## 2 Materials and Methods
### Surface Roughness Measurement  
In this study, a high-speed non-contact laser displacement sensor (Keyence LK-H052) with 0.025 \(\upmu\)m repeatability and 50 \(\upmu\)m spot size was used for surface scanning to determine the roughness of the as-built samples and materials removed after the machining process. The as-built samples had a very high roughness as shown in Figure 3a and measuring the  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline
**Sample No.** & **13** & **14** & **15** & **16** & **17** & **18** & **19** & **20** & **21** & **22** & **23** & **24** & **25** & **26** & **27** & **28** \\ \hline Travel speed (mm/min) & 300 & 300 & 300 & 450 & 450 & 450 & 450 & 600 & 600 & 600 & 600 & 750 & 750 & 750 & 750 \\ \hline CW laser power (W) & 1000 & 1200 & 1400 & 1600 & 1000 & 1200 & 1400 & 1600 & 1000 & 1200 & 1400 & 1600 & 1000 & 1200 & 1400 & 1600 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Different process parameters used for the macro-polishing of samples #13 to #28.  
Figure 5: Surface texture of samples (**a**) #29 to #36 and (**b**) #37 to #44 after the micro-polishing process.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline \hline
**Sample No.** & **29** & **30** & **31** & **32** & **33** & **34** & **35** & **36** & **37** & **38** & **39** & **40** & **41** & **42** & **43** & **44** \\ \hline Travel speed (mm/min) & 300 & 300 & 300 & 300 & 450 & 450 & 450 & 450 & 600 & 600 & 600 & 600 & 750 & 750 & 750 & 750 & 750 \\ \hline Pulsed laser power (W) & 40 & 60 & 80 & 100 & 40 & 60 roughness using a surface profilometer might have damaged the touch probe. Therefore, a laser displacement sensor was employed. To scan the surface of the samples, the laser displacement sensor was mounted on the tool holder of a CNC milling machine. A point on the surface of the substrate was fixed as the reference point for scanning the surface both before and after the machining process. A CNC program for raster patterns with 50 \(\upmu\)m increments was written to automate the scanning process. The data acquisition rate for the sensor and the scan speed for the motion table were set at 1000 samples/s and 1.25 mm/s, respectively.  
The common practice of laser line scanning is along one direction only. The average of the roughness remains the same regardless of the scanning direction. In this study, the as-built samples were scanned along the Y-axis of the deposition. Later, the data were processed to determine the surface roughness. The average roughness (\(R_{a}\)) was calculated according to the ASME B46.1 standard using the following Equation (4),  
\[R_{a}=\frac{1}{n}\sum_{i=1}^{n}|Z_{i}-Z_{mean}| \tag{4}\]  
where \(n\), \(i\), and \(Z\) are the number of total data points, the data number, and the height measured, respectively. We also scanned a few surfaces along the X-axis and compared them with the results obtained from the Y-axis scan. No significant difference was observed since Equation (4) uses millions of scan points and averaging them yields no significant difference. In this study, the laser scanning process was used for the as-built and machined surfaces while a surface profilometer (Mitutoyo Surftest-212) was utilized to measure the surface roughness after the macro-polishing and micro-polishing processes.