Influence of Geometry and Size on Precision and Accuracy in Fused Deposition Modeling (FDM) Additive Manufacturing

Abstract

This study presents a systematic evaluation of the dimensional accuracy and process capability of fused deposition modeling (FDM) additive manufacturing, with emphasis on the influence of process-induced thermal and kinematic effects on dimensional performance. Two geometries made of polylactic acid (PLA) were considered: a staircase specimen to assess process capability and directional effects, and a geometric benchmark test artifact (GBTA) to evaluate dimensional reliability across representative features. Measurements were performed using a digital caliper for the staircase model and a coordinate measuring machine (CMM) for the GBTA. Under manufacturer-recommended, unoptimized printing conditions, staircase analysis showed that the investigated FDM system achieved process performance indices (P_m and P_mk) ≥ 1.33 at a 95% confidence level. Dimensional stability varied across the build chamber due to spatially nonuniform cooling conditions, with statistically significant position-dependent deviations observed particularly along the build direction. Larger features exhibited higher relative precision. Achievable ISO 286-1 International Tolerance grades ranged from IT9 to IT14. GBTA results confirmed systematic undersizing of cylindrical and curved features. Absolute dimensional deviations remained approximately constant across nominal sizes, whereas percentage errors increased for smaller features due to scale effects. Despite these variations, the geometric form was preserved, demonstrating high repeatability. The proposed capability-based evaluation framework provides a structured approach to quantifying dimensional reliability in polymer-based material extrusion processes for functional components.