Metal Injection Molding Research Articles

Structural features of near equiatomic FeCo-2V semi-hard magnetic alloy prepared by MIM technology

The structural properties of a magnetically semi-hard near equiatomic FeCo-2wt%V (FeCoV) alloy produced by Powder Injection Moulding (PIM) (option by fine metal powder - Metal Injection Moulding (MIM) technology) were investigated in this paper. Starting granulate was prepared by mixing FeCoV powder with a low-viscosity binder. After injection, the green samples were first treated with a solvent and then thermally with the same aim of removing the binder. MIM technology was completed by high-temperature sintering for 3.5 hours at temperatures from 1370 OC to 1460 OC in a hydrogen atmosphere, which provides the necessary magnetic and mechanical characteristics. The influence of sintering temperature was investigated concerning the aspects of the processes of structural transformation by the methods of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The appearance of an intense diffraction peak of the ?'-FeCo phase (crystal structure type B2) was registered for all investigated samples. Structural parameters particle size Dmax, Feret X, and Feret Y exhibit constant increase with increase of sintering temperature.

Effects of injection Moulding Parameters on the Produced Parts

The publication deals with an innovative technology called powder-based metal injection moulding, which is a combination of traditional polymer injection moulding and powder metallurgy. With the technology, it is possible to produce metal components with complex geometry in large series. There is an extremely large selection of materials that can be used, mostly steel, copper, titanium or nickel-based alloys. In this research, the material used is type 17-4PH, martensitic corrosion-resistant steel, and since it is a widely used material, it is examined in many international articles and research studies, and it is also common in industry, so it is advisable to use this type of material for further comparability. Little information can be found in the literature about spraying parameters and their effects, which is why this research focusses on this. On the other hand, these data can also serve as useful information for the industry. During the production of so-called green products, the effects of product shrinkage were measured by changing the most important parameters and comparing the effects of these parameters to traditional polymer injection moulding.

Influence of sintering on mechanical response of metal injection moulded parts

ABSTRACT Sintering is often the final step during Metal Injection Molding (MIM) and does in an observable way contribute to influencing both the characteristics and performance of final products. In this research paper, the influence of sintering parameters on dimensional stability and mechanical properties of parts having three different shapes is presented and adequately discussed. A CI 90 feedstock having 90 weight percent of Carbonyl Iron powder was prepared by mixing the carbonyl iron powder with an organic binder. The GSGR75 feedstock has 75 weight percent of powder of grinding sludge and graphite. The green samples were subject to thermal debinding at 750°C. The brown samples were sintered at the temperatures of 1100°C, 1200°C, and 1300°C for 60 minutes and in atmospheres of vacuum, argon, and nitrogen. The sintering characteristics of the parts that were produced from the use of the grinding sludge powder (GSGR) were found to be inferior to those produced from the use of the carbonyl iron (CI) powder. This is essentially because of the limited degree of reduction coupled with the presence and distribution of a sizable number of pores. The sintering parameters did exert an influence on the properties of the as-sintered end-product. Distinct empirical relations were developed and verified for the purpose of predicting properties of the sintered product based on the sintering parameters used.

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.

Evaluation of different particle size distribution and morphology characterization techniques

• Six metallic powders characterised in terms of PSD using a range of techniques. • Laser diffraction compared to optical dynamic and static imaging. • Spherical powder produced more acceptable results over range of equipment used. • Larger differences arose as the morphology deviated away from spherical. • Presence of satellites, irregular particles and agglomerates caused differences. In this paper, the particle size distribution (PSD) and morphology for six different metal powders were measured and compared using a range of techniques which included laser diffraction, static imaging, and dynamic imaging. The metal powders were chosen from a diverse end-use (Metal Injection Moulding, Laser - Powder Bed Fusion, Electron Beam - Powder Bed Fusion, and Hot Isostatic Pressing) and varied in powder size distribution and morphology. While the results for particles that were predominantly spherical showed some general agreement for the measured PSD across the range of measurement techniques investigated, larger variation than industrial tolerances would allow was identified when comparing the results between the different measurement techniques. The technique did influence the measured PSD at times, with differences large enough to require compensation if used for critical applications with tight tolerances. For samples that had particle morphologies that deviated away from spherical (agglomerated, irregular, or satellited), the difference in the measured PSD was more significant when comparing the results from the different measurement techniques. This was due to the under/overestimation of the PSD due to the measurement principles of the system being employed. Thus, when reporting PSD, it is of paramount importance to align specification requirements, and the certification test methods, with the industrial controls (i.e., laser diffraction when used in production to tune air classification). If different instruments or techniques are to be used by a purchaser and supplier, any inherent bias must be understood. For morphology, static imaging tends to result in a higher measured value for sphericity and aspect ratio in comparison to dynamic imaging. This is believed to be due to the influence of orientation during measurement as well as the resolution of the optics.

Material extrusion additive manufacturing of low-viscosity metallic feedstocks: Performances of the plunger-based approach

In recent years, increasing attention has been directed at the material extrusion additive manufacturing of highly-filled polymers (MEAM-HP). This is because conventional polymer 3D printers, which are low cost and readily available, can easily be adapted for use with metal powder-filled polymer filaments. However, fabricating the latter is time-consuming and their formulations differ from regular metal injection molding (MIM) feedstocks by lower powder solids loadings and higher elastomer contents, thus requiring significant efforts to optimize their debinding and sintering conditions. Favorably, other types of MEAM-HP printers, such as screw- and piston-based ones, can process available MIM feedstocks and apply the debinding and sintering procedures that have already been optimized. In this study, a novel ram extruder-based printer with a 100 mm-diameter ― 250 mm-high build volume was developed to print a low-viscosity MIM feedstock composed of 65% of 17-4PH powder, 23% of paraffin wax, 10% of ethylene vinyl acetate and 2% of stearic acid (all in vol. %). The printer calibration and the process optimization procedures are detailed herein. The kinematic accuracy of the build platform revealed a maximum deviation of 29 and 92 µm in the vertical (Z) and horizontal (XY) directions, respectively. Prior to printing, a relative feedstock density of 99.8% was obtained using a one-minute degassing procedure. During printing, a 52.5°C build platform temperature was used and an 85°C extrusion temperature conferred to the feedstock a viscosity of 142 Pa·s at a shear strain rate of 180 s -1 (Ø0.4 mm E3D V6 nozzle, 1 mm 3 /s flow rate). Indirect measurements of the extrusion pressure using a load cell positioned under the piston allowed to maximize the accuracy of start/stop extrusion sequences by adjusting the retraction volumes. An overlap printing path technique was introduced to eliminate typical MEAM voids between printed lines. Finally, six parts exhibiting complex geometries were printed to validate the capacity of the printer to produce functional components using conventional low-viscosity MIM feedstocks.

Integrated Numerical Simulations and Experimental Measurements for the Sintering Process of Injection-Molded Ti-6Al-4V Alloy.

Metal injection molding (MIM) is an advanced manufacturing technology that enables the mass production of high-performance and complex materials, such as the Ti-6Al-4V alloy. The determination of the size change and deformation of the Ti-6Al-4V alloy after the sintering process is challenging and critical for quality control. The numerical simulation could be a fast and cost-effective way to predict size change and deformation, given the large degrees of freedom for the sintering process. Herein, a finite element method based on the thermal-elastic-viscoplastic macroscopic model is developed to predict the shrinkage, deformation, relative density, and crack of injection-molded Ti-6Al-4V after sintering, using the Simufact software. Excellent agreements between experimental measurements and numerical simulations of the size and deformation are demonstrated (within a 3% error), confirming the accuracy of the numerical model. This approach can serve as a guideline for the mold design and sintering optimization of the MIM process.

Improving an easy-to-debind PEG/PPC/PMMA-based binder

In this work, we developed a new polymeric binder based on polyethylene glycol/polypropylene carbonate (PEG/PPC). The effect of polyvinyl acetate (PVAc) on the rheological properties, homogeneity, phase morphology, and thermal behaviour of the PEG/PPC/polymethyl methacrylate (PMMA)-based feedstock was investigated. Mechanical properties and microstructures of the sintered samples were reported alongside the impurity measurements. The rheological analysis confirms that incorporating PVAc into the PEG/PPC/PMMA blend can improve the rheological properties and homogeneity of the feedstock. The phase morphology study further indicates that PVAc effectively improves PPC dispersion in the PEG matrix. The Ti metal injection moulding feedstocks, formulated from this new binder system, demonstrated good rheological properties and homogeneity, leading to Ti products with good mechanical properties (relative sintered density 98%, ultimate tensile strength (UTS) 598 MPa, and elongation 13.7%).

Additive manufacturing of metal filament: when it can replace metal injection moulding

Additive manufacturing of metal filament: when it can replace metal injection moulding

Development of the design and technology of extrusion of metal-polymer mixtures for the production of feedstocks

The paper is devoted to the development of new equipment for the production of metal-polymer thread. 3D printing with metal-polymer thread is one of the advanced directions in the technology of manufacturing metal parts of complex shape. The proposed technology is an alternative to the currently existing metal injection molding (MIM) technology and selective laser melting printing technology. An important step in this work was to conduct computational experiments to determine the effect of screw rotation on the process pressure parameter and the design of the main assembly of the screw extruder. As a result of the research, the pressures on the metal-polymer composition were determined depending on the rotation speed of the screw. With a rotation of 30 rpm, the pressure reached 0.05 Pa and the maximum pressure was 0.18 MPa. The experiments were carried out in the CradelSFlow program. The computer calculation showed a margin of the screw strength coefficient k=1.8, and a maximum deflection of 2.8∙10–4 m, which meets the condition of static rigidity. To determine the correct value of the gap δ between the screw ridge and the extruder walls, an analysis of the rotor dynamics was carried out. The result of this study is the critical extruder rotation speed of 60 rpm at which the phenomenon of precession may occur. Amplitude-frequency characteristics ydin=7∙10–4 m. According to the results of the dynamic calculation, the screw dimensions were adjusted, the geometry was reduced by ∆=0.5 mm. The experiments made it possible to verify the optimal parameters of the technological process of metal-polymer mixture extrusion. The data obtained are important for the improvement and development of 3D printing technology for metal parts of complex geometric shape.

On amine treated polyoxymethylene (POM) blends with low formaldehyde emission for metal injection moulding (MIM)

When polyoxymethylene (POM)—a common polymer used in metal injection moulding feedstock—is exposed to heat and oxygen during compounding, it can be easily decomposed, releasing undesired gaseous formaldehyde products. In order to reduce the formaldehyde emission from POM, amine treatment was performed. The effectiveness of propylamine at different concentrations and its role as a formaldehyde scavenger was studied via the UV–vis Spectrophotometry, Fourier Transform Infra-red, Thermogravimetric Analysis, Scanning Electron Microscopy, and melt flow index. The results proved that a simple amine, such as propylamine, is a promising candidate for scavenging formaldehyde in POM. It is also demonstrated that the best concentration of propylamine is 2 wt.% (POM-PA2) with a minimum formaldehyde emission of 1.44 mg/L. Further, when used in formulating metal injection moulding feedstock (MIM), the POM-PA2 reveals good rheological properties and high green strength. These advantages make the modified polyoxymethylene (POM-PA2) a promising binder system for MIM feedstock.

Investigation and Improvement of Processing Parameters of a Copper‐Filled Polymer Filament in Fused Filament Fabrication as a Basis for the Fabrication of Low‐Porosity Metal Parts

AbstractIndividualized and complex additively manufactured metal components are increasingly used in an industrial environment. One possibility to manufacture such metal components is the fused filament fabrication (FFF) process. Here, a metal powder‐filled polymer filament is processed (green part). For the realization of purely metallic components, the FFF‐manufactured components are subjected to a post‐process, which corresponds to the metal injection molding (MIM) process chain. In a first step, the polymer binder contained in the components is removed (brown part). Afterwards, the metal particles are sintered (white part). For the production of high‐quality components, the porosity of the components must be considered. Essentially, the porosity of the components results from the characteristic FFF structure caused by the deposition of single strands. This has a direct influence on the porosity of the white parts and accordingly on the resulting part properties. Within this study, a filament consisting of copper particles and a polymer binder matrix of polylactide acid (PLA) is used. This filament offers the possibility to produce complex, thermally conductive, and electrically conductive components. During the examinations, the influence of the FFF‐specific process parameters on the manufactured green parts is investigated. For this purpose, the stationary and non‐stationary extrusion areas will be considered. The aim is to achieve a homogeneous strand geometry and, thus, the highest possible part density. This should lead to the reliable processing of copper‐filled polymer filaments in FFF and provide a good basis for the production of pure copper components.

Effects of C and Nb on Pore-Grain Boundary Separation Behavior during Sintering of 420 Stainless Steel

This study investigated the evolution of density, grain size, and pore characteristics during the sintering of metal injection molding (MIM) 420, 420 + 0.3C and pre-alloyed 420Nb stainless steel powders. The results show that C promotes the reduction of oxides on the surface of stainless steel, thereby accelerating sintering at 1330 °C, which is the initial sintering stage of MIM 420. MIM 420Nb showed the slowest sintering rate due to the strong binding force between Nb and C. At 1350 °C, the sintering densities of MIM 420 and 420 + 0.3C slightly improved, whereas their grain sizes grew significantly. Scanning electron microscopy images show grain boundary-pore separation, which significantly retarded the grain boundary diffusion mechanism and hence reduced the densification rate. The addition of C accelerated the pore-grain boundary separation; thus MIM 420 + 0.3C showed the lowest density at this temperature among the materials analyzed in this study. Nb suppressed the grain growth rate; thus, MIM 420Nb exhibited the highest density among the three materials. At 1370 °C, MIM 420 + 0.3C reached the highest density owing to the creation of a liquid phase. Theoretical calculations proved that there is a linear relationship between the grain boundary area per unit volume and the interfacial pore area per unit volume. Furthermore, when the ratio of grain size to pore size is 28, the contact probability between the grain boundaries and pores is significantly reduced to approximately 10%, leading to an extremely slow densification rate and a rapid grain growth rate, which is consistent with the experimental results.

Self-lubrication of porous metal injection molded (MIM) 17-4PH stainless steel by impregnated paraffin wax

Paraffin impregnation into the internal pore structure of porous 17-4PH was used as a lubricant storage. Porous 17-4PH specimens were fabricated by metal injection molding (MIM) combined with powder space holder (PSH) technique for samples with three different porosities. Sodium chloride was used as a space holder material. Paraffin impregnation was achieved by immersing the 17-4PH specimens into melted paraffin wax. Dynamic coefficient of friction (COF) of porous and non-porous specimens was measured in dry sliding and paraffin-lubricated conditions. Significant COF reduction in paraffin-lubricated results was observed with the porous samples compared to the non-porous reference samples. The lowest COF value was observed for specimens with 20 and 30 wt% porosity.

Jet Penetration Performance of a Shaped Charge Liner Prepared by Metal Injection Molding

The metal injection molding (MIM) method was applied to manufacture a shaped charge liner (SCL) used for petroleum perforating bombs. Its application could overcome the drawback of heterogeneous density distribution prepared using the traditional powder metallurgy and spinning process. The sintering results showed that because of the limitation in the sintering temperature, the relative density of the W–Cu alloy shaped charge liners prepared by metal injection molding (MIM W–Cu SCLs) ranged from 48.05% at 1050 °C to 52.52% at 1100 °C, which was far below those prepared by spinning. Further increase to higher temperature led to the W–Cu separation, cracks, and distortion of the SCL. The explosive test proved that the shaped charge liners prepared by metal injection molding (MIM SCLs) could achieve comparable or even better penetration performance than those prepared by spinning. The particle size of tungsten played a significant role in the penetration performance in which the sample prepared from a −250-mesh tungsten powder showed the highest penetration depth, which was 18.44% deeper than that of the spinning process. From the observation of ballistic holes, the jet of the MIM SCL was composed of dispersed W–Cu particles without a slug. The diameters of the holes bored by the MIM SCLs were larger than those SCLs produced by spinning, which proved that the MIM SCL jet is noncoherent.

3D Printing of parts using metal extrusion: an overview of shaping debinding and sintering technology

Additive Manufacturing (AM) is the fabrication of real three-dimensional objects from plastics and metals by adding material, layer by layer. One of the most common AM processes is the Material Extrusion (ME) based on different approaches: plunger, filament and screw. Material Extrusion technologies of metal-polymer composites is expanding and it mainly uses the filament or plunger-based approaches. The feedstock used is a mixture of metal powder (from 55 vol% to about 80 vol%) dispersed in a thermoplastic matrix, as the Metal Injection Molding (MIM) materials. The process consists of three steps: shaping, debinding and sintering. The first step provides the extrusion of filament to realize a primary piece called “green part”; subsequent steps, debinding and sintering, allow to obtain a full metal part by dissolving the polymeric binder. The latter can be carried out using solvents, heat and the combination of them. The interest toward this technology is driven by the possibility to replace other Metal AM technologies, such as Selective Laser Melting or Direct Energy Deposition, in sectors like rapid-tooling or mass production, with several benefits: simplicity, safety to use and saving material and energy. The aim of this keynote is to provide a general overview of the main metal ME technologies considering the more technical aspects such as process methodologies, 3D printing strategy, process parameters, materials and possible applications for the manufacturing of samples on a 3D consumer printer.

Development of paste extrusion-based metal additive manufacturing process

PurposeThis study aims to explore a technique of metal additive manufacturing (MAM) for producing parts in aluminium. The proposed technique mimics the process of metal injection moulding but with the tools meant for fused freeform fabrication machines.Design/methodology/approachThe work focusses on the preparation of novel feedstock by mixing the aluminium powder with binders made from different compositions of high-density polyethylene, paraffin wax, petroleum jelly and stearic acid. Further, a novel experimental setup with a paste extruder was designed to print the test samples. A sintering cycle was developed in-house along with a thermal debinding procedure. An experimental campaign was also carried with the proposed technique to establish a proof-of-concept. Produced samples were tested for part density, hardness, compressive strength and tensile strength.FindingsThe results indicate geometrical accuracy was an issue owing to the presence of petroleum jelly in the binder-powder mixture. Therefore, machining as a post-processing operation seems to be unavoidable. The study also elucidates that the printed specimen may require further heat treatment to replace wrought alloys. However, the sintered parts show hardness and compressive strength similar to that of wrought aluminium alloy.Originality/valueThe novelty of the work is to develop the cost effective and scalable powder extrusion-based MAM process for printing the aluminium parts.

Optimization of composite extrusion modeling process parameters for 3D printing of low-alloy steel AISI 8740 using metal injection moulding feedstock

Composite Extrusion Modeling (CEM) is an advanced material extrusion additive manufacturing technique for low-cost rapid production of complex parts. In this work, a conventional Metal Injection Moulding (MIM) feedstock is used for 3D printing of low alloy-steel AISI 8740 via CEM. This steel is widely used in aircraft, aerospace, and MIM industries. However, it has, so far, not been processed using CEM-based 3D printing. The influence of four printing parameters, extrusion multiplier, extrusion temperature, nozzle velocity, and layer thickness on green density and surface roughness was explored following the feedstock's investigation. Full-factorial and face-centered response designs were utilized to study the influence of printing parameters and their optimization to achieve maximum green density and minimum surface roughness. The optimized parameters were found to be an extrusion multiplier of 107.6 %, extrusion temperature of 180 °C, nozzle velocity of 20 mm/s and layer thickness of 0.050 mm through a multiple response optimization process. The dense green part with relative densities of ≥ 98 % was achieved with minimum surface roughness of Ra = (2.3 ± 0.1) μm and Rz = (16.1 ± 1.1) μm. Moreover, a scanning electron microscope was utilized to study the surfaces of green parts. The parts printed with optimized printing parameters showed the best quality with minimized printing voids and smooth extrusion.

Growth inhibiting during ultra-high temperature sintering of injection moulded 17-4 PH stainless steel through the dispersion of ZrO2 particle as a thermal stabiliser

ABSTRACT The present work deals with the metal injection moulding and ultra-high temperature sintering of 17-4 PH powder. Purposefully, 5 mass% ZrO2 particles were dispersed by applying high shear stress during feedstock preparation. Uniformly distributed particles effectively hindered the powder boundary migration and limited their growth during ultra-high sintering temperatures. The achieved thermal stability provided a proper condition for reducing the final porosity to 3% and significantly improved the ultimate strength to 1070 MPa after sintering at 1380°C. Also, the ZrO2 particles acted as facilitators of sliding between solid powders and substantially reduced the required pressure for injecting to 700 Bar. Through introducing such a new approach in the field of powder injection moulding by ZrO2 particles, the amount of anisotropic shrinkage was reduced to 2%.

Metal Injection Molding Using Gas-Assisted Technology for Optimizing Density Uniformity and Part Weight Reduction

To control the product density uniformity and weight reduction for metal injection molding (MIM), this study investigated the influence of using gas-assisted technology to assess if uniform part density can be achieved. The findings show that gas-assisted molding has great potential for improving density uniformity, particularly for the part density at the position far away from the gate. The green parts and final parts also significantly improve density uniformity and shrinkage. Interestingly, the gas-assisted technology applied to MIM shows similar molding characteristics and advantages over gas-assisted injection molding of polymers. This also enables the design of MIM parts with a non-uniform thickness with a hollowed core in the thick portion.