Relationships among manufacturing parameters, apparent density, ultimate tensile strength, and post-machining surface roughness of FFF 316L stainless steel parts

This study investigated the relationships among manufacturing parameters, apparent density, ultimate tensile strength (UTS), and post-machining surface roughness of 316L stainless steel parts fabricated by fused filament fabrication (FFF). Specimens were produced using two layer thicknesses, three raster angles, and two build orientations. Following thermal debinding and sintering, apparent density and UTS were measured. The fractured specimens were subsequently micro milled at three workpiece orientations (AngleCut = 0°, 30°, and 45°), and surface roughness was evaluated in three profilometer traverse directions. The experimental data were analyzed using descriptive statistics, Pearson correlation analysis, Type III analysis of variance (ANOVA), multiple linear regression, and regression diagnostics. Pearson correlation analysis revealed negligible to weak associations between apparent density or UTS and surface roughness. After accounting for the manufacturing parameters, regression analysis demonstrated that neither apparent density nor UTS exhibited statistically significant independent associations with post-machining surface roughness. In contrast, workpiece orientation (AngleCut) was identified as the dominant manufacturing factor affecting surface finish, whereas layer thickness exhibited only a marginal influence. Regression diagnostic analyses confirmed that the fitted models satisfied the assumptions of linear regression. Overall, the results indicate that, within the investigated conditions, workpiece orientation during micro milling exhibited the strongest statistical association with post-machining surface quality, whereas apparent density and UTS did not exhibit statistically significant independent associations. These findings provide practical guidance for optimizing hybrid additive–subtractive manufacturing processes to improve surface finish while maintaining desirable mechanical performance.