Geometric deviation and compensation for thin-walled shell lattice structures fabricated by high precision laser powder bed fusion

Abstract

With the continuous improvement in the precision of the laser powder bed fusion (LPBF) process, printing parts with highly complex geometries and fine details has been realized. Given the large design freedom provided by LPBF, various shell lattice structures have been designed and fabricated successfully. However, few works focus on predicting and minimizing the discrepancy between as-designed and as-printed structures, which is crucial for the geometric fidelity and resulting structural performance. This is partially due to the complexity of structures with thin-walled features and continuously changing overhang angles. This paper proposed a new method and workflow to predict the printing deviation and conduct the compensation for the thin-walled shell lattice structures fabricated by the high-precision LPBF (hp-LPBF). Numerical simulation, which was used to capture dynamic interaction behavior between the rake, powder particles, and samples, was performed using the discrete element method (DEM) to identify the key factors affecting the deviation prediction. Subsequently, a semi-analytical model was proposed to predict the as-printed thicknesses, in which the molten depth-induced staircase effect, compression-induced thickening effect, and scrape-induced thinning effect were considered. Both inclination angles and wall thickness were observed to have significant influences on the roughness and dimensional accuracy, of which three types of deviation were determined: (1) non-compensable deviation; (2) large but compensable deviation; (3) negligible deviation under 5 %. Experimental results show that, by pre-compensation, the geometric deviation of thin walls with thicknesses of 135 µm and 185 µm was controlled to less than 10 µm. The effectiveness and generality of this method for the thin-walled shell structures were further demonstrated by a case study of Schwarz Primitive triply periodic minimal surface lattice structure, which is characterized by micro-CT using the proposed workflow to predict and modify the lattice thickness and generate the compensated geometry for printing.