Metal Injection Moulding Technique Research Articles

Opportunity and Challenges of Iron Powders for Metal Injection Molding

Design flexibility, mass customization, waste reduction and the ability to manufacture near-net complex-shape structures, as well as rapid prototyping, are the main advantages of Metal Injection Molding (MIM). A brief review of the MIM technique, materials and their development to trending applications using iron powders was delineated. The ground-breaking applications of MIM in automotive, medical, and magnetic materials were discussed. The current-status of iron powder product development prepared for MIM was reviewed. In addition, this paper discussed the main processing challenges considering the MIM technology for producing high-end applications. Overall, this paper gives a summary of MIM, including a study on its benefits and opportunities and as a roadmap for future research and development in iron and steel powder manufacturing technique.

Metal Injection Moulding of Titanium Medical Components

The metal injection moulding technique is already established for serial production of complex parts, mostly from various stainless steels. However, for other materials, especially for titanium parts there is still the need for superior purity and enhanced surface quality. Facing the challenge of obtaining suitable medical titanium MIM parts, advances have been made at Fraunhofer IFAM over the last few years.One strategy to overcome the high risk of carbon up-take was to adjust the sintering program. Very low Argon flow rates, 50 mbar pressure and two hours dwell time at 1350°C were found to be optimal parameters. A cleaning cycle prior to the actual sintering at 1450°C under hydrogen was also found to enhance the results.Another strategy involved the choice of binder components. Stearic acid, which is often used to improve wettability of binder to powder particle, and high polymer content affect the oxygen content of the titanium parts. Low amounts of both are beneficial for high purity parts.Other investigations were performed concerning the surface quality. It was found that the surface roughness of the mould has an effect on the surface roughness of the sintered parts. Although sintered titanium surfaces as such exhibit quite rough surfaces of about 2-3 µm (Ra value) the influence of the surface finish of the mould was detectable. Using very fine powders of only 15 µm mean particle size and a polished mould a very low surface roughness of less than 1.2 µm on the sintered part was obtainable.

Metal Injection Molding (MIM) of Magnesium and Its Alloys

Current research has highlighted that magnesium and its alloys as biodegradable material are highly suitable for biomedical applications. The new material fully degrades into nontoxic elements and offers material properties matching those of human bone tissue. As biomedical implants are rather small and complex in shape, the metal injection molding (MIM) technique seems to be well suited for the near net shape mass production of such parts. Furthermore, MIM of Mg-alloys is of high interest in further technical fields. This study focusses on the performance of MIM-processing of magnesium alloy powders. It includes Mg-specific development of powder blending, feedstock preparation, injection molding, solvent and thermal debinding and final sintering. Even though Mg is a highly oxygen-affine material forming a stable oxide layer on each particle surface, the material can be sintered to nearly dense parts, providing mechanical properties matching those of as cast material. An ultimate tensile strength of 142 MPa, yield strength of 67 MPa, elastic modulus of 40 GPa and 8% elongation at fracture could be achieved using novel organic polymer binders for the feedstock preparation. Thus, first implant demonstrator parts could be successfully produced by the MIM technique.

Analysis of the Rheological Behavior of Copper Metal Injection Molding (MIM) Feedstock

Metal Injection Molding (MIM) technique allows for the production of highly porous metallic foams with porosity levels up to 90%. It makes use of the pressure built up by the decomposition of a foaming agent which is incorporated in a foamable precursor copper material obtained by powder compaction. Rheological is one of the key factors to ensure the successful of MIM technique and to predict failure, whether due to the binder component and compositions, powder loading or unsuitable process parameters. The balanced ratio feedstock contains of 63 vol.% of copper powder, different percentage of potassium carbonate; Batch 1 (0.4 vol.%), Batch 2 (0.5 vol.%) and Batch 3 (0.6 vol.%), and the remaining volume percentage of binder system has been mixed to form copper feedstock. The rheological behaviors were investigated using a capillary rheometer (CFT-500D, Shimadzu) at various temperature and loads. From the experiments, it was concluded that the MIM feedstock exhibit a shear thinning or pseudo-plastic behavior based on the trend of graph which is suitable for MIM process. This result is within the ideal range of viscosity theoretical for MIM feedstock which is in the range of between 10Pa.s to 1000Pa.s at all temperature tested. The viscosity of a pseudo-plastic substance decreases as the shear rate increases (shear thinning). This could be due to particle orientation and ordering with flow as well as breakage of particle agglomerates released together with the binder.

Development of Porous Ti-6Al-4V Mix with Palm Stearin Binder by Metal Injection Molding Technique

Good potential of biocompatibility and excellent mechanical properties, porous Ti-6Al-4V has become a great interest for biomedical applications. In this study, porous Ti-6Al-4V was fabricated by Metal Injection Molding (MIM) using Palm Stearin (PS) and Polyethylene (PE) binder together with sodium chloride (NaCl) as a space holder. Rheological characterization was performed to evaluate the flowability of the feedstocks for injection molding and the feedstocks exhibited a pseudoplastic behavior which is suitable for injection. The as-sintered parts were fabricated as the mixing, injection molding, debinding and sintering were conducted successfully. The mechanical properties of the as-sintered parts were investigated via tensile test and the results obtained were closed with the established range. Shrinkage, density and X-Ray Diffractometry (XRD) of the as-sintered parts were compared with the theoretical values which were found closed to the acceptable ranges. The microstructure of the surface and cross-section were observed under Scanning Electron Micrograph (SEM) and optical microscope to analyze the specimens before and after sintering. Generally, palm stearin binder system added with space holder to fabricate porous Ti-6Al-4V by MIM is feasible and has shown a good potential for biomedical applications.

Magnesium powder injection moulding for biomedical application

Currently, commercial biodegradable implants are mainly made from degradable polymers, such as polyglycolic acid or polylactide acid (PLA). These polymer implants, produced by injection moulding technique, suffer from long degradation times between 18 and 36 months, poor mechanical properties and acidic degradation behaviour. On the other hand, magnesium alloys are drawing increasing interest as biodegradable medical implant material for orthopaedic applications in bone tissue; thus, a replacement of polymers by Mg would be attractive. The production of biomedical and biodegradable Mg alloy parts and implants by powder metallurgy and metal injection moulding (MIM) respectively offers the opportunity for economic manufacturing of parts with mechanical properties matching those of cortical bone tissue, as well as the provision of porous surface structures beneficial for cell ingrowth and vascularisation. Furthermore, the technique guarantees a homogenous microstructure being crucial for a predictable degradation process. This study shows how magnesium powder can be processed successfully by MIM. Recent magnesium alloy implant prototypes and tensile test specimen, produced by MIM technique, provide strength and stiffness twice as high compared to modern polymer based implants. Ultimate tensile strength (UTS) of 131 MPa, yield strength of 64 MPa, residual porosity of 2–6% and elastic modulus of 46 GPa, measured by dynamic method, were achieved under application of special sintering technique and sintering atmosphere control. The paper is focussing on sintering methods and porosity control and measurement.

Production of medical devices prototype through metal injection moulding technique

Metal injection moulding (MIM) is an advanced near net shape forming process for high quality of complex shapes combined with high properties of materials. For economic reasons, it is necessary to have demand for a large quantity of parts. This paper presents the attempt to fabricate medical devices, particularly fracture fixation plates, for orthopaedic applications for commercial purposes by MIM process. The stainless steel powder with median particle size of 15 m m and a binder consisting of polyethylene, paraffin wax and stearic acid were mixed at 160°C using a sigma blade mixer for 1 h to prepare the feedstock of fracture fixation plates. The fracture fixation plates component was injection moulded using 80 ton MIM machine with the nozzle temperature of 200°C. Before sintering, the specimens were debound using a combination of solvent extraction and thermal pyrolysis method. The specimens were then sintered under vacuum atmosphere. The properties of the fracture fixation plates such as physical appearance and densities were presented and discussed. The results show that the mechanical properties of the plates made by MIM comply with the MPIF standard 35.

High cycle fatigue behaviour of Ti–6Al–4V fabricated by metal injection moulding technology

Titanium alloys exhibit an excellent combination of properties, including high specific strength and excellent bio-compatibility. Recently, parts made from titanium alloys such as Ti–6Al–4V have been manufactured by metal injection moulding (MIM) and exhibited excellent tensile properties (UTS > 800 MPa and ɛ > 15%). However to date, few information concerning the fatigue properties of such material has been presented in the literature. Thus, in the present study, the influence on the high cycle four-point bending fatigue behaviour of Ti–6Al–4V alloy processed by standard and MIM techniques was examined. The first results indicated that the fatigue strength of components fabricated by MIM technique is significant lower than parts made by standard process. This behaviour is discussed in terms of mechanical properties, microstructure, composition, surface quality and crack initiation mechanisms.

Metal injection moulding of aluminium alloy 6061 with tin

A metal injection moulding technique for the production of aluminium alloy components is described. A part is formed by injection moulding a mixture of alloy 6061 and 2 wt-%Sn with a resin consisting of stearic acid, palm oil wax and high density polyethylene. The resin is removed by a combination of solvent and thermal processing. The parts are then sintered in a nitrogen atmosphere to a density of 97%. Sacrificial magnesium blocks which act as an oxygen and moisture getter are placed in the vicinity of the parts during sintering. This ensures surface integrity. Aluminium nitride forms throughout the part, which provides structural rigidity and dimensional stability and limits grain growth. After artificial aging, the tensile strength is 300 MPa. The technique allows the production of small complicated shapes and provides an additional means to manufacture aluminium components for a wide variety of applications.

金属粉末射出成形法によるチタン基アパタイト分散系歯科インプラントの作製とその特性評価

金属粉末射出成形法によるチタン基アパタイト分散系歯科インプラントの作製とその特性評価

粉末射出成形（ＰＩＭ） ＭＩＭプロセスにおけるＦｅ‐５０ｍａｓｓ％Ｎｉの磁気特性改善

Metal injection molding(MIM)process is hoped to be one of processing for required to more complicated parts of magnetic components.In this study, the effect of different types of powders(prealloyed and mixed elemental powders)on the magnetic properties of permalloy(Fe-50mass%Ni)through the MIM technique was investigated. Approximately 94% of theoretical density was obtained by using the prealloyed powder, and the retained carbon and oxygen contents were controlled to be low. On the other hand, 96% of theoretical density was obtained by using the mixed elemental powder, but the magnetic properties were inferior to that of prealloyed powder's because of high retaind oxygen content. By using the carbonyl Fe powder with high carbon, the retained oxygen and carbon content could be controlled to be low, resulting in the improved magnetic properties.

Investigation of core loss in PM micro-motor made using MIM technology

Research has been conducted into the effects of particle size on the core losses of soft magnetic materials. Various types of micro PM BLDC motors, produced with solid hog-out alloy steel, laminated alloy steel and Metal Injection Molding (MIM) alloy steel powders have been studied. The results show that the core loss of micro PM BLDC motors made by the MIM technique is in the acceptable level when compared with the laminated core motor.

Nickel-Free High Nitrogen Austenitic Stainless Steels Produced by Metal Injection Moulding

Nickel can cause allergic reactions to human beings. In the last several years the need of nickel free stainless steels for applications at and in the human body has become more and more urgent. Such Ni-free steels have recently been developed at ETH Zurich. They are characterized by a full replacement of nickel by nitrogen. The production of Ni-free HNS through ingot metallurgy requires special high pressure facilities, while no special equipment is necessary when powder metallurgy routes are applied. The paper describes the P/M-processing of the new biocompatible Ni-free stainless steel Catamold®P.A.N.A.C.E.A. by using the metal injection moulding technique (MIM). With this process the desired nitrogen content can be added easily during consolidation. It is shown that with well balanced processing parameters (chemical composition, sintering atmosphere and temperature) a fully austenitic structure with low porosity can be achieved. The MIM components are nonmagnetic and exhibit a high corrosion resistance as well as excellent mechanical properties.

粉末プロセスの制御と製品評価ＩＩ ＭＩＭプロセスによる４６００鋼の疲労特性に及ぼす均質および不均質組織の影響

The homogeneous microstructure has been utilized preferably for the P/M materials such as machine structural parts required high strength. For the low alloy steels such as AIS14600 produced by Metal Injection Molding (MIM) process, however, the static fracture strength such as tensile strength of mixed elemental powder compacts which showed the fine heterogeneous microstructure was superior to that of homogeneous prealloyed powder compacts in our previous studies. Therefore, the effect of microstructure on the dynamic fracture strength such as fatigue strength of injection molded 4600 steels by MIM process using prealloyed and mixed elemental powders were investigated in this study.The heat treated compacts using prealloyed powder showed the fine homogeneous tempered martensitic microstructure. On the other hand, the mixed elemental powder compacts heat treated showed the fine heterogeneous microstructure, which consisted of tempered martensitic matrix and retained martensite or austenite phases caused by the segregation of Ni added alloying element. The fatigue strength of the latter were about 100MPa higher than that of the former. Thus the fine heterogeneous microstructure seemed to contribute to improve not only the static but also the dynamic fracture strength. This result indicated that the MIM technique is more effective route for manufacturing high performance low alloy steel compacts using mixed elemental powder.