High-speed Printing Research Articles

Multiphysics Simulation of Continuous Liquid Interface Production (CLIP) 3D Printing Technology

Abstract This study explores the advancements of 3D printing through Continuous Liquid Interface Production (CLIP), which has achieved a remarkable 100-fold increase in print speed over conventional stereolithography. CLIP’s rapid printing is enabled by an oxygen inhibition layer above the resin-vat window, initiating photopolymerization above the deadzone for faster resin flow. Despite CLIP’s notable speed advantage, it struggles with artifacts arising from non-optimal print cofigurations. Our research addresses this challenge by developing a novel multiphysics simulation tool. In order to evaluate the effects of various parameters, this study introduces a 2D-CLIP multiphysics simulation tool integrating optical and chemical models. The simulation tool employs a MATLAB-PDE solver that incorporates multiphysics equations to forecast deadzone thickness and cured dimensions at various print settings. This approach allows for a comprehensive understanding of the CLIP process and its variables. The simulation tool effectively predicts key parameters, aiding in the fine-tuning of the printing process. It significantly reduces experimental costs and time while enhancing the precision of CLIP 3D printing. The tool’s predictions are instrumental in optimizing print parameters, thereby mitigating the prevalent artifacts in printed objects. This research contributes a pioneering simulation tool for CLIP 3D printing, addressing the critical gap in optimizing print configurations. Its innovative approach in integrating multiphysics models within a simulation framework offers a valuable asset in advancing the capabilities of high-speed 3D printing technologies.

Enhancing the Mechanical Strength of a Photocurable 3D Printing Material Using Potassium Titanate Additives for Craniofacial Applications.

Photopolymerization-based three-dimensional (3D) printing techniques such as stereolithography (SLA) attract considerable attention owing to their superior resolution, low cost, and relatively high printing speed. However, the lack of studies on improving the mechanical properties of 3D materials highlights the importance of delving deeper into additive manufacturing research. These materials possess considerable potential in the medical field, particularly for applications such as anatomical models, medical devices, and implants. In this study, we investigated the enhancement of mechanical strength in 3D-printed photopolymers through the incorporation of potassium titanate powder (K2Ti8O17), with a particular focus on potential applications in medical devices. The mechanical strength of the photopolymer containing potassium titanate was analyzed by measuring its flexural strength, hardness, and tensile strength. Additionally, poly(ethylene glycol) (PEG) was used as a stabilizer to optimize the dispersion of potassium titanate in the photopolymer. The flexural strengths of the printed specimens were in the range of 15-39 MPa (Megapascals), while the measured surface hardness and tensile strength were in the range of 41-80 HDD (Hardness shore D) and 2.3-15 MPa, respectively. Furthermore, the output resolution was investigated by testing it with a line-patterned structure. The 3D-printing photopolymer without PEG stabilizers produced line patterns with a thickness of 0.3 mm, whereas the 3D-printed resin containing a PEG stabilizer produced line patterns with a thickness of 0.2 mm. These findings demonstrate that the composite materials not only exhibit improved mechanical performance but also allow for high-resolution printing. Furthermore, this composite material was successfully utilized to print implants for pre-surgical inspection. This process ensures the precision and quality of medical device production, emphasizing the material's practical value in advanced medical applications.

One-step high-speed thermal-electric aerosol printing of piezoelectric bio-organic films for wirelessly powering bioelectronics.

Piezoelectric biomaterials hold a pivotal role in the progression of bioelectronics and biomedicine, owing to their remarkable electromechanical properties, biocompatibility, and bioresorbability. However, their technological potential is restrained by certain challenges, including precise manipulation of nanobiomolecules, controlling their growth across nano-to-macro hierarchy, and tuning desirable mechanical properties. We report a high-speed thermal-electric driven aerosol (TEA) printing method capable of fabricating piezoelectric biofilms in a singular step. Electrohydrodynamic aerosolizing and in situ electrical poling allow instantaneous tuning of the spatial organization of biomolecular inks. We demonstrate TEA printing of β-glycine/polyvinylpyrrolidone films, and such films exhibit the piezoelectric voltage coefficient of 190 × 10-3 volt-meters per newton, surpassing that of industry-standard lead zirconate titanate by approximately 10-fold. Furthermore, these films demonstrate nearly two orders of magnitude improvement in mechanical flexibility compared to glycine crystals. We also demonstrate the ultrasonic energy harvesters based on the biofilms, providing the possibility of wirelessly powering bioelectronics.

How the Laser Found Problems to Solve

While some initially wondered about practical applications for the laser—an invention born out of basic research—within a few decades after its first appearance, it was offering solutions ranging from high-speed printing to crystal-clear music.

Printing of low-viscosity materials using tomographic additive manufacturing

Tomographic volumetric additive manufacturing (VAM) is a high-speed 3D printing technique that overcomes many of the challenges faced by conventional layer-by-layer based approaches. However, unlike other vat photopolymerization techniques, VAM must use much higher viscosity resins prohibiting the use of more commonly available lower-viscosity materials. Low-viscosity poly(ethylene glycol) diacrylate (PEGDA) has seen wide usage in bioprinting techniques but has eluded printing in VAM. Using a VAM printer with a high angular dose delivery rate, as well as tomographic projections optimized for low-viscosity printing conditions, we demonstrate high-fidelity VAM printing in PEGDA with viscosities as low as 12 cP. Micro-computed tomography imaging of printed parts reveal close-to voxel resolution limited performance. Furthermore, we have demonstrated the first direct printing of a low-viscosity hydrogel in VAM. The proposed method expands the viscosity range, and in turn the catalogue of materials accessible to VAM, giving this printing modality the broadest viscosity range of any vat photopolymerization technique.

Optimisation of microstructures from filament extrusion additive manufacturing based on numerical simulation with VOLCO-X

The mechanical properties of parts built with material extrusion additive manufacturing are highly dependent on the material distribution within parts’ microstructure. This varies with the choice of process parameters. Therefore, when designing a functional printed part, one must tailor the printing parameters in order to obtain the desired properties, such as minimal voids. The present work proposes an optimisation method that designs printing parameters to minimise manufacturing time while keeping the void volume fraction at very low values (hence improving mechanical properties), keeping dimensions within tight tolerances and guaranteeing structural integrity. The new optimisation method utilises the authors’ previously developed software VOLCO-X, which is capable of efficiently predicting material distribution from filament extrusion within printed parts, including print track dimensions and microstructure geometry, without the need for any experimental calibration. In order to validate the proposed optimisation scheme, optimised printed parts using the scheme and parts using printing parameters determined by a commercial slicing software were manufactured and compared for different printing speeds and deposition strategies. At printing speed of 16 mm/s, it was possible to decrease the manufacturing time by more than 20% and structural mass by more than 5% in comparison to the commercial slicer printed part, whilst maintaining similar mechanical properties. At printing speed of 96 mm/s, due to the high printing speed, the commercial printed part presented gap faults between deposited strands, while the optimised part had structural integrity. At this printing speed, the optimised printed part presented significant improvements in terms of mechanical properties. The proposed optimisation methodology, in conjunction with VOLCO-X, is a powerful tool that can be used to improve manufacturing by filament extrusion. This innovative tool allows the identification of printing parameters without experiments and trial-and-error approaches, thus saving time and expense.

Contact-force-based closed-loop control of shell structure additive manufacturing with continuous-fiber-reinforced polymer composites

Additive manufacturing (AM) is an automated process for fabricating complex structures, especially for continuous fiber-reinforced polymer (CFRP) composites with exceptional mechanical performance and reduced weight. The extrusion-based CFRP-AM process has been widely adopted but faces challenges with insufficient impregnation/adhesion and lack of geometrical accuracy. Existing research efforts exploit various mechatronics approaches and printing parameter adjustment techniques to enhance CFRP quality. Nevertheless, most of them are static or slow-varying; thus, they cannot dynamically adjust to local geometrical features and faults, which are particularly representative of the CFRP-AM process in high-curvature regions. To enable dynamic and rapid adjustment, this study exploits contact forces as major real-time feedback signals to dynamically control the feed velocity, layer height, and fiber extrusion rate. To create a continuous feedback control environment for dynamic adjustment, the study also proposes a novel helical CFRP-AM printing trajectory generation method for closed shell structures, such that the helical angles indirectly adjust the layer height of the parts. A material extrusion CFRP-AM platform combining a co-extrusion nozzle, an industrial robot, a six-degree-of-freedom load cell, and a real-time closed-loop control system is built to verify the proposed control framework. Three representative case studies are introduced to show the enhancements of the closed-loop CFRP-AM process, particularly in layer height adjustment, high-speed printing, and large curvature regions.

Tracking control of non-minimum phase systems: a kernel-based approach

Feedforward control with model inversion is a widely-used solution for high-precision output tracking. However, because inverting a non-minimum phase model generates unbounded control input, model-inversion only applies to limited types of systems. This paper presents a new non-parametric pseudo-inversion approach to design bounded optimal control input with desirable properties for arbitrary types of systems. Closed-form equations are presented for the batch (full preview) and recursive (limited preview) implementations of this approach, and its performance is compared against existing pseudo-inversion methods in benchmark numerical examples. Furthermore, the practical implementation of the proposed method is demonstrated by designing a feedforward controller for a commercial 3-Dimensional (3D) printer. The results show that the proposed approach effectively compensates for the structural vibrations of the printer, preventing layer-shifting errors that usually happen during high-speed printing.

High-speed 3D printing temperature system with optimized PlD parameters based on improved ant lion optimization algorithm

An Ant Lion Optimization algorithm based on elite Opposition-based learning and Cosine factors (OCALO) is proposed to address the problem of poor response and stability during heating process in high-speed 3D printing temperature system.The generation of the initial solution in OCALO algorithm is enhanced by the introduction of a new Tent-Logistic-Cotangent composite chaotic mapping, which guarantees the diversity of population. The PID parameters are optimized using the improved algorithm. Compared with two existing classical algorithms and three improved ALO algorithms, the proposed algorithm improves the convergence speed, global search ability and the ability to jump out of the local optimal solution. The outcomes of simulation and experimentation demonstrate that the algorithm improves the transient and steady-state performance of temperature control with better accuracy and robustness. It takes at least 123 s faster than other controllers to reach stability and is more than two times stronger than other PID controllers, making it better suited to high-speed 3D printing temperature systems.

Evaluation of multi-walled carbon nanotubes alignment during 3D printing of poly(acrylonitrile-butadiene-styrene) nanocomposite filaments

Nanocomposites incorporated with one-dimensional electrical conductive materials such as carbon nanotubes have been used in many applications in various industries. In this research, the filaments made of poly (acrylonitrile-butadiene-styrene) (ABS) containing 1, 3, and 5 wt% multi-walled carbon nanotubes (MWCNT) were first prepared and then printed in three directions and two printing speeds. The rheological and electrical percolation thresholds were found to take place at 0.32 and 0.96 wt% MWCNT, respectively. Using the Casson plot, it was revealed that the yield stress of the nanocomposites containing 5 wt% MWCNT was 70 times higher than that of the pristine ABS. The results also indicated that the electrical resistance decreased from 17.4 to 6.8 Ω with the increase in printing speed from 4 to 20 mm/s, respectively. The alignment of the nanofillers was examined using X-ray diffraction method. It was found from the azimuth angle that the materials printed at higher printing speed had more orientation, with respect to the director, in comparison with that of printed at lower speed.

Fiber bundle deposition model and variable speed printing strategy for in-situ impregnation 3D printing of continuous fiber reinforced thermoplastic composites

In the in-situ impregnation 3D printing of continuous fiber reinforced thermoplastic composites (CFRTPCs) at constant printing speed, in order to pursue higher printing efficiency, a higher speed for printing is adopted generally, which has no effect on the printing of the straight section, but at the same speed of printing at the corner, the printing speed will cause the fiber bundle to deviate from the printing path at the corner, which affects the accurate laying of fiber bundle along the printing path. Obviously, reducing the printing speed is an effective method to improve the print quality at the turn, but printing the entire part at the reduced speed will greatly limit the overall printing speed. However, the problem of different corner angles and shifting points from the straight section of high-speed printing to the corner section of low-speed printing has been puzzling researchers. In this paper, a fiber bundle deposition model has been proposed to reveal the deposition of fiber bundles, and the maximum offsets of fiber bundles were predicted under different turning angles. Compared with the measured results, the prediction error at different turning angles ranged from −1.07 % to 10.30 %. Then, combining with the finite element analysis method, the fiber bundle deposition model was adopted to study the effects of printing speeds, and the maximum printing speeds for different printing angles and the variable printing speed strategy have been put forward. The results have revealed that, by using the optimized variable printing speed strategy, the surface quality of the fabricated parts and the deposition of the fiber bundles along the designed printing path were significantly improved. The fiber bundle deposition model and the variable speed printing strategy could be helpful for the high-precision 3D printing of CFRTPCs.

A study of the temperature-dependent stress yielding behavior of a gelatin-based hydrogel ink and its effects on the enhancement of the 3D printing resolution

Though existing studies had continuously improved the hydrogel printing resolution by facilitating ink solidification, it was literally challenging to exceed the size limit of the printing needle even if there was an ideal ink that could solidify instantaneously. One possible solution to this hurdle is to stretch the hydrogel ink with a high printing speed and try maintaining its deformation without strain recovery. In this study, a gelatin/alginate/hydroxyapatite(HA) ink was printed at multiple temperatures, and a much lower yielding strain occurred at −1 °C than 2–5 °C according to our rheological tests. At −1 °C, the hydrogel ink could be highly stretched to produce an ultrahigh resolution at 81 ± 13 μm while maintaining uniform and continuous. Furthermore, our biological tests found a high scaffold resolution greatly promoted cell adhesion, proliferation, osteogenic differentiation and biomineralization. We stepped further from existing studies, by coming up with a new concept of utilizing ink stress-yielding in improving printing resolution, which would broaden our understanding to the processing-structure-property relationship in hydrogel-based 3D printing.

Optofluidic crystallithography for directed growth of single-crystalline halide perovskites

Crystallization is a fundamental phenomenon which describes how the atomic building blocks such as atoms and molecules are arranged into ordered or quasi-ordered structure and form solid-state materials. While numerous studies have focused on the nucleation behavior, the precise and spatiotemporal control of growth kinetics, which dictates the defect density, the micromorphology, as well as the properties of the grown materials, remains elusive so far. Herein, we propose an optical strategy, termed optofluidic crystallithography (OCL), to solve this fundamental problem. Taking halide perovskites as an example, we use a laser beam to manipulate the molecular motion in the native precursor environment and create inhomogeneous spatial distribution of the molecular species. Harnessing the coordinated effect of laser-controlled local supersaturation and interfacial energy, we precisely steer the ionic reaction at the growth interface and directly print arbitrary single crystals of halide perovskites of high surface quality, crystallinity, and uniformity at a high printing speed of 102 μm s−1. The OCL technique can be potentially extended to the fabrication of single-crystal structures beyond halide perovskites, once crystallization can be triggered under the laser-directed local supersaturation.

Simultaneously improving fabrication accuracy and interfacial bonding strength of multi-material projection stereolithography by multi-step exposure

ABSTRACT Multi-material additive manufacturing (MMAM) takes full advantage of the ability to arbitrarily place materials of additive manufacturing technology, enabling immense design freedom and functional print capabilities. Among MMAM technologies, projection stereolithography (PSL) exhibits a great balance of high resolution and fast printing speed. However, fabrication accuracy of multi-material PSL is hindered by large overcure used to strengthen interfacial bonding weakened by chemical affinity and material-exchange process. We present a novel multi-step exposure method for multi-material PSL process to overcome this shortcoming. Firstly, the whole layer is moderately exposed producing overcure of single-material PSL level to generate geometries. Then weakened interfaces are strengthened individually with additional steps of exposure. The multi-step exposure is integrated into the already efficient materials printing order of multi-material PSL process. Curing depth and overcure of photocurable resins are modeled and characterized. Exposure required to achieve sufficient interfacial bonding of single-material interfaces built through material-exchange process and multi-material interfaces with altering materials printing order is determined with tensile tests. Microfluidic channels are used to compare fabrication accuracy of traditional single-step exposure and our multi-step exposure method. This method can be widely applied in multi-material PSL to improve fabrication accuracy in a variety of applications including microfluidic devices.

Numerical study of the heat transfer characteristics of wide-format thermal print head

Thermal printing technology has achieved remarkable success in the realm of portable printing due to its advantages such as high printing speed, easy maintenance, and energy efficiency. Nevertheless, there have been no reports on the application of thermal print technology in the booming field of wide-format printing. This article presents the design and construction of a primordial wide-format thermal printer. The corresponding heat transfer model used to design it is proposed subsequently, and the accuracy of the model is validated through experimental methods. The heat transfer characteristics of the wide-format thermal printer during operation are investigated using the model, providing essential technical support for the advancement and proliferation of thermal printing technology in the wide-format printing domain. The findings demonstrate that, during stable operation of the wide-format thermal printer, 84.7% of the heat generated by the heat generator is effectively transferred to the protective film for dye melting, while 13.3% of the heat is dissipated as waste heat to the glass substrate. The temperature distribution in the splicing area is greatly affected due to the non-working heat generation dots. Furthermore, the heat flux between adjacent heat generation dots is nonnegligible and exerts a mutual effect on the respective temperatures.

Study of print suitability of environment-friendly plastics using flexography printing

Environmental-friendly plastics (EFP) are new alternatives of fossil-based plastics. The EFP family mainly constitutes bio-plastics/bio-attributed plastics and post-consumer recycled plastics (PCR). EFP contributes around 10% of total plastics production in global plastic production. Presently EFP are mostly used in grocery bags, bin liners, compostable garbage bags and single-use plastics with single or spot color printing. Multi-color printing can add value or open new horizons for these materials, leading to high-value applications. It can also be used for high-speed printing or flexible packaging applications. Plastics available in this category come from both fossil-based and bio-based sources. Fossil-based bioplastics has almost similar degree of print suitability but materials coming from bio-based sources are yet to be explored for print suitability, especially with high-speed multi-color printing machines. Flexographic printing is known for high-quality and high-speed printing on different substrates, including paper, conventional plastics and fossil-based bio-plastics. The advantage of having a common impression cylinder (CIC) arrangement and the requirement of less pressure during printing makes it suitable for consideration for printing on EFP. Hence, this study, print suitability of EFP using flexography printing, is an attempt to explore the mutual compatibility of these substrates and printing process, which will prove to be a boon in the future for establishing EFP as a strong substitute for replacing conventional plastics.

High-speed electrolyte jet 3D printing of ultrasmooth and robust Cu microelectrodes

Electrochemical 3D printing technology built on computer numerical control platforms has enabled multi-dimensional and multi-scale manufacturing of various metal materials through layered electrochemical deposition. Compared to thermal 3D printing technology, electrolyte meniscus-confined 3D printing can manufacture Cu microstructures with fewer defects and smoother surfaces. In the meantime, it is still susceptible to unstable liquid–solid-air interfaces, low deposition rates, and limited printing geometry. This work combined jet electrochemical deposition with a portable 3-axis platform to develop a cyclic high-speed electrolyte jet (HSEJ) 3D printer. It offers a faster deposition rate of 53.4 µm/h when printing ultrasmooth Cu microelectrodes with surface average roughness down to 1.1 nm and microhardness of 3.3 GPa which is much higher than the best result of 2.4 GPa obtained by the other ECD methods. It is identified that the fluctuation of cathode current density plays a crucial role in defining the nucleation morphology on the Cu surface, while the cathode current efficiency is a reliable indicator to assess the deposition localization by reflecting the variation of diffusion percentage. HSEJ 3D printing provides a sustainable pathway for the facile recycling of waste cables into high-grade metal microelectronics with controllable surface morphology and 3D dimensions.Graphical

Development and comprehensive investigation on PLA / carbon fiber reinforced PLA based structurally alternate layered polymer composites

Progressive research on polymer composites is encouraged in this current era in order to create a new functional structured material for various integrated engineering applications. The present investigation entails developing a novel Structurally alternate-layered Material (SAM) with a common Polylactic Acid (PLA) and Carbon Fiber Reinforced Polymer (CFRP) via theirsuccessive alternate layer deposition using the non-toxic and high printing speed capacity 3D printing approach - Filament Freedom Fabrication (FFF) with raster angle of 0°. Extensive experimental studies on mechanical behavior and microscopic observation of SAM are carried out. Furthermore, SAM is subjected to numerical simulation via ABACUS on mechanical testing for identifying its tensile and compression behaviour. The resulting data are compared to those of PLA and CFRP. The results obtained from both the numerical and experimental methodologies are congruent, indicating that the mechanical behaviour of SAM is superior to PLA and marginally comparable to CFRP. Overall, the newly synthesized SAM is advantageous and could be potentially considered as a mechanically stabled, cost-effectiveand feasible alternative polymer composite material for any integrated engineering applications.

Evaluation of direct ink write processing parameter window via machine learning

Direct ink writing 3D printing offers significant advantages for fabricating soft materials. It is a process of forming solid parts from extruded line structures, so the uniformity and stability of the line is critical for successful printing. This study mainly focuses on the process parameter window for achieving uniform and stable printed lines. Four machine learning models (support vector machine, backpropagation neural network, decision tree, and K-nearest neighbour) are built to predict the success of printing. These models exhibited robust predictive capabilities, particularly the backpropagation neural network and support vector machine models, both achieving an accuracy of 0.9091. Utilizing these models, the reasonable processing parameter window and the relationships among printing parameters were analysed. The results indicate that high printing speeds require large extrusion pressure to achieve a high success rate. An increase in nondimensional nozzle height enhances the possibility of successful printing with small pressure and low speed. The predicted processing parameters derived from the machine learning model were applied to print representative structures, showing good prediction performance.

Recent innovations in interfacial strategies for DLP 3D printing process optimization.

Three-dimensional (3D) printing, also known as additive manufacturing, is capable of transforming computer-aided designs into intricate structures directly and on demand. This technology has garnered significant attention in recent years. Among the various approaches, digital light processing (DLP) 3D printing, which utilizes polymers or prepolymers as the ink, has emerged as the leading new technology, driven by high demand across diverse fields such as customized production, healthcare, education, and art design. DLP 3D printing technology employs cured slices as molding units and is recognized for its potential to achieve both high printing speed and resolution. Recent insights into the DLP printing process highlight its inherent interface transformations between liquid and solid states. This review summarizes key aspects of the printing process, speed, precision, and material diversity optimization, from the view of interfacial interactions between solid and liquid phases which are influenced by resin formation, curing surfaces and light source properties. These interactions include those at the liquid resin-UV pattern interface, the cured structure-curing surface interface, the liquid resin-curing surface interface, and the liquid resin-cured structure interface, each contributing to the unique characteristics of the printed results. Finally, this review addresses the current challenges and limitations of DLP 3D printing, providing valuable insights for future improvements and guiding potential innovations in the field.