THERMAL MONITORING AND MODELING OF TI-6AL-4V THIN WALL TEMPERATURE DISTRIBUTION DURING BLOWN POWDER LASER DIRECTED ENERGY DEPOSITION

The effects of Ti-6Al-4V part size on its temperature distribution during the blown-powder directed energy deposition (DED) process was investigated through dual-thermographic monitoring and a unique modeling technique. Results demonstrate that the duration of dwell times presented to be a significant contributing factor affecting the rate at which a steady-state temperature field is achieved. As a result, the longer wall took significantly more layers/time to achieve a uniform temperature profile within the wall. Maximum and average melt pool temperatures appear to be near independent of part size at a steady state. Finite element simulation results showed that a quasi-steady melt pool temperature may be unique to a layer, especially during earlier cladding process near the substrate and that the layer-wise steady melt pool was achieved within the first few seconds of track scanning. A proposed fin modeling-based temperature distribution was found to predict the thermal profile in a ‘substrate affected zone’ (SAZ) along the scan direction within 5%. A method to predict the onset of the SAZ has also been proposed. Process parameters used for the DED of component volumes are not necessarily optimal for thin-walled structures due to significantly less thermal capacity.

Thermal Monitoring and Modeling of Ti-6Al-4V Thin Wall Temperature Distribution During Blown Powder Laser Directed Energy Deposition

The effects of Ti-6Al-4V part size on its temperature distribution during the blown-powder directed energy deposition-laser (DED-L) process was investigated through dual-thermographic monitoring and a unique modeling technique. Results demonstrate that the duration of dwell times are a significant contributing factor affecting the rate at which a steady-state temperature field is achieved. Longer walls took significantly more layers/time to achieve a uniform temperature profile. Maximum and average melt pool temperatures appear to be near independent of part size at a steady state. Finite element simulation results show that a quasi-steady melt pool temperature may be unique to a layer, especially for layers near the substrate. Layer-wise steady melt pool temperatures were achieved within the first few seconds of track scanning. A proposed fin modeling-based temperature distribution was found to predict the thermal profile in a ‘substrate affected zone’ (SAZ) along the scan direction within 5%. A method to predict the onset of the SAZ has also been proposed. Process parameters used for the DED-L of component volumes are not necessarily optimal for thin-walled structures due to their significantly lower thermal capacity.

Experimental and Numerical Analysis of the Powder Flow in a Multi-Channel Coaxial Nozzle of a Direct Metal Deposition System

The work explores the powder transport process, using numerical simulation to address the dynamics of the powder flow in an in-house built multi-channel coaxial nozzle of a direct metal deposition (DMD) system. The fluid turbulence is handled by the standard k–ɛ and k–ω turbulence models, and the results are compared in order to predict their suitability. An image-based technique using CMOS camera is adopted to determine the powder flow characteristics. The model is validated with the in-house experimental results and verified available results in the literature. The findings of this work confirms the application of the k–ω model for powder gas flow investigations in blown powder additive manufacturing (AM) processes due to its better predictive capability. The proposed model will assist in simulating the direct metal deposition process.

Structural Integrity Assessments for Validating Directed Energy Deposition Repairs of Integrally Bladed Rotor

Considerable steps to assess the structural capability of laser directed energy deposition (DED) aim to determine the viability of repair processes for integrally bladed rotors (IBRs). Two laser DED processes are under investigation in this study: wire fed and blown powder feedstock. Using a small subsonic Titanium 6Al-4V fan as the component of interest, a series of tests and associated models for laboratory specimens, subcomponents, and components are necessary for proper assessment of material structural properties pertaining to the intended mission of the IBR. Experimentation on laboratory specimens acquire properties such as tensile strength, elongation, low cycle fatigue (LCF), high cycle fatigue (HCF), crack growth rate, and fracture toughness. Subcomponent test articles fabrication occurs by sectioning an operational IBR into individual blades for vibration HCF assessment. Component level testing focuses on LCF and overspeed strength acquired from spin rig testing. Even though the full IBR repair validation of laboratory specimen, subcomponent, and component testing has yet to be completed, the results to-date for laser DED repairs are promising. Furthermore, this plan for structural integrity assessment can serve as a reference for validation of future IBR repair processes.

An Innovative Approach on Directed Energy Deposition Optimization: A Study of the Process Environment’s Influence on the Quality of Ti-6Al-4V Samples

Blown powder additive manufacturing technologies are not restricted to the use of a process chamber. This feature allows to build larger components with respect to conventional powder bed processes. This peculiarity is mostly promising for manufacturing large components or repairing/rebuilding parts of large systems. The main downside of using an open environment, even if a protective shielding gas system is adopted, is the lack of control of process atmosphere. This is particularly critical for titanium alloys which are very sensitive to oxygen/nitrogen pick-up; they have a detrimental effect on ductility, by causing embrittlement and possibly leading to the formation of cracks. It is then important to address how environmental factors, such as process atmosphere and platform temperature, impact not only on the processability but also on the final component properties, both from a compositional and mechanical point of view. The correlations between these environmental factors and microstructure, interstitials content, grain size, and hardness were investigated. Moreover, the Hall–Petch equation was then adopted to additive manufacturing microstructures, characterized by a columnar grain morphology, and used to further investigate the relationship intercurring between grains and hardness and how different microstructures might influence this correlation.