Thermal-structural hybrid Lagrangian solver and numerical simulation-based correction of shape deformation of stainless-steel parts produced by laser powder bed fusion.

An efficient thermal-structural numerical solver for Additive Manufacturing has been developed based on a modified Lagrangian approach to solve the energy conservation equations in differential form. The heat transfer is modeled using the finite difference method applied to a deforming Lagrangian mesh. The structural solver has been enhanced with the proposed effective quasi-elastic differential approach for modeling the elastoplastic behavior of materials. The algorithm is relatively simple to implement yet is highly effective. The solver can predict shape deformations of metal parts printed using the laser powder bed fusion technique. The second key capability of the solver is the auto-compensation of distortions of 3D-printed parts by proposing a corrected geometry of a surface to be printed, in order to ensure minimal deviation of the actual printed part from the desired one, even under non-optimal operating conditions or for complex shapes. All the simulation results have been verified in real-life experiments for 3D parts of sizes ranging from 10 to 15 mm up to 40 mm.

Characterization of ultrafine particles emitted during laser-based additive manufacturing of metal parts.

Particulate matter (PM) emitted during laser additive manufacturing with stainless steel powder materials has been studied in detail. Three different additive manufacturing techniques were studied: selective laser melting, direct metal deposition and laser cladding. Gas flow and temperature fields accompanying the processes were numerically modeled for understanding particle growth and oxidation. Transmission and scanning electron microscopy were used for primary particle and PM characterization. The PM collected in the atmosphere during manufacturing consisted of complex aggregates/agglomerates with fractal-like geometries. The overwhelming number of particles formed in the three processes had equivalent projected area diameters within the 4-16 nm size range, with median sizes of 8.0, 9.4 and 11.2 nm. The primary particles were spherical in shape and consisted of oxides of the main steel alloying elements. Larger primary particles (> 30 nm) were not fully oxidized, but where characterized by a metallic core and an oxidic surface shell.