speed, the \(L_{PT}\) of the ultrasonic trepenning with a vibration amplitude of 20 \(\upmu\)m is reduced by 38% compared with non-ultrasonic trepenning, and the \(L_{PT}\) of ultrasonic trepenning with a vibration amplitude of 10 \(\upmu\)m is reduced by 30% on average. The ultrasonic vibration significantly reduces the \(L_{PT}\) of the trepenning incision at a different rotating speed, and improves the quality of trepenning incision. The quantitatively analytical result of the trepenning incision quality demonstrates that the ultrasonic trepenning incision is straighter and better in quality. The introduction of ultrasonic vibration significantly improves the quality of trepenning incision under the different process parameters.