Polymer Jetting Research Articles

Bio-inspired space-filling fractal metamaterial

Inspired by mammal cranial sutures with spatiotemporal morphological variation, two-phase space-filling fractal metamaterial was designed. Designs with different levels of complexity are fabricated via multi-material polymer jetting. Mechanical tests and systematic finite element (FE) simulations are conducted to evaluate the mechanical performance of the designs. It is found that the hierarchical number N of two-phase space-filling fractal metamaterial played an important role in their mechanical behaviors. The experimental results show that with increasing the hierarchical number N, these metamaterials show enhanced stiffness, strength, and toughness under tensile tests. From the simulation results, we found by decoupling the strain energy density in two phases, with increasing N, the soft phase has contributed almost the same energy level, however, the hard phase has contributed increasing energy level. Moreover, we found the volume fraction and the stiffness ratio of the hard phase dominate the overall mechanical properties of these two-phase space-filling fractal metamaterial. The bio-inspired mechanical metamaterials have broad applications in engineering materials for dissipating energy dissipation, mitigating impact, and retarding damages.

Superior damage tolerance observed in interpenetrating phase composites composed of aperiodic lattice structures

Interpenetrating Phase Composite (IPC) metamaterials, based on lattice topologies, have garnered significant attention as advanced materials for structural applications. However, conventional IPCs, which rely on periodic lattice unit cells, are prone to catastrophic failure due to their global deformation modes. To overcome this limitation, we present a novel IPC design utilizing aperiodic truss unit cells, inspired by the elusive “Einstein” monotile pattern. Our concept is demonstrated through IPC 3D printed via polymer jetting, using a hard polymer as the lattice filler and a soft polymer as the matrix. The distinctive mechanical properties of IPCs are characterized through single and cyclic quasi-static compression testing. Our findings demonstrate that aperiodic IPCs enable progressive deformation with gradual compression stress plateaus. Additionally, aperiodic IPCs exhibit remarkable damage tolerance, retaining 67.59 % of residual energy absorption and 73.83 % of ultimate strength after multiple cyclic compressions up to 30 % strain. These mechanisms are attributed to the synergistic deformation of interconnected unit cells, which lead to self-adjusting plastic collapse, progressive displacement evolution and delocalized deformation. This aperiodic concept paves the way for developing high-performance cushioning protection materials.

Auxetic Two‐Phase Chevron Mechanical Metamaterial

This investigation explores novel two‐phase chevron mechanical metamaterials that exhibit auxetic properties. Unlike traditional foam‐like cellular or porous auxetic materials, these designs are composed of chevron patterned layers embedded in anisotropic matrix. This innovation design allows for auxeticity in two orthogonal in‐plane directions (bi‐auxeticity) or in all in‐plane directions (complete auxeticity), providing not only a general strategy but also detailed guidelines for designing non‐porous auxetic mechanical metamaterials with tunable auxetic behaviors. One goal of this work is to explore the mechanical behavior, specifically effective stiffness and Poisson's ratio, of these new designs and to identify the design space for auxetic behavior using numerical and experimental methods. Systematic finite element (FE) simulations are conducted using ABAQUS and Python scripts to quantify effective stiffness and Poisson's ratio within a small strain range. To validate the numerical predictions, three representative designs are selected and fabricated via multi‐material polymer jetting. Uniaxial tension experiments are conducted on these specimens. Design spaces for non‐auxeticity, partial‐auxeticity, and complete auxeticity are identified through an integrated numerical approach. Theoretical criteria for determining the completeness of auxeticity are proposed and verified via FE simulations.

Evaluation on Surface Characteristics, Accuracy, and Dimensional Stability of Tooth Preparation Dies Fabricated by Conventional Gypsum and 3D-Printed Workflows.

To evaluate the surface characteristics, accuracy (trueness and precision), and dimensional stability of tooth preparation dies fabricated using conventional gypsum and direct light processing (DLP), stereolithography (SLA), and polymer jetting printing (PJP) techniques. Gypsum preparation dies were replicated according to the reference data and imported into DLP, SLA, and PJP printers, and the test data were obtained by scanning after 0, 1, 3, 7, 14, 28, and 42 days. After analyzing the surface characteristics, a best-fit algorithm between the test and the reference data was used to evaluate the accuracy and dimensional stability of the preparation dies. The data were analyzed by one-way analysis of variance and Tukey test or Kruskal-Wallis H test (α = .05). Compared with the gypsum group (3.61 ± 0.59 μm), the root mean square error (RMSE) values of the SLA group (5.33 ± 0.48 μm) was rougher (P < .05), the PJP group (2.43 ± 0.37 μm) was smoother (P < .05), and the DLP group (2.92 ± 0.91 μm) had no significant difference (P > .05). For trueness, the RMSE was greater in the PJP (34.90 ± 4.91 μm) and SLA (19.01 ± 0.95 μm) groups than in the gypsum (16.47 ± 0.47 μm) group (P < .05), and no significant difference was found between the DLP (17.10 Å} 1.77 μm) and gypsum groups. Regarding precision, the RMSE ranking was gypsum = DLP = SLA < PJP group. The RMSE ranges in the gypsum, DLP, PJP, and SLA groups at different times were 6.79 to 8.86 μm, 5.44 to 10.17 μm, 10.16 to 11.28 μm, and 10.94 to 32.74 μm, respectively. Although gypsum and printed preparation dies showed statistically significant differences in surface characteristics, accuracy, and dimensional stability, all tooth preparation dies were clinically tolerated and used to produce fixed restorations.

New Methodology for Evaluating Surface Quality of Experimental Aerodynamic Models Manufactured by Polymer Jetting Additive Manufacturing.

The additive manufacturing (AM) applications have attracted a great deal of interest with regard to experimental aerodynamic studies. There is a need for a universal roughness scale that characterizes different materials used in aerodynamic research. The main purpose of this paper is identification of the potential of a material jetting AM process to produce accurate aerodynamic surfaces. A new methodology to evaluate the roughness of aerodynamic profiles (airfoils) was proposed. A very short-span wing artifact for preliminary tests and a long-span wing model were proposed for design of experiments. Different artifacts orientations were analyzed, maintaining the same surface quality on the upper and lower surface of the wing. A translucent polymeric resin was used for samples manufacturing by polymer jetting (PolyJet) technology. The effects of main factors on the surface roughness of the wing were investigated using the statistical design of experiments. Three interest locations, meaning the leading-edge, central, and trailing-edge zones, on the upper and lower surfaces of the airfoil were considered. The best results were obtained for a sample oriented at XY on the build platform, in matte finish type, with a mean Ra roughness in the range of 2 to 3.5 μm. Microscopy studies were performed to analyze and characterize the surfaces of the wing samples on their different zones.

Designing a 3D Printed Model of the Skull-Base: A Collaboration Between Clinicians and Industry

IntroductionThe role of three dimensional (3D) printing in neurosurgical education is becoming increasingly common. Notably, 3D printing can simulate complex anatomical pathways that may be difficult to regularly and accurately reproduce in cadavers. One such example is the course of the facial nerve within the temporal bone and its relation to the labyrinth. This can aid pre-surgical planning and minimise surgical complications. Here we aim to develop a novel anatomically accurate model of the skull base which demonstrates key neuro vascular components and the course of the facial nerve within the temporal bone by developing a 3D printed model of the skull-base that can be used for medical education and pre-surgical planning.Materials and MethodsWe utilised a combination of Computed Tomography (CT) and angiography scans to reconstruct the skull base and its vascular contents. Neural components were digitally incorporated under the guidance of the Oxford neurosurgical team and the anatomy department. The model was integrated and printed using polymer jetting.ResultsThe model was successfully printed, with all neurovascular components included. Notably we were able to highlight the intra-temporal course of the facial nerve by creating a bony window within the temporal bone.ConclusionThrough a collaboration with industry and a multidisciplinary team, we were able to reproduce the base of the skull from patient neuro-imaging. Our model is both cost-effective, reproducible and can aid both medical students and neurosurgical trainees in their training/education.

A Design for Additive Manufacturing Strategy for Dimensional and Geometrical Quality Improvement of PolyJet-Manufactured Glossy Cylindrical Features.

The dimensional and geometrical quality of additively manufactured parts must be increased to match industrial requirements before they can be incorporated to mass production. Such an objective has a great relevance in the case of features of linear size that are affected by dimensional or geometrical tolerances. This work proposes a design for additive manufacturing strategy that uses the re-parameterization of part design to minimize shape deviations from cylindrical geometries. An analysis of shape deviations in the frequency domain is used to define a re-parameterization strategy, imposing a bi-univocal correspondence between verification parameters and design parameters. Then, the significance of variations in the process and design factors upon part quality is analyzed using design of experiments to determine the appropriate extension for modelling form deviation. Finally, local deviations are mapped for design parameters, and a new part design including local compensations is obtained. This strategy has been evaluated upon glossy surfaces manufactured in a Vero™ material by polymer jetting. The results of the proposed example showed a relevant improvement in dimensional quality, as well as a reduction of geometrical deviations, outperforming the results obtained with a conventional scaling compensation.

3D Rapid-Prototyped 21-31-GHz Hollow SIWs for Low-Cost 5G IoT and Robotic Applications

This article presents, for the first time, new design and fabrication techniques for Hollow Substrate Integrated Waveguides (HSIWs), demonstrated in the nominal frequency from 21 to 31 GHz, for use in wireless communication applications such as 5G, IoT and robotics. The design and fabrication techniques introduced in this paper feature: 1) the use of low-cost rapid prototyping additive manufacturing based on polymer jetting (PJ), and 2) the use of commercially available through-substrate copper via transitions. In contrast to the conventional SIW designs and fabrications, this new approach does not rely on through-substrate via fabrication, hence avoiding some difficult manufacturing steps, such as through-substrate etching, via formation and via metallization, which are considered complex and expensive to implement. The 3D printed HSIWs in this article can achieve a propagation loss of lower than 1.56 Np/m (13.55 dB/m), which is considered one of the results with the lowest propagation loss achieved to date, when compared to the state-of-the-art.

UV LED Assisted Printing Platform for Fabrication of Micro-Scale Polymer Pillars

Ultraviolet (UV) assisted printing has emerged as a promising additive manufacturing (AM) technology, which puts UV light sources with focused emission in high demand. Unfortunately, current ultraviolet light-emitting diodes (UV LEDs) are not able to provide adequately focused UV emission required for printing. Thus, a UV LED package with focused UV emission was proposed and fabricated using microelectromechanical system (MEMS) technology in this study. An optical model of the UV LED package with focused UV emission was developed. Based on the designed model, a silicon reflector stacked on another was achieved. By assembling the stacked silicon reflector and hemispherical quartz lenses, the UV LED package with focused UV emission was successfully achieved. A narrow beam with a beam angle of 16° between half maximum intensity was achieved, while the intensity at 0° was greater than 1000 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the focal point. The UV LED curing system using two focused UV LED packages was successfully developed based on the optical simulation results. Polymer pillars were fabricated by instantaneous UV curing process with synchronized UV curable polymer jetting process in one shot, and micro-scale polymer pillars with a diameter of 20 μm were achieved. Thanks to the high intensity and focused UV emission, polymer pillars can be formed in as little as 100 ms. 13600 polymer pillars were printed on a silicon wafer with uniform diameter and geometry in a single dispensing cycle. The UV LED assisted printing platform was successfully demonstrated for fabrication of micro-scale 3D structures in a fast speed with smooth printing process.

System Performance and Process Capability in Additive Manufacturing: Quality Control for Polymer Jetting.

Polymer-based additive manufacturing (AM) gathers a great deal of interest with regard to standardization and implementation in mass production. A new methodology for the system and process capabilities analysis in additive manufacturing, using statistical quality tools for production management, is proposed. A large sample of small specimens of circular shape was manufactured of photopolymer resins using polymer jetting (PolyJet) technology. Two critical geometrical features of the specimen were investigated. The variability of the measurement system was determined by Gage repeatability and reproducibility (Gage R&R) methodology. Machine and process capabilities were performed in relation to the defined tolerance limits and the results were analyzed based on the requirements from the statistical process control. The results showed that the EDEN 350 system capability and PolyJet process capability enables obtaining capability indices over 1.67 within the capable tolerance interval of 0.22 mm. Furthermore, PolyJet technology depositing thin layers of resins droplets of 0.016 mm allows for manufacturing in a short time of a high volume of parts for mass production with a tolerance matching the ISO 286 IT9 grade for radial dimension and IT10 grade for linear dimensions on the Z-axis, respectively. Using microscopy analysis some results were explained and validated from the capability study.

Additive manufacturing of dental polymers: An overview on processes, materials and applications.

Additive manufacturing (AM) processes are increasingly used in dentistry. The underlying process is the joining of material layer by layer based on 3D data models. Four additive processes (laser stereolithography, polymer jetting, digital light processing, fused deposition modeling) are mainly used for processing dental polymers. The number of polymer materials that can be used for AM in dentistry is small compared to other areas. Applications in dentistry using AM are limited (e.g. study models, maxillo-facial prostheses, orthodontic appliances etc.). New and further developments of materials are currently taking place due to the increasing demand for safer and other applications. Biocompatibility and the possibility of using materials not only as temporarily but as definitive reconstructions under oral conditions, mechanically more stable materials where less or no post-processing is needed are current targets in AM technologies. Printing parameters are also open for further development where optical aspects are also important.

A Systematic Review on 3D-Printed Imaging and Dosimetry Phantoms in Radiation Therapy.

Introduction:Additive manufacturing or 3-dimensional printing has become a widespread technology with many applications in medicine. We have conducted a systematic review of its application in radiation oncology with a particular emphasis on the creation of phantoms for image quality assessment and radiation dosimetry. Traditionally used phantoms for quality assurance in radiotherapy are often constraint by simplified geometry and homogenous nature to perform imaging analysis or pretreatment dosimetric verification. Such phantoms are limited due to their ability in only representing the average human body, not only in proportion and radiation properties but also do not accommodate pathological features. These limiting factors restrict the patient-specific quality assurance process to verify image-guided positioning accuracy and/or dose accuracy in “water-like” condition.Methods and Results:English speaking manuscripts published since 2008 were searched in 5 databases (Google Scholar, Scopus, PubMed, IEEE Xplore, and Web of Science). A significant increase in publications over the 10 years was observed with imaging and dosimetry phantoms about the same total number (52 vs 50). Key features of additive manufacturing are the customization with creation of realistic pathology as well as the ability to vary density and as such contrast. Commonly used printing materials, such as polylactic acid, acrylonitrile butadiene styrene, high-impact polystyrene and many more, are utilized to achieve a wide range of achievable X-ray attenuation values from −1000 HU to 500 HU and higher. Not surprisingly, multimaterial printing using the polymer jetting technology is emerging as an important printing process with its ability to create heterogeneous phantoms for dosimetry in radiotherapy.Conclusion:Given the flexibility and increasing availability and low cost of additive manufacturing, it can be expected that its applications for radiation medicine will continue to increase.

Evaluation of the rheological properties of photopolymers used in Polymer Jetting technology

The paper presents the results of tests related to relaxation of stresses in models of samples made using the technology of photo-curing of liquid polymer resins polyjet modeling (PJM). The models of the samples were made using two types of materials: VeroWhite and FullCure 720. The tests were performed on samples in compliance with the PN-EN ISO 3384 standard. The technological parameter whose impact was analyzed was the orientation of the models on the virtual building platform, which was defined with three variability levels (0°, 45°, and 90°). The tests demonstrated that the position of the models on the building platform has a significant impact on the relaxation of compressive stresses. Moreover, the most advantageous positions of the models on the building platform from the standpoint of relaxation of stresses were determined.

Lightweight and Low-Loss 3-D Printed Millimeter-Wave Bandpass Filter Based on Gap-Waveguide

This paper presents a comprehensive study of a groove gap waveguide (also known as a waffle-iron) bandpass filter at Ka-band (26.5-40 GHz), fabricated using high resolution polymer jetting (Polyjet) 3-D printing technology. The same filter was previously fabricated using brass CNC milling technology. The metalized Polyjet 3-D printed filter is lower loss, lighter in weight and more cost-effective, when compared to the solid metal case. The filter operates at a center frequency of 35.65 GHz and has a 500 MHz bandwidth (1.4% fractional bandwidth), having a transmission zero below and above the passband. Without any design iterations, the measured S-parameters for the Polyjet 3-D printed filter are presented and compared with simulated results, showing excellent agreement. A comparison is then made between the measured results and that of its brass machined counterpart. The new Polyjet 3-D printed filter is 85% lighter than the conventional machined version. All these features prove the important potential of 3-D printing technology for millimeter-wave applications, which include aerospace.

Dielectric strength heterogeneity associated with printing orientation in additively manufactured polymer materials

Anisotropy in dielectric properties can have deleterious effects in structures intended for use in high-field environments. We show that dielectric anisotropy is introduced into parts fabricated using additive manufacturing techniques based on the orientation in which the part is printed. Dielectric strength testing data, based on the ASTM D149 standard, are presented for samples fabricated using the polymer jetting (PolyJet), stereolithography (SLA), fused deposition modeling (FDM), and selective laser sintering (SLS) additive manufacturing techniques. Each unique printing direction available, based on the printing method, was examined in turn. Each printing technique was found to introduce anisotropic dielectric properties within the sample coupons that were a function of the original orientation in which the part was printed, and the direction of structural susceptibility was found to be print-method dependent. Differences in dielectric strength for coupons printed in different orientations were found to exceed 70% for some combinations of printing technique and polymer. Overall, test coupons printed with stereolithography (SLA) were found to exhibit the lowest degree of dielectric strength anisotropy between print orientations. Dielectric failure mechanisms are discussed.

Additive manufacturing of low cost and efficient proof of concepts for microwave passive components

A study on the passive microwave components made by polymer additive manufacturing (polymer jetting) is presented. Different types of components (waveguides, couplers, power dividers, filters and antennas) are designed to be made in a single part. Using a simple and cost-effective metallisation by applying silver paint, various prototypes with complex geometries have been manufactured to evaluate these proofs of concept and the robustness of the low-cost approach to make microwave components. Different measurements show that the obtained filters can provide an acceptable unloaded Q factor of 400–500 for the operating frequencies of 12–22 GHz. Waveguiding structures such as a mode converter, which is used as a broadband antenna, have also notably efficiently worked up to the Ka band (36 GHz). Due to a remarkable accuracy of nearly 80 µm, the obtained results of the proposed coupler, power divider and antennas are consistent with the full wave simulations, which prove that the currently available three-dimensional plastic printers can provide notably accurate prototypes to design original components.

3-D-Printed Microwave and THz Devices Using Polymer Jetting Techniques

3-D additive manufacturing (AM) offers unprecedented flexibility in the realization of complicated 3-D structures. Polymer jetting is one of the promising 3-D AM techniques that utilizes photosensitive polymers as the build material and is capable of precisely printing electromagnetic (EM) components up into the THz range. In this paper, important design and implementation aspects of polymer-jetting-based 3-D-printed EM components are discussed. A number of 3-D-printable polymer materials and their broadband EM characterization from GHz to THz are introduced. Design methodologies specific for 3-D-printed antennas and other EM components are presented. As examples, various 3-D-printed devices operating from GHz to THz frequency, including electromagnetic crystals (EMXT), waveguide, horn antenna, gradient index (GRIN) lenses, as well as 3-D AM-enabled new designs, such as millimeter wave (mmW)/THz, reflect array antennas, computer-generated THz holograms, and so on are reviewed. Moreover, current limitations and possible future improvements of the polymer jetting technique for EM applications are discussed. This type of 3-D AM technique is likely to enable many novel antenna and circuit architectures as well as various interesting 3-D metamaterial structures.

3D printed fluidics with embedded analytic functionality for automated reaction optimisation.

Additive manufacturing or ‘3D printing’ is being developed as a novel manufacturing process for the production of bespoke micro- and milliscale fluidic devices. When coupled with online monitoring and optimisation software, this offers an advanced, customised method for performing automated chemical synthesis. This paper reports the use of two additive manufacturing processes, stereolithography and selective laser melting, to create multifunctional fluidic devices with embedded reaction monitoring capability. The selectively laser melted parts are the first published examples of multifunctional 3D printed metal fluidic devices. These devices allow high temperature and pressure chemistry to be performed in solvent systems destructive to the majority of devices manufactured via stereolithography, polymer jetting and fused deposition modelling processes previously utilised for this application. These devices were integrated with commercially available flow chemistry, chromatographic and spectroscopic analysis equipment, allowing automated online and inline optimisation of the reaction medium. This set-up allowed the optimisation of two reactions, a ketone functional group interconversion and a fused polycyclic heterocycle formation, via spectroscopic and chromatographic analysis.

Evaluation of Additive Manufacturing Processes in Fabrication of Personalized Robot

Customer participation in the design stage of creating personalized products is increasing. Additive manufacturing (AM) has become a popular enabler of personalization. In this study, we evaluate the fabrication of an open-source robot arm in terms of cost, build time, dimensional and locational accuracy, end-effector accuracy, and mechanical properties. The mechanical components of the table-top robot were fabricated using two different AM processes of fused deposition modeling (FDM) and material jetting (polymer jetting or PolyJet). A reduction of infill density by 50% in the FDM process slightly decreased the building time, material cost, and tensile strength, but induced a 95% reduction in yield strength. A simulation of the mechanical assembly using the CAD models for the robot and the expected tolerances of the components estimated the end-effector positioning accuracy as 0.01–0.22 mm. The 3D printed robot arm was redesigned and fabricated using the best evaluated process in this study.

Polyjet technology applications for rapid tooling

Polymer Jetting (PolyJet) has proved to be one of the most accurate additive manufacturing technologies, in order to manufacture rapid tools. Rapid Tooling (RT) is different from conventional tooling as follow: manufacturing time is shorter, the cost is much less, but the tool life is shorter and tolerances are wider. The purpose of this paper is to make a comparative study between the soft tools (silicon moulds) and hard tools (acrylic thermoplastic moulds) based on the Polymer Jetting technology. Thus, two types of moulds have been made in order to manufacture a test part. Reaction injection moulding (RIM) and casting techniques were used to fill these moulds with resins that simulate the plastic injection materials. Rapid tooling applications, such as indirect tooling and direct tooling, based on PolyJet technology were experimentally investigated.