Improving Consistency and Efficiency Across Builds

The aerospace industry, a staple of the economy in the Pacific Northwest, is beginning to capitalize on the versatility of additive manufacturing to produce parts that might otherwise be impossible or prohibitively difficult to produce. The industry and regulators enforce the strictest tolerances for consistency and performance, regardless of the production method. Our group collaborates with several prominent aerospace companies nationwide as well as metal additive manufacturing system producers to better understand the variables that significantly impact the porosity, fatigue life, and mechanical performance of 3D printed metal parts. Only once those parameters are understood can they be optimized to produce ever more efficient parts.

 

Certification of the 3D printing process is a major hurdle to using this technology to produce parts for commercial aerospace. In order to meet or exceed the reliability requirements of the FAA, a better understanding of the underlying causes of variability in 3D printed metal parts is needed. Our research focuses on identifying sources of defects in the metal. We look at factors such as powder quality, gas flow dynamics, process monitoring, laser-powder interactions, and part design, to determine the most significant factors contributing to defect formation and metal variability.

Render of the build file for a design of experiments for titanium fatigue test coupons. Three parameters are indicated, the gage thickness T of a coupon, and the height H and radial distance R from the center of the base plate. From https://doi.org/10.3390/ma15165617

Post-processing treatments such as stress-relief heat treatments, hot isostatic pressing (HIP), and cavitation abrasive surface finishing (CASF) are used to modify the microstructure of the part to achieve the desired properties. We use micro-computed tomography to monitor pores, along with fractographic analysis of tensile and fatigue coupons to identify where pores are likely to happen and how much of a problem they may be. Ti-6Al-4V (6 wt.% aluminum, 4 wt.% vanadium) is an alpha-beta alloy, meaning that the final microstructure is a complex mixture of both alpha and beta phases. The rapid melting and solidification cycles that the printed material experiences during printing, followed by the heat treatment for densification, only complicate this further. As with any other alloy, the microstructure is one of the primary controlling factors of the properties of the final part. For these reasons, we also perform metallographic analysis of the alpha-lathes and prior beta grains and how they change in response to the print parameters (e.g. powder reuse, location in the build chamber) and post-print treatments to ensure the optimal final part is produced.

Extraction of 3D printed titanium parts from the 3D printer machine. Loose, unmelted powder is vacuumed away to expose the parts.

Particle image velocimetry (PIV) gas flow analysis inside a mock build chamber constructed to evaluate the turbulence in the inert gas used during the 3D printing process

Select Publications

S. Ghods, R. Schur, A. Montelione, R. Schleusener, D.D. Arola, M. Ramulu, Importance of Build Design Parameters to the Fatigue Strength of Ti6Al4V in Electron Beam Melting Additive Manufacturing, Materials 15 (2022). https://doi.org/10.3390/ma15165617.

R. Schur, S. Ghods, C. Wisdom, R. Pahuja, A. Montelione, D. Arola, M. Ramulu, Mechanical anisotropy and its evolution with powder reuse in Electron Beam Melting AM of Ti6Al4V, Materials and Design 200 (2021). https://doi.org/10.1016/j.matdes.2021.109450.

S. Ghods, E. Schultz, C. Wisdom, R. Schur, R. Pahuja, A. Montelione, D. Arola, M. Ramulu, Electron Beam Additive Manufacturing of Ti6Al4V: Evolution of Powder Morphology and Part Microstructure with Powder Reuse, Materialia 9 (2020). https://doi.org/10.1016/j.mtla.2020.100631.

A. Montelione, S. Ghods, R. Schur, C. Wisdom, D. Arola, M. Ramulu, Powder Reuse in Electron Beam Melting Additive Manufacturing of Ti6Al4V: Particle Microstructure, Oxygen Content and Mechanical Properties, Additive Manufacturing 35 (2020). https://doi.org/10.1016/j.addma.2020.101216.

R. Schur, S. Ghods, E. Schultz, C. Wisdom, R. Pahuja, A. Montelione, D. Arola, M. Ramulu, A Fractographic Analysis of Additively Manufactured Ti6Al4V by Electron Beam Melting: Effects of Powder Reuse, J. Fail. Anal. Prev. 20 (2020). https://doi.org/10.1007/s11668-020-00875-0.