Feedstock Formulation Research Articles

Binder System Composition on the Rheological and Magnetic Properties of Nd-Fe-B Feedstocks for Metal Injection Molding

The applications of Nd-Fe-B-based magnets are experiencing significant diversification to achieve efficiency and miniaturization in different technologies. Metal injection molding (MIM) provides new opportunities to manufacture Nd-Fe-B magnets with high geometrical complexity efficiently. In this study, the impacts of the binder system composition and powder loading on the rheological behavior, contamination, and magnetic properties of the Nd-Fe-B MIM parts were investigated. A high-pressure capillary rheometer was used to measure the apparent viscosity and pressure drops for feedstocks with different binder formulations and powder contents. Also, oxygen and carbon contamination, density, and magnetic properties were measured for different feedstock formulations and powder loadings. From the rheological, density, and magnetic properties points of view, the binder system consisting of 45 vol.% LLDPE as backbone was selected as the optimum formulation. The findings indicated that the sample with this binder system and 55 vol.% powder content had a high density (6.83 g/cm3), remanence (0.591 T), and coercivity (744.6 kA/m) compared to other binder compositions. By using 58 vol.% powder loading, the values of density (7.54 g/cm3), remanence (0.618 T), and carbon residue (982 ppm) improved, and a suitable rheological behavior was still observed. Thus, a suitable feedstock formulation was developed.

Fused Filament Fabrication of WC-10Co Hardmetals: A Study on Binder Formulations and Printing Variables

This research explores the utilization of powder fused filament fabrication (PFFF) for producing tungsten carbide-cobalt (WC-10Co) hardmetals, focusing on binder formulations and their impact on extrusion force as well as the influence of printing variables on the green and sintered density of samples. By examining the interplay between various binder compositions and backbone contents, this study aims to enhance the mechanical properties of the sintered parts while reducing defects inherent in the printing process. Evidence suggests that formulated feedstocks affect the hardness of the sintered hardmetal—not due to microstructural changes but macrostructural responses such as macro defects introduced during printing, debinding, and sintering of samples. The results demonstrate the critical role of polypropylene grafted with maleic anhydride (PP-MA) content in improving part density and sintered hardness, indicating the need for tailored thermal debinding protocols tailored to each feedstock. This study provides insights into feedstock formulation for hardmetal PFFF, proposing a path toward refining manufacturing processes to achieve better quality and performance of 3D printed hardmetal components.

3D printing of low carbon steel using novel slurry feedstock formulation via material extrusion method

Conventional 3D metal printing methods, such as laser sintering and binder jetting are often associated with high initial capital costs that make them inaccessible to many consumers. In this article, an economical alternative approach to 3D metal printing is presented, which uses a slurry-based formulation with the material extrusion method. This method involves a novel slurry feedstock of metal powder and liquid binder, which can be printed at room temperature to form green samples without the need for equipment such as a laser source, binder jetting head, or heated nozzle. It is followed by a thermal treatment process to fuse the printed samples into a metal article. The slurry is prepared by blending carbon steel powder with a cellulose derivative binder and additives. Rheological behaviours of different metal contents and binder concentrations are being investigated to determine the optimum printable slurry formulation. It is found that the optimum slurry feedstock formulation comprises 45 vol% metal content, 54 vol% cellulose derivative binder solution at a concentration of 300 g/L, and 1 vol% defoamer. The resulting slurry has fast-drying shear-thinning behaviour and a high storage modulus of 4 × 107 Pa to sustain the printed article at room temperature. The printed articles exhibited an average linear shrinkage of 12.36%, with less than a 1% linear shrinkage difference between X, Y, and Z directions after thermal treatment. The measured densities of the sintered articles were 95% ± 2% compared to the ASTM B783 (material code F-0000). The sintered articles have a measured carbon content of 0.28 ± 0.02%, hardness of 64.15 ± 9 HV, ultimate tensile strength of 255.33 MPa and Young's modulus of 130.47 GPa. This work demonstrates the viability of this additive manufacturing method in producing metal parts with comparable properties to conventional manufacturing.

Polymeric composites in extrusion‐based additive manufacturing: a systematic review

AbstractSolid composites used in material extrusion additive manufacturing have experienced considerable expansion over the past 5 years, incorporating functional properties into 3D‐printed objects. This paper presents a systematic review that aims to: (I) analyze the current state of development in the field; (II) quantify and categorize the adopted polymeric matrices, reinforcing materials, feedstock shapes, characterization strategies, and extrusion mechanisms; and (III) identify the applications, limitations, and trends for future research. The PRISMA statement was followed and the databases Scopus, Web of Science, and PubMed were consulted. Among the 116 included studies, the use of customized filaments surpassed the commercially available ones, with particulate matter being the most common form of filler when melt‐mixed with the polymer. Polyamide is the most widely adopted matrix (30.3%), followed by PLA (22.0%) and ABS (17.4%). In terms of reinforcements, carbon fiber (32.4%), glass fiber (12.5%), and ceramics (12.5%) compose the podium as the most frequently used, with nanofillers receiving increasing attention. In the conducted analysis, no standardized protocols were identified that clearly encompassed the entire process from feedstock formulation to technical prototype fabrication. At last, recycling, exploration of biodegradable materials, and 4D printing were identified as the main opportunities for future research.Highlights Reinforced polymers enable the enhancement of properties for 3D‐printed parts. Composite feedstock is usually formulated and mixed before printing. 3D printers with filament‐ or screw‐based extrusion mechanisms have been used. Mechanical and morphological analyses are common in material characterization. No identified applications were employed in real‐world scenarios.

Silica-based ceramic cores for high-pressure turbine airfoil blades in aircraft engines

Ceramic cores for high-pressure turbine airfoil blades in aircraft engines are characterised by very complicated shapes and the presence of small diameter holes and thin long grooves. In this paper, eight starting powder mixtures having different contents of fused silica, zirconium silicate, alumina and borosilicate glass were used for preparation of core material. The composition, which satisfies every demand for core application in the investment casting of high-pressure turbine blades, contains 69.0wt.% fused silica, 13.0 wt.% zirconium silicate, 12.0wt.% alumina and 6.0wt.% borosilicate glass. This material was characterised by a mechanical strength of 33.1MPa, a coefficient of thermal expansion of 2.56 ? 10?6 1/K, surface roughness of 1.8 ?m, shrinkage of less than 0.8% and an average pore size diameter of 2.7 ?m. The thin-walled ceramic cores were formed by the high-pressure injection moulding method, which required the selection of a thermoplasticiser, feedstock formulation and determination of the optimal processing conditions protecting the injected cores from defects and deformation. The post-shaping process of the cores included both water and thermal debinding, sintering, precision machining and dimension measurements.

Metal Injection Molding of Low Alloy Steel by Using a Palm Stearin/HDPE Binder System

Metal injection molding (MIM) is a proven technology for fabricating complex geometry and low-cost components. The binder system formulation and powder loading are the key parameters affecting the final properties of the manufactured parts in this process. This study investigates the influence of palm stearin (PS) content in a PS/High-Density Polyethylene (HDPE) binder system for three powder loadings of 60, 65, and 70 Vol.%. The manufactured feedstocks are characterized using scanning electron micrograph (SEM), thermo gravimetric analysis (TGA), and differential scanning calorimeter (DSC), rheological and mechanical tests. The results show that PS enhances mechanical properties at increased powder loading. In addition, residual carbon following changing the PS percentages has a significant role in determining the final characteristics of parts. Findings demonstrated that PS could drastically alter the rheological behavior, a crucial criterion for optimizing the feedstock formulation in the MIM process.

Rheology of dry powders and metal injection molding feedstocks formulated on their base

The influence of powder characteristics on the moldability of metal injection molding feedstock is relatively well understood, but remains difficult to quantify other than by real-scale injections. This study aims to correlate feedstock moldability performances with melt viscosity and dry powder rheology. Four stainless steel powders exhibiting different particle sizes and shapes were tested in dry conditions using an FT4 powder rheometer to obtain thirteen different powder rheology-related metrics. These powders were subsequently mixed with a wax-based binder to formulate four feedstocks that were tested in melt conditions using a rotational rheometer to characterize the injection-related rheology of the feedstock formulations. The moldability of the feedstocks was finally quantified using real-scale injections performed into a spiral mold cavity to measure the injected lengths, and the correlation between the dry and melt rheology metrics and the real-scale injection moldability was evaluated. Results showed that the feedstock melt viscosities and the injected lengths were almost perfectly correlated. Furthermore, two dry powder rheology metrics, namely, the normalized basic flow energy and the conditioned powder bulk density, showed the correlation with the feedstock moldability which is comparable to that obtained with the melt rheology. The results of this study indicate that although the feedstock melt viscosity and the dry powder rheology take fewer variables into account as compared to real-scale injections, these simplified tests (especially dry powder rheology) could be considered as rapid and reliable approaches to assessing the impact of powder characteristics on the moldability of powder-binder feedstocks used in metal injection molding.

Role of Microbial Biomechanics in Composting with Special Reference to Lignocellulose Biomass Digestion

Biomass transformation of lignocellulose into compost offers ‘green’ technology for sustainable agricultural development. So far, biomass conversion into compost outweighs fossil resources and other conversational techniques due to the low production cost and environmental pollution reduction. Although composting has aesthetically been resorted to in the digestibility of lignocellulose biomass, its realization has keenly been directed towards adding chemical reagents. However, inclining massively to this treatment instigated research bias as microorganisms’ biomass digestibility remains mostly inadequate. Besides, proliferated growth and activities of microorganisms native to lignocellulose biomass are usually disrupted by chemical treatment. The microbial flora (fungi, bacteria, actinomycetes, archaea, and yeast) involved in composting synthesizes complex biocatalysts (enzymes) that are crucial for solubilizing the biopolymers of lignocellulose materials at a density of 1012 cells g-1. Filamentous fungi are by far excellent degraders of lignocellulose in nature. To adequately ensure sustainable lignocellulose digestibility, microbial engineers must subject research studies to surpassing conditions (feedstock formulation and management processes) suitable for inducing ligninolytic, cellulolytic, and hemicellulolytic enzymes. Hence, the state-of-the-art-method of this review provides insights that relate to mechanisms of microbial reactions on the digestibility of lignocellulose biomass during composting.

Effect of Binder Constituents and Solids Loading on the Rheological Behavior of Irregular Iron-Based Feedstocks

Abstract This work presents an experimental approach used to evaluate the influence of binder constituents and solids loading on the rheological behavior and molding properties of irregular shape iron-based feedstocks used in low-pressure powder injection molding (LPIM). Thirty-six (36) different feedstocks formulated from one new in-development iron-based powder and different wax-based binder systems (paraffin wax (PW) with surfactant and thickening agents) were obtained for solids loading varying from 50 to 68 vol%. The viscosity profiles were experimentally measured at different temperatures using a rotational rheometer in order to quantify the threshold proportions of each ingredient in the binder systems, identify the best feedstock candidates, and calculate their moldability indices, which were finally validated using real-scale injections. Results confirmed that the best feedstock formulation was the one containing paraffin wax with 1 vol% stearic acid (SA) used as a surfactant, 2 vol% ethylene-vinyl acetate (EVA) used as a thickening agent, and 2 vol% carnauba wax (CW) used as a shrinking agent. An irregular shape iron-based feedstock with maximum solids loading of 58 vol% was successfully injected.

Fast Pyrolysis of Lignin Pretreated with Magnesium Formate and Magnesium Hydroxide

Kraft lignin (Indulin AT) pretreated with magnesium formate and magnesium hydroxide was fast-pyrolyzed in a continuously fed, bench-scale system. To avoid fouling issues typically associated with lignin pyrolysis, a simple laboratory test was used to determine suitable ranges of magnesium hydroxide and formic acid to lignin for feeding without plugging problems. Various feedstock formulations of lignin pretreated with magnesium hydroxide and formic acid were pyrolyzed. For comparison, calcium formate pretreated lignin was also tested. The organic oil yield ranged from 9% to 17% wt % on a lignin basis. Carbon yields in the oil ranged from 10% to 18% wt % on a lignin basis. Magnesium formate pretreatment increased oil yield and carbon yield in the oil up to 35% relative to the higher 1:1 g magnesium hydroxide/g lignin pretreatment. However, a lower magnesium hydroxide pretreatment (0.5:1 g magnesium hydroxide/g lignin) resulted in oil yields and carbon yields in the oils similar to the magnesium formate pretreatments. Magnesium formate pretreatment produced more oil but with a higher oxygen content than calcium formate under the same conditions. The GC-MS analysis of product oils indicated that phenols and aromatics were more prevalent in pyrolyzed magnesium-formate-pretreated lignin.

Threshold Concentration of Surfactant Agent in Feedstocks Used for Low-Pressure Powder Injection Molding

Abstract In this work, 32 different feedstocks formulated from four different stainless steel powders and two wax-based binder systems (paraffin wax and beeswax), for which the proportion of two different surfactant agents was varied from 0 to 5 vol.% (stearic acid and oleic acid), were obtained. The viscosity of the feedstocks according to the shear rate was measured using a rotational rheometer. The moldability of the mixtures was assessed using the injected length following real-scale injections. The results show that the influence of surfactant agents on viscosity depends on the main binder constituent used in the feedstock formulation. The moldability of paraffin wax–based feedstocks was significantly affected by the proportion of the surfactant agents, whereas that of beeswax-based feedstocks was not affected by the presence of stearic acid or oleic acid. It was confirmed that as little as 0.20 vol.% of stearic acid or oleic acid in paraffin wax–based feedstock is enough to produce the surfactant effect, leading to a significant increase in the moldability of feedstocks (e.g., fourfold longer injected length). This threshold concentration of surfactant agent in paraffin wax–based feedstocks was also established with different powder grades, shapes, and sizes. For feedstocks containing paraffin wax and surfactant agents, the presence of a discontinuity in the viscosity profiles was confirmed not to be an experimental artifact because the phenomenon was reproduced using three different measurement approaches.

Direct Ink Writing Technology (3D Printing) of Graphene-Based Ceramic Nanocomposites: A Review.

In the present work, the state of the art of the most common additive manufacturing (AM) technologies used for the manufacturing of complex shape structures of graphene-based ceramic nanocomposites, ceramic and graphene-based parts is explained. A brief overview of the AM processes for ceramic, which are grouped by the type of feedstock used in each technology, is presented. The main technical factors that affect the quality of the final product were reviewed. The AM processes used for 3D printing of graphene-based materials are described in more detail; moreover, some studies in a wide range of applications related to these AM techniques are cited. Furthermore, different feedstock formulations and their corresponding rheological behavior were explained. Additionally, the most important works about the fabrication of composites using graphene-based ceramic pastes by Direct Ink Writing (DIW) are disclosed in detail and illustrated with representative examples. Various examples of the most relevant approaches for the manufacturing of graphene-based ceramic nanocomposites by DIW are provided.

Numerical simulation and experimental investigation of mold filling and segregation in low-pressure powder injection molding of metallic feedstock

The mold filling stage of the low-pressure powder injection molding process and the segregation of the injected part were numerically simulated and validated by an experimental approach. The numerical simulations were performed using the Autodesk Moldflow Synergy 2019 package to specifically investigate the injected length, the front velocity, the filling time, the pressure, and the shear rate, as well as to assess the magnitude of powder segregation after an injection. Furthermore, thermal and rheological characteristics of feedstock were experimentally measured to establish the constitutive equations to be provided to Moldflow. Numerical simulation results were validated with real-scale injections (with feedstock temperatures varying between 80 and 100 °C), using a laboratory injection press. Experimental characterization and injection were conducted using a feedstock formulation based on 17–4 PH stainless steel powder (60 vol% of powder) combined with a low-viscosity binder system. The injected length, the melt front velocity, and the filling times predicted by the numerical model were in good agreement with the experimental observations, with relative differences varying from 3.1 to 4.4%. Since the injections were performed and simulated at constant volumetric flow in a constant cross-section mold cavity, the mold filling results confirm that the feedstock temperature has no influence on the injected lengths, but rather, on the injection pressure. Moldflow also captured the absence of segregation occurring during injection, with experimental measurements of the local solid loading confirming the ability of the numerical model to successfully predict the homogeneous distribution of the powder (i.e., no segregation) within a simple shape mold cavity. Although theses interesting simulation capabilities of the injection and segregation behaviors were obtained for simple-shape components, the present work represents, to the best of the authors’ knowledge, the first simulation of low-pressure injection molding of metallic feedstock.

Novel silicon-wollastonite based scaffolds for bone tissue engineering produced by selective laser melting

Engineered bone tissue or scaffold is a potential alternative to the common use of bone grafts due to limitless supply and no disease transmission. We present a novel way to manufacture the highly efficient bioceramics combining osteoinductive and bioactive elements using additive manufacturing through selective laser melting without polymer based binder addition and post-processing sintering steps. A formulation of powder feedstock for the production of the scaffolds with an optimized geometry and a high strength is proposed. The structure with circular pores of 400 μm in diameter and porosity level of 35% exhibits density of around 1.4 g/cm3 and a compressive strength of 110 MPa, which is only slightly decreased after the immersion into Tris buffer for two weeks being of 90 MPa. The scaffolds demonstrate a high bioactivity and a controlled growth of the hydroxyapatite-like layer on the surface of the structures. The results of this work illustrate the ability for fabrication of complex-shaped ceramic based structures to be used as novel bone scaffolds and implants by SLM, and the promise for development of other ceramic – based materials using the proper precursor powders feedstock.

Effect of Powder Shape and Size on Rheological, Thermal, and Segregation Properties of Low-Pressure Powder Injection Molding Feedstocks

Optimization of molding parameters at different filling stages requires that the characteristics of low-viscosity feedstocks must be properly known. In this study, the influence of the particle size (3, 7, and 12 μm) and powder morphology (gas- and water-atomized) was quantified using different feedstock formulations based on a 17-4 PH stainless steel powder, all combined with the same binder system. The specific heat capacity, viscosity, and segregation levels were assessed using a differential scanning calorimeter, a rotational rheometer, and a thermogravimetric analyzer, respectively. It was then shown that the feedstock prepared with the gas-atomized powder exhibits a higher specific heat capacity value when compared to a water-atomized powder (i.e., Cp varying from 0.6 to 0.3 J/g K, respectively). It was also shown that the feedstock viscosity profiles and the intensity of segregation both depend significantly on the powder shape and size used in the feedstock formulation. For short processing times (e.g., < 1 min spent in molten state), a feedstock formulated with coarse gas-atomized powder can be considered to be the best candidate for an injection process because its viscosity and segregation potential are relatively low (with a viscosity varying from 0.5 to 2 Pa s, and a volume fraction of powder close to 60 vol.%). Following this, the moldability index was used to predict that coarser water-atomized powder (i.e., 12 versus 7 μm) will not have a significant effect on the molding properties, and can be seen as a potential means of decreasing shrinkage during sintering without impacting the injection properties. For very long processing times, the magnitude of segregation remains insignificant for feedstock formulated with fine powder (i.e., a volume fraction of powder remaining close to 60 vol.%). However, this important gain (i.e., no segregation) comes with a significant increase in viscosity varying from 2 to 10 Pa s, resulting in a decrease in the molding properties.

Ultrathin Ceramic Piezoelectric Films via Room-Temperature Electrospray Deposition of ZnO Nanoparticles for Printed GHz Devices.

High-frequency devices are key enablers of state-of-the-art electronics used in a wide and diverse range of exciting applications such as inertial navigation, communications, power conversion, medicine, and parallel computing. However, high-frequency additively manufactured piezoelectric devices are yet to be demonstrated due to shortcomings in the properties of the printed transducing material and the attainable film thickness. In this study, we report the first room-temperature-printed, piezoelectric, ultrathin (<100 nm) ceramic films compatible with high-frequency (>1 GHz) operation. The films are made of zinc oxide (ZnO) nanoparticles via near-field electrohydrodynamic jetting, achieving film piezoelectricity, without high-temperature processing, through a novel mechanism that is controlled during the deposition. Optimization of the printing process and feedstock formulation results in homogeneous traces as narrow as 213 μm and as thin as 53 nm as well as uniform field films as thin as 91 nm; the printing technique can be used with flexible and rigid, conductive and insulating substrates. The crystallographic orientation of the imprints toward the (100) plane increases if the rastering speed during printing is augmented, resulting in a larger piezoelectric response. The resonant frequency of film bulk acoustic resonators increases monotonically with the rastering speed, achieving transmission values as high as 4.99 GHz, which corresponds to an acoustic velocity of 2094 m/s, similar to the expected transverse value in high-temperature-grown ZnO films. Piezoresponse force microscopy maps of printed field films show local variation in the piezoelectric behavior across the film, with an average piezoelectric response as high as 21.5 pm/V, significantly higher than the d33 piezoelectric coefficient of single-crystal, high-temperature-grown ZnO, and comparable with reported values from ZnO nanostructures.

Control of Rheological Properties of Disperse Systems to Meet Current Petroleum Road Asphalt Specifications

A feedstock formulation for production of road asphalts based on Arlan oil heavy resids is developed. The applicable scientific-technological solutions, which include purposeful control of fractional and group chemical composition of Arlan oil heavy resid while mixing it with components-intermediate products that control these compositions, allow production of road-binding materials conforming to the current specifications of the road-building industry. It is shown that use of Arlan heavy resid as a constituent of asphalt is economically and technologically sound because it frees up substantial volumes of West Siberian oil residues for their processing into high-quality coke, and the resinous-asphaltic matters contained in the Arlan heavy resid ensure long durability of the obtained road asphalt binding materials.

PVB/PEG-Based Feedstocks for Injection Molding of Alumina Microreactor Components.

The ceramic injection molding (CIM) process is a cost-effective powder-based near net shape manufacturing process for large-scale production of complex-shaped ceramic functional components. This paper presents the rheological analysis of environmentally friendly CIM feedstock formulations based on the binder components polyvinyl butyral (PVB) and polyethylene gycol (PEG). The prepared PVB/PEG-based alumina molding compounds were investigated with respect to their PVB:PEG ratios as well as to their powder filling degrees in the range between 50 and 64 vol.%. Corresponding viscosities and shear stresses were determined for increasing shear rates to show the effects of increased PEG content and solid loadings on them. Two single reactor components were injection molded and subsequently joined in their green state for fabrication of an alumina microreactor. The intended purpose of the alumina microreactors is their potential application as wear-resistant and hydrothermal stable multifunctional devices (µ-mixer, µ-reactor, µ-analyzer) for continuous hydrothermal synthesis (CHTS) of metal oxide nanoparticles in supercritical water (sc-H2O) as the reaction medium.

Experimental study on moldability and segregation of Inconel 718 feedstocks used in low-pressure powder injection molding

Moldability and segregation of feedstock are linked to the rheological behavior of the powder-binder mixture. In this study, the impact of binders on viscosity and segregation of feedstocks was investigated. The experiments were conducted on several feedstocks obtained by mixing Inconel 718 powder with paraffin wax-based binder systems. The viscosity of feedstocks was measured by a rotational rheometer while the segregation within green parts was evaluated using a thermogravimetric analyzer. It was demonstrated that the variation in solid loading within a molded part can be measured with a sensitivity of at least ±0.25 vol% of powder. The results indicated that the predominant powder-binder separation appears clearly at the top and the bottom of the molded part. It was also shown that the viscosity profiles of feedstocks and the intensity of segregation depends significantly on the binder constituents used in feedstock formulation. The mixture containing only paraffin wax produced the best trade-off between high moldability and low segregation for an injection process requiring an extended time range between injection and solidification of the part (e.g. up to 10 min). For a short processing time (e.g. <1 min spent in molten state), the feedstocks containing paraffin wax with stearic acid or small amount of ethylene vinyl acetate can be also considered as good candidates for LPIM process because their viscosity and segregation potential are relatively low.

Processing of MIM feedstocks based on Inconel 718 powder and partially water-soluble binder varying in PEG molecular weight

This paper deals with a complex characterization of metal injection molding (MIM) feedstocks based on Inconel 718 powder and partially water-soluble binder systems. Polyethylene glycol (PEG) is a well-known component in design of feedstock formulations due to its low viscosity, solubility in the water, eco-friendly nature and commercial availability. The main objective of this paper is to investigate the influence of PEG molecular weight on overall MIM process chain including its eventual impact on final mechanical properties. For this purpose, 7 feedstocks with a fixed amount of powder loading (59 vol%) and the binder composition differing in molecular weight of PEG (in a range from 1500 to 20,000g/mol) were investigated. The PEG molecular weight was found to have the considerable impact on the feedstock moldability and debinding kinetics.