Modeling and Its Applications to Metal Additive Manufacturing Processes

This paper addresses current developments in predictive tools for metal additive manufacturing processes.  The experimental methods used to provide fundamental properties, and establish validation data are presented.  Metal additive processes encompass a class of processes that use a focused heat source to create a melt pool on a substrate. Examples include Electron Beam Fabrication and Direct Metal Deposition. This type of additive process enables fabrication of fully dense metal parts directly from CAD drawings.  Past modeling efforts in the field of solidification-based manufacturing processes were focused towards determining the influence of operating conditions on the temperature distribution within the heated work piece, without including the prediction of microstructures generated for different processing conditions.  The formation of these microstructural features is caused by the solidification of the molten material during the cooling cycle.  On the macroscopic level, a flat, smooth clad is desirable since this will reduce the amount of post-processing and facilitate the achievement of designed dimensions.  Assessing the impact of specific processing parameters and predicting optimized conditions with numerical modeling, is an effective method for achieving the desired material geometry and mechanical properties in the final product.

The current work models metal additive processes using a multi-scale and multi-physics approach.  The macroscopic phenomena addressed include; heat transfer, phase change with mushy zone, incompressible free-surface flow, solute redistribution, surface tension, and residual stresses. Microscopic phenomena addressed include; heterogeneous nucleation, dendritic grain growth, eutectic and peritectic grain growth, epitaxial growth of columnar grains, columnar-to-equiaxed transition, and grain transport in melt.