Laser ablation parameters as fundamental key factors for controlling the 3D Additive Manufacturing process: considerations

Full text: The ability of processing through laser beams different kind of powders for direct production of components with complex geometries by 3D printing has been gaining an impressive and growing attention for specific industrial applications. The process which can be distinguished as Selective Laser Sintering or Selective Laser Melting is even considered, more generally, as Additive Manufacturing where layer by layer material is built by interaction between a laser beam and a powder bed. All effects occurring during the interaction between the laser beam and the powder properties are usually neglected and phenomenological approaches are rather followed. From the work here presented some considerations related to the defect observed during the employment of the Additive Manufacturing process such as: balling, pores production, thermal stresses, micro-structural inhomogeneities, presence of unprocessed powder, capillary instability and so on will be discussed. With this aim, laser parameters (power, spot size, duration, wavelength) both, in plane laser scanning and vertical powder bed translation features (speed, pattern and spacing) power properties (size, density, distribution, composition and layer thickness) already reported in literature will be introduced. In such a way a deep insight view about the effects played by these parameter will be reported in order to provide some indications on the manifold mechanisms involved. Although non equilibria processes can be considered, thermal effects will be taken into account in first approximation. The rapid heating of the powder due to the laser beam energy transfer process followed by a rapid cooling rate can provide a local latent heat during the solidification process and induce unexpected phases of the final manufactured component. On these bases and taking into account other hypothesis connected to the underneath heat diffusion of the growing up piece of manufacture, heat accumulation effects and sharp decrease of the melted material viscosity, the presence of different kind of defects can be foreseen. In this manner the generated 3D component features and the production parameters used in this survey will be considered for drawing a relationship between fundamental mechanisms occurring during the laser ablation process and the Additive Manufacturing technique. (author)