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The purpose of this paper is to present the findings on jet array instabilities of molten caprolactam. Initial investigations showed that although a suitable range of parameters was found for stable jetting, there were cases where instabilities occurred due to external sources such as contamination.

The inkjet system consisted of a melt supply unit, filtration unit and printhead with pneumatic and thermal control. A start‐up strategy was developed to initiate the jetting trials. A digital microscope camera monitored the printhead nozzle plate to record the jet array stability within the recommended range of parameters from earlier research. The trials with jet instabilities were studied to analyse the instability behaviour.

It was found that instabilities occurred in three forms which were jet trajectory error, single jet failure and jet array failure. Occasionally, the jet with incorrect trajectory remained stable. When a jet failed, bleeding of melt from the nozzle due to the actuations influenced the adjacent jets initiating an array of jets to fail similar to falling dominos.

The research concept is novel and investigating the jet array instability behaviours could give an understanding on jetting reliability issues.

Understanding how material jetting process parameters affect material properties can inform design and print orientation when manufacturing end-use components. This study aims to explore the robustness of material properties in material jetted components to variations in processing environment and build orientation.

The authors characterized the properties of six different material gradients produced from preset “digital material” mixes of polypropylene-like (VeroWhitePlus) and elastomer-like (TangoBlackPlus) materials. Tensile stress, modulus of elasticity and elongation at break were analyzed for each material printed at three different build orientations. In a separate ten-week study, the authors investigated the effects of aging in different lighting conditions on material properties.

Specimens fabricated with their longest dimension along the direction of the print head travel (X-axis) tended to have the largest tensile strength, but trends in elastic modulus and elongation at break varied between the rigid and flexible photopolymers. The aging study showed that the ultimate tensile stress of VeroWhitePlus parts increased and the elongation decreased over time. Material properties were not significantly altered by lighting conditions.

Many tensile specimens failed at the neck region, especially for the more elastomeric parts. It is hypothesized that this is due to the material jetting process approximating curves with a pixelated droplet arrangement, instead of curved contour as seen in other additive manufacturing processes. A new tensile specimen design that performs more consistently with elastomer-like materials should be considered. The aging component of this study is focused solely on polypropylene-like (VeroWhitePlus) material; additional research into the effects of aging on multiple composite materials is needed.

The study provides the first known description of orientation effects on the mechanical behavior of photopolymers containing varied concentrations of elastomeric (TangoBlackPlus) material. The aging study presents the first findings on how time affects parts made via material jetting.

The use of additive manufacturing in many branches of industry is increasing significantly because of its many advantages, such as being able to produce complex parts that cannot be produced by classical methods, using fewer materials, easing the supply chain with on-site production, being able to produce with all kinds of materials and producing lighter parts. The binder jetting technique, one of the additive manufacturing methods researched within the scope of this work, is predicted to be the additive manufacturing method that will grow the most in the next decade, according to many economic reports. Although additive manufacturing methods have many advantages, they can be slower than classical manufacturing methods regarding production speed. For this reason, this study aims to increase the manufacturing speed in the binder jetting method.

Adaptive slicing and variable binder amount algorithm (VBAA) were used to increase manufacturing speed in binder jetting. Taguchi method was used to optimize the layer thickness and saturation ratio in VBAA. According to the Taguchi experimental design, 27 samples were produced in nine different conditions, three replicates each. The width of the samples in their raw form was measured. Afterward, the samples were sintered at 1,500 °C for 2 h. After sintering, surface roughness and density tests were performed. Therefore, the methods used have been proven to be successful. In addition, measurement possibilities with image processing were investigated to make surface roughness measurements more accessible and more economical.

As a result of the tests, the optimum printing condition was decided to be 180–250 µm for layer thickness and 50% for saturation. A separate test sample was then designed to implement adaptive slicing. This test sample was produced in three pieces: adaptive (180–250 µm), thin layer (180 µm) and thick layer (250 µm) with the determined parameters. The roughness values of the adaptive sliced sample and the thin layer sample were similar and better than the thick layer sample. A similar result was obtained using 12.31% fewer layers in the adaptive sample than in the thin layer sample.

The use of adaptive slicing in binder jetting has become more efficient. In this way, it will increase the use of adaptive slicing in binder jetting. In addition, a cheap and straightforward image processing method has been developed to calculate the surface roughness of the parts.

This study aims to develop an experimentally validated three-dimensional numerical model for predicting different flow patterns produced with a gas dynamic virtual nozzle (GDVN).

The physical model is posed in the mixture formulation and copes with the unsteady, incompressible, isothermal, Newtonian, low turbulent two-phase flow. The computational fluid dynamics numerical solution is based on the half-space finite volume discretisation. The geo-reconstruct volume-of-fluid scheme tracks the interphase boundary between the gas and the liquid. To ensure numerical stability in the transition regime and adequately account for turbulent behaviour, the k-ω shear stress transport turbulence model is used. The model is validated by comparison with the experimental measurements on a vertical, downward-positioned GDVN configuration. Three different combinations of air and water volumetric flow rates have been solved numerically in the range of Reynolds numbers for airflow 1,009–2,596 and water 61–133, respectively, at Weber numbers 1.2–6.2.

The half-space symmetry allows the numerical reconstruction of the dripping, jetting and indication of the whipping mode. The kinetic energy transfer from the gas to the liquid is analysed, and locations with locally increased gas kinetic energy are observed. The calculated jet shapes reasonably well match the experimentally obtained high-speed camera videos.

The model is used for the virtual studies of new GDVN nozzle designs and optimisation of their operation.

To the best of the authors’ knowledge, the developed model numerically reconstructs all three GDVN flow regimes for the first time.

Binder jetting is one of the essential additive manufacturing methods because it is cost-effective, has no thermal stress problems and has a wide range of different materials. Using binder jetting technology in the industry is becoming more common recently. However, it has disadvantages compared to traditional manufacturing methods regarding speed. This study aims to increase the manufacturing speed of binder jetting.

This study used adaptive slicing to increase the manufacturing speed of binder jetting. In addition, a variable binder amount algorithm has been developed to use adaptive slicing efficiently. Quarter-spherical shaped samples were manufactured using a variable binder amount algorithm and adaptive slicing method.

Samples were sintered at 1250°C for 2 h with 10°C/min heating and cooling ramp. Scanning electron microscope analysis, surface roughness tests, and density calculations were done. According to the results obtained from the analyzes, similar surface quality is achieved by using 38% fewer layers than uniform slicing.

More work is needed to implement adaptive slicing to binder jetting. Because the software of commercial printers is very difficult to modify, an open-source printer was used. For this reason, it can be challenging to produce perfect samples. However, a good start has been made in this area.

To the best of the authors’ knowledge, the actual use of adaptive slicing in binder jetting was applied for the first time in this study. A variable binder amount algorithm has been developed to implement adaptive slicing in binder jetting.

The purpose of this paper is to explore the use of binder jetting to fabricate high-purity copper parts. The ability to fabricate geometrically complex copper shapes would have implications on the design and manufacture of components for thermal management systems and structural electronics.

To explore the feasibility of processing copper via binder jetting, the authors followed an established material development process that encompasses powder selection and tuning process parameters in printing and thermal cycles. Specifically, the authors varied powder size and sintering cycles to explore their effects on densification.

Three differently sized copper powders were successfully printed, followed by sintering in a reducing atmosphere. It was found that a 15-μm-diameter powder with a sintering cycle featuring a 1,080°C maximum temperature provides the most dense (85 per cent) and pure (97 per cent) final copper parts of the parameters tested.

Due to powder-based additive manufacturing techniques’ inherent limitations in powder packing and particle size diameter, there are difficulties in creating fully dense copper parts. To improve thermal, electrical and mechanical properties, future work will focus on improving densification.

The paper demonstrates the first use of binder jetting to fabricate copper artifacts. The resulting copper parts are denser than what is typically found in binder jetting of metal powders (without infiltration); significant opportunity remains to further optimize the manufacturing process by introducing novel techniques to tailor the material properties for thermal/electrical applications.

Binder jetting is a promising route to produce complex copper components for electronic/thermal applications. This paper aims to lay a framework for determining the effects of sintering parameters on the final microstructure of copper parts fabricated through binder jetting.

The knowledge gained from well-established powder metallurgy processes was leveraged to study the densification behaviour of a fine high-purity copper powder (D₅₀ of 3.4 µm) processed via binder jetting, by performing dilatometry and microstructural characterization. The effects of sintering parameters on densification of samples obtained with a commercial water-based binder were also explored.

Sintering started at lower temperature in cold-pressed (∼680 °C) than in binder jetted parts (∼900 °C), because the strain energy introduced by powder compression reduces the sintering activation energy. Vacuum sintering promoted pore closure, resulting in greater and more uniform densification than sintering in argon, as argon pressure stabilizes the residual porosity. About 6.9% residual porosity was obtained with air sintering in the presence of graphite, promoting solid-state diffusion by copper oxide reduction.

This paper reports the first systematic characterization of the thermal events occurring during solid-state sintering of high-purity copper under different atmospheres. The results can be used to optimize the sintering parameters for the manufacturing of complex copper components through binder jetting.

The purpose of this paper is to investigate the effects of layer thickness, aspect ratio, part thickness and build orientation on distortion to have a better understanding of its behavior in material jetting technology.

Specimens with two layer thicknesses (14 and 28 µm) were printed in two aspect ratios (2:1) and (10:1), four thickness values (1, 2, 3 and 4 mm) and three build orientations (45d, XY and YX) and scanned with a wide-area 3D surface scanner to quantify distortion. The material used to build the test specimens was a commercially available resin, VeroWhitePlus RGD835.

The results of this study showed that all printed specimens by material jetting 3D printers had some level of distortion. The 1-mm thickness specimens, for both layer thicknesses of 14 µm and 28 µm, showed a wide range of anomalies including reverse coil set (RCS), reverse cross bow (RCB), cross bow (CB), wavy edge (WE) and some moderate twisting (T). Similar occurrences were observed for the 2-mm thickness specimens as there were RCS, WE, RCB and T anomalies that show the difference between the thinner specimens (1- and 2-mm) with the thicker ones (3- and 4-mm). In both 3- and 4-mm thickness specimens, there was more consistency in terms of distortion with mainly RCS and RCB anomalies. In total, six different types of flatness anomalies were found to occur with the following incidences: reverse coil set (91 specimens, 63.19%), reverse cross bow (50 specimens, 34.72%), wavy edge (23 specimens, 15.97%), twist (19 specimens, 12.50%), coil set (11 specimens, 7.64%) and cross bow (7 specimens, 4.86%).

This study expands the research on how the preprocess parameters such as layer thickness and build orientation and the geometrical parameters such as part thickness and aspect ratio cause dimensional distortion. Distortion is a pervasive consequence of the curing process in photopolymerization and explores one of the most common defects that come across in polymeric-based additive manufacturing. In addition to the characterization of the type and magnitude of distortion, the contributions of this work also include establishing the foundation for design guidelines aiming at minimizing distortion in material jetting.

Jetting‐based additive manufacturing processes are gaining attention due to their high speed of operation, accuracy and resolution. Support material plays an important role in the additive manufacturing of parts by using processes that utilise jetting (inkjet) technology. This research aims to present novel support material compositions consisting of methylcellulose (MC) and propylene glycol or butylene glycol. These compositions form gels which are easy to remove and provide the advantage of reusability.

MC was mixed in propylene glycol or butylene glycol in different concentrations and examined for gel formation on heating and subsequent cooling. The viscosity and surface tension of these compositions were measured at temperatures suitable for jetting. Gel strength was characterised using texture analysis.

The viscosity and surface tension values at elevated temperatures (i.e. 800°C) show the suitability of these compositions for jetting‐based additive manufacturing processes. Due to their softness, these gels can be removed easily and their low melting points (i.e. near 500°C) allow their reusability as support materials.

This paper provides a novel approach of using polymer gels as support materials for additive manufacturing processes. These gels are easy to prepare and enhance the sustainability due to their reusability.

Although, MC in water have shown to form gels and these aqueous gels have been used in many applications such as medicine and food industries, the compositions presented in this paper are unique. Such combinations of MC and non‐aqueous solvents (i.e. propylene glycol and butylene glycol) have not been discussed before and provide an early step towards a new application area (i.e. additive manufacturing) for these gels.

The material-jetting-type (MJ) 3-D printing technology has advantages in resolution and color printing. During the printing process, a leveling technique is needed to precisely control the thickness and flatness of each layer. Roller-type leveling mechanism has been adopted in commercial MJ 3-D printers, but it is lack of research on roller leveling process parameters and establishing experimental procedures. Therefore, in this study, a roller-type leveling mechanism for a MJ color 3 D printer was developed, and experimental approaches were utilized to determine process parameters.

The roller-type leveling mechanism was chosen to provide functions of flattening and removal of excess material. The parameters studied were roller speed and rotational direction. Surface roughness, Ra, of printed single-layered specimens was measured at 15 locations for plane roughness and along five lines for line roughness to evaluate the leveling results. Adopting suitable parameters, color samples with and without leveling were printed for comparison and verification.

According to plane roughness results, forward rotation achieved better leveling. Plane roughness was the major criteria to determine roller speed with the assistance of standard deviation of line roughness. The best parameters of the self-developed MJ color 3-D printer were found to be rolling forward at 1,100 rpm. In addition, printed color samples showed great improvement in surface roughness with leveling and no obvious color mixing after leveling.

Leveling is important to achieve desired layer thickness, smooth surface and good color quality in color 3-D printing. For MJ 3-D printing, only patents were revealed regarding roller design, but paper publications have not been presented. This research practically proposed to use experimental approach to understand the effects of roller operating parameters and to find the suitable ones based on surface roughness results.

This research established the experimental procedures and also suggested guidelines of experimentally obtaining suitable roller leveling process parameters. Developers can refer to this study results to design and adjust leveling mechanism in a new MJ 3-D printer.

The experimental approach can be applied to similar MJ 3-D printing systems if different materials are introduced or the platform speed is changed. The observed trends suggested several guidelines to plan limited experiments only to obtain suitable roller process parameters.