Shrink line formation in laser powder bed fusion process: an experimental and numerical study

Shrink line formation is a phenomenon commonly observed, particularly at sharp cross-sectional area changes in metal parts produced using the powder bed fusion laser beam (PBF-LB/M) additive manufacturing process. These lines negatively impact the part’s appearance, dimensional accuracy, and fatigue life. This study focused on shrink line formation in specimens featuring hole patterns in both horizontal and vertical directions, manufactured using PBF-LB/M with Inconel 718 powder material. Experimental results revealed that shrink lines formed at the upper layer of the holes, where cross-sectional area changes reached up to 15% between successive layers. Thermomechanical finite element method (FEM) simulations were also conducted, demonstrating that shrink lines can be predicted through process simulation. This prediction was enabled by using an appropriate voxel element size, determined through a mesh convergence study. Voxel elements were employed as they are a powerful tool for discretizing and analyzing three-dimensional volumes, offering a balance between computational efficiency and the ability to model complex internal behaviors. The shrink line height from the bottom of the parts and their depth were predicted with error margins of 0.4% and 14%, respectively. Finally, microhardness and microstructure evaluations were performed, revealing that microhardness at shrink line locations was lower than in the surrounding areas.