Residual stresses in laser-deposited metal parts

Several laser-based techniques to fabricate parts by depositing metals, ceramic powders, or a combination thereof have been developed in recent years. These fabrication techniques are incomplete and not fully useful to an operator without any predictive capability to calculate the geometries of the fabricated parts or equations to calculate their expected yield and ultimate strengths. Data concerning the energy transfer from the processing laser beam to the material powder, such as the metal vapor-plasma plume temperature and plume absorption coefficient, the efficiency of laser energy transfer and mathematical analysis for the thermal and dimensional process characteristics are unavailable. Also, the characterization of the mechanical properties of such laser-fabricated parts has just begun. A one-dimensional model to calculate the thermal and dimensional process characteristics is developed. The model accounts for the transmission of the laser beam through the plume, energy transfer in the molten phase, and the Stefan conditions at the solid-liquid and liquid-vapor interfaces. The yield and ultimate strengths of laser-fabricated stainless steel (SS 304) parts have been measured. A mathematical model is developed accounting for directionally preferred solidification to calculate the residual stresses generated in the part during solidification. (C) 2001 Laser Institute of America.