Metal Injection Molding Research Articles

Argon-atmospheric sintering process of stainless steel 17-4 precipitation hardening from metal injection molding product

Metal injection moulding (MIM) is a metalworking technology for producing a small and complex product as well as high efficiency. In this process, the sintering parameter is an important process that must be controlled especially the sintering atmosphere to optimise the product. In the previous study, the sintering process was conducted by using a vacuum atmosphere that resulted in the formation of porosity as a major problem. This study was aimed to understand the influence of argon atmosphere in the sintering process with different temperature in order to improve the relative density of 17-4 PH Stainless Steel. The 17-4 PH Stainless Steel feedstock injected to the mould using injection moulding machine. After injection, the solvent debinding process was carried out at 50 oC with hexane solution for 1.5 h. Thermal debinding was performed at 510 oC using a vacuum furnace with heating rate and holding time were 1 °C min−1 and 60 min, respectively. Afterwards, the resulting sample was heated at the various sintering temperature of 1320 °C, 1340 °C, 1360 °C, and 1380 °C with 5 °C min−1 heating rate and 90 min holding time in an argon atmosphere with flowing rate of 1 litre min−1. These study revealed an argon atmosphere sintering process influenced the content reduction of porosity due to increasing relative density. According to these results, the optimum sintering temperature by using an argon atmosphere was achieved at 1360 oC.

Experimental and numerical analysis of effects of supercritical carbon dioxide debinding on Inconel 718 MIM components

Polymer extraction is a key step of the metal injection moulding (MIM) process. An innovative method for extracting an organic binder involves the use of supercritical fluid instead of a regular solvent. The supercritical fluid selected was carbon dioxide due to its affinity toward polyethylene glycol. The supercritical carbon dioxide parameters were optimised in order to complete the extraction of this polymer from the Inconel 718 superalloy feedstock. The effects on the surface quality of the components and on the microstructure of the densified component were also investigated. A finite element model, which combines the fluid model and structural mechanics, enabled the estimation of the stress distribution during the supercritical debinding step. The study was completed by a parametric analysis of the pressure variation inside the equipment with respect to the processing parameters for the MIM components.

Fracture Toughness and Charpy Impact Test of MIM Steels and Correlation of Results by K<sub>IC</sub>- CVN Relationships

This paper presents results of fracture toughness and Charpy impact tests of 4 steels prepared by metal injection moulding (MIM) method: AISI 4140, 4605, 17-4 PH and SS 420W Grade. Charpy impact testing was performed on the series of machined specimens with sub-size cross-section to obtain values of CVN impact energy. Fracture toughness test method according to ASTM E1820 was performed on SENB specimens, fatigue pre-cracked, to obtain values of KIC. All tests were performed at the room temperature. After the material testing, next step was to evaluate the results and apply known correlation relationships between fracture toughness KIC and Charpy impact CVN energies. Many empirical relations exist and describe existence of such relationship. Procedure was used to correlate energies of sub-size Charpy specimens to full-size specimens. Several proposed correlation relationships from transition and upper shelf region of transition curve were used, where the best correlation was found to be Robert-Newtons with average deviation of 22% in comparison to tested values.

Microstructure and Mechanical Properties of Metal Injection Molding HK30 Stainless Steel Sintered in N2 and Ar Atmosphere

Microstructure and Mechanical Properties of Metal Injection Molding HK30 Stainless Steel Sintered in N2 and Ar Atmosphere

Extrusion of metal powder-polymer mixtures: Melt rheology and process stability

The mixture of metal powder and a viscous polymeric binder (often referred to as feedstock) is commonly used for Metal Injection Moulding (MIM) applications. Recently, the interest towards the extrudability of metal/binder feedstocks is increasing, especially because of the growth of additive manufacturing techniques based on the vertical extrusion and layered deposition of filaments. In this experimental work, a feedstock prepared as a mixture of stainless steel 316 L powder with water-soluble binder was tested. The rheological behaviour of different mixtures (with powder loading between 50 and 63% in volume) was assessed using a capillary rheometer. The theoretical window of optimal extrudability was determined, in terms of temperature, shear rate and powder loading. Then, a specially designed CNC controlled extrusion system was used for performing vertical extrusion tests. The analysis of extrusion pressure profiles and the dimensional variability of the filaments was used to correlate the theoretical extrudability predicted by the rheological model with the actual extrusion tests. All results indicate that the conditions which yield better stability of the extrusion process are those that allow higher viscosity of the mixtures.

Metal injection moulding (MIM) as an alternative fabrication process for the production of TWIP steel

ABSTRACTTwinning Induced Plasticity (TWIP) steels are high manganese austenitic steels that have caused growing interest over the last decade due to their unique combination of strength and elongation. Nevertheless, the problems presented during their current fabrication process (continuous casting) complicate their production and commercialisation. Powder metallurgy may be an attractive alternative route of solving these problems in certain components. In this work, Metal Injection Moulding (MIM) is explored as an alternative fabrication method for TWIP steels, having the additional benefit of reaching a near-theoretical densification. The feedstock of this study is composed of a metallic prealloyed Fe–Mn–C–Al–Si powder and a binder system based on wax-HDPE. The feedstock was optimised by examining different metallic loads. A suitable powder–binder ratio was determined based on mixing torque and melt flow index measurements. It was optimised a two-stage debinding process and a sintering process in an argon atmosphere to obtain the correct microstructure.

May 1994

Political big gun's METCUT attendance boosts industry's mood; UK robot milestone; metal injection moulding; rapid prototyping & mould tools; manual/CNC lathe development; UK motion control anniversary; political/industrial news, and more

Incorporation of HA into porous titanium to form Ti-HA biocomposite foams

Ti foams are advanced materials with great potential for biomedical applications as they can promote bone ingrowth, cell migration and attachment through providing interconnected porous channels that allow the penetration of the bone-forming cells and provide them with anchorage sites. However, Ti is a bio-inert material and thus only mechanical integration is achieved between the porous implant and the surrounding tissue, not the chemical integration which would be desirable. In this work particles of a biologically active material (Hydroxyapatite, HA) are blended with titanium powder, and used to produce Ti foams through the use of Metal Injection Moulding (MIM) in combination with a space holder. This produces titanium foams with incorporated HA, potentially inducing more favourable bone response to an implant from the surrounding tissue and improving the osseointegration of the Ti foams. To be able to do this, samples need to show sufficient mechanical and biocompatibility properties, and the foams produced were assessed for their mechanical behaviour and in vitro biological response. It was found that the incorporation of high levels of HA into the Ti foams induces brittleness in the structure and reduces the load bearing ability of the titanium foams as the chemical interaction between Ti and HA results in weak ceramic phases. However, adding small amounts of HA (about 2 vol%) was found to increase the yield strength of the Ti foams by 61% from 31.6 MPa to 50.9 MPa. Biological tests were also carried out in order to investigate the suitability of the foams for biomedical applications. It was found that Ti foams both with and without HA (at the 2 vol% addition level) support calcium and collagen production and have a good level of biocompatibility, with no significant difference observed between samples with and without the HA addition.

Tensile properties of sintered 17-4PH stainless steel fabricated by material extrusion additive manufacturing

Material extrusion additive manufacturing can be used for producing metal specimens when combined with debinding and sintering, similar to metal injection moulding. A highly-filled polymeric filament containing 55 vol% of 17-4PH stainless steel powder was prepared and used to print dog-bone specimens. Printed specimens were debound and sintered to obtain metallic specimens. The tensile properties were investigated. The average Young’s modulus was determined to be 196 GPa, the average maximum stress was 696 MPa and the strain at break 4%. Adequate cohesion between layers during material extrusion additive manufacturing is crucial for improving the mechanical properties of sintered specimens.

Sintered Strength of Ti-6Al-4V by Metal Injection Molding (MIM) using Palm Stearin Binder

Metal injection molding (MIM) is a metal working process used to compact Titanium, Ti-6Al-4V and the binder through injection moulding process. In this work, Titanium Ti-6Al-4V was mixed with palm stearin (PS) and polyethylene (PE) which act as a binder. Palm stearin (PS) is a potential binder system that can be used because it is inexpensive and highly available in Malaysia. Besides that, the application of MIM can reduce time and energy compared to the conventional process which high cost in production and difficulty of producing complex shape of materials. The green parts were then gone through of debinding process and sintering process. This project is to study the effect of the sintered Ti-Al-4V using palm stearin as a binder system. The properties of sintered specimen were investigated by physical properties such as its shrinkage and density. The average shrinkage of the sintered specimen was about 10.35% in length and 10.96% of width body of the specimen. Density of the sintered specimen was about 4.0343 g/cm3 and the tensile strength of the specimen was about 805.7 MPa.

The Technological Design of Geometrically Complex Ti-6Al-4V Parts by Metal Injection Molding

In this study, the metal injection molding (MIM) process is applied to produce Ti-6Al-4V parts using blended and prealloyed powders, respectively. The feedstocks are prepared from a polyformaldehyde-based binder system with a powder loading of 60 vol%, exhibiting a low viscosity. The decomposition behavior of the binders is investigated and the thermal debinding procedure is designed accordingly. The debound parts are subsequently sintered at 1200 and 1300 °C. The results show the mechanical properties of the sintered samples prepared from blended powder are comparable to those prepared from prealloyed powder, with yield strength of 810 MPa, ultimate tensile strength (UTS) of 927 MPa, and elongation of 4.6%. The density of the as-sintered samples can reach 4.26 g/cm3 while oxygen content is ~0.3%. Based on the results, watch cases with complex shapes are successfully produced from Ti-6Al-4V blended powder. The case gives a good example of applying metal injection molding to mass production of precise Ti-6Al-4V parts with complex shapes in a cost-effective way.

Microstructure and High Temperature Oxidation Properties of FE-CR-NI HK30 Alloy Manufactured by Metal Injection Molding

Microstructure and High Temperature Oxidation Properties of FE-CR-NI HK30 Alloy Manufactured by Metal Injection Molding

Development of Grain Growth Promotion Technique of Ni-based Superalloy IN713 Fabricated by Metal Injection Molding

Development of Grain Growth Promotion Technique of Ni-based Superalloy IN713 Fabricated by Metal Injection Molding

Processability of SS316L powder - binder mixtures for vertical extrusion and deposition on table tests

ABSTRACT Metal injection molding (MIM) feedstocks are mixtures made of a solid metal powder and a viscous polymeric binder. Vertical extrusion of MIM feedstock has seldom been investigated in the scientific literature, but it is the enabling technology for extrusion-based additive manufacturing processes (EAM). The EAM process adopts the movement of an extruder, relative to a build table, to deposit thin strands (roads) of the mixture and grow a 3D object, layer by layer. EAM may find applications for the consumer as well as industrial products. This paper addresses some of the challenges involved in achieving a consistent flow of molten feedstock mixture and discusses the consequences of the main process parameters on the extrusion-based manufacturing process. This work also relates the rheological behaviour of feedstock to the extrusion process, aiming at the dimensional stability of parts. An experimental study was performed on SS316L feedstock with a water-soluble binder system, by varying the percentage powder content of the mixtures, the extrusion temperature, the extrusion rate, the deposition table speed and the nozzle shape. The study evidences and explains why higher powder loading values and lower extrusion temperatures are the most useful conditions in order to obtain a stable flow with reduced swelling/shrinking phenomena.

Microstructural comparison and mechanical properties of stainless steel 316L fabricated by selective laser melting and metal injection moulding processes

Selective laser melting (SLM) process is one of an additive manufacturing technology that has the capabilities of fabricating complex geometries with an excellent accuracy and resolution. Compared to conventional powder metallurgy techniques metal injection moulding (MIM), SLM has several advantages such as low production cost for small batch fabrication, high degrees of geometrical freedom and customisation, and short cycle time. The present work analyses and compares the tensile properties and metallography differences of the stainless steel 316L compacts fabricated by two powder-based manufacturing processes; SLM and MIM, respectively. The SLM compact was built at 0-degree building orientation by SLM 125 HL machine with default optimum processing parameters for stainless steel 316L powder. On the other hand, MIM process produced similar dimension of tensile-shaped compacts differently that by sintered at three different sintering conditions in highly pure argon flow atmosphere. The tensile testing revealed that SLM tensile compact was higher in tensile strength (29% more) and elongation (62% more) at fracture as compared to MIM compact. From microstructure observation, the MIM compact showed the presence of significant amount of porosity which led to moderate mechanical properties compared to SLM compact performances.

Microstructural comparison and mechanical properties of stainless steel 316L fabricated by selective laser melting and metal injection moulding processes

Selective laser melting (SLM) process is one of an additive manufacturing technology that has the capabilities of fabricating complex geometries with an excellent accuracy and resolution. Compared to conventional powder metallurgy techniques metal injection moulding (MIM), SLM has several advantages such as low production cost for small batch fabrication, high degrees of geometrical freedom and customisation, and short cycle time. The present work analyses and compares the tensile properties and metallography differences of the stainless steel 316L compacts fabricated by two powder-based manufacturing processes; SLM and MIM, respectively. The SLM compact was built at 0-degree building orientation by SLM 125 HL machine with default optimum processing parameters for stainless steel 316L powder. On the other hand, MIM process produced similar dimension of tensile-shaped compacts differently that by sintered at three different sintering conditions in highly pure argon flow atmosphere. The tensile testing revealed that SLM tensile compact was higher in tensile strength (29% more) and elongation (62% more) at fracture as compared to MIM compact. From microstructure observation, the MIM compact showed the presence of significant amount of porosity which led to moderate mechanical properties compared to SLM compact performances.

Sintering temperature effects on the properties of stainless steel 316L compact fabricated by metal injection moulding

Stainless steel (SS) 316L powder was prepared with polyethylene glycol (PEG), polymethyl methacrylate (PMMA), and stearic acid (SA) with powder loading 61 vol.%. The sintering parameter in metal injection moulding (MIM) process was manipulated to study its effects on physical, mechanical, and corrosion properties of SS 316L compact. The compacts was fabricated by MIM, and then sintered at 1,100, 1,200, and 1,300°C for 3 h using argon. Then, the compact was tested for density, shrinkage, tensile strength, microstructure, and corrosion behaviours. The compacts sintered at 1,300°C demonstrated highest relative density (94%) and tensile strength (309 MPa), with small porosity was noticed from microstructure. The corrosion potential (Ecorr) and corrosion current (Icorr) values showed higher corrosion resistance which were −3.25E-01 V and 4.93E-0.7 A.cm−2, respectively. The SS 316L compacts with sintering temperature of 1,300°C for 3h produces excellent physical, mechanical and corrosion properties compared to other temperatures.

Determination of optimised solvent debinding parameters of injection moulded 316L stainless steel using Taguchi approach

Abstract Metal Injection Moulding (MIM) is widely utilized in various manufacturing industries due to its ability to produce near net shaped components in high volume without compromising surface finish and mechanical properties. Debinding is one of the most crucial phases in the MIM process, as it affects the final properties of the end product. The use of 316L SS is widespread especially in the medical industry, specifically for implants and metallic biomaterials due to its favourable combination of mechanical properties and biological consistency The present work deals with utilization of the Taguchi method to investigate the influence of solvent debinding parameters on the characteristics of injection moulded 316L stainless steel (316L SS) using thermoplastic rice starch binder as one of the binder components. In this study, the 316L SS powder along with a binder system consisting of Thermoplastic Rice Starch (TPRS), Polyethylene (PE), Palm Stearin (PS) and Stearic Acid (SA) were mixed for 1 hour at a speed of 50 rev/min and at a temperature of 150°C using a Z-blade mixer. The feedstock was then injection moulded using a vertical injection moulding machine with parameters of injection pressure, injection temperature and time and holding time of 7 bar, 160°C, 10 seconds and 25 seconds respectively. , this research was done utilizing the Taguchi approach to investigate the influence of solvent debinding parameters of injection molded 316L SS The effects of three solvent debinding parameters: solvent type, debinding time and debinding temperature were investigated to obtain the highest percentage of binder removal. The interactions of the parameters were laid out using the L 9 orthogonal array. It was found through ANOVA that solvent type had the most significant effects on solvent debinding, followed by debinding temperature and debinding time. The optimized solvent debinding parameters are solvent type of methanol, debinding temperature of 80°C and debinding time of 4 hours. The confirmation experiment however did not achieve the required range of expected result with a 3.80% error due to the unstable behaviour of the optimized solvent type, methanol.

Densification Behavior and Magnetic Properties of Fe-2%Ni Sintered Compact Fabricated by Metal Injection Molding

Densification Behavior and Magnetic Properties of Fe-2%Ni Sintered Compact Fabricated by Metal Injection Molding

Applying environmental-friendly binder system for net shaped forming of 316L stainless steel implants

Abstract Over the years, Metal Injection Moulding (MIM) has thrived into an advanced near net shape forming of metallic components having intricate shapes and excellent properties. In the recent research work, the feedstock was prepared at a powder loading of 63 vol% using 316L stainless steel powder with particle size of 14.2 µm and environmental friendly binder system comprising of thermoplastic rice starch, palm stearin, polyethylene and stearic acid. The feedstock which possessed a pseudoplastic behaviour was injection-moulded into a tensile test part at a pressure of 400 bars and temperature of 170 °C. Following the injection moulding stage, the green part was debound using water at a temperature of 50 °C for 4 h. The part was then sintered in vacuum atmosphere at a temperature of 1380 °C. Approximately, 7.8 g/cm3 theoretical density, hardness of 216.18 HV and tensile strength of 81.68 MPa were achieved. The findings suggested that the physical and mechanical properties of sintered 316L stainless steel are in satisfactory agreement with the international benchmark.