Printing Performance Research Articles

Controls and process planning strategies for 5-axis laser directed energy deposition of Ti-6Al-4V using an 8-axis industrial robot and rotary motion

Interest in multi-axis additive manufacturing has grown significantly in recent years due to associated benefits that range from improved quality to support for greater geometric complexity. A method of 5-axis Laser Hot-Wire Directed Energy Deposition is developed and demonstrated in this study using an 8-axis industrial robot, comprised of a 6-axis serial link robot and a 2 degree‐of‐freedom positioner. Coordinated 5-axis motion is used to print Ti-6Al-4V objects predominantly through build plate rotation. Methods of slicing and toolpath generation are presented, including the use of an alternating toolpath direction philosophy and the manipulation of the CAD model surface normal vectors for determining the required build plate tilt angles for maintaining consistent deposition orientations relative to gravity. Another objective of the study was to determine the limits of conventional slicing and layer height control techniques for printing geometries with significant unsupported overhangs. A comparison is made between the behavior of normal and conformal bead alignment in this regard, and the performance of the layer height controller is reported as it relates to process stability and the limits of printing overhang geometries. Unsupported overhangs were successfully printed at 35° without build plate tilt and 45° with build plate tilt. Toolpath velocity and net-shape printing performance are reported as well, with 3D scans of the printed surfaces used for net-shape characterization. In all, the printing of three geometries is presented, including the overhang geometry, a 5-axis toolpath geometry, and a large-scale, multi-bead demonstrator part, which exceeded 500 mm in height and weighed 44 kg (97 lbs).

Correlating rheology with 3D printing performance based on thermo-responsive κ-carrageenan/Pleurotus ostreatus protein with regard to interaction mechanism

Accurate 3D printing of thermo-responsive gel inks is a great challenge as the sol-gel transition and rheological properties change during extrusion are not easy to precisely regulate with 3D printing behavior has not been sufficiently studied. The effect of Pleurotus ostreatus protein (POP) correlated with the rheological properties and thermo-responsive behavior of the system on 3D printing performance of the thermo-responsive gel, namely κ-carrageenan (KG). Afterwards, their interaction mechanism was further clarified and final printed samples were evaluated in terms of antioxidant performance. Results indicated that POP addition increased the gelatinization temperature (Tg), significantly affecting the selection of optimum printing temperature. POP addition also improved viscosity and consistency index (K) of the printing ink, ultimately affecting the extrusion behavior. Temperature recovery property was facilitated by POP incorporation and was critical to the formability during recovery stage in 3D printing. Mechanical strength was improved with POP addition, which played an important role for the printed structures to be self-supportive. A lower concentration of POP (10%∼40%) was dispersed in a continuous KG-rich gel network and visible phase separation occurred when POP level was increased to 50%. Molecular interaction analysis showed that electrostatic interactions, hydrophobic interactions, ion on the correlation between the rheological properties and thermo-responsive behavior of gum-based 3D printing ink. In addition, POP presented a certain antioxidant activity. This study not only provided useful information on the correlation between the rheological and thermo-responsive behavior of gum-based 3D printing ink, but also provided a way to regulate 3D printing behavior of gum-based gel by protein incorporation. Moreover, it also showed the way to improve the nutritional value of the 3D printed sample. • 3D printing behavior was correlated with thermo-responsive and rheology properties. • 3D printed KG based gel rich in protein was created. • The interactive mechanism between POP and KG was investigated.

Method of formulating 3D-printable strain-hardening alkali-activated composites for additive construction

One of the major limitations of the current 3D-concrete-printing technology is the incorporation of reinforcement. Furthermore, there is a need to decrease the ecological footprint of printable concrete. As a possible solution for these challenges, this paper presents a 3D-printable strain-hardening alkali-activated composite (3DP-SHAAC) that shows pseudo-ductile behaviour under direct tension. The developed 3DP-SHAAC is composed of a one-part (just-add-water) alkali-activated binder made of slag (GGBFS), fly ash (FA) and solid activators. The one-part alkali-activated binder eliminates the need for elevated temperature curing and handling of corrosive alkaline liquids. At first, an optimum matrix was identified by studying the effects of FA to GGBFS ratio on the rheological properties and compressive strength. Subsequently, the optimum matrix was reinforced by PVA fibres to make the 3DP-SHAAC, and printing performance and rheological properties were evaluated. In addition, the influences of curing temperature on the compressive, flexural and tensile performances of the printed specimens were also investigated. The results were compared with those obtained for the mould-cast specimens. The 3DP-SHAAC exhibited superior flexural performance, higher tensile strength, and comparable tensile strain capacity to the mould-cast counterpart. Further, the curing temperature had influence on the mechanical properties of both 3D-printed and mould-cast SHAACs. The underlying reasons for the differences are discussed.

Three-Dimensional Printing Properties of Polysaccharide Hydrocolloids-Unrinsed Sturgeon Surimi Complex Hydrogels.

Herein, the microstructure and mechanical properties of hydrogels consisting of unrinsed sturgeon surimi (URSS) and plant-derived polysaccharides such as κ-carrageenan (KC), konjac gum (KG), xanthan gum (XG), guar gum (GG) and sodium alginate (SA), were studied by texture analysis, rheological measurement and scanning electron microscopy (SEM). Rheological results showed that the apparent viscosity, storage modulus (G′) and loss modulus (G″) of URSS increased by addition of KC, KG, GG and SA. The gel strength of resultant surimi products fabricated with KG/URSS mixture was significantly higher than that of other groups. KG could significantly improve the hardness (44.14 ± 1.14 N), chewiness (160.34 ± 8.33 mJ) and cohesiveness (0.56 ± 0.02) of the unrinsed surimi gel. Adding SA and KC had no significant effect on the textural characteristics of printed gels. However, an apparent decrease in the relevant mechanical properties of printed hydrogels was observed when XG and GG were added into surimi. SEM indicated that the incorporation of KG and KC could further integrate the gel structure of URSS as compared to hindering the cross-linking of surimi protein by XG and GG, which were in accordance with gel strength and water-holding capacity. These results provided useful information to regulate the 3D printing performance in functionalized surimi-based material.

Utilization of recycled construction powder in 3D concrete printable materials through particle packing optimization

With the enhancement of awareness of environmental protection and sustainable development, reuse of industrial solid waste has gradually attracted people’s attention. The utilization of recycled construction powder (RCP) and recycled construction aggregate(RCA)in the production of 3D concrete printable material(3DPM) can not only reduce carbon emissions, but also promote the application of 3D printing technology by reducing material costs. Considering the defect of low-reactivity and inferior property of RCP, the appropriate RCP is screened out according to the modified Andreasen and Andersen model to optimize the gradation of printable materials. Influence of RCP on the fresh property is investigated by rheological experiment and the incipient failure height test. The results show that the addition of 10%RCP would increase the yield stress from 1423Pa to 1573Pa and maintain the viscosity of the material. Moreover, unconfined compressive strength test, isothermal calorimetry and mercury intrusion porosimetry test are also used to characterize the properties of 3DPM. The results show that although the addition of RCP reduces the total heat release of 3DPM, it also reduces the macropore(¿1000 nm) of 3DPM from 10.7% to 7.1%, and keep the compressive strength within an acceptable range through the gradation optimization. Finally, the results of laboratory printing or industrial printing also confirm the printing performance of 3DPM.

Improving 3D food printing performance using computer vision and feedforward nozzle motion control

3D food printing is an emerging technology to customize food designs and produce personalized foods. Food printing materials are diverse in rheological properties, which makes reliable extrusion-based 3D printing with constant printing parameters a challenge. Food printing often suffers from improper extrusion because of the varying elasticity of the food materials. In this study, a computer vision (CV)-based method is developed to measure the instant extrusion rate and width under constant extrusion pressure/force. The measured extrusion rate and extruded filament width were used to conduct a feedforward control of nozzle motion for a pneumatic 3D food printer. As a result, the CV-based control method improves extrusion line accuracy to 97.6–100% and prevents under-extrusion of white chocolate spread, cookie dough, and processed cheese. The method can also be used to customize filament width with less than 8% of deviation from the target. With a simple measurement setup and a user-friendly software interface, this CV-based method is deployable to most food printing applications to reduce trial-and-error experiments when printing a new food material.

Direct electrohydrodynamic printing of aqueous silver nanowires ink on hydrophobic substrates for flexible and stretchable electronics

Stretchable conductors based on metal nanowires, such as silver nanowires (AgNWs), are essential for the fabrication of stretchable electronics. Electrohydrodynamic (EHD) printing has been developed as a promising technique for patterning various conductive nanomaterials on stretchable substrates. However, the printing performance is adversely affected by poor wettability of the ink on the surface of the stretchable substrates, which are mostly low-surface-energy elastomeric polymers, like polydimethylsiloxane (PDMS). The surface treatments of the substrate surface could improve the printability of the ink on these substrates, but also impose many limitations, as the surface treatment could unfavorably affect the mechanical properties of the polymer and may cause damage to the underlying layer or other existing features on the substrate. The paper investigates EHD direct printing of aqueous AgNWs ink on untreated PDMS using surfactant (i.e., Capstone FS30) modified ink for the fabrication of stretchable electronics. The static contact angles at the different FS30 ratios were measured to analyze their effect on regulating the ink wettability. A set of printing experiments were performance to select the right ink composition to tailor and optimize the ink printability and printing performance. The morphology and electrical properties of printed AgNWs-based conductors can be controlled by selecting different the EHD printing speed. Furthermore, to illustrate the potential for reliable EHD direct printing of AgNWs for stretchable electronics, a wearable electronic patch with a fractal design of the AgNWs pattern was printed on an untreated PDMS substrate using the surfactant modified AgNWs ink, which provides stable electronic response under the bending, tension and compression.

Material extrusion additive manufacturing of zirconia parts using powder injection molding feedstock compositions

The aim of this study is the evaluation of powder injection molding (PIM) binder compositions for the material extrusion (MEX) additive manufacturing of zirconia parts. Four commercial PIM binder compositions were selected and mixed with 45 vol% of yttria-stabilized zirconia powder. Due to the brittle characteristic of the obtained ceramic feedstocks, a screw based pellet printing head was used for printing dense zirconia structures. To compare 3D printing performance, additionally a commercially available zirconia filament was used in this study. Application of PIM binder compositions was limited either due to phase separation during processing, poor printing performance or delamination during solvent debinding. Only one of the PIM based feedstock compositions could be successfully printed, debound and sintered. A ring-on-ring setup was used to investigate the equibiaxial flexural strength after sintering for both pellet and filament printed disks. For benchmarking, cold isostatic pressed (CIP) ceramic discs were fabricated by commercial, ready-to-press, zirconia powder. The ring-on-ring results showed a low Weibull modulus (3 <m<5) for all samples, regardless of the manufacturing process. Fractography on selected samples demonstrated, that the origins of failures are close to the area of the loading ring which indicates an uneven stress distribution along the contact area between the setup and the sample. The pointwise stress concentration is the reason for the immature failure of the samples and the low Weibull modulus. The characteristic strength and 90% confidence intervals were used to compare the strength of ceramic samples produced via additive manufacturing and CIP. Almost similar mechanical properties were obtained for the CIP pressed (σ0 = 657 MPa) and filament printed (σ0 = 531 MPa) samples. However, a lower strength was obtained by the pellet printed samples based on commercial PIM Binder (σ0 = 203 MPa). Fractography analysis indicated poor fusion of printed layers for the samples produced with PIM binder composition as the main reason for poor mechanical performance.

An impulse response formulation for small-sample learning and control of additive manufacturing quality

Machine learning for additive manufacturing (ML4AM) has emerged as a viable strategy in recent years to enhance 3D printing performance. However, the amount of data required for model training and the lack of ability to infer AM process insights can be serious barriers for black-box learning methods. Due to the nature of low-volume fabrication of infinite product variety in AM, ML4AM also faces “small data, big tasks” challenges to learn heterogeneous point cloud data and control the quality of new designs. To address these challenges, this work establishes an impulse response formulation of layer-wise AM processes to relate design inputs with the deformed final products. To enable prescriptive learning from a small sample of printed parts with different 3D shapes, we develop a fabrication-aware input–output representation, where each product is constructed by a large amount of basic shap primitives. The impulse response model depicts how the 2D shape primitives (circular sectors, line segments, and corner segments) in each layer are stacked up to become final 3D shape primitives. A geometric quality of a new design can therefore be predicted through the construction of learned shape primitives. Essentially, the small-sample learning of printed products is transformed into a large-sample learning of printed shape primitives under the impulse response formulation of AM. This fabrication-aware formulation builds the foundation for applying well-established control theory to the intelligent quality control in AM. It not only provides theoretical underpinning and justification of our previous work, but also enable new opportunities in ML4AM. As an example, it leads to transfer function characterization of AM processes to uncover process insights. It also provides block-diagram representation of AM processes to design and optimize the control of AM quality.

Enhanced Reactive Dye Inkjet Printing Performance of Antimicrobial Silk Fabrics Surface Modified with Plasma and Chitosan

Enhanced Reactive Dye Inkjet Printing Performance of Antimicrobial Silk Fabrics Surface Modified with Plasma and Chitosan

The Silver Ion and Nanocrystalline Pattern in the Glass Substrate, the Electric Field-Induced Thermal Transfer and Ink Absorption Layer Structure and Printing Performance

People’s research on nanocrystals is getting more in-depth with the development of science and technology, and the patterned arrangement of nanocrystals can greatly improve the performance of our equipment in related fields, allowing people to control the patterning of nanocrystals. Research on thermal transfer is also increasing. Glass materials doped with patterned metal nanocrystals have great application potential, and the search for a simple and efficient patterned preparation method has attracted great attention of many researchers. Using the directional induced migration effect of the high temperature and high voltage DC electric field, combined with the subsequent heat treatment process, the distribution of silver nanocrystals corresponding to the surface silver film pattern can be formed in the silicate glass substrate, to realize the electric field-induced thermal transfer of the nanocrystal pattern print. This article aims to study the patterned thermal transfer of silver ions and nanocrystals on the glass substrate by applying an electric field to induce and analyze the ink absorption layer structure and printing performance. On this basis, an electron beam-induced thermal transfer method and Maxwell’s equation are proposed to investigate and calculate the structure of the ink absorption layer. The experimental structure shows that using this method increases the success rate of the preparation of silver ions and nanocrystal patterns on the glass substrate by 30%, which improves the ink absorption layer and printing performance to different degrees.

4D printing of a citrus pectin/β-CD Pickering emulsion: A study on temperature induced color transformation

The 4D printing of a Pickering emulsion stabilized by citrus pectin/β-Cyclodextrin (β-CD) complexes was realized utilizing pH-sensitive curcumin. The fabrication, microstructure, and mechanical properties of the Pickering emulsion were investigated with laser confocal microscopy observations, rheological measurements and TPA. Results indicated that the emulsion prepared with an oil phase mass fraction (φ) of 65 %, composition ratio (Rβ/C) of 2:2, and citrus pectin/β-CD concentration (W) of 2 % exhibited smaller droplet size, strong gel network, and best printing performance. In addition, pH-sensitive curcumin was added to the emulsion to evaluate its 4D printing capabilities. The decomposition of HCO3- into CO32- resulted in the increase of pH after heating, induced the printed samples to change color from yellowish to red and the chroma of the samples changed accordingly: L*and b* value decreased while a* value increased. These findings offer greater flexibility to produce novel food formats and designs.

Master Structure Dependence of Double Magnet Master on Performance of Magnetic Printing Onto Energy-Assisted Magnetic Recording Media

The dependence of double magnet master (DMM) printing characteristics on master thickness and non-magnetic separator (NMS) thickness is investigated using micromagnetic simulation. It is found that the recording field difference saturates when the master thickness reaches the bit length. The NMS, which separates the two magnetic materials of the DMM, shifts the maximum points of the recording field distribution into the softer magnet regions, decreasing the island-like non-reversed regions, thus enhancing the printing performance. The effective switching field is important for understanding magnetic printing characteristics. The printed magnetization distributions are in accordance with the switching field distribution of the recording field generated by the DMM. Therefore, optimizing the master thickness and NMS thickness effectively improves the DMM printing characteristics for various servo patterns.

The enhancement of wool reactive dyes ink-jet printing through air plasma pretreatment

Ink-jet printing is a clean and high-definition printing method for wool fabrics. However, due to the existence of scale layers, the dyes were hardly absorbed into the wool fibers, resulting in poor printing quality. In this work, a green and efficient air plasma pretreatment method was proposed to improve ink-jet printing performance of wool fabrics using reactive dye inks. The results showed that the wool surface was etched after plasma treatment, which led to the increased contact area between wool fiber and dyes. Meanwhile, due to the introduction of more oxygen-containing functional groups on the fiber surface, and part of the –SH and –S-S- were oxidized into –S-O-, the wettability of wool was obviously enhanced with the contact angle decreasing from 135° to 27.5°. The breaks of C–C and C–N bonds resulted in the increase of binding sites between reactive dyes and wool fibers. Because of the above changes, the inks were easily absorbed into the fiber, which promoted the covalent binding of dyes and fibers. As a result, compared with the untreated wool fabric (K/S value of 14.64), the wool fabrics treated by air plasma for 3 min obtained a wonderful printing effect with a K/S value of 22.34. This pretreatment method provides an environmental and efficient approach for the improvement of wool fabrics ink-jet printing performance.

Effect of gums on the multi-scale characteristics and 3D printing performance of potato starch gel

This research investigated the multi-scale characteristics of potato starch gel (PSG) with different addition ratios of xanthan gum (XG) and locust bean gum (LBG). These characteristics are closely related and had significant impacts on 3D printing performance. Both xanthan gum and locust bean gum were able to increase the apparent viscosity, storage modulus (G′) and loss modulus (G″) of the blended gel system to varying degrees. Large amplitude oscillation shear (LAOS) was used to detect slight rheological differences led by microstructure changes. The critical strain values of the blended gel system rose as the addition ratio of locust bean gum increased. At the same time, the elastic and viscous Lissajous curves could characterize the viscoelastic changes under large strains. Fourier transforms infrared spectroscopy (FT-IR) illustrated that locust bean gum could strengthen the hydrogen bonds so that the gel had stronger mechanical properties compared with the addition of xanthan gum. Scanning electron microscopy (SEM) could observe the changes in the microstructure of the blended gel systems with addition of different addition ratios of gums. From the perspectives of 3D printing results and data analysis, the appropriate amount of xanthan gum improved the fineness and fluidity of the gels by virtue of its lubricating and coating characteristics, while the locust bean gum enabled them to have stronger shape retention abilities and better performances of resisting compressed deformation.

Preparation of porous SiC ceramics skeleton with low-cost and controllable gradient based on liquid crystal display 3D printing

In recent years, the demand for gradient porous ceramics is increasing in engineering field. By traditional process, the disadvantage of prepared gradient porous ceramics is its low porosity and uncontrollable pore gradient, which limits the wide application of gradient porous ceramics. In this study, the gradient porous ceramic skeleton (GPCS) was prepared by combining liquid crystal display (LCD) 3D printer with liquid silicon infiltration (LSI). Experimental results showed that the mass of ceramic powder in the ceramic slurry with optimal printing performance accounts for 45% of the mass of photosensitive resin, and the thermal decomposition rate of photosensitive resin is faster in the range of 300–450 °C. Furthermore, the effect of LSI temperature on the composition, microstructure and mechanical properties of GPCS was investigated. The GPCS is expected to be applied in the fields of energy storage, heat transfer and biofouling, among others.

Investigation of the mechanism of casein protein to enhance 3D printing accuracy of cassava starch gel

This work evaluated the potential mechanism of casein protein (CP) in enhancing the 3D printing performance of cassava starch (CS) gel in terms of the multi-scale structure of starch and gel properties. The addition of CP could increase the average molecular weight (−Rh) of starch after thermal processing, which reduced the line width and increased the centre height of the 3D-printed product, despite the reduction of the structural recovery of the gel system. In addition, the increase in CS content caused a decrease in the short-range ordered structure of starch, resulting in a decline in relaxation time and an increase in free water content (A23), which in turn provided the gel system with a greater elastic modulus and ultimately increased the printing precision of 3D printed products. This study presented meaningful information for the application of 3D printing to starch-protein complex foods.

Rheological Behavior and Dynamic Mechanical Properties for Interpretation of Layer Adhesion in FDM 3D Printing.

Commercial filaments of poly(lactic acid) (PLA) composites with particulate filler, carbon fiber, and copper powder with different contents were fabricated by FDM 3D printing in XZ-direction at bed temperatures of 45 °C and 60 °C. The effects of additives and bed temperatures on layer adhesion, fracture behavior, and mechanical performance of the PLA composites 3D printing were evaluated. Rheological properties informed viscous nature of all filaments and interface bonding in the PLA composites, which improved printability and dimensional stability of the 3D printing. Crystallinity of the PLA composites 3D printing increased with increasing bed temperature resulting in an improvement of storage modulus, tensile, and flexural properties. On the contrary, the ductility of the 3D printing was raised when printed at low bed temperature. Dynamic mechanical properties, the degree of entanglement, the adhesion factor, the effectiveness coefficient, the reinforcing efficiency factor, and the Cole–Cole analysis were used to understand the layer adhesion, and the interfacial interaction of the composites as compared to the compression molded sheets. SEM images revealed good adhesion between the additives and the PLA matrix. However, the additives induced faster solidification and showed larger voids in the 3D printing, which indicated lower layer adhesion as compared to neat PLA. It can be noted that the combination of the additives and the optimized 3D printing conditions would be obtain superior mechanical performance even layer adhesion has been restricted.

Effects of spatial and temporal offset during landing on mixing performance in intersecting-jets printing

Intersecting-jets printing extends the inkjet printing capability to allow the deposition of different materials using a printing-then-mixing approach. This study focuses on the analysis of the robustness of mixing performance under spatial and temporal offset conditions during intersecting-jets printing and how this robustness is affected by the ink rheological properties and reactivity. Reactive sodium alginate and calcium chloride solutions have been used as the model materials. Shannon’s entropy has been used to measure the mixing efficiency, and high-speed imaging and particle image velocimetry have been used to characterize the ink motion after intersecting collision and landing onto a receiving substrate to better understand its mixing dynamics. While optimal mixing performance (> 90%) can be obtained under ideal printing conditions, the presence of a spatial offset may result in a smaller post-landing velocity but it may not affect significantly the time required to reach an equilibrium state depending on ink materials used. The spatial offset may induce a negative effect on the mixing performance, and selecting a less viscous or low reactivity ink can largely attenuate the effects of spatial offset on the mixing performance. Due to the gelation of the first deposited droplet, even small temporal offsets, on the order of 0.5 – 2.0 ms, may still lead to inconsistencies in the mixing performance. While the intersecting-jets printing process is a complicated process that may involve complex fluids as inks, the mixing performance can still be satisfactorily predicted by using an artificial neural network-based modeling approach.

Investigation of Thermal Performance of 3D Printing Integrated Phase Change Materials in Building Structure

This paper aims to create an experimental building structure using 3D printing technology to reduce the interior temperature. Because of its sensitivity to high temperatures, particularly its low heat deflection temperature, and susceptibility to deterioration over time, the Polylactic acid (PLA) material has been preferred to print the layer. In this model, an effort was made to decrease the building's overall cooling load, which may result in a higher amount of ordinary power being required. For the study, a new model of the intended wall was developed and tested. The studies were carried out in two modes: the first without any PCM in the wall, and the second with an additional new model of PCM 3D-printing layer within the wall. The test results demonstrated that the PCM 3D-printing layer inside the wall building lowered the temperature of the outer wall surface, the inner wall surface, and subsequently the building temperature of the indoor area to a huge amount. The achievements are in the percentage peak temperature reduction of 9.8% for the wall's outer surface, 22.6% of the inner wall surface, and 13.4% of the room temperature. With the help of the PCM 3D-printing layer, the peak indoor temperature was decreased by 5℃.