Thermomechanical Modeling of Successive Material Deposition in Layered Manufacturing

Residual stress build-up due to successive deposition of superheated molten metal onto metal substrates is modeled for application to layered manufacturing methods. This work is specifically applied to microcasting, which is a deposition process used within shape deposition manufacturing. One-dimensional thennal and mechanical models are used to predict temperature and stress evolution related to two physical phenomena. First, the effect of thennal cycling by newly deposited material on stress states in previously deposited and cooled layers is investigated. Here, deposited molten metal solidifies and cools to room temperature before new molten metal is deposited. For this case, predicted stress distributions as a function of depth are relatively uncomplicated and can be related to residual stress-induced part tolerance loss. In the second case, the effect of localized preheating by previously deposited material is investigated. In this model, molten metal is successively deposited at a rate comparable to that used to deposit individual droplets in the microcasting process. Results indicate that although preheating by previously deposited material strongly affects transient stresses, final stress states are not substantially altered.