Increased shielding of a direct energy deposition process to enable deposition of reactive materials; an investigation into deposition of 15-5 PH stainless steel, Inconel 718 and Ti-6Al-4V.

Hybrid additive and subtractive machining combines the flexibility of additive manufacturing (AM) with the high precision and geometrical accuracy of computer numerical control (CNC) machining. Of the many metal AM strategies blown powder direct energy deposition (DED) is the method most commonly chosen for incorporation into hybrid additive and subtractive platforms. Due to the necessity for coolant during machining operations, these platforms are usually not sealed environments meaning the deposition of reactive metals such as titanium to acceptable standards is not possible due to oxygen absorption from the surrounding environment. The research presented focuses on the investigation of the effect of a series of shielding methods in the geometry and microstructure of the materials deposited in a hybrid-manufacturing platform. The ultimate objective is to select the method with the biggest potential to enable the deposition of reactive materials with the aim of successfully depositing low oxygen content titanium, enabling the creation of Ti-6Al-4V at grade 5 and grade 23. To achieve this, bath and bag shielding strategies were compared with the standard through nozzle shielding when depositing in 15-5 PH stainless steel, Inconel 718 and Ti-6Al-4V. Based on the results of the post machining analysis the oxygen content of a multi-layer titanium sample was found to be 0.079%, lower than the maximum limit for grade 23 Ti-6Al-4V.