Droplet-level thermo-mechanical analysis of the microcasting process

Abstract: "Thermal and mechanical modeling of the microcasting stage of Shape Deposition Manufacturing is presented. Thermal modeling is needed because during the solidification and subsequent cooling of deposited molten metal, thermal aspects determine important effects such as substrate remelting, microstructure development, and build-up of residual stress. Also, temperature control is needed to protect existing machined features. Mechanical modeling is needed because thermally-induced residual stresses can lead to detrimental effects such as part warping, debonding between deposited layers, and reduced apparent strength or life. In this study, thermo-mechanical models of carbon steel deposited onto an existing carbon steel substrate are described. Current thermal modeling is centered on reliably predicting localized remelting of previously deposited substrate material by newly deposited molten droplets. Temperatures from a one-dimensional model are compared to those obtained at the axis of an axisymmetric model. In this region, the axisymmetric model predicts temperatures that agree with those from the simpler one-dimensional model for times less than that needed for complete droplet solidification. Current mechanics modeling is centered on the issue of residual stress buid-up. The effects of yielding and creep on the build-up of residual stresses are shown. Results show that thermal cycling from newly applied droplets drastically changes the stress state in the top of the substrate. Originally unstressed regions go through a cycle of yield in compression followed by yield in tension. Residual stresses close to the yield stress are predicted during part manufacture. It is likely that these stresses will be substantially relaxed, however, after a part is completed and then separated from the pallet upon which it is built."