# Towards Lunar In-Situ Resource Utilization Based Subtractive Manufacturing
## 2 Methods and Materials
### Experimental Procedure  
The self-constructed five-axis fine jet test rig, partly shown in Figure 7, was used for the experimental investigation. A cutting head configuration with a water nozzle diameter of 0.1 mm and a focusing tube diameter of 0.3 mm was used (Figure 7, left). To convey the regolith simulate abrasive, a dosing unit (Allfi Group AG) adapted for lowest delivery rates was used (Figure 7, right). The latter can be adjusted via the speed control of the conveyor belt speed (Figure 7, right). Moreover, the flowability of the regolith simulate abrasive was supported using a vibration motor (Figure 7, right). The basic prerequisite for a stable cutting process in abrasive water jet machining is a homogeneous abrasive flow. This requires a free-flowing abrasive since the smallest particles adhere to larger ones and consequently agglomerate with others (Figure 8a). To avoid agglomeration, small particles were removed from the abrasive by wet sieving (Figure 8b). The dried screenings were sieved and divided into fractions with particle sizes of 45-63 \(\upmu\)m, 63-90 \(\upmu\)m and 90-125 \(\upmu\)m. These fractions were chosen because coarser particles can clog the focusing tube, whereas finer particles cannot be conveyed homogeneously. Due to the lower density of the regolith simulant (2.90-3.25 g/cm\({}^{3}\)) [90], compared to conventional abrasives, such as garnet sand (4.12 g/cm\({}^{3}\)) [74], the common mass flow was reduced from a rate of 10 g/min [91] for garnet sand to 8.5 g/min for the regolith simulants. A test plan was set up for the aluminum material. For this purpose, the nozzle diameter d\({}_{d}\), the stand-off distance s between the focusing tube outlet and the workpiece surface (Figure 9), the abrasive mass flow rate \(\dot{m}_{p}\) and the material thickness h are set as constant (Table 15). Four parameters were selected for the feasibility study. The pressure p, converts the hydraulic power built up in the pump into the kinetic energy of the water and, thus, also of the abrasive particles. In preliminary tests, it was found that below a pressure of 200 MPa, no stable abrasive conveyance occurred due to powder agglomeration. The particle size fraction SF was chosen as the second factor. The three selected factor levels represent the particle sizes available on the Moon for potential lunar abrasive water jet processing. Furthermore, the particle size influences their mass and, thus, their material removal rate. The third factor is the chemical composition of the regolith material. The fourth factor is chosen to evaluate the performance of the process. For this purpose, the parameter of the related abrasive mass flow per 1 mm of machined workpiece surface \(\dot{m}_{h}\) is calculated from \begin{table}
\begin{tabular}{c c} \hline \hline
**Main Crystal Phase** & **Temperature Program** \\ \hline Lithium metasilicate & 620 \({}^{\circ}\)C/60 min \\ Lithium disilicate & 620 \({}^{\circ}\)C/60 min + 850 \({}^{\circ}\)C/10 min \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Crystallization programs of the lithium silicate glass ceramics (heating rate 10 K/min). the ratio of feed rate \(\
u_{f}\) and \(m^{\prime}_{l}\). For the adjustment of \(\dot{m}_{l}\), the abrasive mass flow was kept constant and \(\
u_{f}\) was varied. All factors and factor levels are summarized in Table 16 with reference to Figure 9. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Symbol** & **Value** & **Unit** \\ \hline Nozzle diameter & \(d_{d}\) & 0.1 & mm \\ Focusing tube diameter & \(D_{F}\) & 0.3 & mm \\ Stand-off distance & s & 2 & mm \\ Abrasive mass flow rate & \(\dot{m}_{P}\) & 8.5 & g/min \\ Al material thickness & \(h_{Al}\) & 2.286 & mm \\ Lithium silicate material thickness (all conditions) & \(h_{Li}\) & 7 & mm \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Constant test parameters. Figure 8: Regolith simulant before (**a**) and after wet sieving (**b**). Figure 7: Experimental Setup.