Metal Injection Molding Process Research Articles

The metal injection moulding process and its applications : A.Suzuki.(IHI Corp, Japan.) Kogyo Kanetsu, vol 32, no 6, 1995, 16–28. (In Japanese.)

Niobium aluminides for structural applications to operate beyond the operating temperatures of conventional nickel-base superalloys have been assessed over the past few years. The niobium aluminides have extremely high strength at elevated temperatures, above 1000°C. Brittleness at ambient temperatures is alleviated by incorporating a ductile phase, and poor oxidation resistance is being improved by macro- or micro-alloying.

先端粉体加工プロセス‐ＭＩＭ

Metal Injection Molding (MIM) process allows fully dense and net shaping of a variety of engineering materials. Therefore, MIM process is hoped to be an advanced powder processing technique to replace the conventional powder metallurgy (P/M) processes for exceeding the proven P/M capabilities.This presentation introduces a few examples of how and what products are made via MIM process today, and reviews the progress being made in the elimination of critical technological barriers to the widespread application of MIM as a manufacturing process. The application of MIM process to wide variety of ferrous materials are also introduced from our studies, and comments are focused on the microstructure control needed for the MIM fabrication of high performance ferrous material components.

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.

射出成形 射出成形Ｆｅ‐Ｎｉ合金の衝撃，疲労破壊特性

It is well known that many high performance sintered alloys have been produced by Metal Injection Molding (MIM) process so far. A Fe-Ni system is one of the objected alloys, and they are used for machine structural parts. Although assessment of the dynamic fracture properties such as fatigue strength is important to design a reliable sintered structual parts, there are few reports for the dynamic properties of MIM alloys even at the present time.In this study, the behaviore of dynamic properties (impact and fatigue strength) for Fe-Ni (Fe-2, 4 and 7mass%Ni) alloys produced by MIM process has been investigated. Approximately 96% of theoretical density was obtained in all Fe-Ni alloys. Impact strength of MIM alloys was superior to that of the conventional P/M alloys, because the pore structure of the former was fine and spheroidized as compared to that of the latter. Fatigue strength was increased with increasing Ni content because of the solution strengthening and grain refining effects. Endurance ratio of MIM alloys was similar to that of the wrought alloys.

粉末プロセスの制御と製品評価ＩＩ 金属粉末射出成形法によるＳＵＳ３ｌ６Ｌステンレス鋼の疲労破壊特性

Recently, it has been well-known that various materials produced by metal injection molding(MIM) process show the excellent mechanical properties which are normally evaluated by the static rupture test such as tensile test. However, the assesment of the dynamic rupture properties such as fatigue strength is more important for the practical machine parts.In this study, the behavior of fatigue properties for a stainless steel (SUS316L) produced by MIM process were investigated taking the process conditions and microstructures into account. The fatigue strength of hydrogen sintered steels were higher than that of the vacuum sintered steels. This seemed to be due to the difference of pore distribution in the surface and inside between the hydrogen and vacuum sintered steels. Both tensile and fatigue strength of hydrogen sintered steels which had still not the full density were equivalent to those of the wrought steels. This result indicates that the MIM process is applicable to high performance machine structural parts required high static and dynamic strength as well.

金属粉末射出成形プロセスによって作製した超硬合金（ＷＣ‐１６ｍａｓｓ％Ｃｏ）の諸特性

Metal injection molding (MIM) process has an advantage of fabricating three dimensional complex shaped components, which alleviates the need for secondary working operations. Therefore, MIM process is hoped to be a suitable production route for the hard materials such as cemented carbides. In this study, the effects of MIM processing variations on the mechanical properties and microstructures of WC-16, mass%., Co alloy were investigated. The results obtained were as follows:(1) It was very difficult to debind completely and control the carbon content by using N2 gas as the thermal debinding atmosphere after solvent debinding.(2) An adequate carbon level of the alloy was achieved by thermal debinding in H2 gas atmosphere, and the sintered alloys showed the finer microstructure and higher mechanical properties compared with those of coventional P/M alloys.

粉末プロセスの制御と製品評価ＩＩ ＭＩＭプロセスによる部品の多機能・複雑形状化のための接合

Metal injection molding(MIM) process is hoped to be an advanced powder processing technique for the attributes of the near net shape forming the high density, high performance, and complicated parts. However, there remains the issue that the shape and volume of MIM compacts are still limited because of the shape deformation during debinding and sintering.In this work, as one of new approaches to improve the above problems in MIM process, joining of MIM parts by using the exuded wax during solvent debinding has been attempted to produce the larger, more complicated andfunctional parts by combination of the different materials such as iron and stainless steel. On the solvent debinding, the deformation was prevented from covering the couple of compacts with Al2O3 powder. As the solvent debinding temperature increased, the binder removal and bonding property were increased. For the combination of the same materials(Fe/Fe, SUS304L/SUS304L, SUS410C/SUS410C) and different materials (SUS304L/SUS410C), the joining properties after sintering depended on the solvent debinding temperature, that is, high joined strength was obtained at high temperature.

射出成形 金属射出成形法によるチタンおよびチタン合金の製品化技術

The properties of typical pure Ti and Ti-6Al-4V alloys produced by Metal Injection Molding (MIM) process have been investigated in detail after optimization of the powder characteristic, debinding and sintering conditions for the process.(1) Sintered pure Ti using the blended in equal amount of hydrided-dehydrided and gas-atomized powders has better tensile strength (640MPa) and elongation (21%), which properties are similar to the JIS 3 grade of wrought pure Ti.(2) Sintered Ti-6Al-4V alloys produced by both mixed elemental and prealloyed powders have good tensile strength (970MPa) and elongation (12%), which are almost comparable to those of wrought Ti-6Al-4V alloys.(3) Polishability of sintered pure Ti is generally poor. However, the specific heat treatment leads to fairly improved polishability because of the grain refining which is also favorable for the mechanical properties.

射出成形 微細不均質組織を呈する射出成形４６００鋼（熱処理材）の機械的諸特性

In our previous studies on the 4600 steels produced by Metal Injection Molding (MIM) process using mixed elemental powder, the fine heterogeneous microstructure caused by the agglomeration of spiky Ni powders was reported to be significantly effective for the static and dynamic fracture properties. In this study, the effects of heat treatment condition and different type of Ni powder on the mechanical properties of injection molded 4600 steels using prealloyed and mixed elemental powders were investigated to secure the efficacy of the fine heterogeneous microstructure. The obtained results are as follows:1) The heat treated steels using the prealloyed powder showed the homogeneous tempered martensitic microstructure, while the steels using mixed elemental powder showed the fine heterogeneous microstructure consisted of tempered martensitic matrix and martensite or retained austenite phases, which were caused by the segregation of Ni powders.2) For the tempered steels at 473K, the fine heterogeneous microstructure contained Ni rich phases was effective for the tensile and fatigue strengths. On the other hand, there was not clearly seen the efficacy of the heterogeneous microstructure in the tempered steels at 823K because of the homogenization.3) The agglomeration of Ni powders with spherical shape investigated with the debound steels was fewer than that of Ni powders with spiky shape, which lead the decrease of Ni rich phases even in the heat treated steels, resulted in poor tensile strength.

射出成形 ＭＩＭプロセスによる軟質磁性材料（センダスト）の磁気特性

For miniaturization and complication of the shape of electronic devices in recent years, improvement of magnetic properties are also being required to the soft magnetic components. Fe-Si-Al alloy is well known to be a soft magnetic material suited for a magnetic head because of high permeability and magnetic flux density as well as high wear-resistance. However, this alloy is very brittle and difficultly workable. Therefore, metal injection molding (MIM) process is hoped to be a suitable production route for hard and brittle materials such as Fe-Si-Al alloy because of providing net shape components.In this study, the effect of MIM process conditions on the magnetic properties of Fe-Si-Al alloys has been investigated using a gas-atomized powder. Since this alloy melted at high temperature over 1523K, the optimum sintering temperature was found to be 1523K at which the obtained relative density was more than 98%. However, the magnetic properties of the compacts sintered in both hydrogen and vacuum atmospheres were relatively inferior to that of the wrought materials. This was seemed that the domain wall migration was prevented by the fine grain size and the retained oxides. By the continuous process including the debinding and sintering steps together, the compacts showed good magnetic properties because of the small amomts of oxides and coarse grain size.

Production methods for different injection moulding feedstocks: K.F. Hens, D. Kupp (Pennsylvania State University, USA)

The chapter deals with processing metal injection molding (MIM) parts after they have been molded. Primary debinding depends on the feedstock type being used. The reason for primary debinding and the process for major feedstock types are discussed. The equipment and process for the commercially used feedstocks are described. Secondary debinding and sintering have been combined into one step from the old three-step process used in the original MIM process. Thermal debinding of the secondary binder is described and the consequences of incomplete debinding discussed. Sintering, mass transport during sintering and the practical aspects of sintering are explained. Guidelines are provided for obtaining optimum properties by MIM for most MIM materials including the effect of different atmospheres. Settering of parts with both flat surfaces and complex shapes and setter materials are described. Both continuous and batch equipment may be used.

高強度ＭＩＭ焼結合金鋼の疲労破壊試験

It is well-known that the high performance sintered alloys were obtained by a Metal Injection Molding (MIM) process. Although assessment of the dynamic properties such as fatigue strength is important to design a reliable structural sintered steels, especially for the high strength steels, there are very few reports about the dynamic properties of MIM steels at the present time. In this study, the behavior of fatigue properties for high strength 4600 steels (Fe-1.8%Ni-0.5%Mo-0.2%Mn) produced by the MIM process using mixed elemental powders were investigated taking the microstructure into account.Sintered and heat treated steels showed the fine heterogeneous microstructures with the segregation of Niadded as one of the alloying elements. The fatigue strength of heat treated MIM 4600 steels were higher than that of the conventional P/M steels because of the near full-densification and the spheroidization of pores. Additionally, the regions of a high nickel concentration, which were hard martensite or retained austenite and were uniformly distributed within the tempered martensitic matrix, were also effective against the crack propagation. This result indicated that it is possible to attain high performance structural steels combined with high static and dynamic strength by MIM techniques.

自動車焼結部品の最近の進歩 ＭＩＭプロセスによる高性能鉄系摺動材料の開発

Metal injection molding (MIM) is a suitable processing route for the mass production of complex-shaped and high performance components. Therefore, MIM process is hoped to be quite useful for improvement of the quality and productivity in the automotive sintered parts.This study has been performed to develop the high performance ferrous sliding abrasive wear-resistant materials through MIM process. A prealloyed powder (SCM440) was used as the matrix and also 3mass%TiN powder was added to improve the wear-resistance. Those compacts were densified to about 95% of relative by sintering, and the final carbon content was almost exactly controlled to be 0.4mass% by adjusting the debinding and sintering atmospheres and conditions. Sintered compacts showed the dual homogeneous microstructures consisted of ferrite and fine pearlite, and the pores and TiN powder particles were distributed uniformly, regardless of the injecting direction. Thus, the wear characteristics were not influenced by the injecting direction. Injection molded SCM440 steel showed the same wear-resistance as the wrought SCM440 steel. However, addition of 3mass%TiN powder caused a remarkable improvement of wear-resistance, which indicate that MIM process has enormous potential to produce high performance ferrous composites for the automotive parts.

ＭＩＭプロセスによる軟質磁性材料の磁気特性に及ぽすプロセス条件の影響

For miniaturization and complication of the shape of electronic devices in recent years, both high magnetic and mechanical properties are also being required to the soft magnetic components. A metal injection molding(MIM) process has the attributes of forming the high density, complex shaped and high performance components, which seems to be a suitables process for fabricating the higher performance soft magnetic components.In this paper, the effect of MIM process conditions on the magnetic and mechanical properties of soft magnetic materials such as Fe-Ni and Fe-Si alloys were investigated. Although the final density was obtained approximately 96% of theoretical in both steels, the magnetic properties were similar or inferior to that of the pure iron. Especially, the coercive force was increased with an addition of alloying elements, because the orientation of domain walls were prevented from the grain refining and the residual oxides. Generally, taking account of the improvement in the mechanical properties which are superior to that of the conventional P/M materials, it will be able to apply a MIM process to the soft magnetic components.

Establishment of Metal Injection Molding (MIM) Process and Its Application.

This study with metal injection molding considers the combined influences of powder characteristics and subsequent debinding and sintering conditions on the control of carbon content and microstructure for many types of high performance ferrous materials. Carbon retention and sintered structure vary significantly with the powder characteristics. Although carbon retention is sensitive to the debinding and sintering atmosphere and conditions, the carbon content can be successfully controlled by adjusting the weight loss after debinding. Mechanical properties are also investigated and compared with that of conventional P/M and wrought materials, and some factors affecting the properties are discussed taking the structure into account. Finally, high performance properties depend on two types of microstructure, one is the fine homogeneous structure in the case of high alloy steels and the other is the fine heterogeneous structure in the case of low alloy steels.

Influence of Binder Content and Particle Size on Green Strength of WPP Parts

AbstractWet powder pouring (WPP) was developed as an alternative near net shape process to metal injection moulding (MIM). The amount of binder, which is necessary to obtain a sufficient green strength, is relatively low (2–5 vol.-%) compared to the amount used in the MIM process (about 30 vol.-%). This is advantageous with respect to short debinding times and low residual carbon and oxygen contaminations. A further reduction of the binder content or the application of the WPP process to new materials would be promoted by an understanding of the dependence of green strength on particle characteristics and binder content. In the present investigation the green strengths of stainless steel WPP parts were determined for different particle size distributions and different binder contents (2–8 vol.-%). The green strength was in the range 3 to 7 MN m−2 and the fracture mode was always brittle. A simple fracture mechanical model was developed, which was able to explain the observed relations between binder conte...

特集 粉末の成形・加工 金属粉末射出成形プロセスによるマルエージング鋼の創製

The unique combinations of high toughness and high strength available with the maraging steels have made them desirable for structural applications. However, it was very difficult to produce the high performance maraging steels by conventional powder metallurgy (P/M) processes because of hard material. Metal Injection Molding (MIM) process alleviates the need for secondary working operations because of providing the net shape components, which is a suitable production route for hard materials. In this paper, the characteristics of debinding, sintering and aging behavior were studied for injection molded maraging steel compacts, and also the mechanical properties were investigated by tensile and impact test. The results are summarized as follows:1) By using the continuous process which went on through thermal debinding and sintering at 1623K for 3.6ks in hydrogen atmosphere, the compacts were considerably densified to a relative density of 96%.2) Aging hardness at 758K for 10.8ks reached to HRC46.5 which was as hard as the densified steels by HIP, and this aging condition was lower temperature and shorter time as compared to the condition of conventional P/M process.3) Optimum aged MIM maraging steel showed the same strength of 1640MPa as the wrought steels, but the ductility and toughness were considerably poor.

粉末プロセスの制御と製品評価 焼結合金鋼における均質および不均質組織と機械的性質との関係

High performance sintered 4600 steels were obtained by Metal Injection Molding (MIM) process in our previous study. This seemed to be due to the fine heterogeneous structure which were consisted of bainite, martensite and retained austenite by the segregation of Ni added as alloying element. This study has been performed to clarify the relationship between the mechanical properties and the homogeneous and heterogeneous structures of 4600 steels using conventional powder metallurgy (P/M) process.For the wide sintered density range, the final carbon content was properly controlled by adjusting the additional carbon content and the sintering atmosphere in both prealloyed and elemental mixed powder compacts. Sintered microstructures of the prealloyed powder compacts showed the dual homogeneous structures consisted of ferrite and bainite. On the other hand, the heterogeneous structure including martensite appeared in the elemental mixed powder compacts. In the high density range over 7.3Mg/m3 at which the pores were closed, the strength of the latter was higher than that of the former. However, the strength of the P/M steels were smaller than that of the MIM steels because of the coarse heterogenous structure.

粉末プロセスの制御と製品評価 金属粉末射出成形プロセスによる１７‐４ＰＨステンレス鋼の諸特性

Metal injection molding (MIM) process is hoped to be an advanced powder processing technique for the attributes of forming the high density, complex shaped and high performance components. This process also alleviates the need for secondary working operations because of the net shape forming, which is a suitable production route for the hard materials.In this study, the effects of MIM processing variations on the mechanical properties and microstructures of precipitation-hardenable 17-4 PH stainless steels were investigated. Carbon content, density, structure, and properties of the MIM steels were very dependent on the debinding, sintering, and heat treatment conditions. Especially, the amount of retained austenite in the structure increased with an increase of the residual carbon content, resulting in poor mechanical properties. Accordingly, the carbon control was a very important operation for this steel, which was successfully performed by adjusting the weight loss of debound compacts. Finally, high performance properties comparable to those of wrought steels were obtained by optimizing the heat treatments.

Monitoring of metal powder-binder mixing process by eddy-current sensor

Metal Injection Molding (MIM) is a technology by which metal products of high density and complex shape can be mass-produced in a cost-effective manner. The raw input to the MIM process is a compound consisting of metal powder and thermoplastic binder. The distribution of metal powder throughout the compound must be uniform if high-quality products are to be obtained.This paper describes a new method for monitoring the metal powder distribution using an eddy-current sensor. Experimental sensor readings were gathered using two different compounds, each with a different binding agent. Analysis of the data showed clearly that the sensor output was proportional not to the powder to binder ratio at the sensor location, as originally expected, but rather to the metal powder contents per unit volume. This phenomenon may have arisen from the fact that the density of the compound varies with the powder to binder ratio. A series of sensor readings taken at regular time intervals was used to monitor the overall distribution of metal powder within the compound.The merit of this technique is its reliance on a simple and inexpensive sensor probe. The drawback is that the sensor measurements are affected by the mixer's metal rotor and by temperature drift. The effects of temperature drift can be compensated by monitoring the temperature of the compound. The interference of the metal rotor was an obstacle to in-process monitoring in the present research. In the future, in-process measurements may be achieved by changing the shape of the mixing container from a “bowl” to a circular channel, in which the sensor will be able to measure the compound at a safe distance from the rotor.