## 2 Experiments
In the preliminary experiment, the thrust forces and tool wear of CFRP and titanium alloys under different feeds were compared at 200 rpm. According to [22], the feed rate range of CFRP and the titanium alloy is 5, 10, 20, and 25 mm/min. Under these parameters, the CFRP is suitable for 25 mm/min feed and the titanium alloy is suitable for 10 mm/min feed. The feed speed of the two materials is more than three times different. In the case of a similar feed speed, only the smaller one can be used, which will reduce the efficiency of processing. It has been shown that a low feedrate should be used for UVR of Ti, but high feedrate could be used for UVR of CFRP [17]. In addition, using a variable feedrate led to a lower cutting force. Therefore, the experiments were carried out using different cutting parameters according to the different material properties, and lower thrust forces and higher machining efficiency were achieved compared to machining using the same parameters. In this experiment, a faster speed of 0.41 mm/s was used to ream holes in CFRP for machining and a slower speed of 0.16 mm/s for machining titanium alloys. Near the end of CFRP machining, the feedrate changes from 0.41 mm/s to 0.16 mm/s. The pattern of variation of feedrate with feed depth is shown in Figure 3. The other parameters used in the experiments are described in Tables 5 and 6. The error bars were based on three repetitions in each of the following groups. A multicomponent dynamometer (9139 AA, Kistler Instrumente AG, Winterthur, Switzerland) was used to measure the thrust force in experiments. The thrust force was converted into electrical signals by dynamometer, which were processed by a multichannel charge amplifier (5080A, Kistler Instrumente AG, Switzerland), converted, and transmitted to a computer through an analog to digital converter card (5697A1, Kistler Instrumente AG, Winterthur, Switzerland). \begin{table}
\begin{tabular}{c c} \hline
**Item** & **Value** \\ \hline Drill bit & Uncoated tungsten carbide drill \\ Rotation speed in CFRP/Ti (rpm) & 2000/700 \\ Feed rate (mm/min) & 20 \\ Cutting condition & Drilling with coolant \\ \hline \end{tabular}
\end{table} 
Table 6: Drilling experimental conditions. Figure 3: The feed rate varies with the feed depth. \begin{table}
\begin{tabular}{c c} \hline
**Item** & **Value** \\ \hline Rotation speed, \(n\) (rpm) & 200, 400, 600, 800, 1000 \\ Frequency,\(f\) (kHz) & 21.5 \\ Amplitude \(A\) (\(\upmu\)m) & 2, 4, 6 \\ Reaming margin (mm) & 0.15 \\ Cutting condition & Dry cutting \\ \hline \end{tabular}
\end{table} 
Table 5: Experimental conditions for reaming. The hole quality was analyzed after reaming from aspects of geometric parameters (hole diameter, roundness), internal hole surface defects, the roughness of CFRP and titanium alloy holes, CFRP hole entrance, and exit morphology. The measurements of CFRP and titanium alloy hole diameter and roundness were performed using a coordinate measuring machine (PRISMO12020222, ZEISS, Oberkochen, Germany). CFRP and titanium alloy hole walls are measured, respectively. When measuring, 50 points are taken every week to fit the circle at the hole position every 1 mm. Average values are taken to obtain the hole diameter and roundness. The surface roughness of holes was measured with the [PERSON] surface profiler (CLI2000, Taylor Hobson Ltd., Leicester, UK). The roughness of CFRP and titanium alloys is measured separately. For the reliability of the results, the probe of the roughness analyzer runs through almost the entire pore size. The CFRP test length is 5.6 mm, and the titanium alloy test length is 6.6 mm. The optical microscope (OM; VHV-600E, KEYENCY, Osaka, Japan) was applied to observe the hole exit morphology. The inner wall morphology of the pores was observed with a scanning electron microscope (SU5000, Hitachi-hightech, Tokyo, Japan). The laser displacement sensor (OPTEX) is used to measure ultrasonic amplitude.