Open PhD position: Multiscale characterization and controllability by laser ultrasounds of WLAM components: towards a physics-based and ML enhanced online monitoring

Numerical modelling of the WLAM process in the framework of the ANR Project COLUMBO, including thermo-mechanical and microstructural methods at the REV scale in order to enhance CND analysis.

The ANR project COLUMBO gathers five academic partners (CEMEF, CEA LIST, MssMAT, ICMMO and LURPA). It aims to develop the controllability of the WLAM (Wire and Laser Additive Manufacturing) process. This additive manufacturing process is based on the fusion of a metal filler wire via a laser source. It makes it possible to develop material deposition of quality, under controlled conditions in terms of energy source and added material rate. However, the operating conditions lead to marked thermomechanical changes (temperature gradient, stresses, …). The resulting microstructure is thus highly textured and anisotropic. In addition, the surfaces of the parts are marked by significant roughness. The NDT (Non-Destructive Testing) analyzes of the components are consequently affected by phenomena of attenuation and ultrasonic dispersion. The COLUMBO project thus aims to propose – at the end - methods for controlling parts during manufacturing process, based on an in-depth knowledge and associated control of the solidification microstructures formed during the process.

CEMEF has developed, in recent years, various tools for numerical modeling of additive manufacturing processes. The first is dedicated to investigate the scale of the incremental deposition of metallic material to develop the beads as presented in figure a). This model solves a thermohydraulic problem with a free interface. It can be applied to a few millimeters of bead in variable deposition strategies [1,2]. The counterpart to this piece-scale model is shown in figure c). It focuses on the thermomechanical evolution during manufacturing [4]. Finally, the REV of the solidification structure shown in figure b) can be deduced by developing coupling with the previous strategies. The numerical methods used in the modeling of these processes are finite elements (thermo-mechanical resolution), cellular automata (grain structure) and level set approach (monitoring of the free metal-gas interface).

The COLUMBO project is thus based on the methods and tools currently available at CEMEF, which will be applied and adapted to the WLAM process. COLUMBO aims, firstly, at developing a reliable prediction of the thermo-mechanical evolutions of the WLAM pieces at different manufacturing scales. Then, the module of microstructural evolution will be applied. The computed microstructures will be diffused to the project partners, as a virtual material, for the analysis of the propagation of ultrasonic waves to investigate the reliability of the NDT analysis methods. To fulfill these objectives, it may be necessary to consider models of dendritic growth kinetics as well as the mechanical behavior of the material. All the information provided by the model would make possible to investigate the potential occurrence of defects during manufacturing. At the end, the model and associated simulation tool should help the manufacturing of defect-free parts.

The experimental data will be provided by the other COLUMBO partners, considering the regular exchanges developed to follow the progress of the project. These data will be used to calibrate the numerical model. The influence of the physical properties of the materials and the process parameters on the bead (geometry and size of microstructure, deformation, etc.) and manufacturing defects will be consequently analyzed.

The numerical developments will enrich CEMEF's collaborative computing library, Cimlib (C++). The PhD student will thus benefit, in return, from the developments made by other users (re-meshing method, numerical resolution, parallelized approach, …). The PhD student will receive training and will develop skills in the field of materials science, computational mechanics and transfers of energy and momentum with free interface. In addition, he/she will receive training in the field of scientific computing and programming, in particular to master CEMEF's computer tools.

References:

[1] Alexis Queva, Simulation numérique multiphysique du procédé de fusion laser de lit de poudre - Application aux alliages métalliques d'intérêt aéronautique, Doctorat MINES ParisTech, CEMEF – Sophia Antipolis, 2021

[2] C. Xue, N. Blanc, F. Soulié, C. Bordreuil, F. Deschaux-Beaume, G. Guillemot, M. Bellet, Ch.-A. Gandin, Structure and texture simulations in fusion welding processes – comparison with experimental data, Materialia (2021), 101305

[3] T. Camus, Modelling of microstructures development in laser powder bed fusion process - Application on an IN718 nickel-base superalloy, European Congress And Exhibition On Advanced Materials And Processes – EUROMAT 2021

[4] Y. Zhang, G. Guillemot, M. Bernacki, M. Bellet, Macroscopic thermal finite element modeling of additive metal manufacturing by selective laser melting process, Computer Methods in Applied Mechanics and Engineering 331 (2018), 514-535