Metal Injection Molding Research Articles

Enhanced Mechanical Performance of a Biodegradable Fe–Mn Alloy Manufactured by Metal Injection Molding and Minor Carbon Addition

At present, FeMn-based degradable alloys prepared by direct sintering generally face the problems of Mn volatilization, difficult densification, and poor mechanical properties. In this work, a Fe-35Mn-0.5C alloy with low Mn volatility, high density, and favorable mechanical properties is fabricated by the metal injection molding (MIM) process. The effects of sintering pressure and minor carbon addition on microstructure and mechanical properties were studied. The corresponding mechanical deformation mechanism was discussed. The results show that a significant reduction in the proportion of Mn volatilization to less than 0.5% and higher relative density of 97 ± 0.30% are achieved in the MIM-treated Fe-35Mn-0.5C alloy by pressurized sintering at 5 atm and 0.5 wt.% carbon addition. The optimized tensile properties are attained, with an ultimate tensile strength of 772 MPa, yield strength of 290 MPa, and elongation of 35% at room temperature, which meets the mechanical needs of metallic materials for biologically implantable medical devices.

Influence of defects on damage tolerance of Metal-Injection-Molded β titanium alloys under static and dynamic loading

ABSTRACT The β titanium alloys are key materials in lightweight and biomedical applications, due to the combination of excellent biocompatibility and mechanical properties. However, the Binder-based Powder Technologies such as Metal-Injection-Molding (MIM), Binder-Jetting and Fused-Filament-Fabrication, normally introduce three major processing-related defects in the as-sintered Ti-parts: (i) residual porosity, (ii) high impurity level and (iii) coarse-grained structure. The previous studies revealed that these processing defects invariably tend to be even more severe in β titanium alloys than in α/β Ti-6Al-4V alloy, all fabricated by powder metallurgical route. In this work, these processing defects and their likely origins in MIM β titanium alloys are analysed. Furthermore, the influence of these defects on damage tolerance and fracture mechanisms of MIM β titanium alloys under either static or dynamic loading is investigated. Based on the studies, strategic technical improvements in the processing to improve the reliability of MIM β titanium alloys products are proposed.

An Overview of Highly Porous Titanium Processed via Metal Injection Molding in Combination with the Space Holder Method

In the past two decades, titanium foams have attracted greater interest from the biomedical industry due to their excellent chemical and mechanical biocompatibility when used as biomimetic implants. The porous structure plays an important role in bone adhesion to an implant, allowing its growth into the component. Moreover, the voids reduce the elastic modulus, promoting greater compatibility with the bone, avoiding the stress shielding effect. In this regard, metal injection molding is an attractive process for titanium foams manufacturing due to the high microstructural control and the possibility of producing, on a large scale, parts with complex near-net-shaped structures. In this review, recent discoveries and advantages regarding the processing of titanium powders and alloys via metal injection molding combined with the space holder method are presented. This approach can be used to obtain foams with high biocompatibility with the human body at a microstructural, chemical, and mechanical level.

Low cost 3D printing of metals using filled polymer pellets

Nowadays, additive manufacturing of metallic materials is most often carried out using expensive and complex tools that leave the user with limited control and no possibility of modification. In order to make the printing of metal parts more accessible to small structures but also better suited for academic research, the use of a mixture of thermoplastic polymer and metal powder is a good solution as many granular feedstocks already exist for Metal Injection Molding applications. To perform the shaping process, the Fused Granular Fabrication 3D printing technology is set up by diverting the use of a feedstock in the form of pellets that are directly inserted into the print head. This solution, which is less costly, is implemented here by modifying a mid-range printer, the Tool Changer from E3D, and by making the hardware and software adaptations to mount a compact granulates extruder on it, which is also available on the market. The polymer portion present in the green part can then be removed in order to perform the heat treatments that will densify the powder by sintering and give a fully metallic dense object.

A Review of Metal Injection Moulding on WC-Co Cemented Carbide Comprised of Grain Growth Inhibitors (GGI)

This paper aims to provide a summary of metal injection moulding technologies utilising cemented WC-Co carbides comprised of grain growth inhibitors (GGI). The advanced manufacturing of metal injection moulding (MIM) has the ability to produce cement nanostructured carbides. In addition, the nature of the feedstock plays a crucial role when manufacturing a defect-free component at each point of the MIM phase, thus the interactions between the metal powder and the binder combining, moulding, and debinding are important to be recognised. The primary objective of this analysis is to investigate the characterization of feedstock to form a homogenous mixture. There are five criteria to classify features of the feedstock which include powder characteristics, binder composition, powder content ratio, mixing cycle, and approaches to palletization. Not only that, the feedstock must meet specific criteria; higher powder loading with excellent flowability by the rheological approaches. The second goal of the research is to re-evaluate feedstock’s flow properties in relation to rheological activity in terms of index flow behaviour (n), activation energy (E), and mouldability (α). MIM practitioners have continued to underestimate erratic product quality, including inadequate regulation, distortion, and internal and external defects. These defects can arise in the early processing phases, but often occur only after sintering or debinding. The approaches are also challenging to provide. This chapter includes a description of MIM defects. Explanations are listed and recommendations are provided for these defects.

A new model for predicting the flow properties of Ti-6Al-4V-MIM feedstocks

Titanium and its alloys have high specific strength and high resistance to corrosion but are expensive to manufacture. Manufacturing cost can be reduced by using metal injection moulding (MIM) to produce near-net shaped intricate parts. Feedstock rheology affects feedstock homogeneity, injection moulding and quality of the MIM parts. Methods to quickly obtain these rheological parameters will help optimise processing conditions and hence decrease manufacturing cost. Feedstocks were produced from hydride-dehydride titanium alloy powder and binder containing polyethylene glycol, polyvinyl butyral and stearic acid using a four-stage mixing process. Feedstock rheology and morphology were investigated using a capillary rheometer and a scanning electron microscope. A new model, which incorporates a newly defined parameter, feedstock flow index (p), was developed for predicting the rheological properties of titanium-based feedstocks using shear stress and melt flow rate. The MRF value, obtained from these low-cost rheological tests predicted HDH Ti-6Al-4V-MIM feedstock flow properties well.

A Review on Material Extrusion Additive Manufacturing of Metal and How It Compares with Metal Injection Moulding

Material extrusion additive manufacturing of metal (metal MEX), which is one of the 3D printing processes, has gained more interests because of its simplicity and economics. Metal MEX process is similar to the conventional metal injection moulding (MIM) process, consisting of feedstock preparation of metal powder and polymer binders, layer-by-layer 3D printing (metal MEX) or injection (MIM) to create green parts, debinding to remove the binders and sintering to create the consolidated metallic parts. Due to the recent rapid development of metal MEX, it is important to review current research work on this topic to further understand the critical process parameters and the related physical and mechanical properties of metal MEX parts relevant to further studies and real applications. In this review, the available literature is systematically summarised and concluded in terms of feedstock, printing, debinding and sintering. The processing-related physical and mechanical properties, i.e., solid loading vs. dimensional shrinkage maps, sintering temperature vs. relative sintered density maps, stress vs. elongation maps for the three main alloys (316L stainless steel, 17-4PH stainless steel and Ti-6Al-4V), are also discussed and compared with well-established MIM properties and MIM international standards to assess the current stage of metal MEX development.

In Situ X-ray Synchrotron Radiation Analysis, Tensile- and Biodegradation Testing of Redox-Alloyed and Sintered MgCa-Alloy Parts Produced by Metal Injection Moulding

Binary MgCa alloys are one of the promising and well investigated biodegradable metals and therefore a good standard for the study of novel processing routes. In this investigation, novel powder metallurgical (PM) blending and sintering methods were applied for the generation of biodegradable MgCa test specimens, using metal injection moulding (MIM). In addition to the classical PM-blending route using Ca-containing master-alloys, Ca-containing ceramics and hydrides, as there are CaO and CaH2, were used separately and in a stoichiometric mixture. In situ X-ray synchrotron radiation experiments were performed for a deeper understanding of alloy forming mechanisms during sintering. Mechanical and degradation performance was investigated by tensile testing and the monitoring of biodegradation under physiological conditions. Besides its sound strength of up to 144 MPa and degradation rate of 0.25 mm/a, the new redox alloying technique avoids the usage of any greenhouse active SF6 gas (global warming potential 22,800) during alloying, keeping the earth’s atmosphere safer. Therefore, it can be concluded that Ca-containing ceramics and hybrids are attractive alternatives to obtain, comparable to Mg-based materials, thus enabling safer processing.

Solid Lubrication on Hard Metal Specimens with Micropits Under Normal and Elevated Temperatures

Solid lubrication in tribological applications was studied on hard metal specimens with micropits fabricated using metal injection molding (MIM). This study investigated synergy effects of paraffin wax mixed with 5 wt% MoS2 on the lubricating potential both under normal and elevated temperatures. Pin-on-plate sliding tests were performed on a CSM tribometer in which WC–Co pins oscillated against microstructured and flat reference WC–Co specimens under 10 N applied normal load. Surface morphology characterization of test specimens was carried out before and after tribological tests using scanning electron microscopy. Solid paraffin wax displayed enhanced lubrication compared to solid paraffin wax mixed with 5 wt% MoS2 on micropit specimens under normal temperature. On the contrary, under heating conditions, solid paraffin mixed with 5 wt% MoS2 significantly reduced the dynamic coefficient of friction (COF) values for both flat and micropit specimens. The results showed that the micropits in textured specimens can be used as a reservoir for the lubricant that can significantly reduce friction compared to flat reference specimens.Graphical

Metal fused filament fabrication of the nickel-base superalloy IN 718

This study demonstrates metal fused filament fabrication (MF3) as an alternative additive and highly flexible manufacturing method for free-form fabrication of high-performance alloys. This novel processing, which is similar to Metal injection molding (MIM), enables a significant reduction in manufacturing costs for complex geometries, since expensive machining can be avoided. Utilizing existing equipment and reducing material expense, MF3 can pave the way for new and low-cost applications of IN 718, which were previously limited by high manufacturing costs. Iterative process optimization is used to find the most suitable MF3 process parameters. High relative density above 97% after pressureless sintering can be achieved if temperature profiles and atmospheres are well adjusted for thermal debinding and sintering. In this study, the influence of processing parameters on the resulting microstructure of MF3 IN 718 is investigated. Samples sintered in vacuum show coarse-grained microstructure with an area fraction of 0.36% NbC at grain boundaries. Morphology and composition of formed precipitates are analyzed using transmission electron microscopy and atom probe tomography. The γ/γ″/γ′ phases’ characteristics for IN 718 were identified. Conventional heat treatment is applied for further tailoring of mechanical properties like hardness, toughness and creep behavior. Fabricated samples achieve mechanical properties similar to MIM IN 718 presented in literature.Graphical abstract

Biocompatibility of vascular stents manufactured using metal injection molding in animal experiments

This study aimed to evaluate the feasibility and safety of a novel stent manufactured by metal injection molding (MIM) in clinical practice through animal experiments. Vessel stents were prepared using powder injection molding technology to considerably improve material utilization. The influence of MIM carbon impurity variation on the mechanical properties and corrosion resistance of 316L stainless steel was studied. In vitro cytotoxicity and animal transplantation tests were also carried out to evaluate the safety of MIM stents. The results showed that the performance of 316L stainless steel was very sensitive to the carbon content. Carbon fluctuations should be precisely controlled during MIM. All MIM stents were successfully implanted into the aortas of the dogs, and the MIM 316L stents had no significant cytotoxicity. The novel intravascular stent manufactured using MIM can maintain a stable form and structure with fast endothelialization of the luminal surface of the stent and ensure long-term patency in an animal model. The novel intravascular stent manufactured using MIM demonstrates favorable structural, physical, and chemical stability, as well as biocompatibility, offering promising application in clinical practice.

Comparison of Mechanical and Corrosion Properties for 17-4 PH Stainless Steel Fabricated by Metal Injection Moulding Using Varied Powder Sizes

17-4 PH stainless steel is commonly used in sev eral engineering applications because of the combined good mechanical properties and high corrosion resistance. Metal injection moulding (MIM) was used to fabricate 17-4 PH stainless steel specimen with three mean powder sizes (D50), which are 2.82, 4.04 and 12.65 μm. The rheology of three feedstocks were investigated using melt flow index (MFI) and viscosity analysis. Feedstocks were injected at 170 °C. Injected tensile specimens were sintered at 1325 °C for 2 h in argon atmosphere. Surface roughness (Ra) measurement, relative density measurement, tensile test and hardness test (HRC) were carried out. Corrosion properties were determined by cyclic polarisation tests. The results indicated that the relative density of sintered samples is higher than 98% (7.68-7.74 g/cm3). α-Fe (bcc-martensite), δ-Ferrite (delta ferrite) and also SiO2 were observed in all sintered samples, which were detected by scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS). As the mean powder size of injected specimens increases, the elongation and hardness increase, whereas the ultimate tensile strength (UTS) and surface roughness decrease. Moreover, the specimens using the smallest powder (2.82 μm) have shown better corrosion resistance than the specimens using the larger powders as the higher potentials in term of E-pit (the potential of pitting) and E-rep (the potential of repassivation) and the lower potential in term of E-cor (the potential of corrosion).

Eff ect of Injection Moulding Sequences on Mechanical Properties of Two-material Metal Injection Moulding

Two-Material Metal Injection Moulding (2M-MIM) process was developed for a component that requires different properties of materials. The materials used in this study were SCM 415, Fe-2Ni and 316L stainless steel (316L SS). The tensile test specimens were injected into 2M-MIM of SCM 415-Fe-2Ni and SCM 415-316L SS. In addition, each alloy was fabricated by MIM as reference samples. The 2M-MIM processes were injected with two different injection moulding sequences, which are “sequential injection” and “simultaneous injection”. The injection process of “sequential injection” specimens is to fi ll a half of the mould with the fi rst alloy and then inject the second half of the mould with the second alloy. The “simultaneous injection” specimens utilised the co-nozzle and co-injected both alloys simultaneously from each end of tensile specimen. The weld line positions of both injection moulding sequences were controlled in the middle at the gauge length. After injection, all specimens were sintered at 1325°C for 2 hrs. The shrinkage of each single-material specimen is 12.20 ± 0.64%, 14.90 ± 1.95% and 13.84 ± 0.24% for SCM 415, Fe-2Ni and 316L SS respectively. The ultimate tensile strength of SCM 415, Fe-2Ni and 316L SS are 549.62 ± 7.87 MPa, 474.08 ± 8.1 MPa and 351.44 ± 0.42 MPa respectively and the elongation is 9.68 ± 0.71%, 23.05 ± 2.64% and 51.33 ± 3.76% respectively. For 2M-MIM, the mechanical properties of the “sequential injection” specimens are more superior than the “simultaneous injection” specimens. This is due to the difference of weld line interface of 2M-MIM. The interface of sample was investigated by SEM and OM. Cracks were observed at the weld line of SCM – Fe-2Ni using “simultaneous injection” and the sharp crack was observed near the edge of specimen all specimens. The ultimate tensile strength of SCM 415-Fe-2Ni specimens and SCM 415-316L SS specimens are 374.42 ± 13.80 MPa and 403.35 ± 31 MPa respectively for “sequential injection” and 223.87 ± 31.98 MPa and 193.75 ± 15.41 MPa respectively for “simultaneous injection”. EDS results across the weld line of SCM 415-Fe-2Ni “sequential injection” specimen show that nickel diffused from Fe-2Ni to SCM 415 while chromium diffused from SCM 415 to Fe-2Ni.

Influence of design and material characteristics on 3D printed flow-cells for heat transfer-based analytical devices

Redesigning 3D-printed flow cells is reported used for heat transfer based detection of biomolecules from a flow-through system to an addition-type measurement cell. The aim of this study is to assess the performance of this new measurement design and critically analyse the influence of material properties and 3D printing approach on thermal analysis. Particular attention is paid to reduce the time to stabilisation, the sample volume in order to make the technique suitable for clinical applications, and improving the sensitivity of the platform by decreasing the noise and interference of air bubbles. The three different approaches that were studied included a filament polylactic acid cell using only fused filament fabrication (FFF), a resin cell printed using stereolitography (SLA), and finally a design made of copper, which was manufactured by combining metal injection moulding (MIM) with fused filament fabrication (FFF). Computational fluid dynamic (CFD) modelling was undertaken using ANSYS Fluent V18.1 to provide insight into the flow of heat within the measurement cell, facilitating optimisation of the system and theoretical response speed.It was shown that the measurement cells using SLA had the lowest noise (~ 0.6%) and shortest measurement time (15 min), whereas measurement cells produced using other approaches had lower specificity or suffered from voiding issues. Finally, we assessed the potential of these new designs for detection of biomolecules and amoxicillin, a commonly used beta lactam antibiotic, to demonstrate the proof of concept. It can be concluded that the resin addition-type measurement cells produced with SLA are an interesting affordable alternative, which were able to detect amoxicillin with high sensitivity and have great promise for clinical applications due to the disposable nature of the measurement cells in addition to small sample volumes.Graphical abstract

Cost and environmental impact assessment of stainless steel microscale chemical reactor components using conventional and additive manufacturing processes

Modular chemical process intensification improves chemical processes by reducing capital investment, operating costs, and inefficiencies of chemical production. Process intensification is achieved using microscale operations and devices with high surface-to-volume ratios. Microscale chemical device components can be produced using additive manufacturing and conventional powder metallurgy processes. The technical and environmental advantages and disadvantages of these processes have been investigated individually. However, their relative sustainability performance requires further research. The objective of this research is to characterize the economic and environmental performance of metal additive manufacturing and powder metallurgy processes for producing a 316 l stainless steel microscale chemical reactor used in dimethyl ether production. Laser powder bed fusion (LPBF) and binder jet (BJ) additive technology, and metal injection molding (MIM) were studied for producing two reactor plates for a range of market sizes. To quantify cost and environmental impacts, manufacturing process design and life cycle assessment (LCA) methods were applied, respectively. Cost analysis showed MIM has significantly lower unit costs than BJ (by 11–30 %) and LPBF (by 62–82 %) for the range of production volumes studied. However, at low production volumes, LCA results indicated MIM has greater environmental impacts than BJ and LPBF, due to consumables. As production volume increases, environmental impacts per part reduce significantly (up to 85 %) for MIM due to amortization of impacts across more products. Raw materials and utilities have little sensitivity to production volume and are the main environmental impact drivers for BJ and LPBF. Process step yield directly impacts tool count, resulting in the highest sensitivity to unit cost for the three processes. This work reports on model development and a single use case, motivating future investigation to understand process suitability for a range of part sizes and geometries, as well as alternative production routes.

Determining the heat treatment behaviour of metal injection moulded and wrought alloy 718 using differential scanning calorimetry

The heat treatment behaviour of metal injection moulded (MIM) and wrought alloy 718 was investigated using DSC, microscopy and hardness measurements. Reheating solutionized samples in the DSC resulted in a distinct exothermic peak around 725 °C, which was attributed to γ" precipitation. This was followed by a broad endothermic region (~750-900 °C), which was attributed to the dissolution of γ' and γ" precipitates. No DSC peak was observed corresponding to γ' precipitation upon reheat. The endothermic dissolution region (750–900 °C) ended with an abrupt exothermic shoulder around 900 °C, which was attributed to the solvus of the γ'/γ" precipitates and an acceleration of δ phase precipitation. Ageing the samples at progressively higher temperatures and for longer times resulted in a decrease in the 725 °C exothermic γ" precipitation peak and a deepening of the 750–900 °C endothermic dissolution region. Also, samples with higher Al content exhibited a deeper dissolution trough and a small bump in the exothermic shoulder at the end of this trough (~880 °C), which were attributed to the higher levels of γ' observed in the FESEM for these samples. A shallow endothermic trough peaking between 1000 and 1045 °C was observed in samples treated below the δ phase solvus and was attributed to dissolution of the δ phase. Hardness measurements showed an increase in hardness with the amount of γ' and γ" precipitated as expected. Differences in heat treatment behaviour appeared to be driven largely by differences in chemical composition rather than by processing route (wrought vs. MIM). However, the MIM material had smaller, more evenly distributed carbides and additional oxides not present in the wrought material which acted to restrict grain growth in samples solutionized up to 1232 °C.

Effect of sintering temperature on microstructure and properties of MIM420 stainless steel

ABSTRACT This paper investigates the effect of different sintering temperatures on the microstructure and mechanical properties of 420 stainless steel prepared by metal injection molding (MIM). The results show that in the temperature range of 1300 to 1360, the internal structure of MIM420 stainless steel is mainly lath martensite and the fracture mode is quasi cleavage fracture. With the increase of sintering temperature, the relative density, strength and hardness of MIM420 stainless steel increase, and the carbon and oxygen content decreases, but the strength decreases when the sintering temperature exceeds 1340. When the sintering temperature reaches 1360, the sample will be slightly over sintered, so the appropriate sintering temperature is 1340. At 1340, the relative density, hardness, bending strength and ultimate tensile strength of the sample are 98.2 ± 0.4%, 54 ± 1HRC, 1229 ± 28 MPa and 1111 ± 26 MPa respectively.

Mechanical properties, in vitro and in vivo biocompatibility analysis of pure iron porous implant produced by metal injection molding: A new eco-friendly feedstock from natural rubber (Hevea brasiliensis)

Metal injection molding (MIM) has become an important manufacturing technology for biodegradable medical devices. As a biodegradable metal, pure iron is a promising biomaterial due to its mechanical properties and biocompatibility. In light of this, we performed the first study that manufactured and evaluated the in vitro and in vivo biocompatibility of samples of iron porous implants produced by MIM with a new eco-friendly feedstock from natural rubber (Hevea brasiliensis), a promisor binder that provides elastic property in the green parts. The iron samples were submitted to tests to determine density, microhardness, hardness, yield strength, and stretching. The biocompatibility of the samples was studied in vitro with adipose-derived mesenchymal stromal cells (ADSCs) and erythrocytes, and in vivo on a preclinical model with Wistar rats, testing the iron samples after subcutaneous implant. Results showed that the manufactured samples have adequate physical, and mechanical characteristics to biomedical devices and they are cytocompatible with ADSCs, hemocompatible and biocompatible with Wistars rats. Therefore, pure iron produced by MIM can be considered a promising material for biomedical applications.

Boiling Enhanced Lidded Server Packages for Two-Phase Immersion Cooling Using Three-Dimensional Metal Printing and Metal Injection Molding Technologies

Abstract In order to meet the increasing performance demand of high-performance computing and edge computing, thermal design power (TDP) of central processing unit (CPU) and graphics processing unit (GPU) needs to increase. This creates thermal challenge to corresponding electronic packages with respect to heat dissipation. In order to address this challenge, two-phase immersion cooling is gaining attention as its primary mode of heat of removal is via liquid-to-vapor phase change, which can occur at relatively low and constant temperatures. In this paper, an integrated heat spreader (IHS) with boiling enhancement features is proposed. Three-dimensional metal printing and metal injection molding (MIM) are the two approaches used to manufacture the new IHS. The resultant IHS with boiling enhancement features is used to build thermal test vehicles (TTV) by following the standard electronic package assembly process. Experimental results demonstrate that boiling enhanced TVs improved two-phase immersion cooling capability by over 50% as compared to baseline TTV without boiling enhanced features.

Additive manufacturing of 17–4 PH steel using metal injection molding feedstock: Analysis of 3D extrusion printing, debinding and sintering

The amalgamation of 3D extrusion printing (3DEP) and sintering results in a low-cost process compared to other laser-based additive manufacturing techniques. This work used metal injection molding (MIM) raw material of 17–4 PH steel for additive manufacturing. The 3D printing, debinding, and sintering steps were thoroughly evaluated to achieve the highest sintered density. First, the 3DEP of the MIM feedstock was carried out using a screw-based extrusion system at optimum parameters to acquire the high green density and fine surface roughness. The solvent debinding step was carried out on 3D printed samples to remove water-soluble polymer by immersion method. Thermogravimetric analysis was performed to evaluate the decomposition temperature of the backbone material. Further, thermal debinding and sintering steps were conducted in a single step. The thermal debinding temperature was 500 ℃ , and the sintering temperatures were chosen as 1100, 1200, 1300 and 1360 ℃ . The highest density of ~95.6% was attained at a high sintering temperature. The micro-tomography evaluation was carried out on the 3D printed green and high-density sintered samples to evaluate the internal porosity. The mechanical properties and the microstructure were also evaluated for sintered samples. The work opens a way to fabricate metal complex-shaped parts at low cost using market available MIM feedstock.