Within the current duration of the ALABAMA project, three different adaptive laser technologies have been developed for aviation, maritime and automotive use-cases:
Aviation use-case
In the aviation use-case, it has been shown that adjusting laser formations and processing parameters can have a positive impact on a Ti-6Al-4V alloy deposited by DED-LB/M with a wire feedstock.
To assess how laser formations affected the macro and microstructure of deposited Ti-6Al-4V in the aviation use-case, a full factorial design was created. During deposition, different formations were used with different combinations of traverse speed and laser powers, creating varying linear energy outputs. The deposited samples were then etched to reveal macrostructure, and further heat tinted to reveal microstructure. None of the samples have shown imperfections such as lack of fusion or pores, but depending on total linear energy output and formation, considerable differences are seen for prior beta grains that grow initially upon solidification. Results show that a laser formation that induce post heating of the melt pool, together with low linear energy output, creates a more equiaxed microstructure of smaller grains, rather than long columnar prior beta grains. Equiaxed microstructures and smaller grains, In Ti-6Al-4V, typically improve strength and reduce orientation dependent anisotropy.
Maritime use-case
In the maritime use-case a CBC laser source has been integrated into a prototype powder DED-system for deposition of Super Duplex steel 2507. CBC laser sources work by combining sets of small lasers to create interference patterns in the required point. Three problems arise when considering these lasers for DED-systems and have been visualized with high speed 30 000 fps cameras:
A frequency of 50kHz has a significant impact on melt-pool dynamics.
During laser pulse repetition, the power distribution becomes uneven and creates larger melt pools in certain areas.
Secondary interference may be so prominent that it creates separate melt pools.
A full ANOVA design of experiment with 5 laser shapes, 3 power levels and 3 powder feeding rates, was carried out for a total of 45 runs. There was no lack of fusion and negligible melting of the substrate in the pattern that yielded the best results.
Automotive use-case
The automotive use-case aims at developing high-speed beam oscillation for the deposition of aluminum alloys through DED-LB with powder. Careful considerations and process trials have been undergone to pick the suitable aluminum alloy. Furthermore, implementation of sensors for data acquisition has been established to create a robust and repeatable process. The laser beam movement takes on a circular movement and process trials have been utilized to optimize process parameters. On the macroscale, the process proves capable of depositing aluminium of high quality.
Digital models and simulations
The ALABAMA project has also worked on the development of digital tools to optimize the DED-LB/M process through material and laser absorption models. The material models aimed at accurately predicting phase transformations, distortions and residual stresses induced by the DED-LB/M process. A Time-Phase Transformation-Block (TTB) approach has been used to simplify complex thermal cycles into manageable phases, and the models have been validated against experimental data and through small-scale simulations. The currently developed material models will be further incorporated into finite element method (FEM) as the project progresses, enabling the prediction of thermal stresses and distortions that occur during additive manufacturing.
The laser absorption model is crucial as it will further define the boundary conditions that will be used in melt pool simulations. More specifically, the calculations provide estimates for particle distribution on the melt pool, enabling estimates of mass and heat transfer at the melt pool interface which will be simulated in the future. Main achievements are the development of a new FEM algorithm for large eddy simulation of transient turbulent flows with heat transfer. Moreover, software implementation has also been developed for Lagrangian tracking for powder particles, as well as a simple model for their laser absorption.
