Three-Dimensional Prediction of Lack-of-Fusion Porosity Volume Fraction and Morphology for Powder Bed Fusion Additively Manufactured Ti–6Al–4V

Abstract

Powder bed fusion (PBF) is an additive manufacturing technique that has experienced widespread growth in recent years due to various process advantages. However, defects such as porosity and the effects that porosity have on the mechanical performance remain a concern for parts manufactured using PBF. This work develops a three-dimensional framework to simulate lack-of-fusion (LoF) porosity during powder bed fusion using the voxel-based lack-of-fusion model. The framework is calibrated and validated against previously reported LoF porosity measurements and maximum equivalent pore diameter. The framework is used to study the influence of laser power, velocity, hatch spacing, and layer thickness on porosity volume fraction and morphology. Power and velocity have a linear relationship to porosity, and power has a stronger effect than velocity on changing porosity. This stronger effect of power versus velocity contributes to high variability when relating energy density to porosity, and a modified energy density metric that weighs power heavier is shown to reduce variability. In contrast to power and velocity, hatch spacing and layer thickness have a more complicated relationship with porosity, especially at their extrema. The influence of hatch spacing and layer thickness on pore equivalent diameter and sphericity is also explored, and four distinct morphological regimes are characterized. A LoF criteria proposed in a previous work are also confirmed. Overall, the framework offers a methodology to simulate porosity quantity and morphology and interfaces with other process–structure–property prediction techniques to support the design and development of reduced-defect powder bed fusion parts.