Amélioration des états de Surface de Pièces obtenues en fabrication dirECTe par laser – ASPECT

The direct metal laser deposition (DMLD) is a recent process with a real industrial potential that allows manufacturing small series or prototypes of complex shapes from the interaction between a projected powder stream and a laser. Limitations of the process come from : (1) the manufacturing time, (2) the surface finish which necesites post-machining operation, (3) a limited description of local interactions involved. The ASPECT project has two objectives : (1) reaching a high level of understanding of local physical interactions between the laser, the powder and the melt-pool, that generate solid additive layers, (2) using those scientific benefits to manufacture net-shape structures having surface finish close from surface machining (Ra < 3 µm). A dual experimental + numerical approach will be carried out on simple geometries (walls), based upon skills from three complementary partners : LALP (for DMLD tests and corresponding diagnostics) and LIMATB (for numerical simulations of melt-pools on COMSOL Multiphysics). Many innovative options are envisaged : (1) the modification of interaction regime (cw or pulsed in the 0.5-20 ms pulse range, with or without modification of the beam distribution), (2) the use of novel powder feeding conditions (new generation powder feeders allowing to project small powders), (3) the use of adequate gas assistance, with or without tensio-active effect (for instance with N2 shielding). All these options aim at stabilizing melt-pools, limiting melt-pool heights, and avoiding powder sticking in order to provide smooth surfaces. For each configuration, the numerical simulation will provide an essential contribution by allowing to identify, at a local scale, physical mechanisms responsible for the modification of surface finish. A the end of the project, a simulation-based anaytical modelling, using a recently developed morphological model, will be implemented to calculate surface parameters (mainly Wa, Wt) of DMLD structures. Results of this project, focused on the manufacturing of two aluminium alloys should be easily extrapolated to any kind of metallic materials.