Commercial 3D Printer Research Articles

Effect of printing parameters on the sensing performance of a 3D printed elastomeric pressure sensor

Additive manufacturing processes have created new opportunities for the printing of functional electronics. Commercial 3D printers fall short in providing the capabilities to directly print with functional inks, especially, with thermosetting non-Newtonian materials. Also, open-source slicing software are generally designed to generate g-code for thermoplastics. In this work, we modified an inexpensive commercial 3D printer to print functional inks for electronics. A plunger-based extrusion mechanism was developed using a stepper motor and lead screw. The heated extruder in the commercial printer was replaced by the new mechanism. Next, the system was employed to print ionic liquid-based soft pressure sensors, followed by an ultraviolet light curing process to polymerize the printed structure. Sensor ink was prepared by mixing ionic liquid into an acrylate-based monomer. To obtain proper rheology for printing, fumed silica was added to the ink. The effect of different printing parameters on the sensing performance of the printed sensors was studied and presented. The parameters studied were sensor thickness, nozzle diameter, extrusion rate, and raster angle. Multiple sets of sensors were printed by changing these parameters, and they are evaluated for their sensitivity. The sensitivity was measured in terms of relative change in the voltage output from the sensor system. The results show that varying the printing parameters significantly affects the sensing performance. The sensitivity increases with the decrease in sensor thickness, increase in nozzle diameter, and increase in print flow rate. The findings from this study can be employed to modulate the sensitivity of a sensor for different applications by changing various print parameters.

Round-robin testing of commercial two-photon polymerization 3D printers

Round-robin testing of commercial two-photon polymerization 3D printers

Extremely-fast electrostatically-assisted direct ink writing of 2D, 2.5D and 3D functional traces of conducting polymer Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate- polyethylene oxide (PEDOT:PSS-PEO)

HypothesisPoly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is an attractive conducting polymer, albeit its rheological properties are inappropriate for direct ink writing (DIW). Here it is hypothesized that a suspension of PEDOT:PSS with a non-conducting highly spinnable viscoelastic polymer, e.g., polyethylene oxide (PEO), will significantly facilitate printability and enhance the electrical conductivity (EC) of PEDOT:PSS-PEO. It is also hypothesized that high-humidity post-treatment will enhance the EC even further, and the application of the electric field can facilitate the DIW speed beyond the capabilities of current commercial 3D printers. ExperimentsThe rheological behavior of PEDOT:PSS suspensions with several non-conducting polymers was explored in the experiments. The EC of the suspensions was measured, including the effect of high-humidity post-treatment. High-speed DIW of the optimal suspension was experimentally demonstrated with the applied electric field. FindingsThe findings revealed that PEO serves as a secondary dopant, and the suspension of 4.33 wt% PEDOT:PSS-52 wt% PEO possesses the EC > 15 times higher than that of PEDOT:PSS. Many 2D, 2.5D and 3D functional traces were printed at high resolution at the DIW speed up to 8.64 m/s (>10 times faster than current commercial printers), facilitated by the applied electric field. Post-treatment at 80–90% relative humidity enhanced the EC more than twice.

Construction of a radiation beam scanner and investigation of volume averaging correction factor effects on beam-profile.

In radiation beam-profile measurements, an accurate positioning of the detector with high position resolution is essential. For this purpose, we built a scanning device capable of moving a detector in three dimensions (3D) using mainly parts from a commercial 3D-printer. The accuracy and repeatability of movement was tested with caliper, laser displacement sensor and repeated 60Co beam-profile measurements in a water phantom. The results from the caliper and the sensor showed position accuracy for the scanner to be better than $\pm$150μm. The standard deviation of the error in position from laser sensor measurements was approximately 30μm, and the beam profile scans showed a maximum deviation from the mean position of 50μm. The effect of volume averaging correction factors on 60Co beam-profile was investigated with two different sized ionization chambers. The differences in the profiles were reduced significantly after applying the correction factors.

Effects of Slit Edge Notches on Mechanical Properties of 3D-Printed PA12 Nylon Kirigami Specimens.

Kirigami structures, a Japanese paper-cutting art form, has been widely adopted in engineering design, including robotics, biomedicine, energy harvesting, and sensing. This study investigated the effects of slit edge notches on the mechanical properties, particularly the tensile stiffness, of 3D-printed PA12 nylon kirigami specimens. Thirty-five samples were designed with various notch sizes and shapes and printed using a commercial 3D printer with multi-jet fusion (MJF) technique. Finite element analysis (FEA) was employed to determine the mechanical properties of the samples computationally. The results showed that the stiffness of the kirigami samples is positively correlated with the number of edges in the notch shape and quadratically negatively correlated with the notch area of the samples. The mathematical relationship between the stretching tensile stiffness of the samples and their notch area was established and explained from an energy perspective. The relationship established in this study can help fine-tune the stiffness of kirigami-inspired structures without altering the primary parameters of kirigami samples. With the rapid fabrication method (e.g., 3D printing technique), the kirigami samples with suitable mechanical properties can be potentially applied to planar springs for hinge structures or energy-absorbing/harvesting structures. These findings will provide valuable insights into the development and optimization of kirigami-inspired structures for various applications in the future.

Cryogenic tensile performance of 3D printed onyx–continuous carbon fiber composites

PurposeThe aerospace, energy and automotive industries have seen wide use of composite materials because of their excellent mechanical properties, along with the benefit of weight reduction savings. As such, the purpose of this study is to provide an understanding of the mechanical performance of these materials under extreme operational conditions characteristic of in-service environments.Design/methodology/approachThis study is novel in that it has evaluated the tensile performance and fracture response of additively manufactured continuous carbon fiber embedded in an onyx matrix (i.e. nylon with chopped carbon fiber) at cryogenic and room temperatures, for specimens manufactured with an angle between the specimen lying plane and the working build plane of 0°, 45° and 90°.FindingsResearch findings reveal enhanced tensile properties (i.e. ultimate tensile strength and modulus of elasticity) by the 0° (X) built specimens, as compared with the 45° (XZ45) and 90° (Z) built specimens at cryogenic temperature. A reduction in ductility is observed at cryogenic temperature for all build orientations. Fractographic analysis reveals the presence of fiber pullout/elongation, pores within the onyx matrix and chopped carbon fiber near fracture zone of the onyx matrix.Research limitations/implicationsResearch findings present tensile properties (i.e. ultimate tensile strength, modulus of elasticity and elongation%) for three-dimensional (3D)-printed onyx with and without reinforcing continuous carbon fiber composites at cryogenic and room temperatures. Reinforcement of continuous carbon fibers and reduction to cryogenic temperatures appears to result, in general, in an increase in the tensile strength and modulus of elasticity, with a reduction in elongation% as compared with the onyx matrix tensile performance reported at room temperature. Fracture analysis reveals continuous carbon fiber pull out for onyx–carbon fiber samples tested at room temperature and cryogenic temperatures, suggesting weak onyx matrix–continuous carbon fiber adhesion.Originality/valueTo the best of the authors’ knowledge, this study is the first study to report on the cryogenic tensile properties and fracture response exhibited by 3D-printed onyx–continuous carbon fiber composites. Evaluating the viability of common commercial 3D printing techniques in producing composite parts to withstand cryogenic temperatures is of critical import, for aerospace applications.

3D Printing of Ionic Liquid Polymer Networks for Stretchable Conductive Sensors

AbstractStretchable conductive materials have attracted great attention due to their potential applications as strain sensors, wearable electronics, soft robotics, and medical devices. The fabrication of these materials with customized object geometries is desirable, but the methods to achieve them are still highly limited. Additive manufacturing via vat photopolymerization can generate sophisticated object geometries, but there is still a significant need to print with materials that afford improved conductivity, mechanical properties, elastic recovery, and durability. Herein, stretchable strain sensors with a range of 3D printed designs are reported using vat photopolymerization. Ionic liquid resins are optimized for their printability using Sudan‐I as a photoabsorber and used to fabricate 3D objects that are subjected to compression, stretching, and bending loads that are detected as real‐time changes in current. Additionally, the self‐adhesive nature of these materials enables mechanically damaged structures to be mended together to regain its function as a strain sensor. These ionic liquid resins are compatible with commercial 3D printers, which enhances their applicability for on‐demand production of customized devices.

A Wideband Millimeter-Wave Corrugated Horn at 30–50 GHz Taking Advantage of All-Metal 3-D Printing Fabrication

The development of commercial all-metal 3D-printing technology provides a new fabrication method for wideband millimeter-wave corrugated horns up to 50 GHz. Compared with conventional fabrication techniques, such as direct machining, electroforming or recently developed methods relying on the assembly of platelets, all-metal 3D-printing has advantages of low cost, fast delivery, possibility of mass production, flexibility in fabrication of complicated geometries and good mechanical robustness. In this letter, we report the development of a wideband millimeter-wave corrugated horn at 30-50 GHz (50% fractional bandwidth) based on commercial all-metal 3D-printing technology. Measurement results reported in this letter show good performance in terms of both return loss and cross-polarization.

Digital Photopatterning: Designing Functional Multipolymeric Patterning Films

This study proposes a practical patterning technique, digital photopatterning, using a commercial LCD 3D printer to integrate polymeric materials with distinct properties. A parent cross-linked film swollen by additional monomers and a photo radical initiator is irradiated area-selectively using the 3D printer. Polymerization progresses only in the irradiated areas, enabling precise control over material heterogeneity. Through exploring various combinations of parent film and monomers, we demonstrated some unique functions, such as shape morphing and arbitrary gel patterning within the film. This practical and versatile technique has the potential for various applications in materials science and engineering.

Bioinspired Fiber Networks With Tunable Mechanical Properties by Additive Manufacturing

Abstract Soft bioinspired fiber networks offer great potential in biomedical engineering and material design due to their adjustable mechanical behaviors. However, existing strategies to integrate modeling and manufacturing of bioinspired networks do not consider the intrinsic microstructural disorder of biopolymer networks, which limits the ability to tune their mechanical properties. To fill in this gap, we developed a method to generate computer models of aperiodic fiber networks mimicking type I collagen ready to be submitted for additive manufacturing. The models of fiber networks were created in a scripting language wherein key geometric features like connectivity, fiber length, and fiber cross section could be easily tuned to achieve desired mechanical behavior, namely, pretension-induced shear stiffening. The stiffening was first predicted using finite element software, and then a representative network was fabricated using a commercial 3D printer based on digital light processing technology using a soft resin. The stiffening response of the fabricated network was verified experimentally on a novel test device capable of testing the shear stiffness of the specimen under varying levels of uniaxial pretension. The resulting data demonstrated clear pretension-induced stiffening in shear in the fabricated network, with uniaxial pretension of 40% resulting in a factor of 2.65 increase in the small strain shear stiffness. The strategy described in this article addresses current challenges in modeling bioinspired fiber networks and can be readily integrated with advances in fabrication technology to fabricate materials truly replicating the mechanical response of biopolymer networks.

Structural integrity of 3D-printed prosthetic sockets: Experimental study for paediatric applications

Due to unique patient characteristics, prosthetic sockets cannot be included in a standardised testing protocol as the rest major parts of the prosthesis. This makes the mechanical assessment of the socket a difficult process, which still remains crucial, especially nowadays, when new manufacturing technologies, such as additive manufacturing, are gaining ground in the field. In this study, a prototype testing rig was developed according to BS EN ISO 10328 standard, able to recreate the loading conditions of the early stance of the amputee gait on a paediatric transfemoral socket. The load requirements suggested in the standard were recalculated for the case of a 14-year-old male user with their weight in the 98th percentile. A variety of above-knee prosthetic sockets were produced with PLA and carbon-fibre reinforced nylon, using a commercial 3D printer. The sockets were tested under compressive load employing a plaster limb manikin. Video image processing was used to accurately capture the load-displacement relation of the sockets.

Tackling Inequalities in Oral Health: Bone Augmentation in Dental Surgery through the 3D Printing of Poly(ε-caprolactone) Combined with 20% Tricalcium Phosphate.

The concept of personalized medicine and overcoming healthcare inequalities have become extremely popular in recent decades. Polymers can support cost reductions, the simplicity of customized printing processes, and possible future wide-scale expansion. Polymers with β-tricalcium phosphate (TCP) are well known for their synergy with oral tissues and their ability to induce osteoconductivity. However, poor information exists concerning their properties after the printing process and whether they can maintain an unaffected biological role. Poly(ε-caprolactone) (PCL) polymer and PCL compounded with TCP 20% composite were printed with a Prusa Mini-LCD-®3D printer. Samples were sterilised by immersion in a 2% peracetic acid solution. Sample analyses were performed using infrared-spectroscopy and statical mechanical tests. Biocompatibility tests, such as cell adhesion on the substrate, evaluations of the metabolic activity of viable cells on substrates, and F-actin labelling, followed by FilaQuant-Software were performed using a MC3T3-E1 pre-osteoblasts line. PCL+β-TCP-20% composite is satisfactory for commercial 3D printing and appears suitable to sustain an ISO14937:200937 sterilization procedure. In addition, the proper actin cytoskeleton rearrangement clearly shows their biocompatibility as well as their ability to favour osteoblast adhesion, which is a pivotal condition for cell proliferation and differentiation.

Polarization encryption system using commercial LCDs for additive manufacturing

Polarization encryption has long been shown to allow simultaneous encryption of 2D images, but with scarce practical implementations or commercial applications to date. Nevertheless, a possible vector for its use in market products may be additive manufacturing (AM). As more complex and diversified technologies use AM in their production chains, intellectual property (IP) protection of shared data is becoming increasingly crucial. Many AM techniques rely on optical systems, therefore, it is essential to analyze the prospects of safeguarding AM processes using advances in optical secrecy. This work demonstrates the use of polarization encoding by employing liquid crystals for physical layer security. We examine the encoding of the information in a signal’s polarization state and show that linear transformations of polarization can be used to encrypt and decrypt data. We further demonstrate the use of off-the-shelf liquid crystal displays (LCD) in a low-cost commercial resin 3D printer to build a "polarization decryptor". The proposed system does not require any software modification and in hardware only the replacement of the printer’s LCD masking screen. This technique provides a promising methodology to secure part of the supply chain for AM operations.

Evaluation of conductive smart composite polymeric materials for potential applicationsin structural health monitoring and strain detection

The presented work collects results from the evaluation of electrical response to mechanical deformation and formation of defects presented by different polymeric based composite materials with potential for applications in Structural Health Monitoring and Strain Detection. With the aim of showing the variety of key materials in sectors like civil aviation, wind energy, automotive or railway that present this ability, specimens of very different nature have been analyzed: a) thermoplastic commercial 3D printing filaments loaded with carbonic fillers; b) epoxy resin loaded with Carbon Nanotubes and c) long carbon fiber reinforced resin composite. Measurements of electrical properties of these materials were taken to evaluate their capability to detect the presence of structural defects of different sizes as well as its spatial location. On the other hand, simultaneous measurements of electrical resistivity and mechanical strain during tensile tests were performed to analyze the potential of materials as strain detectors. All composites studied have shown a positive response (modification of electrical performance) to external mechanical stimulus: induced damage and deformations.Graphical

Additive Manufacture of Recycled Poly(Ethylene Terephthalate) Using Pyromellitic Dianhydride Targeted for FDM 3D-Printing Applications

The suitability of recycled poly(ethylene terephthalate) (R-PET) for 3D-printing applications was evaluated by studying the melt flow characteristics of the polymer. R-PET is known to experience significant deterioration in its mechanical properties when recycled due to molecular weight loss that results from reprocessing. Lower molecular weight hinders R-PET from being 3D-printable due to low viscosity and melt strength. The hypothesis was that R-PET can be modified with reasonable effort and resources to a 3D-printable thermoplastic if the low viscosity problem is tackled. Higher viscosity will enhance both the melt strength and the melt flow characteristic of the polymer, making it more suitable for processing and 3D printing. Reactive extrusion was selected as the method for modifying the polymer to achieve the objective via a coupling reaction with chain extender PMDA (pyromellitic dianhydride). A decrease in the melt flow index (MFI) from 90 to 1.2 (g/10 min) was recorded when PMDA was added at 0.75 wt% which lowered the MFI of modified R-PET to a comparable value to commercial 3D-printing filaments. Furthermore, FT-IR analysis was performed to investigate the chemical composition of the product. Finally, a 3D-printing filament was made from the modified R-PET by mimicking the main processing stations that exist in the filament-making process, which are the extrusion stage, water bath cooling stage and spooling stage. With 0.75 wt% PMDA, the melt strength was satisfactory for pulling the filament and, therefore, a filament with on-spec dimension was produced. Finally, a small object was successfully 3D-printed using the filament product at a minimum recommended temperature of 275 °C.

Design, Synthesis, and Application of a Water‐soluble Photocage for Aqueous Cyclopentadiene‐based Diels‐Alder Photoclick Chemistry in Hydrogels

AbstractSpatiotemporally functionalized hydrogels have exciting applications in tissue engineering, but their preparation often relies on radical‐based strategies that can be deleterious in biological settings. Herein, the computationally guided design, synthesis, and application of a water‐soluble cyclopentadienone‐norbornadiene (CPD‐NBD) adduct is disclosed as a diene photocage for radical‐free Diels‐Alder photopatterning. We show that this scalable CPD‐NBD derivative is readily incorporated into hydrogel formulations, providing gels that can be patterned with dienophiles upon 365 nm uncaging of cyclopentadiene. Patterning is first visualized through conjugation of cyanine dyes, then biological utility is highlighted by patterning peptides to direct cellular adhesion. Finally, the ease of use and versatility of this CPD‐NBD derivative is demonstrated by direct incorporation into a commercial 3D printing resin to enable the photopatterning of structurally complex, printed hydrogels.

Tensile Strength of 3D Printing Scaffold Design Truncated Hexahedron for Tuberculosis Drug Delivery

Mechanical properties are important characteristics of scaffolds as biomaterials implant in tissue engineering. This study focused on the analysis of the tensile strength of the 3D printing scaffold with a geometric design of the truncated hexahedron unit with pore size variation and combinFive variations of pore size of the scaffold (600, 800, 1,000, 1,200, and 1,400 µm) were fabricated from Polylactide acid (PLA) filament using the Fused Deposition Modelling (FDM) method through an ordinary commercial 3D printer. The IBS paste was synthesized from hydroxyapatite (HA), gelatin, hydroxypropyl methylcellulose (HPMC), and streptomycin. The characterization performed in this study were the pore size test with a digital microscope, tensile strength, elongation test, porosity, and contact angle. The 3D printed scaffold formed micropores after injected with IBS paste from a range of 130-230 µm. The tensile test results showed that the tensile strength of the 3D printing scaffold increased after being injected with IBS paste. In addition, the elongation test also shows a positive trend with increasing values of elongation after injection of IBS paste. The contact angle test results indicated that the scaffold was hydrophilic. From those characterizations, it could be concluded that 3D printing scaffold meet the criteria of scaffold for bone tissue engineering and drug carrier for tuberculosis.

A simple and fast method for screening production of polymer-ceramic filaments for bone implant printing using commercial fused deposition modelling 3D printers

3D printing is a promising technique for obtaining bone implants. However, 3D printed bone implants, especially those printed using fused deposition modelling, are still in the experimental phase despite decades of work. Research on new materials faces numerous limitations, such as reagents' cost and machines' high prices to produce filaments for 3D printing polymer-ceramic composites for fused deposition modelling. This paper presents a simple, low-cost, and fast method of obtaining polymer-ceramic filaments using apparatus consisting of parts available in a hardware store. The method's versatility for producing the filaments was demonstrated on two different biodegradable polymers – polylactic acid and polycaprolactone – and different concentrations of calcium phosphate – β-tricalcium phosphate – in the composite, up to 50 % by weight. For screening purposes, numerous scaffolds were 3D printed from the obtained filaments on a commercial 3D printer. Structural, mechanical, and biological tests show that the 3D printed scaffolds are suitable for bone implants, as their structure, mechanical, and non-cytotoxic properties are evident. Moreover, the proposed method of composite forming is a simplification of the processes of manufacturing and researching 3D printed materials with potential applications in the regeneration of bone tissue.

Experimental and Numerical Investigation of the Die Swell in 3D Printing Processes

Fused deposition modelling is one of the most widely used additive manufacturing techniques and the diffusion of 3D printers has increased in popularity even further in recent times. Since high precision is required in 3D printing, a good control over the extrusion process is necessary. In this regard, a crucial phenomenon to be accounted for is the die or extrudate swell, i.e., the enlargement of the cross-section of the strand when coming out of the printer nozzle. While this phenomenon has been studied in large scale extruders, it has not yet been investigated in depth for 3D printing processes. In this work, the die swell phenomenon observed in a printed PLA filament is studied by experiments and fluid dynamic simulations. A novel, easy-to-use, accurate and fast procedure for measuring the value of the die swell ratio during the printing process is developed, accounting for typical errors related to a non-constant strand diameter and possible oscillations of the filament with respect to the extrusion direction. As the printing velocity is increased, a linearly increasing swelling ratio is observed at low printing speeds. The trend flattens at moderate speed values. A sudden increase is found at high printing velocities. The swelling ratio measured with the proposed technique is compared with the results of multi-mode viscoelastic simulations at different temperatures. A fair agreement between the experimental measurements and the numerical predictions is found for printing velocities that are typically employed in commercial 3D printers, supporting the reliability of the developed procedure.

Vibration compensation of delta 3D printer with position-varying dynamics using filtered B-splines

The delta robot can reach higher speeds than traditional serial-axis machines used in fused filament fabrication 3D printing. However, like serial machines, delta printers suffer from undesirable vibration at high speeds which degrades the quality of fabricated parts. This undesirable vibration has been suppressed in serial printers using linear model-inversion feedforward control methods like the filtered B-splines (FBS) approach. However, techniques like the FBS approach are computationally challenging to implement on delta 3D printers because of their coupled, position-dependent dynamics. In this paper, we propose a methodology to address the computational bottlenecks by (1) parameterizing the position-dependent portions of the dynamics offline to enable efficient computation of the model online, (2) computing models at sampled points (instead of every point) along the given trajectory, and (3) employing QR factorization to reduce the number of floating-point arithmetic operations associated with matrix inversion. In simulations, we report a computation time reduction of up to 23× using the proposed method when compared to using the computationally expensive exact LPV model—all while maintaining high tracking accuracy. Accordingly, we demonstrate significant quality improvements on parts printed at various positions on a commercial delta 3D printer using our proposed controller compared to a baseline alternative, which uses an LTI model from one position. Acceleration measurements during printing show that the improvement in print quality of the proposed controller is due to vibration reductions of up to 39% when compared to the baseline controller.