Thermomechanical modeling of molten metal droplet solidification applied to layered manufacturing

Transient and steady-state distributions of temperature and stress along the centerline of a single, initially molten metal droplet deposited onto a comparatively large substrate are examined. After investigating droplet deposition onto a room temperature substrate, the effect of substrate preheating on residual thermal stresses is quantified. Also, deposition of a second droplet is modeled and the effect on residual stresses of localized preheating by the first deposited droplet is assessed. Temperature-dependent conductivity, specific heat and density are used in coupled thermal models of droplet and substrate domains. Mechanical models include temperature-dependent Young's modulus, linear expansion coefficient and creep. Two-dimensional (2D) axisymmetric thermal and mechanical results are compared to one-dimensional (1D) results which approximate conditions along the droplet/substrate centerline. It is found that the more computationally efficient 1D models aid in interpreting the 2D results and provide reliable estimates of maximum stress magnitudes. Methods and results from this investigation are relevant to processes in which molten superheated metal contacts solid metal, such as welding processes. The specific application of interest in this work is droplet-level thermal and mechanical modeling of the microcasting stage of shape deposition manufacturing, which is a layered manufacturing process for the automated manufacture of complex three-dimensional metal parts.