Publication

Abstract : Since its development in the 1980's, additive manufacturing has progressed from manufacturing polymer prototypes to actual industrial products made from metals, polymers, composites, etc. The focus of the present work is to understand the thermal behavior during Laser Additive Manufacturing (LAM) of Titanium alloy Ti-6Al-4V using thermal finite element models. Transient thermal finite element analysis is carried out to study the effect of distribution of laser power on melt pool and microstructure in laser-deposited Ti-6Al-4V. Three different types of laser power distributions are considered: Moving point heat source, Heat source with uniform distribution of power and Heat source with Gaussian distribution of power. Results indicate significant variation of melt pool depth for different power distributions. Further, cooling rates and thermal gradients extracted from numerical models are interpreted in the context of a solidification map for Ti-6Al-4V material system to understand the effect of power distribution on grain morphology. Solidification map results indicate that the distribution of laser power does not have a significant effect on grain morphology. Next, numerical models using the element birth and death technique are used to simulate the multi-layer deposition of thin-wall geometries in Laser Additive Manufacturing Processes. In the multi-layer model, deposition of 15 layers was simulated. The temperature distribution in each layer is studied to understand the thermal cycling that each layer is subjected to in LAM processes. The temperature history of the multi-layer model showed that for the first few layers the temperatures of successive layers was much higher than the previous layers, indicating the effect of the substrate to act as a heat sink and conduct the heat away in the lower layers. This also results in the increase of melt pool dimensions with the increase in layer number for the first few layers. The melt pool dimensions stabilize as the number of layers increase indicating the diminishing effect of the substrate.