3.1.1. Impact of Nozzle Hole Processing Quality (D = 0.4mm, capillary tip) on F-fiber Structure
Hypothesis
1. Enhanced processing accuracy of the nozzle correlates positively with the uniformity of f-fibers EW.
Results:
1. Under standardized printing conditions (S < 30mm/s, LW100 (f100), infill 80% (i80), and
T > 185C), no significant differences were observed in filament characteristics produced by various nozzles (Fig. 6);
3.1.2. Material Selection for Nozzle Manufacturing: Thermal Conductivity (@TC) and Its Effect on Minimum Printing Temperature
Hypothesis
1. Elevated thermal conductivity enhances melt homogeneity and results in more uniform f-fiber EW;
Results:
1. At lower printing speeds (< 15mm/s), thermal conductivity does not significantly affect f-fiber structure. However, as speeds increase beyond S > 20mm/s, the influence of thermal conductivity on extrudate becomes apparent. This relationship is further modulated by nozzle mass; materials that are both thermally conductive and heavier provide superior heating support. At LW100 (LW = Dn), a more uniform f-fiber was achieved in terms of EW compared to less thermally conductive alternatives. Conversely, decreasing LW and particularly increasing S > 30mm/s resulted in greater variability in f-fiber structure concerning EW when juxtaposed with nozzles exhibiting lower thermal conductivity (Fig. 7, Fig. 8). This phenomenon can be elucidated by recognizing that as extrusion flow diminishes and S increases, temperature reduction is less pronounced in a nozzle that is both thermally conductive and substantial in mass; thus, the viscosity of extrudate remains comparatively lower than that found in materials with reduced thermal conductivity where it tends to rise. These findings underscore the impact of thermal conductivity on f-fiber structure, especially evident at increased S;
3.1.3. Effects of Insert Material within Nozzles on Minimum Printing Temperature, Plastic Oozing During Printing, and Overall Print Quality;
Types of Inserts:
1.3.1 Hardened Steel (HS) (Hardness = 9 GPa)
1.3.2 Diamond (PCD) (Hardness = 50 GPa)
Hypothesis
1. Utilizing HS to achieve a consistent f-fiber EW structure necessitates elevated temperatures compared to brass or more thermally conductive nozzles; furthermore, employing HS may result in inferior f-fiber structures under reduced LW;
2. The use of HS and PCD inserts will prevent nozzle degradation irrespective of filament type utilized;
3. The use of PCD insert may induce plastic oozing during printing or lead to uneven prints due to its lower friction coefficient;
4. Application of PCD insert will contribute to lowering temperature and enhancing print homogeneity at reduced LW relative to other nozzle materials;
Results:
1. At S < 20mm/s and T = 185C, no discernible difference was noted between copper nozzles equipped with HS inserts versus those fitted with more thermally conductive PCD inserts; both configurations yielded favorable outcomes regarding f-fiber EW structural consistency surpassing that observed with brass nozzles in Fig.
9; additionally, upon reducing LW, HS nozzles (or copper integrated with HS insert) demonstrated a more homogeneous filament structure compared to brass counterparts or other thermally conductive nozzles devoid of inserts—suggesting that HS nozzle tips effectively reduce melt temperature during extrusion more than their brass/copper counterparts thereby diminishing melt fluidity;
2. Tests involving the printing of 50 meters TPU + CF across three nozzle types (brass, HS, brass + PCD) revealed no deterioration in either HS or brass + PCD nozzles while minor abrasions were recorded on the inner surface along with slight enlargement of capillary holes within brass—potentially attributable to significant carbon fiber content relative to TPU consistent with prior research [11];
3. The phenomenon known as plastic oozing (stringing) [12] occurs when material approaches its melting point causing spontaneous flow from the nozzle under gravitational influence; variations among nozzle types affect this process distinctly based on three primary characteristics: melt temperature (which also relies on material thermal conductivity), internal wall slip coefficient within the capillary nozzle, and feed angle; although comprehensive measurements were not conducted across all dependencies our observations indicated that the principal characteristic influencing fluidity is indeed material capability towards such ooze alongside the temperature threshold at which this transpires; disparities among each nozzle are closely linked to this temperature which is heavily contingent upon their respective thermal conductivities; for static nozzle (not printing) these factors exert minimal influence aside from mass inducing internal pressure prompting oozing; shape considerations are also relevant—for instance PCD DiamondBack possesses specific manufacturing features (Fig. 10) designed to retain melt internally thereby inhibiting free flow during static states and oozing less during printing or travel move (with filament retract);
4. After conducting experiments by lowering T < 185(PLA) while incrementally increasing S from 10 to 40mm/s it was determined that PCD nozzles exhibited significantly enhanced performance regarding extrusion while maintaining high levels of extrudate homogeneity when contrasted against brass variants (Fig. 11). Nonetheless, reducing LW < 60% once more led toward diminished f-fiber uniformity corroborating earlier findings indicating an inverse correlation between increased thermal conductivity and viscosity.
3.1.4. Coating Material (Plating) of the Nozzle (Tendency for Material to Adhere to the Nozzle);
Hypothesis
1. The coating material is anticipated to have a negligible effect on printing and the adhesion of the extrudate to the nozzle, exhibiting no significant differences compared to uncoated nozzles constructed from materials such as brass, metal, or copper alloys;
2. A nozzle featuring a PCD insert or HS + DLC [9] coating may contribute to a reduction in adhesion of the extrudate;
Results:
1. Our experiments demonstrated that the nozzle coating exerts a considerable influence on extrudate adhesion (which is also contingent upon the filament material utilized), thereby enhancing printing efficiency during travel moves facilitated by retraction; among various coatings tested, PTFE [
10] exhibited superior performance overall; however, it was susceptible to frequent damage during operation, resulting in a rapid decline in its sliding properties. Furthermore, PTFE demonstrates limitations at temperatures exceeding 260°C; consequently, when processing high-temperature materials (above 280°C), this coating undergoes deterioration and loses its effectiveness.
2. Our investigations encompassed several types of coatings presented in Fig. 12, including nickel, DLC treatment, solid diamond tip (PCD), among others. Each type displayed a various degree of sliding capability; nevertheless, our findings indicated that DLC treatment delivered optimal long-term performance due to its ease of cleaning and minimal extrudate adhesion across diverse printing modes or errors typically associated with extrudate adherence to nozzles. It is essential to acknowledge that polishing quality significantly influences performance; nozzles exhibiting superior polishing characteristics demonstrate sliding behaviors akin to those observed with PTFE and DLC coatings while being less prone to issues related to adhesion.
3.1.5. Nozzle Diameter and Clogging (Printing Capability with Composite Materials like TPU + CF)
Hypothesis
1. Clogging is anticipated when Dn ≤ 0.4mm;
2. Uniformity of f-fiber EW is expected to be enhanced when utilizing HS nozzles, PCD, HS + DLC in comparison with nozzles possessing hardness Hardness < 5 GPa, i.e. brass or copper;
Results:
1. Our tests indicated an absence of clogging for both PLA and PET materials as well as TPU + CF at Dn = 0.4mm. However, upon reducing Dn ≤ 0.35mm, we began encountering partial clogging incidents where carbon fibers obstructed the nozzle during printing operations. This complication intensified with reduced LW but alleviated when lowering temperature while increasing pressure within the nozzle alongside augmented LW; for a Dn = 0.25mm nozzle using TPU + CF, clogging was observed across all tested nozzle types.
2. In trials involving varying infill values, we did not detect significant discrepancies among different nozzles concerning f-fiber structure as shown in Fig. 13. It is noteworthy that TPU + CF filament contains a substantial proportion of carbon fiber (up to 40%), complicating our interpretative analysis since variations in LW do not yield considerable changes in plastic content within the composite extrudate.
3.1.6. The Effect of Tip Area S2 Relative to Capillary Diameter D2 on Print Quality and Specifically on Bonding Degree Between Two Adjacent Filaments (Fig. 1, Fig. 21);
Hypothesis
If tip area S2 increases while maintaining D2 constant then:
1. Such a nozzle will enhance f-fiber EW by facilitating the dispersion of melted material while substantially impacting thermal bonding along outline lines of the model;
2. Fusion between adjacent f-fibers (outline or infill lines) will become more probable;
Results:
1. f-fiber EW increases as NBD decreases for each type of nozzle; however, only under conditions where NBD / Dn < 0.25 does an increase in S2 begin influencing EW growth since as the nozzle approaches closer proximity to print bed surface area S2 becomes actively involved in smoothing out melted material thereby potentially enhancing thermal bonding between outline lines or closely situated infill lines when there exists less empty space between them than their LW (Fig. 14).
2. Consistent with point one above, fusion occurs when NBD / Dn decreases; thus, smaller values yield greater influence from S2 on fusion percentage (refer to Fig. 15).
2. The Influence of NBD Variations on F-fiber Structure (NBD/LW Dependency)
Hypothesis (Fig. 16):
1. When NBD / Dn > 1, the printing process may result in detachment of f-fiber from the table;
2. Conversely, when NBD / Dn < 0.5, print quality is likely to deteriorate, potentially leading to embedding of extrudate into the table and subsequent f-fiber breakage;
Results:
1,2. In both scenarios, the hypothesis was validated; however, in scenario two, there exists an additional dependence on printer accuracy and table flatness. Specifically, with a flatness error exceeding 0.1mm and setting LH (NBD) < 0.15mm, errors may arise that could lead to f-fiber breakage. Moreover, modifications to NBD induce alterations in f-fiber shape morphology due to variations in EW: as NBD increases, EW diminishes while EH escalates, culminating in a more voluminous print pattern (Fig. 17)
T10 = variable NBD (from − 0.02 to + 0.02).
3. The Effect of LW (f) Settings on Print Structure While Maintaining a Constant Physical Value of Dn.
Hypothesis
1. Reducing LW (f) from 100–50% of Dn will yield a markedly uneven f-fiber EW structure;
2. Should LW fall below 50% of Dn, then printing of f-fiber may become faulty or unfeasible;
Results:
1. This theoretical proposition holds merit; however, practical outcomes are contingent upon NBD and S dynamics. Furthermore, with NBD/Dn > 0.7, an intriguing "magnetization" effect emerges—where two f-fibers exhibit attraction if inadequately secured to the Fig. 18;
2. With a constant NBD value (as z-offset from LH), unevenness manifests as LW decreases resulting in "pulsating" shape of f-fiber structure; this phenomenon is likely attributable to the stepwise nature of filament feeding coupled with insufficient adhesion of the extrudate to the print bed during printing; thus, as LW (f) diminishes and grip with the print bed lessens the effect becomes more pronounced and vice versa (Fig. 19);
3. This assertion remains valid; achieving high-quality prints with LW < 50% of Dn proves exceedingly challenging necessitating precise adjustments for both NBD and print bed flatness alongside appropriately aligned guide rails;
4. The Impact of Temperature on F-fiber Structure;
Hypothesis
1. An increase in temperature (185–210°C for PLA) will modify the f-fiber EW; at lower temperature ranges (180–185°C) combined with LW (50 − 40% of Dn)—will precipitate f-fiber breaks;
Results:
1. Observations shown in Fig. 20 for Dn = 0.4mm, indicate that the f-fiber exhibits slight thinning at its narrowest point as temperature rises; employing a Dn = 0.25mm reveals significant behavioral changes in extrudate flow, shown in Fig. 18, where elevated temperatures induce stretching and breakage due to enhanced fluidity; at reduced temperatures T = 180–185°C, uniform EW is maintained which further corroborates how material viscosity influences print quality.