Print Head Research Articles

Development of modular extrusion bioprinter prototype

Introduction: The aim of this work was to develop a prototype of a modular extrusion bioprinter capable of performing 2D and 3D printing with hydrogels based on sodium alginate and gelatin. Materials and methods: The bioprinter uses Cartesian coordinate system, the print head is movable in Y and Z axes, the printing platform is in X axis and equipped with cooling system. Constructs were printed with 3 types of gels: based on gelatin with the addition various concentrations of xanthan gum; based on combination of gelatin and sodium alginate; based on gelatin and xanthan gum with the addition of carbon nanotubes. Results: The constructs from various gels corresponded to the structure determined by their digital models. Conclusions: The developed system allows performing 2D and 3D printing with gels based on gelatin, sodium alginate, including those containing carbon nanotubes and/or xanthan gum for a wide range of experimental tasks.

Recent Advances in Additive Friction Stir Deposition: A Critical Review.

Additive friction stir deposition (AFSD) is a novel solid-state additive manufacturing method developed on the principle of stirring friction. Benefits from its solid-phase properties, compared with traditional additive manufacturing based on melting-solidification cycles, AFSD solves the problems of porosity, cracks, and residual stress caused by the melting-solidification process, and has a significant improvement in efficiency. In AFSD, the interaction between feedstocks and high-speed rotating print heads suffers severe plastic deformation at high temperatures below the melting point, ending up in fine, equiaxed recrystallized grains. The above characteristics make components by AFSD show similar mechanical behaviors to the forged ones. This article reviews the development of AFSD technology, elaborates on the basic principles, compares the macroscopic formability and material flow behavior of AFSD processes using different types of feedstocks, summarizes the microstructure and mechanical properties obtained from the AFSD of alloys with different compositions, and finally provides an outlook on the development trends, opportunities, and challenges to the researchers and industrial fields concerning AFSD.

Effect of high-boiling point solvents on inkjet printing of catalyst layers for proton exchange membrane fuel cells

Inkjet printing (IJP) is considered as a promising and flexible method for low cost and drop-on-demand pattern formation in proton exchange membrane (PEM) fuel cells. Although significant advancements have been made in inkjet-printed electrodes, identifying the optimal ink formulations remains challenging due to severe restrictions on the ink properties. Generally, the catalyst layer prepared by IJP using low boiling point solvents (water/alcohol) show reasonable electrochemical performance. However, low boiling point solvents lead to clogging of the printhead nozzle due to fast evaporation of the solvent in the inkjet print head. In this study, high boiling point solvents (propylene glycol (PG) or ethylene glycol (EG)) were used as additives to reduce nozzle clogging and improve printing efficiency. In this context, the relationship between catalyst ink properties, CL microstructure, and electrochemical performance of the MEA is investigated. Results show that printing time is significantly reduced with adding high boiling point solvents in the ink (66.67 % reduction of time with 30 wt% PG). However, an increased amount of additive is detrimental in terms of electrochemical performance due to formation of larger agglomerates, lower porosity of the catalyst layer, and reduced ECSA. The results of this work can be used to develop a strategy to adjust the trade-off between printing time and electrochemical performance of electrodes prepared using IJP.

3D printing single‐stroke path planning, local reinforcement and performance testing of MBB beams and cantilever beams

Abstract3D printing of continuous fiber reinforced thermoplastic composites (CFRTPCs) has been applied for the molding of composite complex structures due to the advantages of flexibility and one‐step forming. In this study, feature points simplification, merging and rearrangement were accomplished for Messerschmitt‐Bölkow‐Blohm (MBB) beam and cantilever beam to generate single‐stroke print paths for the specimens. For the significant stress areas in the finite element analysis results of these structures, a local reinforcement method using orthogonal layups was proposed, which was achieved by raising and lowering the print head and adjusting the fiber volume fraction during the printing. After experimental validation and failure modes analysis, the path planning significantly improved the peak load and structural stiffness of the specimens, and the local reinforcement further enhanced the equivalent specific strength and specific stiffness. This study provides a single‐stroke 3D printing strategy for complex structure molding in conjunction with parameter adjustments.Highlights A single‐stroke path planning was developed for MBB beams and cantilever beams, including simplification, merging and rearrangement methods for feature points. A local reinforcement method was proposed, which was achieved by raising and lowering the print head and adjusting the fiber volume fraction during the printing process. The effect of different print paths on specimen properties was investigated.

A versatile 5-axis melt electrowriting platform for unprecedented design freedom of 3D fibrous scaffolds

Melt electrowriting (MEW) is an electrohydrodynamic additive manufacturing technology for the fabrication of precise microfiber scaffold architectures but is so far restricted to printing onto simple collector geometries and, therefore, constrained in design freedom. This is due to current limitations in print head designs, kinematic systems, and software to generate motion commands. We address these aspects by upgrading a low-cost 5-axis kinematic system and complete it with a custom-designed print head and a collector fabrication workflow to enable collision-free MEW onto arbitrarily shaped multicurvature 3D geometries. A universal graphical approach enables generation of Gcodes customized to the 5-axis MEW requirements. The print head is validated by producing polycaprolactone fibers with diameters ranging from 5.6 ± 1.7 µm to 50.7 ± 5.5 µm and by writing both linear and non-linear fiber patterns onto collectors featuring concave and convex surfaces. Stable printing conditions are achieved by continuously reorienting the print head and collector surface perpendicular to each other at a constant working distance. Ultimately, we demonstrate the system’s potential in shaping anatomically relevant scaffold geometries by stacking microfibers onto collectors resembling a trileaflet valve and a bifurcating vessel. This multi-axis MEW platform unlocks exciting avenues towards unprecedented design freedom for MEW scaffolds.

Non-planar additive manufacturing of pre-impregnated continuous fiber reinforced composites using a three-axis printer

Non-planar additive manufacturing (AM) demonstrates great potential in enhancing interlayer bonding force and surface smoothness of parts, offering a more flexible design and manufacturing approach for continuous fiber composites to fully exploit material capabilities. This study developed a three-axis printer utilizing an adjustable fiber printing head that can achieve non-planar slicing (NPS) AM of pre-impregnated continuous fibers. The research delves into the influence of deposition inclined angle on the surface roughness of printed samples, enabling the design and printing of NPS samples using continuous carbon fiber (CF), glass fiber (GF), and hybrid fiber composites. The investigation also assesses bending failure morphologies of the printed parts and validates the efficacy of the NPS method through the fabrication of the double-sinusoidal curved surface structure and spherical surface grid structure. The results indicated that maintaining a deposition inclined angle below 15° is crucial to ensure surface accuracy in continuous fiber printed parts. Curved surface bending samples printed with NPS method exhibit substantial enhancements in bending performance and surface accuracy compared to those produced using planar slicing (PS). The NPS-CF sample achieves a remarkable increase of over 170% in maximum bending force and a 63% reduction in surface roughness compared to the PS-CF sample.

Material Characterization of Silicones for Additive Manufacturing.

Three-dimensional printing is ideally suited to produce unique and complex shapes. In this study, the material properties of polysiloxanes, commonly named silicones, produced additively by two different methods, namely, multi-jet fusion (MJF) and material extrusion (ME) with liquid printing heads, are investigated. The chemical composition was compared via Fourier-transform infrared spectroscopy, evolved gas analysis mass spectrometry, pyrolysis gas chromatography coupled to mass spectrometry, and thermogravimetry (TGA). Density and low-temperature flexibility, mechanical properties and crosslink distance via freezing point depression were measured before and after post-treatment at elevated temperatures. The results show significant differences in the chemical composition, material properties, as well as surface quality of the tested products produced by the two manufacturing routes. Chemical analysis indicates that the investigated MJF materials contain acrylate moieties, possibly isobornyl acrylate linking branches. The hardness of the MJF samples is associated with crosslinking density. In the ashes after TGA, traces of phosphorus were found, which could originate from initiators or catalysts of the curing process. The ME materials contain fillers, most probably silica, that differ in their amount. It is possible that silica also plays a role in the processing to stabilize the extrusion strand. For the harder material, a higher crosslink density was found, which was supported also by the other tested properties. The MJF samples have smooth surfaces, while the ME samples show grooved surface structures typical for the material extrusion process. Post-treatment did not improve the material properties. In the MJF samples, significant color changes were observed.

Effect of printing parameters on extrudability and buildability of ultra-low carbon cementitious material

Cement-free cementitious materials are important for reducing the carbon footprint of 3D printing. However, for the ultra-low carbon cementitious material for 3D printing, the effect of printing parameters on its extrusion and stacking morphology has not been fully investigated. In this paper, an ultra-low carbon cement-free cementitious material (UCCCM) with ultra-fine slag and spherical fly ash as main components is developed. The influence of print head size (HS), print head height (HH), and printing speed (PS) on the extrudability and buildability are systematically investigated. Results showed that the HS had a clear influence on the extrudability, and a small print head size negatively affected the continuity of the extrudate. The HH had a greater influence on the buildability, and a low HH led to a height loss rate of more than 5 %. The PS had a greater influence on the buildability. When the PS was too slow, the mortar piled up and the printed specimens collapsed with a height loss rate of up to 35 %. When the PS was too fast, the strip cracked, and the height loss rate reached more than 10 %. The developed UCCCM for 3D printing presented optimal extrudability and buildability at a HS of 20 mm, a HH of 90 % and a PS of 20 mm/s.

An exploratory study on miniaturized additive friction stir deposition

Without melting and rapid solidification, additive friction stir deposition offers a deformation processing route to additive manufacturing and repair of high-performance alloys with full density and desirable properties. However, this approach has traditionally relied on expensive and bulky equipment, posing challenges for small-feature creation and portability. Here, we explore miniaturized additive friction stir deposition by modifying an affordable benchtop mill and introducing innovative tool design. With in situ monitoring of temperature and force evolution, we demonstrate the efficacy of this approach by dissimilar metal printing, depositing high-strength martensite steel (AISI 4140) onto mild steel (AISI 1018). Compared to conventional facilities, the present approach reduces the in-plane dimension of the feed-rod by a factor of three and narrows the deposition tracks to a few millimeters in width. The as-deposited steel exhibits full density and retains martensitic characteristics without forming new phases at the interfacial region. The as-deposited steel shows significant microstructure refinement with increased hardness because of the extreme thermomechanical conditions during deposition. We discuss the influences of downsizing on the thermal and mechanical aspects of deposition. Owing to the size effects in heat generation and heat loss, the rotation rate of the print head needs to be significantly increased in miniaturized additive friction stir deposition to ensure good deposition quality. To prevent buckling, the unsupported length of the feed-rod should be reduced in proportion to its in-plane dimension.

3D printing of continuous metal fiber-reinforced recycled ABS with varying fiber loading

PurposeThe current study aims to develop a 3D-printed continuous metal fiber-reinforced recycled thermoplastic composite using an in-nozzle impregnation technique.Design/methodology/approachRecycled acrylonitrile butadiene styrene (RABS) plastic was blended with virgin ABS (VABS) plastic in a ratio of 60:40 weight proportion to develop a 3D printing filament that was used as a matrix material, while post-used continuous brass wire (CBW) was used as a reinforcement. 3D printing was done by using a self-customized print head to fabricate the flexural, compression and interlaminar shear stress (ILSS) test samples to evaluate the bending, compressive and ILSS properties of the build samples and compared with VABS and RABS-B samples. Moreover, the physical properties of the samples were also analyzed.FindingsUpon three-point bend, compression and ILSS testing, it was found that RABS-B/CBW composite 3D printed with 0.7 mm layer width exhibited a notable improvement in maximum flexural load (Lmax), flexural stress at maximum load (sfmax), flex modulus (Ef) and work of fracture (WOF), compression modulus (Ec) and ILSS properties by 30.5%, 49.6%, 88.4% 13.8, 21.6% and 30.3% respectively.Originality/valueLimited research has been conducted on the in-nozzle impregnation technique for 3D printing metal fiber-reinforced recycled thermoplastic composites. Adopting this method holds the potential to create durable and high-strength sustainable composites suitable for engineering applications, thereby diminishing dependence on virgin materials.

Monitoring of the Homogeneity of Primer Layers for Ink Jet Printing on Polyester Fabrics by Hyperspectral Imaging.

Untreated polyester films and fibers can be hardly printed or coated, in particular if aqueous inks or lacquers have to be applied. Therefore, an adequate primer layer has to be applied first. A cationic polymer formulation based on poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine) (PDEHED) was used as primer layer for digital printing on polyester fabrics. Because of the exceedingly high requirements on the homogeneity of such layers, hyperspectral imaging was used for qualitative and quantitative monitoring of the distribution of the primer layer on the textiles. Multivariate data analysis methods based on the PLS algorithm were applied for quantification of the NIR reflection spectra using gravimetry as a reference method. Optimization of the calibration method resulted in various models with prediction errors of about 1.2 g/m2. The prediction performance of the models was proven in external validations using independent samples. Moreover, a special ink jet printing technology was tested for application of the aqueous primer formulation itself. Since possible clogging of jet nozzles in the print head might lead to inhomogeneity in the coatings such as missing tracks, the potential of hyperspectral imaging to detect such defects was investigated. It was demonstrated that simulated missing tracks can be clearly detected. Consequently, hyperspectral imaging has been proven to be a powerful analytical tool for in-line monitoring of the quality of printability improvement layers and similar systems.

Design, modeling and feedforward control of a hybrid extruder for material extrusion additive manufacturing

Material extrusion (MatEx) is the one of the most widely utilized additive manufacturing (AM) methods. The key to high printing quality in MatEx lies in the synchronization between the fast motion system and the slow extrusion system. However, the synchronization is challenged by the slow response of the extrusion system. In MatEx, there are two main types of extrusion systems: Bowden and direct-drive (DD), based on different extruder-hot end arrangements. DD systems have the extruder installed directly above the hot end, providing a relatively fast extrusion response but adding more inertia to the print head. In contrast, Bowden systems position the extruder on the printer’s frame, feeding the filament to the hot end through a long Bowden tube. As a result, this setup leads to a sluggish extrusion response due to the elasticity of the long segment of filament but has a lower print head’s inertia, offering a higher positioning accuracy compared to the DD system. To leverage the advantages of both extrusion systems, this paper proposes a hybrid extrusion system design that combines a Bowden extruder with a low-mass DD extruder for filament feeding. To optimize the design and control of the extruder, a low-order model that characterizes the hybrid extruder dynamics is proposed. The model is used to design a feedforward (FF) controller that minimizes the force exerted by the DD extruder motor in the hybrid extruder while achieving the desired extrusion accuracy. The effectiveness of the proposed extruder and the FF controller is validated experimentally by demonstrating transient responses as fast as those of the standard DD extruder with up to 65% less force required from the DD extruder motor. Data collected from motor torque–mass specifications of three motor series from three different manufacturers indicate that the torque/force reduction could yield up to a 69% mass reduction in the motor used for the DD extruder, adding only 32.5% extra weight of the hot end to the print head. Hence it holds the potential to achieve the same extrusion accuracy as standard DD extruders while significantly reducing print head inertia, hence the resulting vibration of the printer, as demonstrated using a case study.

Structural design of a novel rotary platform 3D printer

Abstract Stair-stepping defects in 3D printing processes can be caused by various reasons, such as the quality of the printing material, the position of the print head, printing speed, printing temperature, and so on. To improve the issue of stair-stepping effects in thin-walled revolving parts during the 3D printing process, this project aims to design a 3D printer that enables the print head to move in the X, Y, and Z axes while the heated bed platform can rotate. This will significantly reduce the stair-stepping effect’s impact and greatly enhance the printing’s quality and accuracy.

Tensile behaviour of continuous carbon fibre reinforced composites fabricated by a modified 3D printer

This study aims to highlight the impact of low-volume (7.5%) continuous carbon fibre reinforcement in three different polymer matrices and the effects of post-processing under hot pressing on the mechanical properties of the structures. A fused deposition modelling (FDM) printer’s print head was modified to directly extrude the polymer matrix and continuous carbon fibre tow together. Both pure and carbon fibre-reinforced samples were cured under hot pressing at 100 °C and 10 kN pressure for 15 min. All samples underwent tensile and hardness tests, and the microstructure of fractured samples was analysed using a scanning electron microscope. The results indicate that continuous carbon fibre reinforcement and hot pressing are crucial for enhancing the mechanical performance of 3D-printed objects.

Ultra-lightweight silicon nitride truss-based structures fabricated via UV-assisted robot direct ink writing

Additive manufacturing techniques have gone beyond their reputation for rapid prototype production and are increasingly adopted for the manufacture of functional components comprising high-end materials and intricate lattice structures. Silicon nitride, renowned for its exceptional mechanical properties and thermal stability, has emerged as a promising candidate for lightweight structural applications. Nonetheless, its high refractive index and density have limited the fabrication of highly complex structures using extrusion and photopolymerization based techniques. In this work, a highly reactive silicon nitride-based ink with high solid loading is developed for the fabrication of ultra-lightweight, truss-based structures. By employing a robot UV-assisted direct ink writing process, it is possible to control the printing head orientation, thus overcoming the limited curing depth of silicon nitride-based inks. The failure behavior of the sintered lattice beam structures under 4-point bending loading has been modeled by applying a linear elastic fracture mechanics (LEFM) based approach to the results of finite element (FE) simulations.

Encapsulation of sodium silicate to attain on demand buildability enhancement in concrete 3D printing

This study investigates the encapsulation of a buildability enhancing additive using a phase change material (PCM) as a thermo-responsive additive for concrete 3D printing. The encapsulated additive is mixed with printable mixes and activated at the print head. The printhead activation via the heating process dissolves the capsules and releases the buildability enhancing additive to attain the required rheological properties for printing. A sodium silicate-based set accelerator was used as the buildability enhancing additive and encapsulated using a paraffinic PCM. The comprehensive experimental study was conducted to understand the effect of encapsulated sodium silicate on the pumpability of concrete followed by buildability after print head heating. It was demonstrated that the smaller addition of encapsulated sodium silicate (5 %) followed by print head activation resulted in the static yield strength (SYS) of 122 kPa after 25 min of placement compared to 8 kPa observed for mixes containing nanoclay as a thixotropic additive. Furthermore, the dissolution process of sodium silicate was assessed via an analytical method using optical technology to determine the diffusion coefficient of sodium silicate in the printable concrete. The proposed method was validated by printing a thin vertical wall with the optimised mix design developed during the study. Consequently, the mechanical properties of the printed specimen were investigated. The mixes containing the encapsulated additive showed a compressive strength reduction by up to 47 % for mould cast and 3D printed specimens and this was correlated to increased porosity of the mixes.

A relaxor-ferroelectric PMN-PZT thin-film-based drop-on-demand printhead for bioprinting applications with high piezoelectricity and low heat dissipation

This article presents a relaxor ferroelectric, lead magnesium niobate-lead zirconate titanate (PMN-PZT)-thin-film-based piezoelectric drop-on-demand printhead exhibiting high jetting capability and thermal stability. Unlike conventional piezoelectric materials such as lead zirconate titanate (PZT), the PMN-PZT film demonstrates high electrical responsiveness to polarization and reduced hysteresis loss due to polar nano regions, thereby improving printhead’s performance. Our research involves a comprehensive exploration of the fabrication and packaging processes for the PMN-PZT-based printhead, along with optimization of driving pulses to maximize its performance. An in-depth investigation into the dynamics of ferroelectric film’s polarization identifies the best driving conditions that minimize self-heating while maximizing the dynamic displacement of the printhead. As demonstrated in the results, the unipolar pulse, capable of maintaining a consistent polarization direction of the film, yielded twice the displacement compared to driving with a bipolar pulse. Simultaneously, it reduced the thermal dissipation of the printhead by 73.4 %. Consequently, we aim to propose a method for developing ferroelectric thin film-based print heads suitable for various biological modeling research, leveraging their high productivity and thermal stability.

Enhanced mechanical properties of continuous carbon fiber reinforced polyether-ether-ketone composites via infrared preheating and high fiber volume fraction

The field of additive manufacturing encounters an innate challenge regarding insufficient interlayer adhesion and anisotropy, which consequently constrains the mechanical properties of printed materials. Continuous fiber-reinforced thermoplastic composite (CFRTP) printing allows ultra-high mechanical properties using a material extrusion (ME) platform but is still significantly affected by the mentioned inherent challenges. The expansion of the usage spectrum for composites manufactured with additive methods depends on overcoming these challenges. Achieving higher fiber volume fractions is a primary method for enhancing the mechanical properties of CFRTP parts. However, it has been proven that high fiber volume fractions can adversely affect mechanical properties due to lower impregnation and reduced interlayer strength. In this study, a high fiber volume fraction of 50 % was utilized, and interlayer strength was further improved by employing an infrared heater to preheat the previous layers. This approach resulted in better interlaminar strength and overall mechanical properties, demonstrating the effectiveness of infrared heating in mitigating the challenges associated with high fiber volume fractions. The infrared heater was positioned in a rotating printing head so it could continuously stay in front of the print path. Mechanical tests showed a flexural strength of 1304 MPa and tensile strength of 995 MPa, with high fiber volume fraction and infrared assistance. As far as we know, these values represent the highest achieved in the literature for CFRTP printing without any post-processing. Optical images and differential scanning calorimeter (DSC) tests were used to investigate the microstructure and thermal properties of the printed samples.

All inkjet-printed organic solar cells on 3D objects

Drop-on-demand inkjet printing is a promising and commercially relevant technology for producing organic electronic devices of arbitrary shape on a wide variety of different substrates. In this work we transfer the inkjet printing process of organic photovoltaic devices from 2D to 3D substrates, using a 5-axis robot system equipped with a multi-nozzle inkjet printing unit. We present a ready-to-use 3D printing system for industrial application, using a 5-axis motion system controlled by commercial 3D motion software, combined with a commonly used multi-nozzle inkjet print head controlled by the corresponding printing software. The very first time inkjet-printed solar cells on glass/ITO with power conversion efficiencies (PCEs) of up to 7% are realized on a 3D object with surfaces tilted by angles of up to 60° against the horizontal direction. Undesired ink flow during deposition of the inkjet-printed layers was avoided by proper ink formulation. In order to be able to print organic (opto-)electronic devices also on substrates without sputtered indium tin oxide bottom electrode, the bottom electrode was inkjet-printed from silver nanoparticle (AgNP) ink, resulting in the first all inkjet-printed (i.e. including bottom electrode) solar cell on a 3D object ever with a record PCE of 2.5%. This work paves the way for functionalizing even complex objects, such as cars, mobile phones, or ‘Internet of Things’ applications with inkjet-printed (opto-)electronic devices.

Utilizing in-nozzle impregnation for enhancing the strength of recycled PET-derived 3D printed continuous banana fiber reinforced bio-composites

PurposeThis study aims to evaluate the potential of using the in-nozzle impregnation approach to reuse recycled PET (RPET) to develop continuous banana fiber (CBF) reinforced bio-composites. The mechanical properties and fracture morphology behavior are evaluated to establish the relationships between layer spacing–microstructural characteristics–mechanical properties of CBF/RPET composite.Design/methodology/approachThis study uses RPET filament developed from post-consumer PET bottles and CBF extracted from agricultural waste banana sap. RPET serves as the matrix material, while CBF acts as the reinforcement. The test specimens were fabricated using a customized fused deposition modeling 3D printer. In this process, customized 3D printer heads were used, which have a unique capability to extrude and deposit print fibers consisting of a CBF core coated with an RPET matrix. The tensile and flexural samples were 3D printed at varying layer spacing.FindingsThe Young’s modulus (E), yield strength (sy) and ultimate tensile strength of the CBF/RPET sample fabricated with 0.7 mm layer spacing are 1.9 times, 1.25 times and 1.8 times greater than neat RPET, respectively. Similarly, the flexural test results showed that the flexural strength of the CBF/RPET sample fabricated at 0.6 mm layer spacing was 47.52 ± 2.00 MPa, which was far greater than the flexural strength of the neat RPET sample (25.12 ± 1.94 MPa).Social implicationsThis study holds significant social implications highlighting the growing environmental sustainability and plastic waste recycling concerns. The use of recycled PET material to develop 3D-printed sustainable structures may reduce resource consumption and encourages responsible production practices.Originality/valueThe key innovation lies in the concept of in-nozzle impregnation approach, where RPET is reinforced with CBF to develop a sustainable composite structure. CBF reinforcement has made RPET a superior, sustainable, environmentally friendly material that can reduce the reliance on virgin plastic material for 3D printing.