Metal Injection Molding Feedstock Research Articles

Effect of Processing Parameters on the Properties of Metal Injection Moulded Titanium Dental Implants

Metal injection moulding (MIM) is a well-established, cost-effective method of fabricating small-to-moderate size near net-shape metal components. MIM is increasingly being employed as a process for fabricating orthopaedic and dental products with complicated shapes. In this study, commercially pure titanium (CP-Ti) powder has been used to fabricate dental implants via MIM. The CP-Ti powder was mixed with binders containing Polyethylene glycol (PEG), High Density Polyethylene (HDPE) and stearic acid (SA) to form the MIM feedstock. Commercially available feedstock was also used to fabricate MIM implants. The MIM compacts were then subjected to debinding and sintering, and then the mechanical and chemical properties of the compacts were investigated for their suitability for dental implantology. The effect of the MIM processing variables on the surface roughness of CP-Ti was also investigated and studies for biocompatibility were carried out using in-vitro cell culture. The results showed that the mechanical and chemical properties of the sintered components were within ASTM Grade MIM 2 and Grade MIM 3 (ASTM F2989 − 13) specifications for titanium. The results also showed that the implants produced by MIM appeared to meet basic biocompatibility requirements. It was concluded that dental implant prototypes may be fabricated successfully using MIM and this approach offers greater opportunities for future manufacturing.

Morphology and Mechanical Properties of MIM Feedstock Using TPNR Backbone Binder

This study has examined the effects of using TPNR backbone polymer on the morphology and mechanical properties of the metal injection moulding feedstock 316L stainless steel with paraffin wax (PW) and palm stearin (PS) respectively as the main binder and stearic acid as a lubricant during mixing and injection moulding process. Tensile behaviour indicates that the green sample of feedstock PW/TPNR/SA system gives higher value compared to PS/TPNR/SA system. Morphology studies showed that green samples of PS/TPNR/SA exhibited brittleness fracture compared to PW/TPNR/SA system.

Suitability of PEG/PMMA-based metal injection moulding feedstock: an experimental study

Due to environment-friendly nature, water-soluble binder systems have received much attention in recent years. Polyethylene glycol (PEG) and polymethyl methacrylate (PMMA) binder system is one such example and has been widely reported in the literature. In this paper, a comprehensive investigation of PEG/PMMA binder system has been carried out. Feedstocks were made using stainless steel 17-4PH powder, and subsequently, conventional and micrometal injection moulding (μMIM) processes were carried out. Differential scanning calorimetry (DSC) and fracture surface analysis of moulded samples were performed for complete evaluation. It was found that despite great potential, there are certain drawbacks associated with this binder system. The main problem is the formation of shrinkage voids during solidification. It is proposed that this binder system is more suitable for μMIM process that has an inherently higher cooling rate.

Rheological Properties of Copper-Graphite MIM Feedstocks Prepared with Waste PET Binder

In this study, waste polyethylene terephthalate (PET) polymer binder systems were used to prepare copper-graphite metal injection molding (MIM) feedstock. A mixer and screw extrusion were used to achieve optimized feedstock, and the rheological properties of the resulting fluids were evaluated using a capillary rheometry to simulate the injection molding process. The solid loadings in the copper-graphite mixes were investigated in the ranges of 51-53% using PET binder system. The effects of shear rate (γ), solid volume fraction (φ) and temperature (T) on the rheological behavior of the copper/graphite MIM feedstocks are discussed.High viscosity trend was notably recorded as shear rate increased relatively. The results indicated that this feedstock system shows dilatant characteristic and lots of further work shall be conducted in attempt to establish this as an ideal binder system.

Rheological Investigation of MIM Feedstocks for Reducing Frictional Effects during Injection Moulding

An experimental investigation of the rheological properties for abrasive Metal Injection Moulding feedstocks is presented for different materials with dissimilar particle sizes and shapes. Tribological issues are inevitable since feedstock has up to 93 wt. % powder loading in the feedstock. In this study, each of the relatively soft carbonyl iron powder and the hard, abrasive Iron oxide powder are mixed with binder system, consisting of HDPE (High-density polyethylene), Paraffin Wax and S.A. (Stearic Acid) at different magnitudes of volumetric powder loading. The rheological properties such as flow rate (cm3/s), shear rate (s-1) and viscosity (Pa.s) are investigated for varying conditions of temperature and pressure. The properties of the feedstocks made from the two materials showed significant variation in flow behaviour (due to difference in inter-particle frictional behaviour) with changing process parameters as well as material parameters. Furthermore, to study flow behaviour of feedstocks apparent viscosity is plotted against temperature and shear rate in order to establish the sensitivity of temperature and pressure. Flow behaviour index was determined by analysing variation of viscosity with shear rate of feedstock. As expected, results show that the feedstock having iron oxide powder with hard irregular shaped particles exhibits a higher viscosity if compared to the spherical particles in the Carbonyl iron powder feedstock. It was observed that the feedstock containing iron oxide powder (75 wt. % powder loading) gives higher shear rate but the feedstock dissociates faster with increasing temperature, whereas carbonyl iron powder feedstocks (90 wt. % powder loading) were found to be more stable (dissociate less) at higher temperatures and flowed at a smaller shear rate. Additions of graphite powder to the hard and abrasive iron oxide powder (to facilitate reduction of the iron oxide during sintering) would also be expected to improve the flow behaviour of the iron oxide feedstock on account of the superior lubricating properties of the graphite powder.

The Effect of Shear Rate and Temperature on Rheology Properties of Magnesium Metal Injection Molding Feedstock

Metal injection molding (MIM) becomes a well-established and promising technology for small and mass production. Feedstock characterization is one of the most important roles in ensuring the properties of the MIM products. Rheology study is compulsory in characterize the feedstock for matches the range of viscosities encountered in practice. The shear rates for molding normally exceed the range obtainable with the rheometer. In this study, the rheological properties and behaviors of magnesium metal injection molding feedstock was investigated. The paraffin wax (PW), high-density polyethylene (HDPE), and stearic acid (SA) were used as the binder for magnesium MIM feedstock. A Brabender Plastogram EC PLUS was used to prepare the magnesium MIM feedstock, and the rheological properties of the resulting feedstock were evaluated by the capillary rheometry. The effect of the relation of shear rate and temperature on viscosity for magnesium MIM feedstock has been investigated. The rheological results exhibited the pseudoplatic behavior. The flow behavior index (n) obtained was less than 1. The viscosity (η) of the magnesium MIM feedstock decreased with increasing shear rate (γ). The magnesium MIM feedstock viscosity also decreased with increasing temperature and found to be suitable for injection molding.

Fabrication and Microstructural Analysis of CNTs Reinforced Copper Matrix Nanocomposites via MIM Technique

Carbon nanotubes (CNTs) reinforced copper (Cu) matrix nanocomposites prepared via advanced fabrication method is presented. Functionalization and ultrasonication processes have been applied to enhance the dispersion of purified CNTs and creates sidewalls groups that have the potential to bond CNTs to the metal matrix. The main part of this approach was metal injection molding (MIM) technique, which is a combination of powder metallurgy and plastic injection molding technique. Preparation of MIM feedstock required a melting and mixing process of binder system (polymers) with the solid loading, which has been carried out using a twin screw rotor machine. This machine provides a viscous media of the molten binder with high shear forces that allow the additives (carbon nanotubes/copper powder) to be mixed properly and exfoliate the CNTs clusters with uniformdispersion inside the Cu matrix. Subsequently, to prove our expected results, observation tests of TEM, SEM, FESEM and CNTS were employed and discussed literally.

An Influence of a Binder System to the Rheological Behavior of the SS316L Metal Injection Molding (MIM) Feedstock

The influence of a binder system to the rheological behavior of a Metal Injection Molding (MIM) feedstock is presented in the paper. The binder systems used are: a) PEG & PMMA b) Palm stearin & LLDPE and, c) Tapioca starch & LLDPE. The viscosity and shear rate of the feedstocks were measured at various range of temperature and shear rate across the L/D = 10 capillary rheometer. The flow behavior index, n and activation energy, E of each feedstock were measured to show its significance as MIM feedstock. Generally, the result indicates all feedstock exhibits a shear thinning behavior and the binders are suitable as MIM binder. Additionally, the present paper has discovered that the binder system does not have much influence to the activation energy. In order to show the relevance of the rheological behavior to the actual injection molding performance, green parts has been injection molded and the result shows an agreement with the rheological behavior result.

Characterisation of Titanium Alloy Feedstock for Metal Injection Moulding Using Palm Stearin Binder System

Metal injection moulding (MIM) is a cost-effective technique for producing small, complex, precision parts in high volume. Each step in MIM process plays a vital role in order to achieve high quality final product. To have a good understanding of the MIM process and successful in manufacturing, characterisation of the material feedstock is essential. This paper presents the characterization of MIM feedstock consisting titanium alloy (Ti-6Al-4V) powder mix with binder 60 wt% of palm stearin and 40 wt% polyethylene. The characterisation of Ti-6Al-4V alloy powder, binders and feedstock includes scanning electron micrograph (SEM), thermo gravimetric analysis (TGA), differential scanning calorimeter (DCS) and rheological test were established. Rheological results exhibited pseudoplastic or shear thinning flow behaviour, where its viscosity decreased with increasing shear rate. The feedstock viscosity also decreased with increasing temperature and was found to be suitable for moulding.

The Characterization and Flow Behavior of 316L Stainless Steel Feedstock for Micro Metal Injection Molding (μMIM)

The rheological behaviors of the Micro Metal Injection Molding feedstock are important for the stability of the feedstock during micro injection molding process and quality of the final micro-components. Homogeneous feedstocks are preferable for MIM process to ensure the dimensional consistency of molded components and prevent the defects of powder-binder separation or particle segregation. In this work, feedstocks with various formulations of 316L stainless steel and binder system were prepared by using Brabender Plastograph EC Plus mixer. The binder system comprises of palm stearin, polyethelene (PE) and stearic acid. In order to obtain the viscosity, activation energy, flow behavior and mold ability index, the rheological characterization of the feedstocks were investigated in numerous conditions by using Shimadzu 500-D capillary rheometer The study showed that all of the 316L stainless steel feedstocks are homogenous with pseudo-plastic behaviors.

Rheological Investigation of ZK60 Magnesium Alloy Feedstock for Metal Injection Moulding Using Palm Stearin Based Binder System

This paper investigates the characteristic important to metal injection moulding (MIM) process via rheological behavior of MIM feedstock. A gas atomized spherical ZK60 magnesium (Mg) alloy powder and the binder of 60wt.% palm stearin (PS) + 40wt.% low density polyethylene (LDPE) were used in this investigation. Prior to mixing process, critical powder volume percentage (CPVP) was determined and subsequently four different feedstocks with powder loading of 62, 64, 66 and 68vol.% were prepared. The properties of the feedstocks were then analyzed rheologically. Here, the flow behavior index n, the flow activation energy E and the mold ability index αSTV of the Mg alloy MIM feedstocks were determined. Results show that feedstock with 64% powder loading has the best rheological properties and therefore it is considered to be the best for the injection moulding process.

Rheological Investigation of Water Atomized Metal Injection Molding (MIM) Feedstock for Processibility Prediction

This paper presents the rheological properties of SS316L water atomized MIM feedstock. Coarse and fine SS316L water atomized powder is mixed with a composite binder consisting of PMMA and PEG to form a homogenous paste, termed as feedstock. The feedstock is loaded with SS316L water atomized powder ranging 62 v/o, 62.5 v/o, 63 v/o, 63.5 v/o and 64 v/o. However, due to the morphology of the water atomized powder which is not spherical compared to the gas atomized ones, fine powder feedstock is unable to produce any significant rheological result due to the powder loading being more than 63.5 v/o. Results show that the fine powder feedstock demonstrates a higher viscosity if compared to the coarse powder feedstock. It can be established that binder separations are likely to occur in the coarse powder feedstock, especially, at high temperatures. The investigation concludes that the fine powder feedstock has its best rheological properties at 62 v/o while the coarse powder feedstock lies between 63 v/o and 63.5 v/o.

Study on Stability of a Novel Binder System Based on Palm Stearin in Metal Injection Moulding Application

Metal Injection Molding (MIM) is a wellestablished technology for manufacturing a variety of complex and small precision parts. In this paper, fundamental rheological characteristics of MIM feedstock using palm stearin are theoretically analyzed and presented. The feedstock consisted of gas atomized 316L stainless steel powder at three different particle size distributions and the binder system of palm stearin (PS) and polyethylene (PE). The powder loading used was 60vol % for all samples (monosize 16 µm, monosize 45 µm, and bimodal 16 µm + 45 µm) and the binder system of 40vol %(PS/PE = 40/60). The viscosity of MIM feedstock at different temperatures and shear rates was measured and evaluated. Results showed that, the feedstock containing palm stearin exhibited suitable rheological properties by increasing the fluidity of feedstock in MIM process. The rheological results also showed a pseudoplastic flow characteristics, which poses higher value of shear sensitivity (n) and lower value of flow activation energy (E), that are both favourable for injection molding process. The green parts were successfully injected and exhibited adequate strength for handling by optimizing the injection pressure and temperature.

Study on Stability of a Novel Binder System Based on Palm Stearin in Metal Injection Moulding Application

Metal Injection Molding (MIM) is a wellestablished technology for manufacturing a variety of complex and small precision parts. In this paper, fundamental rheological characteristics of MIM feedstock using palm stearin are theoretically analyzed and presented. The feedstock consisted of gas atomized 316L stainless steel powder at three different particle size distributions and the binder system of palm stearin (PS) and polyethylene (PE). The powder loading used was 60vol % for all samples (monosize 16 µm, monosize 45 µm, and bimodal 16 µm + 45 µm) and the binder system of 40vol %(PS/PE = 40/60). The viscosity of MIM feedstock at different temperatures and shear rates was measured and evaluated. Results showed that, the feedstock containing palm stearin exhibited suitable rheological properties by increasing the fluidity of feedstock in MIM process. The rheological results also showed a pseudoplastic flow characteristics, which poses higher value of shear sensitivity (n) and lower value of flow activation energy (E), that are both favourable for injection molding process. The green parts were successfully injected and exhibited adequate strength for handling by optimizing the injection pressure and temperature.

The rheology of metal injection molding

In this study, several readily available polymer binder systems were used to prepare Fe/Ni metal injection molding (MIM) feedstock. A Banbury intensive mixer and screw extrusion were used to achieve optimized feedstock, and the rheological properties of the resulting fluids were evaluated using a capillary rheometry. The effects of shear rate ( γ), solid volume fraction ( φ) and temperature ( T) on the rheological behavior of the Fe/Ni MIM feedstocks are discussed.

Viscosity and melt rheology of metal injection moulding feedstocks

Four kinds of Fe–2Ni metal injection moulding (MIM) feedstocks with the same powder loading and with similar binder composition except for minor components were prepared and their viscosities at different temperatures and shear rates determined using a capillary rheometer. The flowability and the sensitivity of viscosity to shear rate and temperature were investigated. The viscosities of the binders and the general rheological indices of feedstocks were compared. The results show that the minor components of the binders play a very important role in the rheology of feedstocks. A feedstock based on a PW–PP binder can not be used for injection moulding owing to severe powder/binder separation. A feedstock based on a PW–EVA binder has the lowest viscosity and is the easiest to flow into the mould. The viscosity of a feedstock based on a PW–EVA–HDPE binder is higher than that of a feedstock based on the PW–EVA binder and is lower than that of a feedstock based on a PW–HDPE binder. The general rheological index, which includes the effect of flowability and the sensitivity of viscosity to shear rate and temperature, can be used to evaluate the general rheological properties of MIM feedstocks. At a reference temperature of 150°C and reference shear rate of 1181 s−1, the general rheological indices for the feedstocks based on the PW–EVA, PW–HDPE, and PW–EVA–HDPE binders are 7·8, 4·0, and 9·3 respectively. The feedstock based on the PW–EVA–HDPE binder has the best general rheological properties and is most suitable for injection moulding. The mechanical properties and shrinkage homogeneity of MIM tensile bars prepared with the feedstock based on the PW–EVA– HDPE binder are also the most acceptable.

Viscosity and melt rheology of metal injection moulding feedstocks

Four kinds of Fe–2Ni metal injection moulding (MIM) feedstocks with the same powder loading and with similar binder composition except for minor components were prepared and their viscosities at different temperatures and shear rates determined using a capillary rheometer. The flowability and the sensitivity of viscosity to shear rate and temperature were investigated. The viscosities of the binders and the general rheological indices of feedstocks were compared. The results show that the minor components of the binders play a very important role in the rheology of feedstocks. A feedstock based on a PW–PP binder can not be used for injection moulding owing to severe powder/binder separation. A feedstock based on a PW–EVA binder has the lowest viscosity and is the easiest to flow into the mould. The viscosity of a feedstock based on a PW–EVA–HDPE binder is higher than that of a feedstock based on the PW–EVA binder and is lower than that of a feedstock based on a PW–HDPE binder. The general rheological index, which includes the effect of flowability and the sensitivity of viscosity to shear rate and temperature, can be used to evaluate the general rheological properties of MIM feedstocks. At a reference temperature of 150°C and reference shear rate of 1181 s−1, the general rheological indices for the feedstocks based on the PW–EVA, PW–HDPE, and PW–EVA–HDPE binders are 7·8, 4·0, and 9·3 respectively. The feedstock based on the PW–EVA–HDPE binder has the best general rheological properties and is most suitable for injection moulding. The mechanical properties and shrinkage homogeneity of MIM tensile bars prepared with the feedstock based on the PW–EVA– HDPE binder are also the most acceptable.

Metal injection moulding — Testing of injection process: D. Bialo et al. (Warsaw Polytechnic, Warsaw, Poland). Pokroky Praskove Metalurgie, vol 28, no 3/4, 1995, 3–9. (In Czech.)

In this study, several readily available polymer binder systems were used to prepare Fe/Ni metal injection molding (MIM) feedstock. A Banbury intensive mixer and screw extrusion were used to achieve optimized feedstock, and the rheological properties of the resulting fluids were evaluated using a capillary rheometry. The effects of shear rate (γ), solid volume fraction (φ) and temperature (T) on the rheological behavior of the Fe/Ni MIM feedstocks are discussed.

Binders for injection moulding of titanium : H-D. Kunze et al (Fraunhöfer Inst. for Applied Materials Research, Bremen, Germany)

In this study, several readily available polymer binder systems were used to prepare Fe/Ni metal injection molding (MIM) feedstock. A Banbury intensive mixer and screw extrusion were used to achieve optimized feedstock, and the rheological properties of the resulting fluids were evaluated using a capillary rheometry. The effects of shear rate (γ), solid volume fraction (φ) and temperature (T) on the rheological behavior of the Fe/Ni MIM feedstocks are discussed.

Batch and continuous mixing of metal injection moulding feedstock: R. Raman, R.M. German (Pennsylvania State University, Pennsylvania, USA).

Batch and continuous mixing of metal injection moulding feedstock: R. Raman, R.M. German (Pennsylvania State University, Pennsylvania, USA).