Multiscale and re-entrant surface analysis of multi jet fusion surfaces and the effect of postprocessing via sandblasting

Abstract

The growing use of Multi Jet Fusion (MJF) 3D printing in industry brings challenges related to surface quality and post-processing effects. This study presents a comprehensive analysis of surface geometry changes in MJF-printed parts before and after sandblasting. A suitable abrasive material was selected and tested, followed by chemical composition analysis to confirm the absence of abrasive residues on the surfaces. Glass beads with a radius of 37.5 to 70 μm were used for sandblasting. Micro-computed tomography (µCT) was used as the only technique capable of capturing complex surface topography, including re-entrant features, both pre- and post-processing. Surface characterization was performed following ISO 25,178 roughness parameters and area-scale analysis for a total of 30 surfaces. A proprietary algorithm was also implemented to quantify re-entrant features. Results showed significant changes in surface texture due to sandblasting, including reduced surface roughness and enhanced uniformity. For instance, Sa decreased from 22.3 μm to 14.6 μm, and Sp dropped by over 30%. Multiscale analysis revealed a 50% reduction in surface fractal complexity (Asfc) and a significant decrease in fine-scale geometric variability. An algorithm for detecting reentrant features was developed, in which original indicators for their quantitative occurrence were introduced: r₁ and r₂. On average r₂ values dropped from 60% to 13%, and r₁ from 260% to 135%. ANOVA confirmed statistically significant differences (p < 0.001) between pre- and post-processing states (MSR coefficients for Srel and Asfc parameters were used). Additionally, a statistical analysis was performed, which showed significant and large impact of post-processing on the geometric character of the surface. The study demonstrates that µCT is uniquely capable of isolating unsintered powder and characterizing complex surface features. Sandblasting significantly alters surface geometry and must be accounted for during design, especially in applications requiring precise topographical control.