Successive Deposition of Metals in Solid Freeform Fabrication Processes, Part 2: Thermomechanical Models of Adjacent Droplets

Abstract

Residual stress-induced tolerance losses are a principal barrier for using Solid Freeform Fabrication (SFF) processes to create functional parts out of engineering materials. In Part 1 of this paper, problems of successively deposited layers and droplets deposited in a column are considered for SFF processes. Models of these problems are used to detail thermal and mechanical interactions between existing and newly deposited material as well as their effects on final residual stress distributions on sub-layer (droplet) and multi-layer scales. In the current study, sub-layer interactions are further considered using models of droplets deposited adjacent to one another. As in Part 1, models are applied to a particular SFF process; however, insights and conclusions are relevant to numerous similar SFF processes. Simulations of separated and connected droplets deposited onto a large substrate indicate very limited thermal interactions between adjacently deposited droplets. However, mechanical interactions between droplets can be significant, which is consistent with the directionality of warping observed in experiments. Results from deposition of droplets on a thin substrate demonstrate the importance of process-induced substrate preheating in reducing residual stresses.