Metal Injection Molding Research Articles

Functionalized porous 316 L stainless-steel with oil reservoir against ice adhesion

Slippery liquid-infused porous surfaces (SLIPSs) are used in anti-fouling, anti-icing and anti-corrosion, but lack of long-term durability is a challenge due to lubricant depletion. SLIPS with self-lubricating properties can achieve extended durability without reapplying the lubricant. Generally, lubricant is stored close to surface, thus lubricant reservoir is limited. Here bulk of porous material acts as lubricant reservoir in 316L stainless-steel SLIPS with self-lubricating properties for lowering ice adhesion. The reservoir was fabricated by using a space holder technique in metal injection molding (MIM) with lubricant reservoir volume up to 17.3%. Surface was activated with vinyltrimethoxysilane (VTMS) to attract lubricant. Ice adhesion strength was increased up to three times against non-porous reference in ice adhesion testing using porous surface without lubrication. The best performing SLIPS showed 6.7 times lower ice adhesion against counterpart porous surface without lubricant and 1.7 times lower than non-porous reference. This self-lubrication was achieved on mechanically durable structure having an adjustable lubricant storage capacity by temperature-driven phenomenon during de-icing.

Influence of a suboptimal environment and sintering temperature on the mechanical properties of fused filament fabricated copper

Metal injection molding (MIM) processes are generally more cost-effective for the generation of metallic AM components. However, the thermal processing required to remove the polymer and sinter the metal powder is not well understood in terms of resulting mechanical response and damage evolution, especially in ambient atmospheres where contamination is present. This study aims to provide a range of achievable mechanical properties of copper produced using a MIM-based method called fused filament fabrication (FFF) that is post-processed in a nonideal environment. These results showed direct correlations between sintering temperature to multiple aspects of material behavior. In addition, Nondestructive Evaluation (NDE) methods are leveraged to understand the variation in damage evolution that results from the processing, and it is shown that the higher sintering temperatures provided more desirable tensile properties for strength-based applications. Moreover, these results demonstrate a potential to tailor mechanical properties of FFF manufactured copper for a specific application.

Enhancing the strength and plasticity of Kovar alloy without sacrificing thermal expansion properties

Enhancing the strengths of most constant-expansion alloys, including Kovar alloys, typically results in reduced plasticities and increased coefficients of thermal expansion (CTEs). In this study, we systematically investigated the effects of carbon on the microstructure, mechanical properties, and CTE of a 4J29 Kovar alloy prepared via metal injection molding (MIM). When the carbon content was in the appropriate range, the strength and plasticity could be improved without compromising the CTE. MIM samples prepared by adding 1000 ppm graphite and oxalic acid for degreasing exhibited increases of 28.2 % and 17.3 % in tensile strength and elongation, respectively, compared to those of samples with low carbon contents of 46 ppm. The average CTE remained stable at 4.92 × 10⁻⁶ ℃–1 (25–400 ℃). The reduced number of pores at the grain boundaries was the main cause of the improvement in plasticity. The low CTE is attributed to the combined effect of the grain boundary volume fraction and porosity. This study provides significant theoretical and practical guidance for use in producing high-performance 4J29 Kovar alloys that may be used in complex components with constant-expansion properties.

Moulding of SS316L surgical component using palm-stearin feedstock: Rheological analysis, process window and parametric optimisation

Metal injection moulding of a thin surgical component using a palm-stearin based SS316L feedstock was investigated. The study first determined the optimal solids loading of the feedstock, followed by examining its sensitivity to the shear rate and temperature, to ensure its pseudo-plastic behaviour. After developing the Mouldability index, a process window was established based on the experiments to present appropriate injection parameters. Using the analysis of variance, the significance and mutual coupling of each parameter was evaluated. The study found that the impact of injection speed was greater than other parameters, while holding pressure showed little effect. The verified optimised injection parameters to maximise the green density were found to be an injection temperature of 155 °C, an injection speed of 80 mm/s, a holding pressure of 83 bar, a holding time of 9 s, and an injection pressure of 132 bar, resulting in a green part density of 4.892 g/cm3.

Technological and Mechanical Studies on Additively Manufactured Cellular Structures Made of the Ultrafuse 316L Composite Filament

Regular cellular materials produced using additive manufacturing (AM) techniques represent a significant development trend in modern engineering materials. Depending on the applied elementary unit cell of topology, it is possible to define the course of the structure deformation process in order to obtain the highest possible energy absorption effectiveness. This feature makes regular cellular structural materials particularly attractive for a number of industrial branches. This paper presents the results of technological trials and the results of experimental studies on the mechanical properties of regular cellular structures made using 3D printing technology under compression test loading conditions. The material used for their production was the Ultrafuse 316L filament and the fused filament fabrication (FFF) technique. The proposed material is a polymer-metal composite with a manufacturing process similar to metal injection moulding (MIM). The adopted research methodology included a feasibility study aimed at achieving material homogeneity and compression tests of the developed and manufactured regular cellular structures under quasi-static loading conditions. Several structural topologies were analysed. Experimental results indicated that regular cellular structures made from 316L steel exhibit high mechanical strength and extensive plastic deformation capabilities. The utilized in this work manufacturing technology used combines the advantages of 3D printing process with the potential of powder metallurgy. The proposed technique of structure manufacturing process is much cheaper than other based on melting metallic powders.

Complex-shaped titanium components fabricated via metal injection molding using hydride-dehydride titanium powder

Metal injection molding (MIM) is a net-shape manufacturing method that lessens the costs of production and increases the affordability of titanium goods. A range of CP-Ti specimens was prepared to confirm the primary manufacturing parameters for titanium metal injection molding utilizing affordable hydride-dehydride (HDH) powders. Mixture of powder and polyformaldehyde-based binder was injection molded, debonded, and then sintered. The optimum powder loading is 55 vol%. The ideal conditions of catalytic debinding were attained by placing the specimens in the catalytic debinding system at 120 °C temperature. Samples with minimal deformation and low impurity content were obtained when thermal debinding was carried out at a modest heating rate of 1.0 K/min and a holding time of 1.5 h. All the sintered samples have a similar microstructure, that is, lamellar α + β structure. The sample exhibits a strength of 739 MPa and an elongation of 6.1 % at the optimum sintering conditions (sintering at 1250 °C for 2 h). The samples prepared by MIM have excellent wear resistance. This process provided a straightforward and cost-effective means of producing complex-shaped titanium components from HDH Ti powder.

Characterization of the Manufacturing Process and Mechanical Properties of CoCrFeMnNi High-Entropy Alloys via Metal Injection Molding and Hot Isostatic Pressing

Characterization of the Manufacturing Process and Mechanical Properties of CoCrFeMnNi High-Entropy Alloys via Metal Injection Molding and Hot Isostatic Pressing

Using fused filament fabrication to improve the tribocorrosion behaviour of 17-4 PH SS in comparison to other metal forming techniques

Fused filament fabrication (FFF) is one of the additive manufacturing processes which has gained more interest because of its simplicity and low-cost. This technology is similar to the conventional metal injection moulding (MIM) process, consisting of the feedstock preparation of metal powder and polymer binders, followed by layer-by-layer 3D printing (FFF) or injection (MIM) to create green parts and, finally, debinding and sintering. Moreover, both technologies provide near-dense parts. This work presents an in-depth study of the processing method’s influence. The porosity, microstructure, hardness, corrosion, and tribocorrosion behaviour are compared for 17-4 PH SS samples processed from powder by additive manufacturing using FFF and MIM, as well as conventional powder metallurgy (PM) samples. MIM samples exhibited the highest macro and microhardness, while corrosion behaviour was similar for both MIM and FFF samples, but superior in comparison to conventional PM samples. However, the FFF-as fabricated samples displayed a significant improvement in tribocorrosion resistance that could be explained by the higher proportion of delta ferrite and retained austenite in their microstructure.

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.

Exploring the Potential of MIM-Manufactured Porous NiTi as a Vascular Drug Delivery Material.

Porous nickel-titanium (NiTi) manufactured using metal injection molding (MIM) has emerged as an innovative generation of drug-loaded stent materials. However, an increase in NiTi porosity may compromise its mechanical properties and cytocompatibility. This study aims to explore the potential of porous NiTi as a vascular drug delivery material and evaluate the impact of porosity on its drug loading and release, mechanical properties, and cytocompatibility. MIM, combined with the powder space-holder method, was used to fabricate porous NiTi alloys with three porosity levels. The mechanical properties of porous NiTi were assessed, as well as the surface cell growth capability. Furthermore, by loading rapamycin nanoparticles onto the surface and within the pores of porous NiTi, we evaluated the in vitro drug release behavior, inhibitory effect on cell proliferation, and inhibition of neointimal hyperplasia in vivo. The results demonstrated that an increase in porosity led to a decrease in the mechanical properties of porous NiTi, including hardness, tensile strength, and elastic modulus, and a decrease in the surface cell growth capability, affecting both cell proliferation and morphology. Concurrently, the loading capacity and release duration of rapamycin were extended with increasing porosity, resulting in enhanced inhibitory effects on cell proliferation in vitro and inhibition of neointimal hyperplasia in vivo. In conclusion, porous NiTi holds promise as a desirable vascular drug delivery material, but a balanced consideration of the influence of porosity on both mechanical properties and cytocompatibility is necessary to achieve an optimal balance among drug-loading and release performance, mechanical properties, and cytocompatibility.

Tailoring high-entropy alloys via commodity powders for metal injection moulding: A feasibility study

High entropy alloys (HEAs) represent a novel frontier in metallurgical advancements, offering exceptional mechanical properties owing to their unique multicomponent nature. This study explores a novel strategy utilising commodity powders - Ni625, Invar36, and CoCrF75 - to tailor HEAs via metal injection moulding (MIM). The objective is to achieve cost-effective manufacturing while maintaining desired properties. The research involves mixing these powders in a specific proportion, integrating them with a sustainable polyethylene glycol-cellulose acetate butyrate binder system, and characterising the resulting feedstocks for MIM processing. Subsequent debinding and sintering steps were executed to densify and form a single face-centered cubic (FCC) phase HEA, followed by comprehensive analyses to evaluate the suitability of the developed HEA compositions. In addition, all MIM stages were thoroughly characterised to control the porosity of the final parts and to ensure a single FCC solid solution with promising mechanical properties in the developed non-equiatomic CoCrFeNiMox-type HEAs.

The effect of printing parameters on the properties of 17-4 PH stainless steel fabricated by material extrusion additive manufacturing

The 17-4PH stainless steel filament was characterised and utilised to study the effect of printing parameters, i.e. printing temperature, layer thickness, infill pattern and extrusion multiplier on the physical properties. The as-printed and as-sintered internal structures were analysed. The results showed that the as-printed density increases with increasing printing temperature and extrusion multiplier and decreasing layer thickness. The use of the line infill pattern also provided slightly higher as-printed density than the concentric infill pattern due to the low fraction of void between deposited paths. After sintering, the trace of these voids can be observed together with smaller-size residual pores from the spaces between powders, which is the nature of the pressureless sintering process. The microstructure of the as-sintered specimens was similar to the typical microstructure of the 17-4PH alloy fabricated by metal injection moulding process, which contains delta ferrite, martensite and Si-rich phases. In additions, the internal void generated during debinding and sintering results in unexpectedly low tensile properties and results in the difference in tensile properties between the concentric and line infill patterns.

Modulated heating rate effect on optimizing sintered density and microstructure in CoCrFeMnNi high-entropy alloy fabricated through metal injection molding

The fabrication of high-entropy alloys (HEAs) using metal injection molding (MIM) represents a significant leap forward in the field of materials engineering, enabling the production of components with complex shapes while maintaining the unique mechanical properties of HEAs. This study investigates the effect of heating rate variations on the densification behavior in the equiatomic CoCrFeMnNi HEA, focused on microstructural analysis and densification behavior for each thermal schedule. By optimizing the sintering behavior with single and double-step heating rates, significant findings reveal that sintering under double-step heating rates leads to marked improvements in densification and microstructural uniformity. Microstructural analyses indicate that the modulated heating rates during sintering crucially affect the segregation of Cr and secondary phase formation. This research highlights the importance of sintering profiles in optimizing the microstructure and properties of HEAs processed through MIM, contributing valuable insights to a refined strategy for the improved microstructure and mechanical strength of HEAs in powder metallurgy.

Ultraviolet–Visible-Near InfraRed spectroscopy for assessing metal powder cross-contamination: A multivariate approach for a quantitative analysis

The last few years have seen an increasing use of spherical metals powders to produce bulk parts through metal forming technologies like Additive Manufacturing and Metal Injection Molding. This, coupled with the wide availability of metal powders, leads to a critical issue: contamination across different systems in different process steps. Consequently, it is necessary to find a new, fast, and reliable analysis sensible to tiny traces of contamination. This work evaluates the applicability of Ultraviolet–Visible-Near InfraRed (UV–Vis-NIR) spectroscopy, a technique providing information on powders’ reflectance, for studying contaminated powders. This work focuses on assessing 3 binary systems obtained from the cross-contamination of 3 components (A92618, C10200 and S31603) in a low contamination range (from 0.5 vol% to vol. 6%) and in a high contamination range (25 vol% and vol.50%). After the UV–Vis-NIR analysis, multivariate analysis has been used to obtain quantitative results. Results show that, as the contamination level increases in the binary system, the shape of spectra changes and becomes progressively more similar to the contaminant one. The chemometric analysis allows the detection of the contaminant type and its concentration percentage in the contaminated powder.

Research on and Application of Feature Recognition and Intelligent Retrieval Method for Multi-Component Alloy Powder Injection Molding Gear Based on Partition Templates

The forming process of multi-alloy gears by metal powder injection molding is tedious, and the current design process mainly depends on the experience of designers, which seriously affects the product development cycle and forming quality. In order to solve the problem of the gear feature expression being missing, which hinders the automatic retrieval of similar parts in the analogical design process, a feature recognition and intelligent retrieval method for a multi-alloy powder injection molding gear based on partition templates is proposed in this paper. The partition templates of the gear are defined, and gear digitization is completed by using the automatic recognition algorithm. Searching for similar gear parts in the knowledge base, designers can analogically design the forming process for new parts according to the mature process of the parts in the knowledge base. The automatic identification and intelligent retrieval system developed according to this method has been implemented in two MIM (metal injection molding) product manufacturing enterprises. Case studies and industrial applications have proved the effectiveness of the system, the efficiency of identification and retrieval has been improved by more than 97%, and the number of mold tests has been reduced by 60%.

Production of Permanent Magnets from Recycled NdFeB Powder with Powder Extrusion Moulding

In the last fifteen years, several groups have investigated metal injection moulding (MIM) of NdFeB powder to produce isotropic or anisotropic rare earth magnets of greater geometric complexity than that achieved by the conventional pressing and sintering approach. However, due to the powder’s high affinity for oxygen and carbon uptake, sufficient remanence and coercivity remains difficult. This article presents a novel approach to producing NdFeB magnets from recycled material using Powder Extrusion Moulding (PEM) in a continuous process. The process route uses powder obtained from recycling rare earth magnets through Hydrogen Processing of Magnetic Scrap (HPMS). This article presents the results of tailored powder processing, the production of mouldable feedstock based on a special binder system, and moulding with PEM to produce green and sintered parts. The magnetic properties and microstructures of debinded and sintered samples are presented and discussed, focusing on the influence of filling ratio and challenging processing conditions on interstitial content as well as density and magnetic properties.

Optimizing metal part distortion in the material extrusion-thermal debinding-sintering process: An experimental and numerical study

The thermal debinding-sintering process plays an essential role in the context of material extrusion-based additive manufacturing (AM) for producing parts using metal injection molding (MIM). During thermal debinding, metal parts often experience material distortion and porosity, which negatively impacts their mechanical properties. Slowing down the debinding speed is a common approach to mitigate material distortion and porosity. However, this leads to a significant increase in the debinding time. In this study, we carried out debinding-sintering experiments to optimize the distortion and porosity in metal parts. These metal parts were manufactured utilizing bronze/polylactide (PLA) blend filaments and placed in crucibles of different sizes (small, medium, and large), with different heating rates and holding times. The results revealed that the small crucible yielded higher porosity levels in the metal parts, which could be reduced from 23% to 12% by extending both the heating and holding times. In contrast, the medium crucible managed to reduce porosity to approximately 15% without requiring an extension of the processing time. The large crucible, on the other hand, couldn't achieve further porosity reduction due to challenges in reaching the desired temperature. To gain a deeper insight into temperature distribution during the debinding process, we performed numerical simulations using the computational fluid dynamics (CFD) technique and obtained temperature profiles within the kiln using the three crucibles. Ultimately, we carried out standard mechanical tests on the resulting metal parts and evaluated the thermal debinding procedure under various conditions. The approach we employed, combining experiments and numerical simulations, demonstrated significant promise for enhancing the quality of metal parts in the thermal debinding-sintering process.

Assessment of Residual Stress Behavior and Material Properties in Steels Produced via Oxynitrocarburized Metal Injection Molding

Assessment of Residual Stress Behavior and Material Properties in Steels Produced via Oxynitrocarburized Metal Injection Molding

Evaluation of the Corrosion Resistance of Watch Links from 316L and 904L Austenitic Stainless Steels Obtained by the Metal Injection Molding (MIM) Technique Intended to Be in Contact with Human Skin

Watchmaking manufacturers obtain their bracelet links from machining drawn metal profiles. But, today, there is another process that represents an alternative to manufacture them: metal injection molding using metal powders (MIM technology). This process is less expensive than the machining of drawn metal profiles. The aim of this study was to evaluate the corrosion behavior and the nickel cation release of two stainless steel alloys: 316L MIM and 904L MIM. The general corrosion behavior was evaluated by the rotating electrode technique; the galvanic corrosion measurements were conducted with a 316L AISI bulk coupling partner. The pitting corrosion behavior was evaluated in FeCl3 0.5 M media (according to ASTM G48-11). For comparison, a complementary study was conducted on 316L and 904L bulk alloys. The Ni cation release tests were conducted on 316L and 904L MIM and bulk samples according to EN 1811. Different electrochemical parameters were measured and calculated (open circuit potential, polarization resistance, corrosion current and Tafel slopes, coulometric analysis). Generally, if MIM steels are compared with conventional steels, their corrosion resistance behavior is inferior. In the couplings studied, the galvanic currents generated are very important. The shape of the curves also reveals the presence of localized corrosion phenomena. According to tests in ferric chloride, MIM steels were noted to have inferior behavior compared to conventional steels. MIM type 904L steels are comparable in behavior to conventional type 316L steels. The quantities of nickel released according to EN 1811 were very significant (2 mg cm−2 week−1 up to 24 mg cm−2 week−1) and did not meet the requirements of the European directive (0.5 µg cm−2 week−1). In conclusion, conventional steels studied under the same experimental conditions revealed a better behavior compared to MIM steels independently of the phenomenological parameters chosen.

Investigating evolution of microstructures and mechanical properties in metal injection molding Ti6Al4V with sintering processing by quasi in-situ strategy

Manipulation of the pore defects, adjustments of α/β phases fractions, optimization of the mechanical properties are helpful for sintered Ti6Al4V alloys fabricated Metal injection molding (MIM) powders. A pseudo quasi in-situ method with vacuum encapsulation and quenching has been proposed to control dynamical characteristics of pores, grain sizes and phase fractions of MIMed Ti6Al4V powders during sintering process. The dependency of pores annihilation and grains growth on sintering time and temperature has been established. Higher sintering temperature shortens the transition period of pore morphology from connected irregular to enclosed spherical characteristics. The annihilation of pores satisfies the exponential function as well as the power law with temperature and time, respectively. The activation energy has been calculated to be 252.2 kJ/mol comparable to self-diffusion activation energy of Ti according to Arrhenius fitting of the changes of grain size with sintering temperature. Additionally, the diffusional kinetic coefficient was 28.57 at 1200 °C, about five times larger than that at 1100 °C. The fraction of α/α′ phase decreases with increasing of sintering temperature and time. The existence of impurity elements (O, C) may result increasing the stability of α phases and morphology transforming of α phases from lamellar to equiaxed. Finally, sintered MIM-ed Ti6Al4V alloys with lowest porosity sintered at 1200 °C for 4 h have the tensile strength of 922 ± 5 MPa, the yield stress of 833 ± 4 MPa and the elongation of 12.8 ± 0.5%.