## 3 Results and Discussion  
The LAMP process is a three-step surface treatment method. Machining, macro-polishing, and micro-polishing together can yield a surface with significantly low roughness. While machining ablates some materials from the top surface to minimize high-wavelength surface features (waviness), macro-polishing and micro-polishing can perform the rough and fine polishing of the surface, respectively. During the machining process with different process parameters, this is very important to determine the materials ablated due to laser-aided machining. In this study, the PL power was kept constant to maintain a consistent Gaussian beam profile for the laser while the travel speed and number of cycles were varied according to the design of experiments. Figure 6a shows the average material removed at different machining cycles with varying travel speed. It is obvious that the average material removed in the laser-aided machining process decreases exponentially with the travel speed at different machining cycles, while the average material removed increases linearly with the number of cycles at different travel speeds (shown in Figure 6b). Therefore, the average material removed can be expressed as Equation (5),  
\[R_{m}=K\times N^{\alpha}\times e^{-  
\[R_{m}=0.927\times N^{1.188}\times e^{-0.00365} \tag{7}\]  
The powder-fed DED parts initially exhibited a high surface roughness due to both the high- and low-wavelength surface characteristics. The surface roughness (\(R_{a}\)) of all the as-built samples in this study was more than 40 \(\upmu\)m on average. The machining process reduces the surface roughness by ablating some materials from the top surface and minimizes the waviness. Figure 7 shows the surface roughness of the samples machined at different travel speeds with varying numbers of cycles. While the 4-cycle machining ablates a comparatively consistent amount of material following the mathematical model, the surface roughness increases when compared with the roughness achieved with 2 cycles. In conventional polishing processes, achieving an optimal roughness, over-polishing increases the roughness of the surface instead of decreasing it. When a material is overly polished by an abrasive material, the polishing process creates additional peaks and valleys on the surface worsening the surface quality. In laser-aided machining, repetitive laser melting or ablation may also create additional peaks and valleys due to the surface tension associated with the temperature gradient of repetitive laser remelting. The objective of these experiments was to determine the machining process parameters with minimal material removal but maximum surface roughness reduction. No significant  
Figure 6: Average materials removed due to machining process at (**a**) different travel speeds and (**b**) machining cycles. surface roughness reduction was observed at the highest speed (375 mm/min) for the unit machining cycle, although as the speed decreases, the roughness reduction increases. This is because the input energy density increases with the decreasing speed. The effect of the number of machining cycles shows that 2-cycle machining (in both X and Y directions) exhibits improved surface quality at different speeds than 4-cycle machining. Additionally, 2-cycle machining ablates fewer materials than 4-cycle machining. Therefore, 2-cycle machining at a 300 mm/min speed was chosen as the optimized machining process. Later, these parameters were used to machine samples #13 to #44. After machining, a reduction in surface roughness was observed. To further improve the surface quality, macro-polishing was performed using the CW laser at different powers and travel speeds. The surface roughness of samples #13 to #28 is shown in Figure 8. At all different laser powers, the surface roughness was reduced but a more than 90% reduction in roughness between machining and macro-polishing processes was observed between 450 and 600 mm/min speeds and 1200 W laser power.