# Towards Lunar In-Situ Resource Utilization Based Subtractive Manufacturing
## 3 Results  
### Water Jet Machining of Al-Miloy  
The aluminum material could be processed with regolith simulants. The identified process limits are shown in Figure 11. This diagram shows a classification of the process stability during AWJ of the aluminum alloy 6061 T6 as a function of the feed rate vf, the pump pressure p and the particle size distribution for the regolith substrates LS-M100 and LS-T100 and the limits for the varied factors indicating where the workpiece could no longer be cut completely. The result, however, is a transition towards surface removal in terms of surface structuring, as explained in Section 2.7.  
As is common for AWJ machining, the kerfs showed tapering gaps (Figure 10). The kerf width on the jet entry side was independent of all factors (Table 17) in the range of 0.3-0.4 mm (Figure 12).  
On the other hand, as shown in Figure 13, all investigated factors show an effect on the angular error u. As expected, u is reduced with increasing pressure. In fact, this is explained by the higher kinetic energy due to the increased particle velocity since higher energy input increases the erosion rate. The energy input, again, increases as the feed rate is reduced or nil is increased. Hence, a high nil also leads to a reduction of the angular  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Symbol** & **Value** & **Unit** \\ \hline p & 200 & MPa \\ SF & 45–63; 63–90 & \(\upmu\)m \\ m\({}_{1}\) & 1.4; 0.7; 0.35 & g/mm \\ v\({}_{\text{f}}\) & 0.1; 0.2; 0.4 & mm/s \\  & Lithium silicate without crystallization & \\ Specim material & Lithium silicate with nucleation & - \\  & Lithium silicate with nucleation and crystallization & \\ Abrasive Material & LS-M100 & - \\ \hline \hline \end{tabular}
\end{table}
Table 17: Parameter combinations used for the individual tests.  
Figure 10: Output parameters of the kerf cross section and the cut surface.  
error. Furthermore, an influence of the particle size on the angular error could be observed. This is explained by the higher mass and the resulting increase in the kinetic energy of the particles. However, the influence of the particle size change on the angular error turns out to be small.  
A higher material removal rate, in turn, can be achieved by varying the particle size at shallower impact angles, as is the case with surface erosion where a full-cut kerf has not yet been formed. This can be deduced from the increase in erosion rate due to the increase in particle size at the lowest m\({}^{\prime}\)!. Furthermore, differences were found due to the variation of the abrasive material used. During the tests, it could be observed that the conveyability of LS-M100 is better than LS-T100. Moreover, the erosion rates of the LS-M100 material were higher than those of LS-T100 and the angular errors were lower. Although LS-T100 has a significantly higher amount of Al\({}_{2}\)O\({}_{3}\) as a hard abrasive than LS-M100, the higher erosion rates can be attributed to the much better conveysability of LS-M100.  
Figure 11: Overview of the process results regarding the process parameters for the aluminum alloy.  
Figure 12: Example of a tapering cut kerf geometry.  
As a result, it was possible to machine the samples with higher feed rates and, thus, higher productivity. As an example, two notches where only the abrasive material was the varied parameter are shown in Figure 14. Either way, determining the cause of this difference requires further investigation, while the chemical composition is expected to be the cause (Table 12). Regarding the roughness (Figure 10), in turn, no effect could be observed for the pressure factor. In fact, minimum roughness's of Ra 2 \(\upmu\)m and Rz 25 \(\upmu\)m could be achieved by increasing m'1.  
Figure 13: Influence P variation for sieved regolith simulant specific feed rates on the angular error of the cut-through kerr.