Manufacturing Letters最新文献

{"title":"Microstructural and Crystallographic Evolution of Ti-Al-B-(Y2O3) Powders with Varying Milling Durations","authors":"Olorundaisi Emmanuel,&nbsp;Peter Apata Olubambi","doi":"10.1016/j.mfglet.2026.07.054","DOIUrl":"10.1016/j.mfglet.2026.07.054","url":null,"abstract":"<div><div>This study investigates the mechanochemical synthesis and microstructural evolution of Ti₆₀Al₄₀+B₃(Y₂O₃)₅ powders subjected to high-energy mechanical alloying for 12, 24, and 48 hours. CALPHAD-based thermodynamic simulations predicted multiphase stability regions and quantified the distribution of Ti, Al, B, and Y in equilibrium phases, including the activities of each constituent, establishing a theoretical baseline for comparison with experimentally induced metastable states. Mechanical alloying produced progressive grain refinement, with median grain sizes decreasing from 0.07 μm (12 h) to 0.04 μm (48 h), consistent with severe plastic deformation and defect accumulation. Crystallite size analysis indicated a significant reduction from 18.054 nm at 12 hours to 7.042 nm at 48 hours, reflecting enhanced lattice strain and grain refinement induced by prolonged milling. SEM and EDS analyses confirmed improved homogenisation, enhanced Ti–Al mixing, and the evolution from discrete elemental regions to a chemically uniform nanostructure. X-ray diffraction revealed a clear reaction pathway characteristic of a fully reactive MA system. At 12 h, only elemental α-Ti, fcc-Al, and residual Y₂O₃ were detected, reflecting limited reaction. After 24 h, the emergence of TiAl, Ti₃Al, and TiB₂ peaks signalled the onset of intermetallic and boride formation. By 48 h, the powders fully transformed into a nanocrystalline TiAl/Ti₃Al matrix reinforced by TiB₂, while Y₂O₃ became largely amorphous and incorporated into a disordered Y–Ti–O phase. The complete disappearance of Ti and Al reflections confirms full consumption of reactants, consistent with a fully reactive mechanochemical process. It was observed that extended milling produced a highly refined, chemically homogeneous nanocomposite consisting of TiAl/Ti₃Al intermetallics, TiB₂ ceramic reinforcements, and an amorphous Y–Ti–O dispersoid phase. These findings provide insight into phase evolution mechanisms and offer valuable guidance for optimizing MA parameters for Ti–Al–B–Y₂O₃ powder systems aimed at high-performance structural applications.</div><div>© 2026 The Authors. Published by ELSEVIER Ltd. This is an open access article under the CC BY-NC-ND license (<span><span>https://creativecommons.org/licenses/by-nc-nd/4.0</span><svg><path></path></svg></span>)</div><div>Peer-review under responsibility of the scientific committee of the NAMRI|SME.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 432-443"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149096299","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Electric Field-Assisted Atomic Force Microscope-Based Nanopatterning of PEDOT: PSS Nanodomes","authors":"Mohammad Alshoul,&nbsp;Xinchen Wang,&nbsp;Zimo Wang,&nbsp;Jia Deng","doi":"10.1016/j.mfglet.2026.07.045","DOIUrl":"10.1016/j.mfglet.2026.07.045","url":null,"abstract":"<div><div>Nanostructured conductive polymers exhibit unique properties over their bulk forms, but the high-resolution nanofabrication process remains challenging. We first experimentally demonstrate a fabrication technique for nanodome fabrication on PEDOT: PSS using an electric field-assisted atomic force microscopy (E-AFM)-based nanopatterning technique. Furthermore, quantitative models were built between control parameters (dwell time and voltage) and feature dimensions. We pair a compact profile model that represents each feature as a bell-shaped peak with a 3×3 full-factorial design. The geometry dimensions of nanofeatures are characterized by their heights and widths. A first-order bilinear model in standardized dwell time and voltage captures nearly all of the output variability: it explains ∼98% of the variance (<span><math><mrow><msup><mrow><mi>R</mi></mrow><mn>2</mn></msup><mo>=</mo><mn>0.976</mn></mrow></math></span>) with a root-mean-squared error (RMSE) around 1.63 nm. Voltage exhibits a dominant influence, while dwell time contributes a smaller but still positive effect. Widths are derived by the coefficients of Gaussian and Cauchy profiles using log-scale, yielding <span><math><mrow><msup><mrow><mi>R</mi></mrow><mn>2</mn></msup><mo>≈</mo><mn>0.95</mn><mspace></mspace><mi>a</mi><mi>n</mi><mi>d</mi><mspace></mspace><mn>0.94</mn></mrow></math></span> and RMSE ≈ 10.7 and 11.3 nm, respectively. Across the parameter window, the measured dimensions span heights from 8 to 37 nm and widths from 233 to 380 nm, with round footprints and low background roughness. The overlay figures, parity plots, and block-wise residuals show a voltage-dominated, time-refined regime, in which voltage sets the overall feature size, and the dwell time provides fine-tuning within the selected parameter ranges. This framework delivers shape metric predictions that support rapid recipe tuning, sensitivity assessment, and cross-study comparison. It also provides a compact descriptor set for benchmarking E-AFM-based nanopatterning, not only for PEDOT: PSS, but also potentially for other conductive polymers.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 351-360"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149096302","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The effect of texture location on ceramic inserts wear when turning Inconel 718 under low- and high-pressure lubrication","authors":"N. Pozzato,&nbsp;R. Bertolini,&nbsp;E. Ukar,&nbsp;H.Gonzalez Barrio,&nbsp;S. Bruschi","doi":"10.1016/j.mfglet.2026.07.062","DOIUrl":"10.1016/j.mfglet.2026.07.062","url":null,"abstract":"<div><div>The low machinability of nickel-based superalloys has been a major concern for researchers over the last few decades, prompting the development of various approaches to enhance it. Within this context, the present study integrates the key concepts of insert texturing and high-pressure lubrication to improve the tool life when turning Inconel 718 using recently introduced inserts named <em>Bidemics^TM</em>. These inserts are composed of a matrix of alumina, providing high hardness, where clusters of tungsten carbide (WC) are dispersed to increase toughness and thermal conductivity. A novel texture was designed and obtained on the inserts’ rake and flank faces by means of a nanosecond laser machine. The texture design includes tapered channels for fluid retention and a grid that facilitates its distribution within the cutting zone. Four categories of round <em>Bidemics^TM</em> inserts were tested: plain (NT), rake textured (RT), flank textured (FT), and a combination of the latter ones (CT). In addition, two lubrication pressures (15 bar and 70 bar) were used.</div><div>SEM and EDS analyses were conducted to assess the wear mechanisms as a function of the texture location. The chip morphology and quality of the machined surface in terms of surface finish and hardness were also investigated. Results show that flank texturing is the most effective strategy for mitigating flank wear, reducing the average flank wear depth (<em>VB_mean</em>) of the FT and CT inserts by around 30% compared with the NT case, regardless of the lubricant pressure. Whereas texturing on the rake face primarily facilitates lubricant penetration and distribution in the cutting zone. In addition, the application of high-pressure lubrication promoted chip fragmentation, while the use of textured inserts successfully reduced the average surface roughness under all investigated conditions.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 513-524"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149096306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coupled Effects of Lubrication on Tool/Chip Interfacial Friction and Primary Shear Deformation in Cutting of Ti-6Al4V","authors":"Victor Sodje,&nbsp;Julius Schoop","doi":"10.1016/j.mfglet.2026.07.064","DOIUrl":"10.1016/j.mfglet.2026.07.064","url":null,"abstract":"<div><div>The mechanics of machining Ti-6Al4V are governed by an intrinsic coupling between tool–chip interfacial friction and primary shear deformation. Conventional cooling and lubrication strategies such as flood cooling, Minimum Quantity Lubrication (MQL), and cryogenic-MQL effectively reduce average friction and improve tool life, yet their continuous delivery and cooling action dynamically alter interfacial conditions, masking the inherent link between frictional behavior and shear deformation.<!--> <!-->In this study, a pre-coated lubrication film (PCFL) was employed as a controlled boundary condition to isolate and examine this coupling during orthogonal cutting of Ti-6Al4V. Synchronized force measurements and high-speed Particle Image Velocimetry (PIV) were employed to characterize chip–tool contact and primary deformation-zone (PDZ) behavior under dry and lubricated conditions for uncut thicknesses (<em>h</em>) of 10, 50, and 100 µm. The cutting force (<em>Ft</em>) remained nearly constant for both conditions, while the feed force (<em>Ff</em>) decreased by about 28 % under lubrication, indicating reduced rake-face adhesion. The corresponding reduction in friction angle (β) reorients the equilibrium resultant force closer to the rake-face, steepening the shear plane and increasing the shear angle (ϕ) in accordance with Merchant’s minimum energy principle, which predicts that the shear plane reorients to minimize total energy under varying frictional conditions. PIV results further confirmed a shorter, more stable PDZ, demonstrating that interfacial friction directly governs shear-zone geometry and deformation stability in titanium machining.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 537-547"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149096308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"UNiCO-AM: Uncertainty-aware Neural Co-design for Additive Manufacturing via an Attention-based Spatio-Temporal Neural Operator and Bayesian Optimization","authors":"Vispi Nevile Karkaria,&nbsp;Ying-Kuan Tsai,&nbsp;Yi-Ping Chen,&nbsp;Dex Doksoo Lee,&nbsp;Jian Cao,&nbsp;Wei Chen","doi":"10.1016/j.mfglet.2026.07.030","DOIUrl":"10.1016/j.mfglet.2026.07.030","url":null,"abstract":"<div><div>Metal Additive Manufacturing (AM) is a complex process where the interaction between material and process parameters can significantly influence melt-pool dynamics, thermal gradients, and solidification behavior, ultimately determining the resulting microstructure, mechanical properties, and overall quality of the fabricated part. However, inherent challenges such as the high-dimensional process-material design space, strong nonlinearity in thermal-physical interactions, and the high computational cost of high-fidelity simulations make it difficult to systematically explore and optimize these interdependencies across diverse alloys and process conditions. To address this challenge, we propose <em>UNiCO-AM</em> (Uncertainty-aware Neural Co-design for Additive Manufacturing), a physics-informed optimization framework that integrates an attention-based spatio-temporal neural operator (ASNO) with Bayesian optimization (BO). In this framework, we develop a material–process-agnostic ASNO model that is capable of learning the coupled spatio-temporal thermodynamics of the additive manufacturing process, accurately predicting full-field temperature evolution across different alloys and laser parameters, and generalizing to unseen material–process combinations. Another key contribution of this work is the quantification of epistemic uncertainty in ASNO using a Linear Laplace-based Approximation (LLA) method. This approach estimates the model’s uncertainty around its learned parameters, providing the confidence information required for effective BO. Incorporating uncertainty quantification not only enables more reliable and data-efficient optimization but also enhances the generalization capability of ASNO across diverse materials and process conditions. Finally, we complete the <em>UNiCO-AM</em> framework by establishing a concurrent material-process BO loop for AM, incorporating a <em>q</em>-Expected Hypervolume Improvement (q-EHVI) strategy to efficiently explore the high-dimensional design space under physical and thermal constraints. The primary objective of the <em>UNiCO-AM</em> framework is to enhance the strength of the fabricated part by promoting finer microstructural grain sizes through joint optimization of process parameters and material properties that regulate cooling rates and solidification behavior during AM. This approach yields a Pareto front of material–process combinations that balance cooling efficiency and thermal stability, leading to improved mechanical performance in fabricated parts while also enabling the discovery of novel material-process property combinations.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 204-215"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149096529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Enhancing the Productivity of Manufacturing Systems using Lean Six Sigma – A Case Study in the Shaving Industry","authors":"Ahmad E. Elhabashy,&nbsp;Hadi Fors","doi":"10.1016/j.mfglet.2026.07.022","DOIUrl":"10.1016/j.mfglet.2026.07.022","url":null,"abstract":"<div><div>Enhancing and sustaining productivity of manufacturing systems could be achieved through efforts directed towards reducing production costs, improving operational efficiency, and minimizing production losses. Among the many available tools for reducing losses, Lean Six Sigma (LSS) has been successfully applied to many manufacturing and service industries. With the overarching goal of this research to improve the productivity of manufacturing systems, this work considers the impact of using the LSS methodology in identifying and reducing production losses that hinder the productivity of a manufacturing system within a shaving products company in Egypt. More specifically, this work applied the DMAIC (Define, Measure, Analyze, Improve, and Control) methodology to identify current issues with a specific manufacturing process within the company and assess the impact of a few hypothetical improvement scenarios. Using the well-known Overall Equipment Efficiency (OEE) metric, a comparison before and after scenarios implementation was conducted. Overall, the OEE metric improved by a range of 6.41% to 31.31% within the studied interval, depending on the scenario considered. Future work will include additional improvement scenarios and more in-depth analysis; yet, the presented work can be considered as an initial step to assist manufacturers with better decision-making and to enhance existing manufacturing systems.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 131-139"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149096602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluating design factors influencing sheet metal bending effort","authors":"Alp Bayar,&nbsp;Aung Nyein Soe,&nbsp;Johan W. Joubert,&nbsp;Joost R. Duflou","doi":"10.1016/j.mfglet.2026.07.023","DOIUrl":"10.1016/j.mfglet.2026.07.023","url":null,"abstract":"<div><div>Understanding how geometric design choices will reflect on manufacturing effort remains a critical challenge for sheet metal working companies. This study proposes and experimentally evaluates a set of geometric features to quantify the bending effort from the design stage. Designs with systematically varying geometric traits, including benchmark parts from prior studies, were manufactured by two different operators using the same sheet thickness and material type. Bending times were extracted using the machine’s programmable logic controller (PLC) logs and evaluated against the mean bending duration and a failure-integrated performance metric: the estimated mean production time for a successful full batch. Ordinary least squares (OLS) regression fit indicates that the proposed design features can explain 88% of the variance in mean production time. Proposed features: Box profiles with perpendicular bend corners, non-parallel bends, asymmetry, flange direction variability, and narrow gauging edges were shown to increase the bending effort. Comparative analysis between part pairs reveals how these features contribute to the effort, with statistical significance validated using one-way analysis of variance (ANOVA) and Welch’s t-tests. The results demonstrate the quantitative relationship between the proposed geometric design features and bending effort, providing a foundation for design for manufacturing research and future integration of human-centric computer-aided design and manufacturing (CAD-CAM) tools.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 140-146"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149096603","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Interfacial turbulence damping effect on the melt pool dimensions and surface topology during powder bed fusion additive manufacturing","authors":"Gaius Chukwuka Nzebuka,&nbsp;Chukwuzubelu Okenwa Ufodike,&nbsp;Lucky Ekene Bernard","doi":"10.1016/j.mfglet.2026.07.102","DOIUrl":"10.1016/j.mfglet.2026.07.102","url":null,"abstract":"<div><div>A physics-based melt pool turbulence model for a multiphase flow was developed to study the effect of turbulence in a powder-based fusion additive manufacturing process. Two-equation eddy viscosity model which include the Realizable <em>k-ε</em> and the Shear Stress Transport (SST)-<em>k-ω</em> were selected to quantify the turbulence level in the melt pool of powder bed fusion under no interfacial damping. The performance of the two turbulence models was assessed based on their ability to better predict the melt pool dimensions. Further, the interfacial turbulence damping was activated for the best-performing turbulence model to analyze its effect on the melt pool surface topology and dimensions. Assessment of the turbulence level using the turbulent viscosity ratio shows a high turbulence production in the melt pool, and it affects the melt pool dimensions. The analysis shows that the SST-<em>k-ω</em> model’s prediction of the melt pool performs better than the Realizable k-ε model. Subsequent simulations revealed that the interfacial turbulence damping affects the melt pool surface topology and melt pool dimensions. Without interfacial damping, the turbulent viscosity ratio is eleven times greater than its molecular values. An increase in the interfacial damping coefficient decreases the turbulence viscosity ratio, increases the backward flow along the interface, and decreases the melt depth and width. The study reveals new knowledge in the melt pool flow structure, which may be useful for better process control of the powder bed fusion additive manufacturing processes.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 876-884"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149096607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fabrication of SiC-Al composites using binder jetting 3D printing and infiltration: effects of printed sample density on infiltration","authors":"Jackson Sanders,&nbsp;Evgenia Dimitriou,&nbsp;Zhijian Pei,&nbsp;Edoardo Ghinatti,&nbsp;Fahim Khan,&nbsp;Stephen Kachur","doi":"10.1016/j.mfglet.2026.07.099","DOIUrl":"10.1016/j.mfglet.2026.07.099","url":null,"abstract":"<div><div>This study examines how powder bed compaction during binder jetting 3D printing of silicon carbide (SiC) samples influences SiC sample density and affects subsequent aluminum-magnesium (Al+Mg) infiltration of the printed SiC samples. SiC samples were printed with and without compaction, then cured, depowdered, sintered at 1600 °C, and infiltrated with Al+Mg to produce composite samples. Green samples (printed samples after curing and depowdering) were evaluated for density, sintered samples for density and porosity, and infiltrated samples for density, porosity, infiltration uniformity, penetration depth, and morphology. Results show that the density of green samples printed with powder bed compaction was 6.79% higher than that of green samples printed without compaction; however, this advantage was largely diminished after sintering, resulting in similar final density (≈2.53 g/cm³) and porosity (≈36%) for both groups of samples. However, infiltration behavior of these two groups of samples differed substantially: the samples printed with compaction exhibited greater infiltration area and deeper penetration than the samples printed without compaction. Quantitative image processing analysis revealed that the sample printed with compaction exhibited greater percentage of infiltration area as well as deeper infiltration penetration across measured edges compared with the sample printed without compaction.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 846-857"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149095909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Continuous Natural‑Fiber Reinforced FFF: Understanding Deposition Geometry and Interfacial Behavior","authors":"Yigit Turan,&nbsp;Jia Deng,&nbsp;Zimo Wang","doi":"10.1016/j.mfglet.2026.07.088","DOIUrl":"10.1016/j.mfglet.2026.07.088","url":null,"abstract":"<div><div>Natural fibers offer a sustainable route to lightweight composite materials, but their integration into fused filament fabrication (FFF) remains constrained by complex, unresolved interactions among bead geometry, melt flow, and the polymer-fiber interface. These coupled effects can introduce quality integrity issues that may consequently reduce the load-bearing performance of the resulting heterogeneous composites. This paper reports a mechanistic baseline for continuous natural-fiber FFF in the inverse nozzle-filament regime, where a full-diameter (1.75 mm) pre-embedded composite filament is extruded through a substantially smaller nozzle under a strict 1:1 feed discipline. With this configuration, formulated as geometric overfill deposition, the imposed dimensional constraint produces stable, near-filament bead geometries and repeatable overfilled-bead stacking, enabling continuous-fiber deposition without specialized printheads. Baseline mechanical tests show that overfilled PLA beads maintain the tensile performance of conventional FFF, demonstrating that the overfill geometry does not intrinsically diminish matrix strength. However, cross-sectional and fracture analyses reveal that low-fraction flax cores (∼2 %) experience only superficial impregnation and generate moisture-driven and interfacial voids that dominate failure via tow pull-out. These results identify interfacial quality (not overfill bead geometry) as the primary limitation to reinforcement in current pre-embedded natural fiber filaments, and they establish a reproducible, stock-hardware-compatible platform for future advances in drying, impregnation, and fiber-surface modification to enable high-performance continuous natural-fiber composites.</div></div>","PeriodicalId":38186,"journal":{"name":"Manufacturing Letters","volume":"49 ","pages":"Pages 742-752"},"PeriodicalIF":2.8,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149095911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}