High-speed Printing Research Articles

Process-induced morphological features in material extrusion-based additive manufacturing of polypropylene

Fused filament fabrication is a material extrusion-based additive manufacturing technique that has been strongly growing in popularity, for it is accessible, versatile, and affordable. The 3D-printing of semi-crystalline polymers still faces major challenges, though. Apart from common issues such as shrinkage and warpage phenomena, a variety of process-related morphological and crystallographic changes can occur. Since these changes strongly influence the resulting material properties, it is crucial to understand the complex relationships between the material, its processing and final properties on a fundamental level. In this context, the present work examines the impact of different nozzle temperatures and printing speeds on 3D-printed polypropylene (PP) samples. One extreme parameter set (high nozzle temperature, low printing speed) reveals a homogeneous morphology, weak flow-induced orientations, isotropic thermal conductivities and a strong inter-layer diffusion. In contrast, the other extreme parameter set (low nozzle temperature, high printing speed) forms an inhomogeneous morphology with a complex growth of shish-kebab structures, a pronounced weld line morphology and a highly anisotropic behaviour. By in-depth analyses of four parameter sets, this paper offers novel insights into the complex formation of crystalline structures in 3D-printed semi-crystalline polymers and suggests how to purposefully design the property portfolio of these materials.

Morphology and Mechanical Properties of 3D Printed Wood Fiber/Polylactic Acid Composite Parts Using Fused Deposition Modeling (FDM): The Effects of Printing Speed.

In this study, a wood fiber/polylactic acid composite (WPC) filament was used as feedstock to print the WPC part by means of fused deposition modeling (FDM). The morphology and mechanical properties of WPC parts printed at different speeds (30, 50, and 70 mm/s) were determined. The results show that the density of the printed WPC part increased as the printing speed decreased, while its surface color became darker than that of parts printed at a high speed. The printing time decreased with an increasing printing speed; however, there was a small difference in the time saving percentage without regard to the dimensions of the printed WPC part at a given printing speed. Additionally, the tensile and flexural properties of the printed WPC part were not significantly influenced by the printing speed, whereas the compressive strength and modulus of the FDM-printed part significantly decreased by 34.3% and 14.6%, respectively, when the printing speed was increased from 30 to 70 mm/s. Furthermore, scanning electronic microscopy (SEM) illustrated that the FDM process at a high printing speed produced an uneven surface of the part with a narrower width of printed layers, and pull-outs of wood fibers were more often observed on the fracture surface of the tensile sample. These results show that FDM manufacturing at different printing speeds has a substantial effect on the surface color, surface roughness, density, and compressive properties of the FDM-printed WPC part.

Experiment-Based Process Modeling and Optimization for High-Quality and Resource-Efficient FFF 3D Printing

This article reports on the investigation of the effects of process parameters and their interactions on as-built part quality and resource-efficiency of the fused filament fabrication 3D printing process. In particular, the influence of five process parameters: infill percentage, layer thickness, printing speed, printing temperature, and surface inclination angle on dimensional accuracy, surface roughness of the built part, energy consumption, and productivity of the process was examined using Taguchi orthogonal array (L50) design of experiment. The experimental results were analyzed using ANOVA and statistical analysis, and the parameters for optimal responses were identified. Regression models were developed to predict different process responses in terms of the five process parameters experimentally examined in this study. It was found that dimensional accuracy is negatively influenced by high values of layer thickness and printing speed, since thick layers of printed material tend to spread out and high printing speeds hinder accurate deposition of the printed material. In addition, the printing temperature, which regulates the viscosity of the used material, plays a significant role and helps to minimize the dimensional error caused by thick layers and high printing speeds, whereas the surface roughness depends very much on surface inclination angle and layer thickness, which together determine the influence of the staircase effect. Energy consumption and productivity are primarily affected by printing speed and layer thickness, due to their high correlation with build time.

Rapid 3D Printing Magnetically Active Microstructures with High Solid Loading

The cover image presents a 3D printed 9-mm-height magnetically-active structure featuring intricate 3D shapes and fine (sub-75-μm) features. The strong magnetic interaction allows it to be suspended against gravity using a small magnet on the top. It was accomplished via the synergy of the optimization of magnetic photopolymerizable resin and the high-speed 3D printing using micro-continuous liquid interface production (μCLIP) process. Further details can be found in the article, number 1900911 by Longqiu Li, Cheng Sun, and co-workers.

Dimensional scaling of high-speed printed organic transistors enabling high-frequency operation

Printed electronics has promised to deliver low-cost, large-area and flexible electronics for mass-market applications for some time; however, so far one limiting factor has been device performance. Over the last decade, great progress has been made in terms of materials, processing and printing resolution for printed transistors. In this article, we review dimensional scaling of printed organic thin-film transistors, which has enabled high-frequency operation. We review different device architectures that require different dimensions to be scaled with accompanying tradeoffs in performance and complexity. Various printing methods have been used to print scaled transistors. Inkjet and gravure printing have seen the greatest improvements. We will focus on gravure printing here as it not only enables high-resolution features but also high-speed printing for low-cost manufacturing. Operating voltage has been scaled down less aggressively due to difficulties with scaling down the thickness of printed gate dielectrics. The performance of organic semiconductor materials has also improved substantially. When processing the semiconductor, the scaling of other device dimensions needs to be considered to optimize performance. Based on these advances, transistor switching frequency has increased dramatically over the last decade with several reports of high-speed printed inverters operating at high kHz to low MHz frequencies, which are promising results for emerging applications of printed electronics.

Development of Low-melt White Toner for High Image Quality and High-speed Printing

Development of Low-melt White Toner for High Image Quality and High-speed Printing

3-Wavelength (UV, Blue, Red) Controlled Photo-Confinement for 3D-Printing: Kinetics and Modeling

Detailed kinetics for a 3-wavelength photopolymerization confinement (PC) system is presented for both numerical solutions and analytic formulas. The dynamic profiles of oxygen, free radicals, and monomer conversion for various situations of: blue-light only, 2-light (red and UV), and 3-light (red, blue, UV) are obtained. Higher oxygen concentration leads to a lower conversion, which could be enhanced by reducing the S-inhibition via a red or blue light pre-irradiation. We found that pre-irradiation time is given by TP = 200 s for red-light only, and reduced to 150 s, for both red and blue-light. The system under UV-only leads to a conversion lower than that of blue-only. However, conversion could be improved by the dual-light (blue and UV), and further enhanced by the pre-irradiation of red-light. The two competing factors, N-inhibition and S-inhibition, could be independently and selectively tailored to achieve: (i) high conversion of blue-light (without UV-light), enhanced by red-light pre-irradiation for minimal S-inhibition; and (ii) efficient PC initiated by UV-light produced N-inhibition for reduced confinement thickness and for high print speed.

Drop-on-demand high-speed 3D printing of flexible milled carbon fiber/silicone composite sensors for wearable biomonitoring devices

Three-dimensionally (3D) printed flexible piezoresistive composite sensors have provided valuable solutions for the personalized therapeutic development due to their promising capability in biomonitoring applications. Silicone rubber (SR) matrix is an important candidate to enable flexibility to the 3D printed devices. However, 3D printing of silicone inks blended with conductive fillers is limited due to the high viscosity, long curing time, and high percolation threshold. In the present study, a novel high-speed material jetting (MJ) 3D printing of high-viscosity conductive inks based on the mixture of a UV crosslinkable silicone rubber and milled carbon fibers (MCF) is demonstrated. The MCF content was optimized for printability, UV curability, and electrical conductivity. The sensors (with 30 wt. % MCF content) show high flexibility and foldability as well as a high resistance sensitivity to sever bending tests. The stretchability of 3D printed sensors was further improved by sandwiching the MCF/SR sensing layer between the SR layers. The electromechanical evaluation of the sandwiched MCF/SR sensors (S-MCF/SR) confirmed the high piezoresistive sensitivity of sensors (gauge factor in order of ∼400). Finally, the 3D printed sensors were employed for monitoring human joint motions to demonstrate the potential application in monitoring biosignals.

Extending the 3D food printing tests at high speed. Material deposition and effect of non-printing movements on the final quality of printed structures

3D Food Printing has unprecedented ambitions but for its practical use the increase of the speed of material deposition is a challenge to tackle. We have extended the information on this aspect by using a workflow that analyzes the screw-based deposition, at medium-high speed and the effect of some undervalued variables on the quality of 3D printed cereal-based structure. The most familiar approach utilized to compute the right extrusion rate for a good replica of the 3D virtual model completely fails at high print speed. Improvements would be possible only by using a flow of 300% or by changing, as input data, the diameter of filament at 1.0 mm. However, additional irregularities are caused by undervalued variables such as retraction distance being the most important for the printing quality while the travel speed and retraction speed are crucial to reduce printing time. Finally, desirability approach was able to define the conditions capable to get a maximum desirability of 0.85 at speed of 200 mm/s.

3D microwave printing temperature control of continuous carbon fiber reinforced composites

Continuous carbon fibers show dramatic promise as reinforcement materials to improve the stiffness, strength properties and design ability of 3D printed polymer parts. Current 3D printing methods have a low printing speed because the intrinsic slow and contact needed heat transfer disadvantages of the traditional resistive heating approach. We present a 3D microwave printing method by using the microwave for instantaneous and volumetric heating the continuous carbon fiber reinforced polymer (CCFRP) filament. This allows fabricating CCFRP components with much higher speed compared to traditional 3D printing technologies. To utilize the benefit of high printing speed, the speed-variation 3D microwave printing is applied to adapt the diverse printing path and reduce the printing period. In this paper, a new 3D microwave printing temperature control method by combining the prediction-model and step-proportional-integral-derivative control is researched to reduce the printing temperature difference of the CCFRP filaments during the speed-variation printing process. Three different CCFRP specimens with variation printing speed are tested, including a spanner, an aircraft and a spider from Nazca lines. The experimental results indicate that the new printing temperature control method for 3D microwave printing process dramatically reduces the temperature deviation. Further mechanical testing results indicate that the CCFRP printed with this method has a high tensile strength up to 358 MPa. This technology solved a key problem of 3D microwave printing of continuous carbon fiber reinforced polymer composites and can be used to manufacture complex polymer-matrix composite materials.

Modeling and Correcting Cure‐Through in Continuous Stereolithographic 3D Printing

AbstractContinuous stereolithography offers significant speed improvements over traditional layer‐by‐layer approaches but is more susceptible to cure‐through, undesired curing along the axis of exposure. Typically, cure‐through is mitigated at the cost of print speed by reducing penetration depth in the photopolymer resin via the addition of nonreactive light absorbers. Here, a mathematical approach is presented to model the dose profile in a part produced using continuous stereolithography. From this model, a correction method is developed to modify the projected images and produce a chosen dose profile, thereby reducing cure‐through while maintaining print speed. The method is verified experimentally on a continuous stereolithographic 3D printer, and the practicality of various dose profiles is investigated. In optimizing the critical dose parameter, the measured gelation dose Dgel is found to be insufficient for accurate reproduction of features, and an optimal value of Dc = 5Dgel is chosen for the test resin. Using optimized parameters with a high‐absorbance height resin (ha = 2000 µm), feature height errors are reduced by over 85% in a test model while maintaining a high print speed (s = 750 mm h−1).

Opportunities and Scope of Desktop 3D Printers in India

AM is an advanced manufacturing technology used for fabricating parts in layers, from a CAD file. Various methods and materials have been developed to cater to its expanding applications. AM has seen tremendous growth in the recent past. While growth in the technical aspect is essential for the development of new techniques, growth in the economic aspect provides the need of innovation. With its ever-increasing industrial and personal applications, the 3D printing technology has experienced advancements in both the aspects. Yet its full potential has not been harnessed in developing countries. In this work, it is proposed to optimize the existing desktop 3D printers for developing countries. A market survey was conducted to recognise the lagging areas and the design modifications were made accordingly to produce a compact, efficient and cost-effective personal 3D printer for the respective needs and applications in developing countries. The data collected was relevant to the Indian market. The construction, testing and analysis of the prototype, 3D printer 1.0 and 3D printer 2.0 resulted in reduced cost, high print speed and improved product quality of the produced personal 3D printers, to make it suitable for the Indian market.

High-speed two-photon polymerization 3D printing with a microchip laser at its fundamental wavelength.

High-resolution, high-speed 3D printing by two-photon polymerization (2PP) with a Nd:YVO4 Q-switched microchip laser at its fundamental wavelength of 1064 nm is demonstrated. Polymerization scan speeds of up to 20 mm/s and feature sizes of 250 nm are achieved using a high repetition rate Q-switched microchip laser with a semiconductor saturable absorber mirror (SESAM) and photoresist with a new photo-initiator bearing 6-dialkylaminobenzufuran as electron donor and indene-1,3-dione moiety as electron acceptor. The obtained results demonstrate the high potential of Q-switched microchip lasers for applications in 2PP 3D printing.

Rapid Open-Air Digital Light 3D Printing of Thermoplastic Polymer.

3D printing has witnessed a new era in which highly complexed customized products become reality. Realizing its ultimate potential requires simultaneous attainment of both printing speed and product versatility. Among various printing techniques, digital light processing (DLP) stands out in its high speed but is limited to intractable light curable thermosets. Thermoplastic polymers, despite their reprocessibility that allows more options for further manipulation, are restricted to intrinsically slow printing methods such as fused deposition modeling. Extending DLP to thermoplastics is highly desirable, but is challenging due to the need to reach rapid liquid-solid separation during the printing process. Here, a successful attempt at DLP printing of thermoplastic polymers is reported, realized by controlling two competing kinetic processes (polymerization and polymer dissolution) simultaneously occurring during printing. With a selected monomer, 4-acryloylmorpholine (ACMO), printing of thermoplastic 3D scaffolds is demonstrated, which can be further converted into various materials/devices utilizing its unique water-soluble characteristic. The ultralow viscosity of ACMO, along with surface oxygen inhibition, allows rapid liquid flow toward high-speed open-air printing. The process simplicity, enabling mechanism, and material versatility broaden the scope of 3D printing in constructing functional 3D devices including reconfigurable antenna, shape-shifting structures, and microfluidics.

Uniaxially aligned microwire networks for flexible transparent electrodes using a novel electrospinning set-up

The present work, reports on combination of precise positioning ability of 3D printers with near field electro spinning (NFES) as a low-cost and scalable approach to generate well-aligned, evenly distributed microfiber mask upon flexible substrates coated with metal thin film. Using a combination of annealing thermal treatment and the wet chemical etching of metal layer a flexible transparent electrode is prepared. Using this high speed and large-area printing technique we can overcome the drawbacks of conventional electrospinning such as fiber structural inhomogeneity, random orientation, and non-reproducible results. In addition, the application of more complicated and expensive methods such as lithography or e-beam lithography or nanoimprint lithography can be avoided using this technique. The most important advantage of the reported fabrication method relative to electro-spinning process is the ability to have a special control on the distribution pattern of the electrodes on the surface which can lead to better control over the ratio of conductivity and transparency of the surface.

A high-speed additive manufacturing approach for achieving high printing speed and accuracy

The primary concern of the Industry 4.0 is the direct digital manufacturing of customized products on demand at high production speed, high accuracy with functional material property. Although the unique capabilities of existing additive manufacturing technologies make it suitable for direct digital manufacturing, there are numerous limitations which include low printing speed, less accuracy and repeatability, and a limited selection of materials for a particular application. Therefore, a high-speed additive manufacturing approach is proposed in this paper, that is capable of achieving high speed of production, high accuracy, and surface finish, and functional material property. For better understanding, authors describe those additive manufacturing technologies that are capable of achieving the aforementioned characteristics. For validation, samples of various dimensions were 3D printed on a selective laser sintering and a high-speed multijet fusion 3D printer. The results were compared in the context of printing speed, surface roughness (Ra), and hardness of printed parts. Results revealed that the multijet fusion process is significantly faster than its counterpart while sacrificing Ra to some extent but the hardness of printed parts is not changed significantly. The selective laser sintering-printed samples had a 15% lower Ra compared with multijet fusion samples. The results also revealed that the multijet fusion process might be able to print composite/multi-materials; however, more research needs to be done.

Fabrication of PEDOT: PSS conductive patterns on photo paper substrate through electro-hydrodynamic jet printing process

Conductive polymers such as PEDOT: PSS have gained popularity in sensor fabrication and integration. The objective of current work is to investigate the effects of process parameters on the final quality of conductive patterns fabricated through electro-hydrodynamic (EHD) jet printing. Solutions of different concentration of PEDOT: PSS in ethylene glycol and isopropyl alcohol were prepared for printing purpose. Effects of operating parameters such as voltage, frequency, pressure and printing speed on quality of printing patterns were experimentally investigated. Solution with higher concentration of PEDOT: PSS in ethylene glycol has shown better jetting stability even at higher frequencies and printing speeds. Increasing the frequency at high printing speed reduced the size of pattern width. Similarly, higher pulse voltage in the working envelope also reduced the pattern size. However, increasing the pressure increased the size of width of pattern. A drastic decrease in the pattern width was observed with increase in printing speed. A pattern width of approximately 19.6 μm was produced at 500 Hz of frequency and 2000 mm/min of printing speed, the electrical resistance of which is 1.03 × 106 Ω/mm. Finally, these results were compared with the same concentration of PEDOT: PSS in isopropyl alcohol reported in previous studies.

Rapid authentication of pharmaceuticals via DNA tagging and field detection.

A small PCR-generated DNA fragment was introduced into a pharmaceutical grade ink as a molecular taggant, and the DNA tagged ink was delivered onto the surface of capsules by standard high-speed offset printing. The amount of DNA in the ink on each capsule is roughly 10−12 fold lower than that allowed as safe by the United States Food and Drug Administration (FDA) and the WHO with regards to acceptable limits of residual DNA. The printed ink on the capsule surface was sampled by swabbing, followed by direct analysis of the DNA-swab complex, without subsequent DNA purification. It was shown that DNA recovered from the ink by swabbing was suitable for PCR-CE analysis—a widely used method in forensic science and was also suitable for qPCR and isothermal DNA amplification, when coupled with portable devices similar to those used for environmental sampling and food safety testing. The data set a precedent: A small DNA fragment could be introduced as an excipient into a pharmaceutical application, and thereafter tracked through the pharmaceutical supply chain via forensic DNA authentication.

Multimaterial 3D Printing of Highly Stretchable Silicone Elastomers.

3D printing of silicone elastomers with the direct ink writing (DIW) process has demonstrated great potential in areas as diverse as flexible electronics, medical devices, and soft robotics. However, most of current silicones are not printable because of their low viscosity and long curing time. The lack of systematic research on materials, devices, and processes during printing makes it a huge challenge to apply the DIW process more deeply and widely. In this report, aiming at the dilemmas in materials, devices, and processes, we proposed a comprehensive guide for printing highly stretchable silicone. Specifically, to improve the printability of silicone elastomers, nanosilica was added as a rheology modifier without sacrificing any stretching ability. To effectively control print speed and accuracy, a theoretical model was built and verified. With this strategy, silicone elastomers with different mechanical properties can all be printed and can realize infinite time and high speed printing (>25 mm/s) while maintaining accuracy. Here, super-stretchable silicone that can be stretched to 2000% was printed for the first time, and complex structures can be printed with high quality. For further demonstration, prosthetic nose, data glove capable of detecting fingers' movement, and artificial muscle that can lift objects were printed directly. We believe that this work could provide a guide for further work using the DIW process to print soft matters in a wide range of application scenarios.

Time-dependent mechanical response of paper during web-fed high-speed inkjet printing

Abstract The influence of wetting and drying during high-speed inkjet (HSI) printing on the time-dependent mechanical behavior of commercial HSI papers was investigated using a custom-built C-Impact tensile tester. In HSI printing the water based ink solvent penetrates into the paper while the colorants adhere onto the surface. We found that water strongly affected paper stiffness and strength already 0.1 s after wetting. Creep compliance and paper strain at a typical HSI printing input tension of 180 N/m are varying strongly during the different process steps of HSI printing. In order to achieve a good color registration and print quality, we thus recommend that the web tension should be dynamically controlled in each process step to prevent straining after wetting or shrinkage during drying.