## 2 Materials and Methods
### Methodology
#### 2.2.3. Machining  
In the laser-aided polishing process, the top surface of an AM part is remelted and the material is redistributed from peaks of the surface to the valleys because of surface tension and gravity [64, 65]. However, laser polishing alone cannot remove certain surface features with high wavelengths. A machining process before polishing can help to minimize high-wavelength surface waviness. In order to ablate materials, the laser machining process may require high input energy, but higher input energy can originate additional wavy features because of the mass transport of the fluid flow in the melting pool. Therefore, we proposed a unique laser-enabled machining process that utilizes low input energy density to ablate materials. In this study, we introduced a novel PL scan pattern. Figure 2b shows the schematic representation of the scan pattern and its travel direction used during machining cycles. The overall diameter of the scan pattern was set at 3.5 mm, which is twice the layer width including hatch spacing during material deposition. This pattern is a modified version of the wobbling scan pattern introduced by [PERSON] et al. [59]. The unique feature of this pattern is that while machining the top surface of the deposited samples, the pattern emulates end mills of multiple sizes commonly used in the CNC milling process. In such a way, these patterns offer a high processing rate with low thermal energy input during machining. The number of laser scanning passes on the top surface of the material depends on the scan speed, travel speed, total diameter of the scan, laser spot size, and the sum of the circumference of the scan pattern. Equation (1) was derived to calculate the number of passes per mm during PL scanning. \[PPM=\frac{S_{S}}{S_{T}}\times\frac{2\times N_{C}}{L_{S}} \tag{1}\]  
where \(S_{S}\), \(S_{T}\), \(PPM\), \(N_{C}\), and \(L_{S}\) are the scan speed, travel speed, number of laser scan passes per mm, number of circles in the scan pattern, and total length of PL scans in the pattern, respectively. The scan length is the sum of the circumference circles in a scan pattern given by Equation (2),  
\[L_{S}=2\times\pi\times\sum_{i=0}^{N_{C}-1}\left(R-i\times r\times(1-O_{p})\right) \tag{2}\]  
where \(R\) and \(r\) are the radius of the scan pattern and laser spot size, respectively. \(O_{p}\) is the overlap. The number of circles in the scan pattern can be calculated using Equation (3). \[N_{C}=\frac{R}{r\times(1-O_{p})} \tag{3}\]  
In this study, a 100 W PL (YLP-V2, IPG Photonics, Oxford, MA, USA) with 1055-1075 nm wavelength, 100 ns pulse duration, and 5 kHz frequency was used for the machining process. The depth of focus and spot size of the PL were 400 \(\upmu\)m and 65 \(\upmu\)m, respectively. Figure 4a shows the focal offset distance used for the machining process in this study. While the PL operates within the depth of focus, it ablates material acting like a machining process. In this work, the PL power and scanning speed were fixed at 100 W and 30 m/min, respectively, while varying the travel speed, the input energy density was changed for different experiments. The experimental design presented in Table 3 was constructed to obtain the optimal process parameters for roughness and material removed by the machining process. While the laser power and scan speed were kept constant, the travel speed was varied from 150 mm/min to 375 mm/min with 75 mm/min increments. Since the low input energy density was used during polishing, the number of machining cycles was also varied in the experimental design. The first and third machining cycles traveled along the X-axis while for the second and fourth cycles, the direction was set to travel along the Y-axis. Among 44 deposited samples, the first 12 samples were used to obtain the optimal machining process parameters for surface roughness and material removal determination. Figure 3b demonstrates the top surface texture of samples #1 to #12 after machining with different process parameters.