Metal additive manufacturing of carbon steel with direct laser deposition: computer simulation

Metal 3D printing technology is commercially available, but the quality of the printed product is still a challenging issue that needs to be improved. More research is needed to address the essential technical details of metal 3D printing. Important technical details are the alloy microstructure, imperfections like pores, distortion, surface roughness, and residual stress, which affect the mechanical properties of the printed sample like fatigue performance. This research has computationally studied metal 3D printing for carbon steel to address the parameters that affect the quality of the final product printed by direct laser deposition. Multiscale multiphysics computational algorithms were coding in Microsoft Visual Basics 2015 to simulate the thermal stress, deformation, and austenite grain topology. Energy and force equilibrium equations were numerically solved to simulate the thermal and mechanical history versus print's adjustable parameters like scan speed, laser power, and rate of metal powders injection through the nozzle. The austenite grain size of steel is an important parameter that is directly related to the local thermal history. A stochastic computational code was developed to simulate grain morphology based on calculated thermal history. The simulation showed the dependence of von Mises stress and thermal history on the rate of metal powders injection, laser power, and scan speed. The simulation showed a rise in von Mises stress by increasing the scan speed and laser power. Print speed and laser power also change the local maximum temperature and the local alloy microstructure. The local austenite grain size increases by reducing scan speed in the heat-affected zone. The simulation showed that the microstructure of the printed part is not uniform, and different layers are distinctive.