Printing Performance Research Articles

Properties and microstructure of a low-carbon clinker-free cementitious binder and its extrusion-based printing performance

The extensive use of cement binders in the construction industry limits the progress of carbon emission reduction. A low-carbon clinker-free cementitious binder (CFCB) was developed by using wet grinding to activate granulated blast furnace slag (GGBS), combining fly ash (FA) spheres as rheology-modified material and calcium carbide slag (CS) together with sodium metasilicate (NS) powder as the compound activator. The effects of FA content and CS/NS ratio on the hydration, performances, and microstructure were systematically investigated. The printability and mechanical anisotropy of extrusion-based printed CFCB were also analyzed. The results show that lower fly ash content and CS/NS ratio positively influenced the yield stress and improved rheology and thixotropy within a certain range. The compressive strength of the CFCB mortar reaches a maximum of 46.6 MPa at 28 days. At the same time, the decrease in the CS/NS ratio is conducive to the development of the hydration process, generating a higher amount of hydration and forming a denser microstructure. The FA20-CS18 group shows suitable extrudability, buildability, and shape retention ability with a height loss of only 0.8 %. The existence of interlayer property differences causes the extrusion-based printed mortar to exhibit anisotropic mechanical properties, with the highest flexural and compressive strength in the Z-direction. The anisotropy coefficient was below 0.25 before 7 days.

Geometric Complexity Control in Topology Optimization of 3D-Printed Fiber Composites for Performance Enhancement.

This paper investigates the impact of varying the part geometric complexity and 3D printing process setup on the resulting structural load bearing capacity of fiber composites. Three levels of geometric complexity are developed through 2.5D topology optimization, 3D topology optimization, and 3D topology optimization with directional material removal. The 3D topology optimization is performed with the SIMP method and accelerated by high-performance computing. The directional material removal is realized by incorporating the advection-diffusion partial differential equation-based filter to prevent interior void or undercut in certain directions. A set of 3D printing and mechanical performance tests are performed. It is interestingly found that, the printing direction affects significantly on the result performance and if subject to the uni direction, the load-bearing capacity increases from the 2.5D samples to the 3D samples with the increased complexity, but the load-bearing capacity further increases for the 3D simplified samples due to directional material removal. Hence, it is concluded that a restricted structural complexity is suitable for topology optimization of 3D-printed fiber composites, since large area cross-sections give more degrees of design freedom to the fiber path layout and also makes the inter-layer bond of the filaments firmer.

Enhancing the 3D printing fidelity of vat photopolymerization with machine learning-driven boundary prediction

Like many pixel-based additive manufacturing (AM) techniques, digital light processing (DLP) based vat photopolymerization faces the challenge that the square pixel based processing strategy can lead to zigzag edges especially when feature sizes come close to single-pixel levels. Introducing greyscale pixels has been a strategy to smoothen such edges, but it is a challenging task to understand which of the many permutations of projected pixels would give the optimal 3D printing performance. To address this challenge, a novel data acquisition strategy based on machine learning (ML) principles is proposed, and a training routine is implemented to reproduce the smallest shape of an intended 3D printed object. Through this approach, a chessboard patterning strategy is developed along with an automated data refining and augmentation workflow, demonstrating its efficiency and effectiveness by reducing the deviation by around 30%.

Characterization of geopolymer composites for 3D printing: a microstructure approach

Given the importance of geopolymer in terms of 3D printing performance and the scarcity of information on the subject, as well as previous research findings, the purpose of this study is to propose a design methodology for geopolymer concrete mix that can be used in the 3D printing process by studying the effect of fine aggregate size and type, binder type (either slag or metakaolin) and ratio (slag/metakaolin), and alkaline solution amount and ratio (NaOH/Na2SiO3). The study concluded that MK has lower fluidity than BFS under the same conditions that used the same amount of SP. However, it can be improved by adding slag. The best dosage was chosen, which is 50% MK and 50% BFS. Because of these proportions, the mixture is very dense, homogeneous and compact, which increases its microstructure analysis behavior.

An engineering approach to the 3D printing of K‐Carrageenan/konjac glucomannan hydrogels

SummaryAqueous solutions of Konjac glucomannan (KGM)/κ‐Carrageenan (κ‐C) of different ratios (1:2, 1:5, 1:8 and 1:10) and a fixed κ‐C content of 1.5%, were proposed as a new 3D food printing ink. Their thermo‐responsive behaviour was evaluated by temperature ramp rheological tests. This characterisation allowed for the evaluation of the synergistic effect between KGM and κ‐C and gave indications useful to the printing performance. Both elastic (G′) and loss (G″) moduli were found to increase by increasing the KGM concentration. Samples were printed by controlling the thermally reversible sol/gel transition occurring during the process. Direct pressure and flow rate measurements in the 3D printer were used to obtain the viscosity versus shear rate curves under processing conditions, useful to validate a scaling law relating the printing filament diameter to the relevant process and material properties (inks viscosity and printing pressure). The 3D printing performance of inks was evaluated by means of a novel, integrated score system. The results obtained indicate that aqueous mixtures of KGM/κ‐C can be successfully employed as a base for 3D printing food hydrogels. The use of the score system above outlined proved to be an easy yet efficient tool for the optimisation of the gel composition.

The preparation and wettability of the Sn-9Zn-2.5Bi-1.5In solder paste for SMT process and high shear ball performance

Purpose This study aims to focus on the surface mount technology (SMT) mass production process of Sn-9Zn-2.5Bi-1.5In solder. It explores it with some components that will provide theoretical support for the industrial SMT application of Sn-Zn solder. Design/methodology/approach This study evaluates the properties of solder pastes and selects a more appropriate reflow parameter by comparing the microstructure of solder joints with different reflow soldering profile parameters. The aim is to provide an economical and reliable process for SMT production in the industry. Findings Solder paste wettability and solder ball testing in a nitrogen environment with an oxygen content of 3,000 ppm meet the requirements of industrial production. The printing performance of the solder paste is good and can achieve a printing rate of 100–160 mm/s. When soldering with a traditional stepped reflow soldering profile, air bubbles are generated on the surface of the solder joint, and there are many voids and defects in the solder joint. A linear reflow soldering profile reduces the residence time below the melting point of the solder paste (approximately 110 s). This reduces the time the zinc is oxidized, reducing solder joint defects. The joint strength of tin-zinc joints soldered with the optimized reflow parameters is close to that of Sn-58Bi and SAC305, with high joint strength. Originality/value This study attempts to industrialize the application of Sn-Zn solder and solves the problem that Sn-Zn solder paste is prone to be oxidized in the application and obtains the SMT process parameters suitable for Sn-9Zn-2.5Bi-1.5In solder.

Improving performance of aerosol jet printing using machine learning‐driven optimization

AbstractAerosol jet printing is a promising technology for printing functional materials on a variety of substrates with high precision and resolution. This technology has the potential to revolutionize the manufacturing industry by providing a low‐cost, high‐resolution printing technique that can be used to produce additively printed electronics, sensors, and energy devices. However, the optimization of this process has traditionally relied on time‐consuming trial‐and‐error methods, hampering its efficiency and scalability. Machine learning (ML) models have the potential to overcome these challenges and improve the quality, speed, and efficiency of the printing process. In this paper, we propose an approach that leverages ML algorithms to streamline and enhance the aerosol jet printing optimization process. Our methodology involves data collection through systematic experimentation with various parameter settings. This data set serves as the foundation for training different ML model capable of predicting printed line characteristics and optimal printing process parameter. We validate our approach by performing experiments on different inks, and we compare the results of our ML‐based optimization approach to those obtained using traditional trial‐and‐error methods. The results demonstrate that our approach offers significantly higher accuracy and efficiency. To enhance our approach's accessibility and ease of use, we incorporate AutoML techniques which automates the process of selecting the most suitable ML algorithms and hyperparameters, reducing the burden of manual configuration. Furthermore, we introduce a user‐friendly web‐based interface that facilitates the entire ML pipeline, from data preprocessing to prediction and batch processing. This interface empowers users to efficiently manage and manipulate their data, select appropriate ML algorithms, and execute predictions, ultimately improving accuracy and model performance.

Blockage mechanism analysis and optimization design of 3D concrete printhead

Fast setting and hardening cement has the advantages of short setting time and high early strength. However, when using screw extrusion for 3D printing, there is often a serious blockage problem, which limits the application. In this study, we presented a novel approach to address this issue. Firstly, the blockage reasons in the printing process were obtained through simulations and experimental tests, then a superhydrophobic coating was applied to reduce the slip coefficient of the screw and the inner surface of the nozzle, the printing performance was improved finally. The results indicated that the pressure gradient in the cylinder decreased by 75.07% compared to the uncoated printhead. The shear rate and the flow velocity at the outlet were homogeneously distributed, and no plug flow was formed in the channel. Even after 60 min of continuous printing, the paste only adhered to the pushing flight flank, and no significant blockage occurred.

Purification of monoclonal antibodies using novel 3D printed ordered stationary phases

3D printing offers the unprecedented ability to fabricate chromatography stationary phases with bespoke 3D morphology as opposed to traditional packed beds of spherical beads. The restricted range of printable materials compatible with chromatography is considered a setback for its industrial implementation. Recently, we proposed a novel ink that exhibits favourable printing performance (printing time ∼100 mL/h, resolution ∼200 µm) and broadens the possibilities for a range of chromatography applications thanks to its customisable surface chemistry. In this work, this ink was used to fabricate 3D printed ordered columns with 300 µm channels for the capture and polishing of therapeutic monoclonal antibodies. The columns were initially assessed for leachables and extractables, revealing no material propensity for leaching. Columns were then functionalised with protein A and SO3 ligands to obtain affinity and strong cation exchangers, respectively. 3D printed protein A columns showed >85 % IgG recovery from harvested cell culture fluid with purities above 98 %. Column reusability was evaluated over 20 cycles showing unaffected performance. Eluate samples were analysed for co-eluted protein A fragments, host cell protein and aggregates. Results demonstrate excellent HCP clearance (logarithmic reduction value of > 2.5) and protein A leakage in the range of commercial affinity resins (<100 ng/mg). SO3 functionalised columns employed for polishing achieved removal of leaked Protein A (down to 10 ng/mg) to meet regulatory expectations of product purity. This work is the first implementation of 3D printed columns for mAb purification and provides strong evidence for their potential in industrial bioseparations.

Stability of inkjet printed lines at elevated substrate temperature

Precise manipulation of line morphologies is crucial for optimizing the performance of inkjet printing. Among various techniques, the utilization of heated substrates as an active control approach stands out due to its good controllability and precision. Thus, this study experimentally investigated the characteristics of inkjet-printed lines with high-temperature substrate, employing high-concentration indium tin oxide nano-ink. The phase diagrams of line patterns were plotted in the space of dimensionless droplet spacing and printing velocity. The transition boundaries between different line modes were obtained in the cases of different substrate temperatures. Two theoretical models have been developed. First, a new printing stability model was developed, which works well for high-temperature substrates. Second, for the newly observed overlapping deposition line pattern on higher temperature substrates, a theoretical model was developed to predict the pattern transition boundaries based on the timescale of droplet interval and evaporation time of each droplet. The findings could be useful for the inkjet printing optimization by means of substrate heating techniques.

3D printed polyvinylpyrrolidone–honey-gel with adhesive and degradable ability applied as bio-tape

This study explored the development of polyvinylpyrrolidone (PVP)–honey-gel (PHG) through 3D printing, aiming to develop a multifunctional bio-tape with adhesive and degradable properties. Based on the potential of honey to promote wound healing due to its antibacterial and anti-inflammatory properties, a PVP–honey-based 3D printing ink was developed by combining honey and PVP to create PHG through 3D printing technology that can form a film with strong adhesion and flexibility. First, the chemical–physical properties of PHG and its 3D printing performance were characterized. The line width achievable in 3D printing for the PHG line can extend to ∼100 µm. In addition, the adhesive properties of the PHG film were evaluated by using a 180° peeling test on various materials (glass, copper, wood, and pig skin), highlighting its potential for diverse applications. Finally, the application of the PHG film as a bio-tape was demonstrated through a successful animal experiment on a rabbit’s skin wound. Due to its adhesive and degradable properties, the bio-tape exhibited 3D conformability and ease of removal without residue.

Characterization of HIPEs stabilized by soy protein isolate with excellent rheological properties for 3D printing: Bridging the correlation among structure, function and application

Currently, the correlation between how protein structural changes affected the function of high internal phase emulsions (HIPEs) and the regulation of 3D printing performance was still unclear. Herein, this study was aimed to research the relationship between interface properties and stability of soy protein isolate (SPI) at different degrees of oxidation and prepare HIPEs with desirable rheological properties and a solid-like structure to use for 3D printing. The findings of this study suggested that moderate oxidation led to the disruption of the protein's main chain skeleton, resulting in enhancing protein flexibility and surface hydrophobicity. The HIPEs stabilized by this condition owned higher apparent viscosity, over 70% of thixotropic recovery rate, sufficient yield stress (160.8 Pa) and higher G′ and G″. This HIPEs with excellent properties could be the food-grade 3D printing inks to produce samples with high resolution. In addition, this HIPEs exhibited a slow-release effect on free fatty acids (FFA) in the gastrointestinal digestion. Finally, the findings of the correlation analysis indicated that the flexibility and surface hydrophobicity of SPI was a key factor to affect the quality of HIPEs and 3D printing. In conclusion, moderate oxidation could change the structure and interfacial characteristics of SPI, thus endowing HIPEs stabilized by modified SPI with better properties and expanding the field of SPI in the food industry. These findings not only were of great significance for guiding protein production and providing new protein-based 3D printable materials, but also this provided new possibilities for preparing fat substitutes with good appearance.

Radio frequency air cold plasma pretreatment to enhance 3D printing performance of tapioca starch by altering its rheological behavior and water migration

This work investigated the effect of radio frequency air cold plasma (RFACP) pretreatment in enhancing 3D printing performance of tapioca starch. The results of 3D printing showed that the cold plasma (CP) treatment enhanced printing precision from 75.88% to 89.16% in starch. On the one hand, it could appropriately weaken the fluidity of starch ink to reduce the printing line width. On the other hand, it could enhance the self-supporting ability of starch ink and alleviate the sagging and collapse of 3D patterns. The results of rheological behavior further demonstrated that CP-treated starch exhibited greater gel structure characterized by the increased viscoelasticity, rigidity, and structural recovery capacity. Additionally, CP treatment facilitated the migration of free water into immobilized states within the starch ink and shortened relaxation times, indicating an enhanced water-binding ability of the CP-treated starch. Correlation analysis showed that rheological properties, firmness and water distribution of starch ink were significantly linked with the printability. The improvement of starch 3D printing performance after CP treatment may be attributed to the higher amylose content and more hydrophilic groups (especially carboxyl) generated by CP depolymerization and oxidation effects, which could lead to a denser network structure with greater mechanical strength of starch gel. Overall, this study not only reveals the mechanism that CP treatment enhances 3D printing performance of starch, but also provides a green and effective way to improve the 3D printing performance of starch.

Stabilization of all-natural water-in-oil high internal phase pickering emulsion by using diosgenin/soybean phosphatidylethanolamine complex: Characterization and application in 3D printing

This study aimed to prepare an all-natural water-in-oil high internal phase Pickering emulsion (W/O-HIPPE) using diosgenin/soybean phosphatidylethanolamine complex (DGSP) and investigate the 3D printing performance. Results suggested that the self-assembly of diosgenin crystal was modified by SP in DGSP (diosgenin-SP ratios at 3:1 and 1:1), revealing a variation from large-size outward radiating needle-like to small-size granular-like shape, which facilitated closely packing at the interface. Hydrophilicity of DGSP was also increased (contact angle varying from 133.3 o to 106.4 o), ensuring more adequate interfacial adsorption to reduce interfacial tension more largely (6.5 mN/m). Thus, the W/O-HIPPE made by DGSP with diosgenin-SP = 1:1, exhibited smaller droplets and better freeze/thawing stability. The W/O-HIPPE was also measured improved rheological properties for 3D printing: satisfied shear-thinning behavior, higher recovery and self-supporting (viscoelasticity and deformation resistance). Consequently, the W/O-HIPPE allowed for printing more delicate patterns. This work provided guidance to prepare W/O-HIPPE for 3D printing.

Effect of guar gum on the rheological properties, microstructure and 3D printing performance of egg yolk powder-potato starch composite gel

This work explored the effects of guar gum (GG) concentration (0, 0.9, 1.8, 2.7, 3.6, 4.5 g) on the rheological properties, water distribution, microstructure and 3D printing performance of egg yolk powder-potato starch (EYP-PS) composite gels. The results showed that EYP-PS inks with GG added showed higher gel modulus, apparent viscosity, and hardness compared to the “Control”. Low-field nuclear magnetic resonance (LF-NMR) results indicated that GG was able to restrict the free movement of water and promote the migration of EYP-PS to tightly bound water. The microstructure results showed that GG could induce EYP-PS to form a denser network structure, and EYP-PS inks with an appropriate amount of GG showed better springiness. Fourier transform infrared spectroscopy (FT-IR) confirmed that the addition of GG did not create new functional groups in EYP-PS, but enhanced the hydrogen bonding in the gels. Overall, GG-1.8 and GG-2.7 exhibited the best 3D printing performance and were more suitable for patients with swallowing disorders. This study contributes to the development of 3D-printed gel food containing egg yolk powder as well as exploring the effect of GG on egg yolk powder-starch composite food materials.

Direct ink writing of viscous inks in variable gravity regimes using parabolic flights

Additive manufacturing (AM) has significant utility for off-planet fabrication where dedicated infrastructure is severely limited, weight reduction and in situ resource utilization is desirable, and demands for complex systems are high. Direct ink writing (DIW) is a useful AM technique since it enables the deposition of a broad set of materials and the co-printing of multiple materials simultaneously. This allows for the fabrication of complex functional devices and systems in addition to structural objects. To evaluate this technique for space applications, this study characterized DIW in low gravity environments. Parabolic flights were used to simulate Martian, Lunar, and Micro gravity, and the effects that these 3 gravity regimes have on two critical print performance parameters, drooping and slumping, was evaluated using viscous paste inks deposited with an auger-driven extrusion head. In the drooping case, bridging structures were printed across gaps without support material, and the deformation was monitored. In the slumping case, a wall was printed through sequential layer deposition, and the vertical displacement of each layer under reduced gravity was explored. As expected, we found that a reduction in apparent gravity led to a decrease in the droop of a printed line, and as apparent gravitational acceleration is decreased its impact on the magnitude of drooping becomes less significant. For wall structures printed in simulated Lunar or Martian gravity regimes, the total structure height was found to be similar to that of a structure printed under Earth's gravitational conditions. In contrast, for prints performed in microgravity, it was found that slumping was significantly reduced and structure height was larger. These results provide experimental data to enable the design and optimization of appropriate structures and tool paths for printing objects using DIW for off-planet manufacturing.

Fabrication and Characterization of novel high internal phase bigels with high mechanical properties: Phase inversion and personalized edible 3D food printing

In this paper, bigels systems were prepared by using 20 wt% palm stearin (POs) structured soybean oil oleogels and 80 wt% xanthan gum hydrogels in different ratios of polyglycerol polyricinoleate (PGPR). The proportion of PGPR in bigels was changed to explore the phase inversion and stabilization mechanism of bigels by multiple microscopy techniques, and the mechanical properties have been evaluated by the rheology analysis and 3D printability. When the PGPR content was less than 0.4 wt%, bigels presented as the O/W type. As the PGPR content was 1.0 wt% and 1.2 wt%, the bigel presented as the W/O type with a high internal phase, and a high level of droplets dispersed closely within an oil phase. The increase in PGPR content slowed down the nonlinear viscoelastic behavior under large strains. In terms of 3D printing capability, bigels (oleogels containing 20 wt% POs) showed an unsatisfactory 3D printing capability. However, with the increase of POs and PGPR content, more plastic and printable W/O high internal phase bigels were obtained due to the formation of a more stable, homogeneous, and strong ink. In addition, the bigels systems were investigated for the preparation of 3D biscuit printing, and it was found that the K′ value of W/O bigels batter (1511.39) was larger than that of O/W bigels batter (1394.82), showing greater hardness and better 3D printing performance. These findings could facilitate the broadening of bigels systems that could be applied for 3D biscuit printing.

Development of 3D printed k-carrageenan-based gummy candies modified by fenugreek gum: Correlating 3D printing performance with sol-gel transition

Temperature-responsive inks were formulated using k-carrageenan, fenugreek gum (FG), rose extracts, and sugar, of which the first two were used as the gelling agents. The interactions among components in these mixed ink formulations were investigated. Sol-gel transition and rheological properties of these inks were also correlated with extrusion, shape formation, and self (shape)-supporting aspects of 3D printing. Results indicated that incorporating FG increased inks' gelation temperature from 39.7 °C to 44.7–49.6 °C, affecting the selection of printing temperature (e.g., 0 % FG: 40 °C, 0.15 % FG: 45 °C, 0.3 % FG-0.6 % FG: 50 °C). Inks in solution states with lower viscosity (<5 Pa·s) were amenable to ensure their smooth extrusion through the tip of the printing nozzle. A shorter sol-gel transition time (approximately 100 s) during the shape formation stage facilitated the solidification of inks after extrusion. The addition of FG significantly (p<0.05) improved the mechanical properties (elastic modulus, hardness, etc.) of the printed models, which facilitated their self-supporting behavior. Low field nuclear magnetic resonance indicated that the inclusion of FG progressively restricted water mobility, consequently reducing the water syneresis rate of the mixed inks by 0.86 %–3.6 %. FG enhanced hydrogen bonding interactions among the components of these mixed inks, and helped to form a denser network.

Study on improving flavor and antioxidant capacity of 3D printed spinach gel system by combining modified atmosphere and ambient temperature

This study aimed to control printing ambient temperature and oxygen content collaboratively to achieve synchronous improvement of the sensory and nutritional quality of printed products. In this study, spinach juice and potato snowflake powder were used as raw materials to prepare printing materials. The results showed that the printing material with a 20% addition of potato snowflake powder had the best printing performance. Enhancing the flavor of the printed products in the printing process by increasing the printing ambient temperature, the printed product with better flavor quality was obtained at 40 °C. However, the increase in ambient temperature had adverse effects on the color and antioxidant capacity of the printed product, the ΔE value of the printed product at 40 °C was 6.18 ± 0.64. Based on this ambient temperature, reducing the oxygen content in the printing environment inhibited the adverse effects of rising temperature on the color and antioxidant capacity of printed products. When the oxygen content was below 1%, the printed product maintained the color and antioxidant capacity before printing, the ΔE value of the printed product was only 0.95 ± 0.09, and there was no significant difference in antioxidant properties (total chlorophyll content, total carotenoid content, total phenolic content, free radical scavenging activity). Therefore, while successfully improving the flavor of the product, this study achieved the maintenance of color, antioxidant capacity, and other qualities, which is an effective exploration of using 3D printing technology to produce high-quality food.

Time-temperature indicator of hydroxyethyl cellulose ink labels for assessing pork freshness

Pork is widely consumed worldwide, and many consumers now utilize sensory evaluation techniques to determine the freshness of pork when buying it. A color-changing ink label utilizing bromocresol purple (BCP) and N-hydroxyphthalimide (NHPI) had been created to help consumers better and more rapidly determine the freshness of pork while it is stored. The ink was easy to prepare and could be readily transferred to A4 paper using screen printing technology. This study delved deeper into the impact of hydroxyethyl cellulose (HEC) on the functional properties of inks to enhance printing performance. The experiment demonstrated that a 1 % mass fraction of HEC improved thixotropy and facilitated the even distribution of ink on A4 paper, as confirmed by scanning electron microscopy. Screen-printed labels with varying concentrations displayed distinct color change rates when stored at different temperatures, indicating their capability to assess pork freshness. FT-IR, laboratory, and stability tests verified the ink's exceptional color change capabilities and printing attributes. An analysis using the Arrhenius equation revealed a substantial synergistic effect between BCP and NHPI, resulting in improved sensitivity and accuracy of the ink. This study offers a practical and feasible method to monitor the storage quality of pork effectively.