# Oxidation-Reduction of Ti-6 Al-4V in Direct Energy Deposition Subject to Minimum Argon Consumption
## 3 Experimental Setup  
In this study, all experiments were conducted in an open-air environment. Due to the COVID-19 pandemic, access to the AM nozzle for manufacturing was limited. Therefore, a 3D-printed AM nozzle was used to attach the shielding gas nozzle attachments as an alternative. Since these attachments were not used in high-temperature applications, they were 3D printed using PLA filament. After printing, the attachments were coated with XTC-3D coating to improve the surface finish and prevent argon leakage from the 3D-printed layers. These prototypes serve as a basis for future modifications in the design of the actual attachments. As the attachments were not connected to an actual AM machine, oxygen concentration measurements were taken using an oxygen sensor. A LuminOX LOX-02 Oxygen Sensor from GasLabs was used in this study, with a measuring range of 0-25% and a resolution of 0.01%. The sensor logged the oxygen concentration every 0.7 s. To control the shielding gas flow into the attachments, NITRA 3-way, 3-port, 2-position solenoid valves were used, which were connected to a P1 AM-100 controller. The eight nozzle attachments were modeled in Fusion 360, with several versions created before finalizing the design. The attachment system, including the AM nozzle, was 3D-printed using a Lulzbot Taz Pro and Mini 3D printer. After coating, brass threaded inserts were added to secure the attachments to the MORI nozzle. Throughout the experiments, 99.99% pure argon gas was used. Since the AM nozzle machine was not in  
Figure 7: Transition of shielding gas from one attachment to another depending on the deposition path. The attachment in use is highlighted. Different attachment number is highlighted depending on the deposition path. operation, the shielding gas flow in the attachments was controlled by commands sent to the controller rather than following a deposition path. The 3D-printed MORI nozzle was attached to plywood and supported by four M6 threaded rods on an optical breadboard. The nozzle attachment system was then mounted to the 3D-printed nozzle, as shown in the figures. The oxygen sensor was placed beneath one of the attachments to monitor the oxygen concentration as shown in Figure 8.  
High usage of shielding gas for the deposition is wasteful, and very low flow can lead to oxidation of the deposit. Hence, an optimal flow rate of the shielding gas from these attachments is essential for effective shielding. For this reason, different flow rates of shielding gas, from 20 SCFH to 35 SCFH with 5 SCFH increments, were used to investigate the oxygen concentration with the nozzle attachments. The sensor was placed at three different locations, as shown in Figure 9, to observe the oxygen concentration. Table 1 shows the test conditions with different attachments in use and the location of the oxygen sensor. Figure 8: Complete setup of the attachment system on the coax AM nozzle. Figure 9: Side view of the system showing the location of the oxygen sensor under the attachment at locations A, B, and C.  
Numerical simulations using Ansys Fluent were performed to model the flow conditions and predict the oxygen concentration based on the shielding gas flow. The validation of these simulation results was achieved using the oxygen sensor readings at different locations under the attachments. Additionally, simulations of the gas flow at four different flow rates were conducted. A plane 10 mm from the base of the nozzle was selected to observe the shielding gas flow, as shown in Figure 13.  
To ensure the statistical consistency in testing, three measurements were conducted at each location under varying shield gas flow rates (20, 25, 30, and 35 SCFH). The results were averaged to enhance the reliability of the data. Additionally, to maintain uniform and precise measurement conditions, the attachment system was placed 10 mm above the sensor for the duration of the testing. A 3D-printed sensor holder was designed and fabricated with integrated M6 threads to ensure repeatability and sensor placement accuracy.