Assessment of Geometry-Dependent Dimensional and Surface Variability in Metal FFF Additive Manufacturing

Material Extrusion (MEX)-based Additive Manufacturing (AM), particularly metal Fused Filament Fabrication (FFF), has gained attention for fabricating metal components due to its operational simplicity, cost-effectiveness, design flexibility, and reduced material waste. Compared with laser powder bed fusion, metal FFF offers lower thermally induced residual stress and avoids direct powder handling. However, dimensional accuracy and surface quality remain affected by process variability, shrinkage during sintering, and geometry-dependent material redistribution. Quantitative relationships among geometric features, dimensional deviation, and surface morphology are still limited. This study investigates geometry-dependent dimensional and surface variability in metal FFF parts using two stress-concentrator geometries: a plate with a circular hole and a specimen with a filleted transition. Geometric features, including hole diameter, fillet radius, and local curvature, were evaluated in relation to dimensional variability and surface roughness. The analysis used RMS-based dimensional error, PCA-based roughness indexing, regression, and clustering. The results showed that hole specimens had lower dimensional behavior, with ΔRMS values ranging from approximately 0.790% to 1.606%, whereas fillet specimens exhibited higher variability, with ΔRMS values ranging from 1.140% to 4.086%. Sensitivity analysis showed that the higher variability of the fillet geometry was primarily associated with the local curved transition rather than the specimen’s global dimensions. Regression indicated that surface roughness alone did not explain dimensional variability, while tensile strength provided an additional performance descriptor. Clustering further showed more compact response groupings for the hole specimens and more dispersed groupings for the fillet specimens, indicating the greater geometry sensitivity of the filleted transition. By combining the parameters studied, a framework was developed to provide a quantitative basis for assessing geometry-dependent variability and to support improved design guidelines for metal FFF parts with filleted transitions and stress-concentrating features.