Numerical and experimental analysis of heat distribution in the laser powder bed fusion of Ti-6Al-4V

Laser Powder Bed Fusion (LPBF) of metallic parts is a complex process involving simultaneous interplay between several physical mechanisms such as solidification, heat transfer (convection, conduction, radiation, etc.), and fluid flow. In the present work, a three-dimensional finite element model is developed for studying the thermal behavior during LPBF of Ti-6Al-4V alloy. Two phase transitions are considered in the model: solid-to-liquid and liquid-to-gas. It is demonstrated that metal evaporation has a notable effect on the thermal history evolution during fabrication and should not be overlooked in contrast with the majority of previous research efforts on modeling and simulation of additive manufacturing processes. The model is validated through experimental measurements of different features including the size and morphology of the Heat-Affected Zone (HAZ), melt pool size, and thermal history. Reasonable agreement with experimental measurements of the HAZ width and depth are obtained with corresponding errors of 3.2% and 10.8%. Qualitative agreement with experimental measurements of the multi-track thermal history is also obtained, with some discrepancies whose sources are discussed in detail. The current work presents one of the first efforts to validate the multi-track thermal history using dual-wavelength pyrometry, as opposed to single-track experiments. The effects of selected model parameters and evaporation on the melt pool/HAZ size, geometry and peak predicted temperature during processing, and their sensitivities to these parameters are also discussed. Sensitivity analysis reveals that thermal conductivity of the liquid phase, porosity level of the powder bed, and absorptivity have direct influence on the model predictions, with the influence of the thermal conductivity of the liquid phase being most significant.