Ramazan Ötüken

Understanding the finishing behavior of hybrid structures produced by additive manufacturing based on FDM is critically important in systems where phases with different thermal and mechanical properties coexist. In this study, the drilling performance of hybrid structures with a PLA/17-4 PH/PLA layer arrangement was comprehensively investigated in terms of thrust force, moment, surface roughness, temperature variation, vibration behavior, and surface integrity. For this purpose, a total of 16 drilling tests were performed on 56 × 56 × 15 mm hybrid specimens with 100% infill density, in a full factorial configuration, at cutting speeds (V) of 80–170 m/min and feed rates (f) of 0.04–0.16 mm/rev. The middle layer was used in the as-printed green state as a 17-4 PH metal-filled filament containing metal particles and binder, without any debinding or sintering step. The results showed that increasing feed rate increased thrust force, moment, and surface roughness in all layers, whereas increasing cutting speed decreased these values and promoted a more stable drilling regime. The middle 17-4 PH layer exhibited lower surface roughness than the outer PLA layers, while thermal measurements indicated limited variation at the hole entrance and higher temperature accumulation at the hole exit. The most favorable drilling condition within the studied hybrid configuration was obtained at 170 m/min and 0.04 mm/rev, whereas the least favorable condition was obtained at 80 m/min and 0.16 mm/rev. Overall, the combination of high cutting speed and low feed rate provided the most suitable drilling window for the studied hybrid structure. The findings also indicated that surface quality was more strongly associated with cutting load and high-frequency vibration components than with vibration level alone.

Fused deposition modeling/fused filament fabrication (FDM/FFF) enables architectural tailoring of mechanical response through layer configuration and multi-material manufacturing strategies. However, the combined effects of layer arrangement, infill ratio, and packing geometry in polymer–metal hybrid structures and interfacial load transfer mechanisms are still not sufficiently elucidated. In this study, the tensile behavior of single- and multi-material structures produced using PLA and 17-4 PH stainless steel filaments was systematically investigated. A total of 24 experimental parameter sets were created with four-layer configurations (PLA, 17-4 PH, PLA/17-4 PH/PLA, and 17-4 PH/PLA/17-4 PH), three infill ratios (20%, 60%, and 100%), and two packing patterns (linear and hexagonal); the samples were tested according to the ASTM D638 standard. Mechanical data were modeled using Response Surface Methodology (RSM) and ANOVA, and the developed regression models showed high accuracy (R² > 0.95). The findings showed that tensile and yield strength are primarily controlled by the layer arrangement, while infill ratio and infill pattern have a secondary effect. The highest strength was measured in 100% infill linear PLA samples (≈10.35 MPa), and the lowest value was measured in 17-4 PH “green part” samples without sintering (≈0.92 MPa). Hybrid structures exhibited intermediate performance in the range of 2.9–4.9 MPa. ANOVA results showed that the majority of the mechanical variance was explained by the layer arrangement (70–85% contribution), while infill ratio and infill pattern had a secondary effect. Fracture surface analyses showed that high performance was associated with homogeneous filament fusion and low porosity; Studies have confirmed that poor performance is associated with delamination and interfacial separation.