Effect of porosity on the quality of 3D printed structures

Among all 3D printing technologies, material extrusion is used predominantly because of its ease of operation and compatibility with versatile polymers. However, the material extrusion process has some inherent disadvantages such as porosity inclusions which limit the potential application of the process in the fabrication of functional parts. The present work aims to investigate the influence of porosity on the geometric accuracy of a 3D printed specimen fabricated using material extrusion process. A numerical model, incorporating void porosity, was developed to simulate the layer-by-layer material deposition, using sequential element activation/deactivation. An experimental study is performed to estimate the porosity in a 3D printed part under specific conditions and validate the numerically estimated deformation in the specimen. The modified 3D inherent strain approach was applied to deduce the residual stresses and deformation in the 3D printed specimen. A parametric study was performed on the ASTM D638 Acrylonitrile Butadiene Styrene specimen to investigate the effect of production parameters like extrusion temperature, chamber temperature, and extrusion speed on the printed component. From the numerical model, it is concluded that porosity has a strong influence on the process. It is shown that the porous specimen was found to have lower residual stresses due to stress relaxation. It was found that the printing residual stresses reduce by similar to 77% on optimizing the chamber temperature. Further, an 80% reduction in part deformation was seen with the optimal extrusion temperature. It is also observed that regions with high residual stress concentrations correlate higher deformation and delamination.