Multi Jet Fusion Research Articles

Modelling of the multi-jet fusion capillarity effect on close facing edges

Purpose The purpose of this paper is to develop a physical model able to predict the shape of the capillarity effect in multi-jet fusion when two facing edges mutually affect each other. The work also aims at testing the consistency of such a model with experimental observations. Design/methodology/approach An analytical model of the phenomenon is developed considering the surface tension of the polymer melt adhering to the unfused powder. The general equilibrium equations are solved by imposing the boundary conditions corresponding to the case of two close facing edges, in which the shapes of the menisci are mutually influenced. The analytical model is validated through an experimental activity. Specifically, a set of parallelepipeds with variable width was manufactured using an HP Multi Jet Fusion 4200. The morphologies of capillarities were captured via three-dimensional scanning and compared with those predicted by the model. Findings The results of this study demonstrate that the average error to the experimental capillarity profile is lower than that obtained by existing methods. Particularly, considerable improvements are achieved as far as the maximum capillarity height is concerned. The manufactured specimens exhibit a change in slope near the edges, which is arguably attributable to coating powder and other effects not included in the analytical model. Originality/value The model presented in this study differs in hypotheses from previous methods in literature by assuming a null derivative of the capillarity shape in the central point of the meniscus. This allows for a more accurate prediction of the defect morphology in the case of close facing edges.

Experimental Characterisation and Finite Element Modelling of Polyamide-12 Fabricated via Multi Jet Fusion.

The HP Multi Jet Fusion (MJF) technology is a relatively recent addition to powder bed fusion additive manufacturing (AM) techniques. It differentiates itself from selective laser sintering (SLS) technology through the use of fusing and detailing agents to control part geometry, and the use of a planar infrared radiation (IR) source that sweeps over the powder bed to initiate the sintering process. Depending on the printing methodology, AM processes can introduce mechanical property anisotropy that is dependent on print orientation. In the case of MJF-fabricated parts, there is a general disagreement over the influence of print orientation on tensile mechanical properties in the literature. In this work, MJF-fabricated PA12 (AM PA12) is printed at various orientations and characterised in terms of tensile and compressive mechanical properties. The orientations have been selected to take into account the alignment of the IR source sweep direction to the test load. We observe that orientating parts towards the vertical direction for printing tends to favour enhanced tensile mechanical properties. The anisotropy in mechanical properties is attributed to more complete polymer powder fusion as a result of the increased number of IR source sweeps when parts are orientated towards the vertical direction. Both tensile and compressive stress-strain data were used as experimental data input for calibrating the Elastic-Plastic with combined hardening (EPC) material model in the commercial finite element analysis (FEA) package-Abaqus. We demonstrate that the EPC material is a suitable material model for the FEA of AM PA12.

Composite strut-plate lattice: A high-stiffness design of cellular metamaterial having excellent strength and energy absorption ability

Although the 3D-printed plate lattices have higher stiffness and strength than the strut lattices, the difficulty in fabricating the plate microlattices limited their potential application. The plate lattices require holes in the plates to remove the powder trapped inside, but introducing holes in plates in a lattice could reduce stiffness and strength. In general, to enhance the mechanical properties of a specific lattice for a particular mass, the size of the unit cell should be reduced. However, small plate unit cells require tiny holes on plates that may not be sufficiently large enough for post-fabrication powder removal. Thus, as an alternative design strategy, this work proposes a composite strut-plate lattice inspired by fiber-reinforced composite materials to achieve high stiffness, strength and energy absorption ability. Further, this study provides a methodology based on the classical rule of mixture for composite materials to determine the threshold volume fraction of the plate lattice reinforcement in the strut lattice matrix to attain a stiffness value that exceeds the maximum theoretical stiffness limit— the Hashin-Shtrikman upper bound. The finite element simulation results were corroborated by quasi-static compression tests on 3D-printed lattices made of polymer PA12 fabricated using multi jet fusion technique. Notably, the yield strength of the lattice exceeded the maximum theoretical yield strength limit— the Suquet upper bound. Also, the energy absorption ability was remarkably improved compared to the strut lattice and was close to that of the plate lattice. • Combined strut and plate unit cells that solve 3D printing's powder entrapment problem. • Stiffness and yield strength beyond their theoretical limits are achieved. • Mechanical properties are tailored using composite rule of mixture. • The designed composite lattice shows excellent energy absorption ability. • Mechanical properties are predicted by FEM and corroborated with experiments.

MECHANICAL ANALYSIS OF THE NEWLY DEVELOPED 3D PRINTED PROSTHETIC SOCKET FROM PA12GB

This paper is focused on the complex evaluation of the prosthetic socket (of a hand) manufactured by the usage of additive technologies. Main advantage of this method is a significantly shorter production time and lower production cost. The durability of the socket is generally between 12 and 24 months. It is caused by the atrophy of the patient's tissues and also by the mechanical loading during the usage. The laminating of the carbon fibers on the model of the internal socket is used nowadays. This method is technologically and time demanding. The newly developed production process is using the 3D printing method by the HP MultiJet Fusion 4200 printer. The considered material is HP PA12GB. It is the thermoplastic material (polyamide) with 40% of glass beads. Production of the socket is reduced to few hours. This paper consists the mechanical comparison of the laminated (old design) and the 3D printed (new design) socket. The real mechanical testing is simulating the most critical loading by impact to the edge of the table. The evaluation in terms of durability and fatigue is performed also using the software nCode and Siemens NX.

PO07: Dosimetric Evaluation of Multichannel Brachytherapy Applicator Prototype Produced by Polyamide 12

<h3>Purpose</h3> In this study, we aimed to produce a multichannel brachytherapy applicator prototype by polyamide 12 and to test it using different dosimetry methods. <h3>Materials and Methods</h3> To achieve the aim of the study, we designed a multichannel brachytherapy applicator prototype similar to those available in the current market with central and peripheral channels. The prototype was produced by polyamide 12 material with a 3D printer using the Multi Jet Fusion technique. Afterward, we placed the produced applicator prototype into the bolus and measured the dose using different dosimetry methods such as treatment planning system (TPS), Gafchromic film dosimetry, and MOSFET dosimetry. Irradiation was performed using one of the peripheral channels as randomly. Three different measurements were made with the same irradiation dose for each measurement method, and the average results were recorded. This project was supported by the Scientific and Technological Research Institution of Turkey (TUBITAK) as Project number: 220S572. <h3>Results</h3> Six channels were positioned at the periphery of the designed applicator prototype and each channel was sized (>1.84 millimeters) to allow the passage of interstitial tubes compatible with the GammaMedplus iX afterloader device. The Euclidean distance between the source position and measuring point was 15.1 millimeters. The calculated irradiation time was 54.9 seconds. Dosimetry results are presented in Table 1. <h3>Conclusion</h3> When we examine the literature, we think that this study is the first experimental study in which polyamide 12 was used as material in the production of brachytherapy applicators. The results of this study should confirm by studies that include different dosimetry methods.

3D printing biocompatible materials with Multi Jet Fusion for bioreactor applications.

In the evolving three-dimensional (3D) printing technology, the involvement of different materials in any new 3D printing process necessitates a thorough evaluation of the product's biocompatibility for biomedical application. Here, we examined the ability of Multi Jet Fusion (MJF)-printed PA-12 to support cell proliferation and osteogenesis. Our results show that leachate from MJF-printed PA-12 does not inhibit the growth of L929 fibroblast and MC3T3e1 osteoblast. The substrate supports the attachment and proliferation of both cell types, though not at a level comparable to conventional polystyrene culture plate. Neither plasma treatment, poly-D-lysine, nor collagen coatings narrowed the gap substantially, suggesting the possible influence of other limiting factors. The substrate can also support MC3T3e1 osteogenesis. However, MJF-printed PA-12 exhibits varying ability in supporting the proliferation of different cell types, especially in subsequent passages. While L929's proliferation is comparable from passage-to-passage, MC3T3e1's growth ability is noticeably compromised. Interestingly, our results show that L929 subcultured back to polystyrene plate retains the ability to grow as robustly as those on the conventional plate, suggesting that MJF-printed PA-12 does not permanently impair cell proliferation. In addition, we have shown the successful culture of bacterial Escherichia coli on MJF-printed PA-12. Together, our study demonstrated the potential of MJF-printed PA-12 for biological applications.

Multi-Jet Fusion 3D Voxel Printing of Conductive Elastomers.

3D voxel printing enables the fabrication of parts with site-specific materials and properties at voxel-scale resolution, while the current research mainly focuses on the variations in mechanical properties and colors. In this work,the design and fabrication of voxelated conductive elastomers using Multi Jet Fusion 3D voxel printing actualized by a newly developed multifunctional agent (MA) are investigated. The MA, mainly consisting of carbon nanotubes and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, servesas an infrared-absorbing colorant, a reinforcement, and a conductive filler simultaneously. By controlling the drop-on-demand dispensing of the agents on thermoplastic polyurethane powder, the electrical conductivity across a single printed part can be tailored over a wide range from 10-10 to 10-1 S cm-1 at a voxel resolution of ≈100µm. Assembly-free strain sensors comprising conductive sensing layers and insulating frames are fabricated to demonstrate the capability of the technique in manufacturing all-printed wearable devices.

Compressive properties of cementitious composites reinforced by 3D printed PA 6 lattice

The lattice-reinforced cementitious composites prepared by placing 3D printed lattices in cementitious matrix has been proved to be effective in improving the bending mechanical properties of cement-based materials, such as improving ductility and brittleness. However, the compressive properties of 3D printed lattice-reinforced cementitious composites are still an open question. In this paper, the compressive properties of 3D printed polyamide 6 (PA6) lattice-reinforced cementitious composites with different structural forms were studies. Six kinds of lattices were fabricated by multi jet fusion (MJF) technique. The volumes of these lattices are identical to ensure that the volume enhancement ratio of the lattices in the cementitious composite specimen is the same. The plain cementitious matrix without lattice was set as the control group, and two nondestructive testing methods, AE and DIC, were used to compare the compressive properties between plain cementitious matrix and lattice-reinforced cementitious composites with different structural forms. The experimental results show that the 3D printed lattice can significantly improve the mechanical properties and failure modes of cement-based materials under uniaxial compression. In contrast, the six lattice forms used in this study can improve the maximum compressive bearing capacity and deformation capacity of the cement-based materials under uniaxial compression test, and reduce the damage of cement-based materials in the elastic deformation stage. This paper confirms that 3D printed lattices can improve the compressive properties of cement-based materials and provide a new method for improving the compressive strength of cement-based materials. At the same time, it provides new ideas for the development of ideal substitutes for steel bars in corrosive environments, energy conservation and emission reduction and the development of green buildings.

Preliminary color characterization of HP Multi Jet Fusion additive manufacturing with different orientations and surface finish

PurposeThis study aims to evaluate the color accuracy of HP Jet Fusion 580 3D printing, comparing 3D-printed outcomes against original digital input colors.Design/methodology/approachA custom cyan, magenta, yellow and black (CMYK) and red, green, blue (RGB) color chart was applied to the top, bottom and side surfaces of a 3D model. Four of each model were 3D-printed on a HP Jet Fusion 580, and half the samples were finished with a cyanoacrylate gloss surface finish, while half were left in raw form. A spectrophotometer was used to document CIELAB (L*a*b*) data, and comparisons made to the original input colors, including calculation of ΔE.FindingsThe CMYK samples were significantly more accurate than RGB samples, and grayscale samples in both color spaces were the most accurate of all. Typically, CMYK swatches were darker than the input values, and gloss samples were consistently darker than raw samples. The chromaticity (a*b*) range was found to be significantly smaller than what can be achieved digitally, with highly saturated colors unable to be produced by the printer.Originality/valueThis is the first study, to the best of the authors’ knowledge, to characterize the full color spectrum possible with the HP Jet Fusion 580, recommending that designers use the CMYK color space when applying colors and textures to 3D models. A quick-reference color chart has been provided; however, it is recommended that future research focus on developing a color management profile to better map digital colors to the capabilities of the printer.

Novel multi jet fusion 3D-printed patient immobilization for radiation therapy.

Thermoplastic immobilizers are used routinely in radiation therapy to achieve positioning accuracy. These devices are variable in quality as they are dependent on the skill of the human fabricator. We examine the potential multi jet fusion (MJF) 3D printing for the production immobilizers with a focus on the surface dosimetry of several MJF-printed PA12-based material candidates. Materials are compared with the goal of minimizing surface dose with comparison to standard thermoplastic. We introduce a novel metamaterial design for the shell of the immobilizer, with the aims of mechanical robustness and low-dose buildup. We demonstrate first examples of adult and pediatric cranial and head-and-neck immobilizers. Three different PA12 materials were examined and compared to fused deposition modeling-printed polylactic acid (PLA), PLA with density lowered by adding hollow glass microspheres, and to perforated or perforated/stretched and solid status quo thermoplastic samples. Build-up dose measurements were made using a parallel plate chamber. A metamaterial design was established based on a packed hexagonal geometry. Radiochromic film dosimetry was performed to determine the dependence of surface dose on the metamaterial design. Full cranial and head-and-neck prototype immobilizers were designed, printed, and assessed with regard to dimensional accuracy. Build-up dose measurements demonstrated the superiority of the PA12 material with a light fusing agent, which yielded a ∼15% dose reduction compared to other MJF materials. Metamaterial samples provided dose reductions ranging from 11% to 40% compared to stretched thermoplastic. MJF-printed immobilizers were produced reliably, demonstrated the versatility of digital design, and showed dimensional accuracy with 97% of sampled points within ±2mm. MJF is a promising technology for an automated fabrication of patient immobilizers. Material selection and metamaterial design can be leveraged to yield surface dose reduction of up to 40%. Immobilizer design is highly customizable, and the first examples of MJF-printed immobilizers demonstrate excellent dimensional accuracy.

Effect of Build Parameters on the Mechanical Behavior of Polymeric Materials Produced by Multijet Fusion

The figure depicts the multi-jet fusion printing of specimens used to study the effect of changing build parameters on mechanical properties. At each layer, heat is applied to a surface with fusing agent (black) deposited atop fresh powder. A transparent build volume shows the temperature distribution (white-red color map) on the printed layer. Further details can be found in the article number 2100974 by Grace X. Gu and co-workers. For the image, we would like to credit: "Fabiola Leyva from HP Labs".

Flexural Properties of Periodic Lattice Structured Lightweight Cantilever Beams Fabricated Using Additive Manufacturing: Experimental and Finite Element Methods.

Lattice structures are a type of lightweight structure that is more commonly being applied to engineering systems as a way to reduce mass and enhance mechanical properties. The cantilever beam case is one of the primary modes of loading in many engineering applications, where light-weighting is also crucial. However, lightweight lattice structured cantilever beams have not been investigated considerably due to design and manufacturing limitations. Therefore, the aim of this study was to investigate the response of four different lattice structured cantilever beams comprising of unit cells made from Schwarz-P, Schwarz-D, Gyroid, and Octet-truss structures fabricated using Multi Jet Fusion additive manufacturing technology. An investigation into the cross-sections of these structures leads to a conclusion that the beams made from such structures are non-prismatic in nature as a result of variation in cross-sections. This led to the development of equations for the moment of inertia of these structures, which helped in calculating symmetric and un-symmetric bending. These beams were subjected to cantilever loading until failure, which provided insights into flexural properties such as flexural stress, stiffness, and strain energy. Experimental results indicate that the surface-based structures, due to better surface-area-to-volume ratio, have better ability in transferring loads and hence perform better than the beam-based Octet-truss beam. The Schwarz-D beam had performed the best among all the beams, which is further supported in literature due to its stretch-dominated topology that results in higher values of modulus. The finite element analysis (FEA) findings also validate these findings in which the distribution of stresses can be seen to be better transmitted than the other structures. The FEA validation shows that the distribution of Von-Mises stress and their position in experimental tests and failure of these structures is also very close, which provides validation to the experimental setup and the testing of beams.

Effect of the fibre length on the mechanical anisotropy of glass fibre–reinforced polymer composites printed by Multi Jet Fusion

ABSTRACT Mechanical anisotropy greatly influences the applications of materials printed by additive manufacturing techniques such as Multi Jet Fusion (MJF) and selective laser sintering. However, the mechanical anisotropy of MJF-printed fibre–reinforced polymer composites has not been well understood. In this work, the effect of the fibre length on the mechanical performance of MJF-printed glass fibre–reinforced polyamide 12 (GF/PA12) composites is systematically investigated. Both experimental and simulation results confirm that longer fibres are in favour of fibre alignment in the powder spreading direction. The composite parts with longer fibres exhibit higher porosity. When GFs with an average length of 226 μm are added, the ultimate tensile strength and tensile modulus of the composites measured in the powder bed spreading direction are remarkably improved by 51% and 326%, respectively, as compared with those of neat PA12 specimens. This work provides guidance for the printing of other high-strength fibre–reinforced polymer composites.

Electromagnetic omnidirectional scanning micromirror with multi jet fusion printed structures for smart factory applications

This paper presents a new omnidirectional scanning micromirror fabricated with a multi jet fusion three-dimensional (3D) printing process. The proposed electromagnetically actuated wobbling scanner has an aluminum-coated 6 mm-diameter mirror supported by quadpod springs and magnets for actuation. The analytic model for optimizing the driving coil is presented and compared with the finite element analysis results. The core part of the structural layer is fabricated by the 3D printing process and assembled with a separately fabricated reflective surface, permanent magnets, and coils. Three different combinations of magnets are tested to improve the optical scan angle of the device and provide a wider field of view (FOV). The one-dimensional (1D) horizontal (H) scan angle of 15.2° is obtained at 415 Hz, and 14.5° is obtained at the vertical (V) scan mode at 406 Hz. The applied current at both scan modes is less than 100 mA rms . The two-dimensional (2D) scan capability is also analyzed by generating the Lissajous, circular, and spiral scan patterns. For the spiral scan, a 2D FOV of 8° is achieved with the driving frequency of 400 Hz and the phase difference of 120°, which is equivalent to the FOV of 360° × 4°, the vertical angular resolution of 0.01°, and frame rate of 1 fps for light detection and ranging (LiDAR) system optics. The amplitude modulation depth and frequency are 100% and 1 Hz, respectively. The developed device can potentially be utilized in various LiDAR applications for the smart factory. • A 6 mm-diameter omnidirectional scanning micromirror has been fabricated by multi jet fusion 3D printing. • Operation principle of the scanner has been analyzed and spiral scan pattern with 8° field-of-view has been generated. • Surface morphology and characteristics of the MJF fabricated device have been analyzed. • Tested various 2D scan capabilities, including of Lissajous, circle, and spiral scan.

The Effect of Physical Aging and Degradation on the Re-Use of Polyamide 12 in Powder Bed Fusion.

Powder bed fusion (PBF) is an additive manufacturing (AM) technique which offers efficient part-production, light-weighting, and the ability to create complex geometries. However, during a build cycle, multiple aging and degradation processes occur which may affect the reusability of the Polyamide 12 (PA-12) powder. Limited understanding of these phenomena can result in discarding re-usable powder unnecessarily, or the production of parts with insufficient properties, both of which lead to significant amounts of waste. This paper examines the thermal, chemical, and mechanical characteristics of PA-12 via an oven storage experiment that simulates multi jet fusion (MJF) conditions. Changes in the properties of PA-12 powder during oven storage showed two separate, time-dependent trends. Initially, differential scanning calorimetry showed a 4.2 °C increase in melting temperature (Tm) and a rise in crystallinity (Xc). This suggests that secondary crystallisation is occurring instead of, or in addition to, the more commonly reported further polycondensation process. However, with extended storage time, there were substantial reductions in Tm and Xc, whilst an 11.6 °C decrease in crystallisation temperature was observed. Fourier transform infrared spectroscopy, a technique rarely used in PBF literature, shows an increased presence of imide bonds—a key marker of thermo-oxidative degradation. Discolouration of samples, an 81% reduction in strength and severe material embrittlement provided further evidence that thermo-oxidative degradation becomes the dominant process following extended storage times beyond 100 h. An additional pre-drying experiment showed how moisture present within PA-12 can also accelerate degradation via hydrolysis.

3D Printed Bioreactor Enabling the Pulsatile Culture of Native and Angioplastied Large Arteries.

Routine interventions such as balloon angioplasty, result in vascular activation and remodeling, often requiring re-intervention. 2D in vitro models and small animal experiments have enabled the discovery of important mechanisms involved in this process, however the clinical translation is often underwhelming. There is a critical need for an ex vivo model representative of the human vascular physiology and encompassing the complexity of the vascular wall and the physical forces regulating its function. Vascular bioreactors for ex vivo culture of large vessels are viable alternatives, but their custom-made design and insufficient characterization often hinders the reproducibility of the experiments. The objective of the study was to design and validate a novel 3D printed cost-efficient and versatile perfusion system, capable of sustaining the viability and functionality of large porcine arteries for 7 days and enabling early post-injury evaluations. MultiJet Fusion 3D printing was used to engineer the EasyFlow insert, converting a conventional 50 ml centrifuge tube into a mini bioreactor. Porcine carotid arteries either left untreated or injured with an angioplasty balloon, were cultured under pulsatile flow for up to 7 days. Pressure, heart rate, medium viscosity and shear conditions were adjusted to resemble arterial in vivo hemodynamics. Tissue viability, cell activation and matrix remodeling were analyzed by immunohistochemistry, and vascular function was monitored by duplex ultrasound. Culture conditions in the EasyFlow bioreactor preserved endothelial coverage and smooth muscle organization and extracellular matrix structure in the vessel wall, as compared to static culture. Injured arteries presented hallmarks of early remodeling, such as intimal denudation, smooth muscle cell disarray and media/adventitia activation in flow culture. Duplex ultrasound confirmed continuous pulsatile blood flow conditions, dose-dependent vasodilator response to nitroglycerin in untreated vessels and impaired dilator response in angioplastied vessels. The scope of this work is to validate a low-cost, robust and reproducible system to explore the culture of native and injured large arteries under pulsatile flow. While the study of vascular pathology is beyond the scope of the present paper, our system enables future investigations and provides a platform to test novel therapies and devices ex vivo, in a patient relevant system.

Organs in Color: Utilizing Free Software and Emerging Multi Jet Fusion Technology to Color and Surface Label 3D-Printed Anatomical Models.

3D printing (3DP) is a rapidly evolving innovative technology that has already been utilized for the development of educational anatomic models. Until recently, it was difficult and tedious to create multi-colored models and especially labels due to technological constraints. In this technical note, a comprehensive guide for creating labeled and color-coded anatomic models was created using free software, Blender. We have composed a step-by-step process for taking an existing 3D model and adding labeling and color that is compatible with modern high-quality 3D printing technologies (Multi Jet Fusion). We provided colored and labeled 3D renderings of the surface anatomy of the brain, ventricular system of the brain, the segments of the liver, and coronary arteries as examples of the diverse potential of this technology. Additionally, we 3D printed actual models of the surface anatomy of the brain and ventricles of the brain using HP Multi Jet Fusion to demonstrate the potential of this technology in the creation of anatomic models.

Design for Additive Manufacturing and Investigation of Surface-Based Lattice Structures for Buckling Properties Using Experimental and Finite Element Methods.

Additive Manufacturing (AM) is rapidly evolving due to its unlimited design freedom to fabricate complex and intricate light-weight geometries with the use of lattice structure that have potential applications including construction, aerospace and biomedical applications, where mechanical properties are the prime focus. Buckling instability in lattice structures is one of the main failure mechanisms that can lead to major failure in structural applications that are subjected to compressive loads, but it has yet to be fully explored. This study aims to investigate the effect of surface-based lattice structure topologies and structured column height on the critical buckling load of lattice structured columns. Four different triply periodic minimal surface (TPMS) lattice topologies were selected and three design configurations (unit cells in x, y, z axis), i.e., 2 × 2 × 4, 2 × 2 × 8 and 2 × 2 × 16 column, for each structure were designed followed by printing using HP MultiJet fusion. Uni-axial compression testing was performed to study the variation in critical buckling load due to change in unit cell topology and column height. The results revealed that the structured column possessing Diamond structures shows the highest critical buckling load followed by Neovius and Gyroid structures, whereas the Schwarz-P unit cell showed least resistance to buckling among the unit cells analyzed in this study. In addition to that, the Diamond design showed a uniform decrease in critical buckling load with a column height maximum of 5193 N, which makes it better for applications in which the column’s height is relatively higher while the Schwarz-P design showed advantages for low height column maximum of 2271 N. Overall, the variations of unit cell morphologies greatly affect the critical buckling load and permits the researchers to select different lattice structures for various applications as per load/stiffness requirement with different height and dimensions. Experimental results were validated by finite element analysis (FEA), which showed same patterns of buckling while the numerical values of critical buckling load show the variation to be up to 10%.

3D-Printed Programmable Mechanical Metamaterials for Vibration Isolation and Buckling Control

Vibration isolation performance at low-frequency ranges before resonance is a vital characteristic that conventional springs cannot exhibit. This paper introduces a novel zero Poisson’s ratio graded cylindrical metamaterial to fulfill two main goals: (1) vibration isolation performance in low-frequency bands prior to resonance and (2) global buckling control of a long cylindrical tube. For this purpose, “soft and stiff” re-entrant unit cells with varying stiffness were developed. The cylindrical metamaterials were then fabricated using a multi-jet fusion HP three-dimensional (3D) printer. The finite element analyses (FEA) and experimental results demonstrate that the simultaneous existence of multi-stiffness unit cells leads to quasi-zero stiffness (QZS) regions in the force-displacement relationship of a cylindrical metamaterial under compression. They possess significant vibration isolation performance at frequency ranges between 10 and 30 Hz. The proposed multi-stiffness re-entrant unit cells also offer global buckling control of long cylindrical tubes (with a length to diameter ratio of 3.7). The simultaneous existence of multi-stiffness re-entrant unit cells provides a feature for designers to adjust and control the deformation patterns and unit cells’ densification throughout cylindrical tubes.

Usage of the 3D printed model for the forming during the development of the casting mould

This paper deals with the usage of the plastic model (created by additive technology), which can be used for the mould production as an internal model for the cavity. This mould is intended for the steel casting technology. The particular plastic model is created by the conventional 3D printer HP Multi Jet Fusion 4200 from the material PA 12 GB. It is polyamide with 40% of glass filling. This material is suitable for this method because of good mechanical properties. The creating of the steel casting mould has some specification which are deeply described in this paper. The comparing of several dimensions between the CAD model, plastic model and the final casted model from steel is performed here. It is obvious that the differences and tolerances are less than 1%. This approach can be used as a replacement of the wood models which are generally used. The benefits of the 3D printed model are higher accuracy of the model, higher complexity of the model and production time which can be less than 3 days (from the CAD model to the plastic model for the casting mould, but depending on complexity and size of the model).