## 3 Results and Discussion
Therefore, 500 mm/min travel speed and 1200 W power were selected as the optimized process parameters for the macro-polishing process. Figure 8: Average surface roughness of samples #13 to #28 after macro-polishing process. Figure 7: Average surface roughness of samples #1 to #12 after machining process. The PL power, focal offset distance, and scan speed were 100 W, 50 μm, and 30 μm/min, respectively. While macro-polishing reduces the surface roughness mostly in the entire LAMP process, the micro-polishing process was implemented in this study for further smoothing the surface quality after the macro-polishing process. Figure 9 illustrates the roughness after micro-polishing the samples with different process parameters. Prior to implementing this process, all the samples were machined and macro-polished using the optimized parameters determined in this study. Increasing the scanning speed during fine polishing of the surface did not help substantially in improving the surface quality since the laser could not originate a significant melt pool to polish the surface at higher speeds. As the PL power increased, no significant improvement in surface quality was observed because increasing the laser power increases the melt pool depth and as a result creates additional roughness due to high energy input. A reduction in surface roughness was seen only for 40 W PL power at all different speeds but the travel speed of 300 mm/min showed the highest improvement in surface quality. However, the parameters for sample #29 showed a nominal surface quality improvement within the boundary of the experimental design, The band of the process parameters chosen in this study does not confine the lower boundary of the parameters for optimal surface quality. As a future study, a new experimental design covering a wide range of PL powers and higher scan speeds can help to obtain optimized process parameters for improved surface quality. For further investigation, to demonstrate the effectiveness of machining prior to polishing, an additional sample was deposited and polished with optimized parameters without machining. Figure 10a-c illustrate the line-scanned surface profile of the as-built, LAMP processed, and polished sample. The as-built sample surface (shown in Figure 10a) shows both high and low waviness in surface topography while the LAMP processed surface in Figure 10b demonstrates the least waviness compared to the polished surface illustrated in Figure 10c. Therefore, the LAMP process (combination of laser-aided machining, macro-polishing, and micro-polishing) can be an effective method for improving the surface quality of AM metals due to minimizing the surface waviness and roughness and achieving an overall surface quality improvement of more than 97% when compared to the as-built part. Due to the limitation in the degree of freedom of the CNC motion table, in this study, the LAMP process was applied only on the XY (horizontal) plane of the deposited materials. However, a five-axis machine or a robotic AM system can facilitate the process with the advantage of machining and polishing at different planes as well. Figure 9: Average surface roughness of samples #29 to #44 after the micro-polishing process. The PL focal offset distance and scan speed were 50 mm and 30 m/min, respectively. Figure 10: Surface profile (scanned line along Y axis) of (**a**) as-built sample, (**b**) sample machined and polished with optimized process parameters, and (**c**) sample not machined but polished with optimized process parameters.