Binder Jet Additive Manufacturing Research Articles

Anisotropy in Green Body Bending Strength due to Additive Direction in the Binder-Jetting Additive Manufacturing Process

Anisotropy in Green Body Bending Strength due to Additive Direction in the Binder-Jetting Additive Manufacturing Process

Graphene oxide humidity sensor built entirely by additive manufacturing approaches

Graphene is emerging as an excellent material choice for high-performance electrical and electrochemical devices such as humidity sensors. The rapid technological evolution in additive manufacturing (AM) enables freedom to design and process multiple materials for scalable fabrication of sensors. Herein, we introduce a hybrid AM approach to fabricate a graphene-based humidity sensor and study its sensing performance. A powder-bed binder-jetting AM technique is used to build a porous 3D-structure of thermally reduced graphene oxide as the humidity sensing element. In parallel, a material extrusion AM approach is used to make a silicone-based hollow cube as the housing of the graphene structure. The AM fabricated sensor shows high sensitivity when tested in the relative humidity (RH) range of 6.4–97.3% with a rapid response time of 7 s at 45% RH due to the open porous structure formed by the binder-jetting approach. Sensing performance was investigated at low and medium RH in the temperature range of 25–80 °C and the device demonstrated a negligible temperature dependence. The presented graphene-based humidity sensor also shows good repeatability in RH measurements.

Binder jetting additive manufacturing of aluminum nitride components

Abstract In this work, we report on the novel fabrication of aluminum nitride (AlN) components using Binder Jetting (BJT) additive manufacturing (AM). The AlN constructs were subjected to post-fabrication thermal treatment by hot isostatic pressing (HIPing) for 8 hours at a pressure of 206 MPa and temperature of 1900 °C. This treatment resulted in a 60.1% relative density maximum densification for AlN. The BJT printed AlN specimens were analyzed using various characterization techniques. The purity, microstructure, and polycrystallinity of the AlN phase formed were confirmed by techniques that included x-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). Second harmonic generation (SHG) microscopy showed polarization dependence and second harmonic signal at 470 nm, indicating the potential to produce thermal and optical-mechanical devices. Mechanical properties obtained by nanoindentation resulted in an elastic modulus of ~251 GPa when measured in fully dense, contiguous crystalline regions, corresponding to an apparent, porous bulk stiffness of ~90 GPa for the final, 60.1 % dense products. Finally, the laser flash method (LFM) was used to measure the thermal conductivity of the material as a function of temperature resulting in values from 4.82 W/mK to 3.17 W/mK for the temperature range from 23 °C to 500 °C, respectively.

Synthesis of titanium orthorhombic alloy using binder jetting additive manufacturing

The presented work demonstrates the capability of producing Ti-22Al-25Nb parts from Ti, Al, Nb elemental powders using Binder Jetting (BJ) additive manufacturing (AM) method followed by high-temperature reactive sintering and subsequent annealing. The microstructural investigation and phase analysis demonstrate that reactive sintering at 800 °C and 1000 °C results in diffusion of Al into Ti particles forming Ti-Al solid solution and Ti3Al-phase, while sintering at 1100 °C allows Nb diffusion into Ti particles. Microstructural analysis showed that the reactive sintering temperature affects the surface morphology of particles due to different wettability of liquid Al. Annealing at 1400 °C resulted in the formation of B2/β-phase with acicular Ti2AlNb precipitates. The results demonstrate that the used approach can be successfully utilized for the production of Ti-22Al-25Nb parts.

Characterizing Binder–Powder Interaction in Binder Jetting Additive Manufacturing Via Sessile Drop Goniometry

Understanding the binder–powder interaction and primitive formation is critical to advancing the binder jetting Additive Manufacturing process and improving the accuracy, precision, and mechanical properties of the printed parts. In this work, the authors propose an experimental approach based on sessile drop goniometry on a powder substrate to characterize the binder wetting powder process. As a binder drop penetrates into a prepared powder substrate, the dynamic contact angle formed in powder pores is calculated based on the measured binder penetration time, and the binder penetration depth is measured from the binder-powder granule retrieved from the powder substrate. Coupled with models of capillary flow, the technique provides a fundamental understanding of the binder–powder interaction that determines the material compatibility and printing parameters in binder jetting. Enabled by this gained understanding, it was determined that suspending nanoparticles in a binder could increase the capillary-driven penetration depth, which was then reduced by the further increase of the nanoparticle solid loading and resultant binder viscosity.

Tailoring green and sintered density of pure iron parts using binder jetting additive manufacturing

Binder jetting additive manufacturing (BJAM) is a comparatively low-cost process that enables manufacturing of complex and customizable metal parts. This process is applied to low-cost water-atomized iron powder with the goal of understanding the effects of printing parameters and sintering schedule on maximizing the green and sintered densities of manufactured samples, respectively. The powder is characterized by using scanning electron microscopy (SEM) and particle size analysis (Camsizer X2). In the AM process, the effects of powder compaction, layer thickness, and liquid binder level on green part density are investigated. Post-process heat treatment is applied to selected samples, and suitable debinding parameters are studied by using thermo-gravimetric analysis (TGA). Sintering at various temperatures and durations results in densities of up to 91.3%. Image processing of x-ray computed tomography (μCT) scans of the samples reveals that porosity distribution is affected by powder spreading, and gradients in pore distribution in the sample are largely reduced after sintering. The resulting shrinkage ranges between 6.7 ± 3.0% and 25.3 ± 2.8%, while surface roughness ranges between 11.6 ± 5.0 μm and 32.1 ± 3.4 μm. The results indicate that the sintering temperature and time might be tailored to achieve target densities anywhere in the range of 64% and 91%, with possibly higher densities by increasing sintering time.

In situ formation of metal matrix composites using binder jet additive manufacturing (3D printing)

Simplifying the manufacturing of metal matrix composites (MMCs) will allow for their wider use in applications that require lower density, higher strength, and high wear resistance when compared to traditional metals. An in-situ method of MMC formation is proposed, using a binder jet additive manufacturing (BJ-AM) process with only Inconel 625 powder and a carbon-containing binder. Carbide formation occurs at elevated temperatures during sintering by combining Cr, Mo and Nb alloying elements in Inconel 625 and carbon from the binder. The core-shell morphology and composition of the final MMC is tuned by controlling the quantity of carbon in the system during the sintering step.

Process development for green part printing using binder jetting additive manufacturing

Originally developed decades ago, the binder jetting additive manufacturing (BJ-AM) process possesses various advantages compared to other additive manufacturing (AM) technologies such as broad material compatibility and technological expandability. However, the adoption of BJ-AM has been limited by the lack of knowledge with the fundamental understanding of the process principles and characteristics, as well as the relatively few systematic design guideline that are available. In this work, the process design considerations for BJ-AM in green part fabrication were discussed in detail in order to provide a comprehensive perspective of the design for additive manufacturing for the process. Various process factors, including binder saturation, in-process drying, powder spreading, powder feedstock characteristics, binder characteristics and post-process curing, could significantly affect the printing quality of the green parts such as geometrical accuracy and part integrity. For powder feedstock with low flowability, even though process parameters could be optimized to partially offset the printing feasibility issue, the qualities of the green parts will be intrinsically limited due to the existence of large internal voids that are inaccessible to the binder. In addition, during the process development, the balanced combination between the saturation level and in-process drying is of critical importance in the quality control of the green parts.

Dynamic simulation of powder packing structure for powder bed additive manufacturing

Powder packing structure is a critical parameter of powder bed-based additive manufacturing (AM). Experimental characterization of powder is typically limited to measuring bulk properties, whereas many numerical models of AM powder packing are based on geometrical consideration without accounting for particle-to-particle interactions. In the present paper, the powder packing dynamics is simulated using a discrete element method (DEM)-based model that solves the mechanical contact forces and moments between individual particles. As DEM uses explicit time integration, a main challenge in modeling dynamics of metallic powder packing is the need for extremely fine time increment size (e.g., in the order of 1 ns for a 10-μm-diameter particle). The effect of mass scaling, employed for speeding up the calculation, on the simulation results is examined in a test case of powder particles packed inside a box container. The calculated packing density for two different particle size distributions is validated against independent literature data for laser powder bed AM with AISI 316L stainless steel powder. The sensitivity of key input parameters (e.g., friction coefficient) is further evaluated in this test case. The powder packing model is then applied to a practical situation of binder jet AM involving rolling of multiple layers of IN718 powder particles onto a powder bed, for which the calculated packing density is also validated with independent literature data.

A new physics-based model for equilibrium saturation determination in binder jetting additive manufacturing process

Abstract In binder jetting additive manufacturing (BJ-AM) process, the features are created through the interaction between droplets of the liquid binding agent and the layered powder bed. The amount of binder, which is termed binder saturation, depends strongly on the liquid binder and powder bed interaction including the spreading (i.e. lateral migration) and penetration (vertical migration) of the binder in powder bed, and is of crucial importance for determining the accuracy and strength of the printed parts. In the present study, a new physics-based model is developed to predict the optimal saturation levels for the green part printing, which is realized via capillary pressure estimation that is based on the binder and powder bed interactions in the equilibrium state. The proposed model was evaluated by both the Ti-6Al-4V and 420 stainless steel powders that exhibit different powder characteristics and packing densities. In order to estimate the equilibrium saturation using the proposed model, the physical characteristics such as average contact angle between the binder and powder material, specific surface area of powder particles, saturation and capillary pressure characterization curve were determined. Features with various degrees of dimensions (1-D, 2-D, 3-D) were printed out using M-Lab ExOne printer for determining the equilibrium saturation. Good agreement was observed between the theoretical predictions and experimentally measured saturation levels for the Ti-6Al-4V powder. On the other hand, the model underestimated the optimal saturation level for the 420 stainless steel powder, which was likely caused by the micro-surface areas from powder particle surface that do not contribute to the binder-powder bed interactions.

On the effect of throughout layer thickness variation on properties of additively manufactured cellular titanium structures

Over the past two decades, additive manufacturing has opened a new window of opportunities in fabricating complex porous matrix structures such as cellular solids. Several factors including design, material and process parameters can selectively be varied to tailor the porous properties of products based on the intended application. This article addresses the effect of variable throughout layer thickness configuration in the binder-jet additive manufacturing of titanium structures for orthopedic applications. Two layer thicknesses of 80 and 150μm are selectively controlled inside of each titanium sample with four different configurations. Several studies were performed, including shrinkage analysis, porosity measurements, and mechanical compression tests to quantify the effect of layer thickness on part quality and mechanical properties. The results of the porosity measurement revealed that there is about 5% variation among the samples with different layer thickness configuration. Bulk porosity values obtained from micro computed tomography (μCT) scan data placed the bulk porosity of the samples combining more than one layer thickness, in between of the results for control specimens, which were manufactured by applying a single layer thickness throughout the samples. Mechanical properties did not show any significant variation, which is attributed to the low range of the porosity deviation (less than 5%). The highest Young’s modulus of 3.50±0.4GPa and yield stress of 175±25MPa were obtained from analysis of the data achieved from the compression test.

Effect of Particle Size Distribution on Powder Packing and Sintering in Binder Jetting Additive Manufacturing of Metals

The binder jetting additive manufacturing (AM) process provides an economical and scalable means of fabricating complex parts from a wide variety of materials. While it is often used to fabricate metal parts, it is typically challenging to fabricate full density parts without large degree of sintering shrinkage. This can be attributed to the inherently low green density and the constraint on powder particle size imposed by challenges in recoating fine powders. To address this issue, the authors explored the use of bimodal powder mixtures in the context of binder jetting of copper. A variety of bimodal powder mixtures of various particle diameters and mixing ratios were printed and sintered to study the impact of bimodal mixtures on the parts' density and shrinkage. It was discovered that, compared to parts printed with monosized fine powders, the use of bimodal powder mixtures improves the powder's packing density (8.2%) and flowability (10.5%), and increases the sintered density (4.0%) while also reducing the sintering shrinkage (6.4%).

A system for selectively encapsulating porogens inside the layers during additive manufacturing: From conceptual design to the first prototype

Additive manufacturing (AM) has greatly expanded the range of part fabrication to encompass both geometrical complexity and material variation. However, challenges still remain with respect to the implementation of AM technologies. One such issue is related to the de-powdering step required for the removal of support powder inside internal channels and voids during powder-bed AM approaches. This study proposes a novel design and methodology for selectively encapsulating the sacrificial paraffin particles inside the powder layers during the binder jet AM process. The paraffin particles will be generated by punching through the sheet of material which includes a mesh structure carrying a thin layer of wax. Several experiments were designed to evaluate the performance of the proposed system, particularly the effect of input parameters on the size, shape and number of porogen particles as well as their distribution on the substrate. The obtained results revealed the direct influence of mesh structural properties on the porogen particle morphology. Moreover, applying the lower voltage (8V) and needle diameter (0.28μm) to separate the porogen improved the repeatability of the range of data (52±3%–80±12%), distributing the particles in the area less than 1mm distance from the center of needle. Then, four categories of the samples were designed for the AM process, 3 samples including porogen of different sizes, and one control sample. The porosity of the specimens measured after sintering process did not show any significant variations among the samples (35.5±1%–37.7±5%), due to the limited number of encapsulated porogen. The average diameter of the pores, after removing porogen during the heat treatment phase, illustrates the close similarity to the porogen particles size.

Binder jetting advanced ceramics for metal-ceramic composite structures

Metal Matrix Composites (MMCs) are a class of materials combining two dissimilar materials (e.g., metal & ceramic) that when combined, provide unique properties including low density, high specific strength, high specific modulus, high thermal conductivity, and wear resistance and can be used in range of applications including high-temperature applications, structural applications, and can act as crack arrestors in fatigue applications. However, MMCs are not widely adopted due to their high cost and are limited in the geometrical configuration of the ceramic cores (e.g., extrusion, tiles, stochastic foams, etc.). In this work, the authors proposed a novel process protocol that takes advantage of the geometrical freedom offered by Additive Manufacturing (AM). Specifically, the authors look to print a complex ceramic structure from precursor powders via Binder Jetting AM technology to incorporate into a bonded sand mold and the subsequently casted metal matrix. The manufacturing process for creating a successful MMC is divided into two distinct steps: i) determination of the printing parameters, pre-and-post sintering ceramic characterization, and ii) molding, casting, and testing MMCs. Through sintering experiments, a sintering temperature of 1375 ∘C was established for the ceramic insert (70 % cordierite). Upon printing and sintering the ceramic, three-point bend tests showed the MMCs had less strength than the matrix material likely due post-processing and geometrical effects, effects of gravity casting, and relatively high porosity developed in the body. It was found that the ceramic metal interface had minimal mechanical interlocking and chemical bonding limiting the strength of the final MMCs. Furthermore, the authors provide directions for future work on how to successfully utilize the proposed manufacturing process to create printed MMCs with more effective properties.

Powder bed binder jet 3D printing of Inconel 718: Densification, microstructural evolution and challenges☆

Traditional manufacturing of Inconel 718 components from castings and thermomechanical processing routes involve extensive post processing and machining to attain the desired geometry. Additive manufacturing (AM) technologies including direct energy deposition (DED), selective laser melting (SLM), electron beam melting (EBM) and binder jet 3D printing (BJ3DP) can minimize scrap generation and reduce lead times. While there is extensive literature on the use of melting and solidification based AM technologies, there has been limited research on the use of binder jet 3D printing. In this paper, a brief review on binder jet additive manufacturing of Inconel 718 is presented. In addition, existing knowledge on sintering of Inconel 718 has been extended to binder jet 3D printing. We found that supersolidus liquid phase sintering (SLPS) is necessary to achieve full densification of Inconel 718. SLPS is sensitive to the feedstock chemistry that has a strong influence on the liquid volume fraction at the processing temperature. Based on these results, we discuss an empirical framework to determine the role of powder particle size and liquid volume fraction on sintering kinetics. The role of powder packing factor and binder saturation on microstructural evolution is discussed. The current challenges in the use of BJ3DP for fabrication of Inconel 718, as well as, extension to other metal systems, are presented.

Effect of Lattice Design and Process Parameters on Dimensional and Mechanical Properties of Binder Jet Additively Manufactured Stainless Steel 316 for Bone Scaffolds

Scaffolds are 3D biocompatible structures that mimic the extracellular matrix properties (mechanical support, cellular activity and protein production) of bones and provide place for cell attachment and bone tissue formation. Their performance depends on chemistry, pore size, pore volume and mechanical strength. Open and interconnected pores allow nutrients and molecules to transport to inner parts of scaffold. Recently, additive manufacturing (AM) has been used as a means to produce these scaffolds. However, there is a need to study the various lattice designs and process parameters of these AM processes to produce the required scaffolds. In this study, the relationship between different lattice designs of additively manufactured scaffolds and their mechanical properties was studied. Four lattice geometries were fabricated with binder jet AM process with Stainless Steel 316 (SS316) as material. We also studied effect of process parameters such as sintering time and sintering temperature on dimensional accuracy and mechanical properties of these geometries. The results showed that the samples with circular geometry have superior mechanical properties compared to others. Trends were obtained on the influence of different lattice designs on compressive strength of the material.

Investigation of Sintering Shrinkage in Binder Jetting Additive Manufacturing Process

Binder jetting process is an additive manufacturing technology that produces objects layer by layer from 3D digital data. After printing process, the secondary post-processing operations, including curing and sintering, are used to solidify the object. The linear dimensional accuracy is one of the most important end-product qualities in manufacturing process. However, it is not easy to control it since the whole process combines several steps and covers different disciplines. Sintering process can affect the shrinkage rate significantly through using different sintering profiles. This project focuses on investigating the effect of sintering parameters on linear dimensional accuracy with stainless steel 316L. The Taguchi method is used to design 9 groups of orthogonal experiments. After that, the results are converted to signal-to-noise (S/N) ratio and using analysis of variance (ANOVA) to analyze. There are 3 sets of recommended sintering parameters to achieve the best dimensional accuracy for each axis and there is also 1 set of recommended sintering parameters which considers dimensional accuracies of all 3 axes. Comparing with the shrinkage rates measured using default sintering profile, the dimensional accuracies are improved.

Energy consumption model of Binder-jetting additive manufacturing processes

Considering the potential for new product design possibilities and the reduction of environmental impacts, Additive Manufacturing (AM) processes are considered to possess significant advantages for automotive, aerospace and medical equipment industries. One of the commercial AM techniques is Binder-jetting (BJ). This technique can be used to process a variety of materials including stainless steel, ceramic, polymer and glass. However, there is very limited research about this AM technology on energy consumption aspect. This paper presents a method to build an energy consumption model for printing stage of BJ process. Mathematical analyses are performed to find out the correlation between the energy consumption and geometry of the manufactured part. Based on the analyses, total energy consumption is calculated as a function of part geometry and printing parameters. Finally, test printing is performed to check the accuracy of the model. This process model provides a tool to optimise part geometry design with respect to energy consumption.

Energy and Material Flow Analysis of Binder-jetting Additive Manufacturing Processes

Manufacturing, where great amount of energy and materials are being consumed, should take response to have cleaner production and to improve its sustainability. Additive manufacturing (AM) technology shows potential to reduce environment impact as a more sustainable manufacturing method; however, the lack of well documented energy consumption and material flow data limits the development of Life-Cycle Inventory (LCI) analysis of AM technology. This paper presents an energy and material consumption model of Binder-Jetting (BJ) process. A Unit-Process (UP) level model is created and validated by experimental data to provide LCI data for further Life-Cycle Analysis (LCA) of BJ additive manufacturing processes. The accurate process model provides a tool to industry to understand the energy consumption and material efficiency aspect of the binder-jetting process and to allow comparisons with traditional processes.