# Abrasive Surface Finishing on SLM 316L Parts Fabricated with Recycled Powder
## 3 Results and Discussion  
### 2D Surface Roughness  
#### 3.1.1 Average of All Surfaces  
This section presents the results of the 2D surface roughness being Ra and Rz. In Table 2 below, different combinations of time and treatments were recorded for two different scanning strategies being meander and stripes. It is worth mentioning that the surface roughness results of all nine sides of the specimens were averaged and rounded to the nearest tenth for generality. In Table 2, the specimens can be grouped according to their numbering as follows: as-built (1), sandblasted (2, 3), tumbled (4, 5, 6), combined (7, 8). The sandblasting process took 50 s with two different media being corundum (aluminum oxide) and steel. The tumbling process with plastic, porcelain took 120 min, and with ceramic, 120, 180, 240 min. The total time was recorded and rounded up to min. Averages of surface roughness values for all the sides, Ra and Rz, were calculated. First and foremost, it can be observed that the \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Specimen No.**} & \multirow{3}{*}{**Scanning Strategy**} & \multicolumn{3}{c}{**Sandblasting**} & \multicolumn{3}{c}{**Tumbling**} & \multicolumn{3}{c}{**Total**} & \multicolumn{3}{c}{**Roughness**} \\ \cline{3-11}  & & \multicolumn{2}{c}{**Corundum Steel**} & & \multicolumn{2}{c}{**Ceramic**} & \multicolumn{2}{c}{**Plastic**} & \multicolumn{2}{c}{**Poreclaim**} & \multicolumn{2}{c}{**Time**} & \multicolumn{2}{c}{**Ra**} \\ \cline{2-11}  & & **Meaner** & **Stripes** & **50** & **50** & **120** & **180** & **240** & **120** & **120** & **120** & **[min]** & **[\(\upmu\)m]** & **[\(\upmu\)m]** \\ \hline
1 & X & & & & & & & & & 0 & 11.0 & 56.6 \\
2 & X & X & & & & & & & & 1 & 6.6 & 37.0 \\
3 & X & X & X & & & & & & & 2 & 4.9 & 25.1 \\
4 & X & & & & X & & X & X & 360 & 3.5 & 20.5 \\
5 & X & & & & & X & X & X & 420 & 2.2 & 15.1 \\
6 & X & & & & & & X & X & 480 & 1.8 & 13.4 \\
7 & X & & X & & & X & X & X & 481 & 1.2 & 9.4 \\
8 & X & & X & & & & X & X & 482 & 1.7 & 10.4 \\ \hline
1 & & X & & & & & & & & 0 & 9.5 & 47.9 \\
2 & X & X & & & & & & & & 1 & 6.4 & 35.6 \\
3 & X & X & & X & & & & & & 2 & 3.7 & 20.6 \\
4 & X & & & & & X & & & & 360 & 2.9 & 17.2 \\
5 & X & & & & & X & & X & & 420 & 1.8 & 12.5 \\
6 & X & & & & & & & X & X & 480 & 1.7 & 12.5 \\
7 & X & X & & & & & X & X & 481 & 1.7 & 12.3 \\
8 & X & X & X & & & & X & X & 482 & 0.5 & 4.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Matrix of scanning strategies, treatment time, and corresponding 2D surface roughness results. Ra values of as-built specimens no. 1 lie within the regular aforementioned range, below 20 \(\upmu\)m.  
For meander no. 3, after 2 min of sandblasting, Rz was reduced 56% (from 56.6 to 25.1 \(\upmu\)m) and Ra 55% (from 11.0 to 4.9 \(\upmu\)m). On the other hand, tumbling meander no. 4, which took considerably more time, produced a better roughness reduction of 64% for Rz (from 56.6 to 20.5 \(\upmu\)m) and 68% for Ra (from 11.0 to 3.5 \(\upmu\)m). Additionally, the roughness value decreased moderately as the time for tumbling with ceramic increased from 120 to 240 min. Last but not least, the two best results are from the combined process. Remarkably, the roughness values for meander no. 8 are slightly higher than those of meander no. 7. This can be due to the imperfection of the manual sandblasting and tumbling process. Eventually, the best result was meander no. 7 with an 83% reduction in Rz (from 56.6 to 9.4 \(\upmu\)m) and an 89% reduction in Ra (from 11.0 to 1.2 \(\upmu\)m). As for the stripes strategy, the surface roughness values of as-built stripes no. 1 are slightly lower than those of the meander. Similarly, 2 min of sandblasting vastly reduced the surface roughness of the stripes no. 3, a 57% reduction of Rz (from 47.9 to 20.6 \(\upmu\)m) and a 61% reduction of Ra (from 9.5 to 3.7 \(\upmu\)m). Solely tumbled stripes no. 4 had a better reduction of roughness, 64% for Rz (from 47.9 to 17.2 \(\upmu\)m) and 69% for Ra (from 9.5 to 2.9 \(\upmu\)m).