Machining of GTAW additively manufactured Ti-6Al-4V structures

Titanium components such as spars, brackets and landing gear assemblies, containing deep pockets, thin walls and fixturing holes are used in almost all aircraft. The traditional method of fabricating these parts involves significant amount of machining resulting in unsustainably high buy-to-fly ratios. For this reason, additive manufacturing (AM) processes are being considered for making near-net shape components. Gas tungsten arc welding (GTAW) is an economical AM process with higher deposition rates which has been employed to fabricate these titanium components. However, the GTAW-fabricated parts require post-finish machining to meet the strict dimensional tolerances as per design. On the other hand, it is well known that titanium is a difficult-to-machine material. Therefore, the primary objective of this study was to evaluate the machinability of Ti-6Al-4V thin wall and pad structures produced using GTAW additive manufacturing in terms of cutting forces, surface roughness and tool wear during milling and drilling operations. The cutting forces were found to be lower by about 13-21% during milling owing to the lower hardness of the additively manufactured wall in comparison to the wrought T-fillet structure. In contrast, the normal drilling force was higher by about 10-15% for the additively manufactured pad due to its higher hardness as compared to the wrought Ti-6Al-4V billet, though the tool wear was noticed to be higher when drilling the wrought billet. Nevertheless, it was concluded that the machinability of the GTAW-fabricated Ti-6Al-4V was better than the wrought counterpart.