On the Z-dimensional accuracy of L-powder bed fusion

Abstract

Laser Powder Bed Fusion (L-PBF) is one of the commonly utilized metal Additive Manufacturing (AM) modalities in highly demanding industries such as biomedical and aerospace. Among other limitations, the dimensional accuracy of the L-PBF parts hinders the adoption of this technology for a wider application. The dimensional accuracy in L-PBF depends on several factors such as beam compensation, process parameters, .stl conversion errors and shrinkage factors. The shrinkage factors are very important and needed to compensate for down-scaling of nominal dimensions. Due to the inherent nature of the process, anisotropic shrinkage occurs due to the thermal recession and the difference of the densities from the powder material and solidified layer. Although, it is generally taken into consideration for XY-plane dimensional accuracy, Z-shrinkage factors are omitted since the layer deposition is assumed to take care of the shrinkage for every layer in addition to deep melt pools to enable layer-to-layer fusion. However, in this study, it is observed that especially for long builds from AlSi10Mg powder material, dimensional errors up to a half of a millimeter may occur along Z-direction depending on the total Z-height. Therefore, a suitable Z-shrinkage factor is calculated based on the obtained experimental results and applied to all builds leading to a much more accurate results along the build direction. Moreover, the suitability of the shrinkage factors along X and Y axes is tested and confirmed.