Powder Injection Molding Process Research Articles

Analysis and modeling of sintering of Sr-hexaferrite produced by PIM technology

The powder injection moulding (PIM) technology is lately becoming more and more significant due to complex design possibilities and good repeatability. This technology requires optimization of all steps starting with material and binder, injection, debinding and sintering parameters. Sintering is one of the key links in this technology. The powder injection moulding process is specific as during feedstock injection powder particles mixed into the binder do not come into mechanical contact. Shrinkage during sintering of PIM samples is high. In this work we have analyzed and modeled the sintering process of isotropic PIM samples of Sr-hexaferrite. The Master Sintering Curve (MSC) principle has been applied to analyze sintering of two types of PIM Sr-hexaferrite samples with completely removed binder and only the extraction step of the debinding procedure (thermal debinding proceeding simultaneously with sintering). Influence of the heating rate on resulting sample microstructures has also been analyzed. Influence of the sintering time and temperature was analyzed using three different phenomenological equations.

The effect of sintering conditions on the properties of WC–10wt%Co PIM compacts

The powder injection molding (PIM) process has an advantage of near net shaping of homogeneous micro structure and density at the complicate form. This study was investigated for microstructure and mechanical properties of WC–10%Co insert tool alloy fabricated by PIM process. The WC–10%Co feedstock mixed with wax binder was fabricated by two blade mixer. After WC–10%Co feedstocks were injection molded, debinding process was carried by two-steps methods with solvent extraction and thermal debinding. The binder was eliminated with normal hexane for 12 h at 50 °C by solvent extraction, and subsequently thermal debinding was examined for 1 h at the temperature 900 °C. After debinding process, the specimens were sintered at vacuum or N2/H2 mixed gas atmosphere at 1380 °C. The microstructure and phase were observed by FE-SEM. In the case of sintered at 1380 °C in vacuum atmosphere, the hardness was 1600 Hv, and the relative density of WC–10%Co was 92.5%. The density of WC–10%Co sintered at 1380 °C in mixed gas atmosphere was 87.5% and the hardness was lower than 1400 Hv. Residual carbon contents of sintered at vacuum and mixed gas atmosphere were 5.4 wt%.

Mechanical alloying of FeAl intermetallic powder for metal injection moulding process

The Fe–48 at.-%Al powder used for powder injection moulding (PIM) was prepared by mechanical alloying in a high energy planetary ball mill and subsequent vacuum annealing. The effects of stearic acid (SA) as the process control agent on powder characteristics were investigated using X-ray diffractometer, laser particle size analysis and scanning electron microscopy. The dependence of solvent debinding efficiency of PIM feedstock on the powder characteristics was also studied. The results indicate that a low SA content for ball milling helps to prepare near spherical, coarse powder particles that exhibit good solvent debinding efficiency. On the contrary, a high SA content leads to thin layered, small particles with poor PIM solvent debinding efficiency. An intermediate SA content such as 1 wt-% makes the ball milled powder combine the advantageous characteristics for PIM process.

Injection Molding of Titanium Alloy Implant For Biomedical Application Using Novel Binder System Based on Palm Oil Derivatives

Problem statement: Titanium alloy (Ti6Al4V) has been widely used as an implant for biomedical application. In this study, the implant had been fabricated using high technology of Powder Injection Molding (PIM) process due to the cost effective technique for producing small, complex and precision parts in high volume compared with conventional method through machining. Approach: Through PIM, the binder system is one of the most important criteria in order to successfully fabricate the implants. Even though, the binder system is a temporary, but failure in the selection and removal of the binder system will affect on the final properties of the sintered parts. Therefore, the binder system based on palm oil derivative which is palm stearin had been formulated and developed to replace the conventional binder system. Results: The rheological studies of the mixture between the powder and binders system had been determined properly in order to be successful during injection into injection molding machine. After molding, the binder held the particles in place. The binder system had to be removed completely through debinding step. During debinding step, solvent debinding and thermal pyrolysis had been used to remove completely of the binder system. The debound part was then sintered to give the required physical and mechanical properties. The in vitro biocompatibility also was tested using Neutral Red (NR) and mouse fibroblast cell lines L-929 for the direct contact assay. Conclusion: The results showed that the properties of the final sintered parts fulfill the Standard Metal Powder Industries Federation (MPIF) 35 for PIM parts except for tensile strength and elongation due to the formation of titanium carbide. The in vitro biocompatibility on the extraction using mouse fibroblast cell line L-929 by means of NR assays showed non toxic for the sintered specimen titanium alloy parts.

Experimental and theoretical methods for optimal solids loading calculation in MIM feedstocks fabricated from powders with different particle characteristics

The aim of this work is to investigate the influence of the particle characteristics of powder to the mixing stage of the powder injection moulding process to identify the best procedure with which to evaluate the optimal solids loading for feedstock fabrication. To perform the present study, powder blends that are made from three bronze and four Inconel 718 powders, with different particle size distributions and morphologies, are mixed with a binder system that is based on polyethylene and wax. Powder–binder blends are prepared by varying the powder content to study how the powder characteristics affect the optimal solids loading. In addition, a new method is presented for determining the optimal solids loading in powder injection moulding feedstocks through the activation energy calculation of powder–binder blends that are prepared with different powder contents. This novel method is compared with the optimal loading values that have been determined by other ways as torque rheometry, determination of the tap-real density ratio and through rheological models.

Rheological characterization of powder injection molding compounds

This review concerns the rheological research related to compounds obtained using powder injection molding (PIM) technology. PIM is a process for making metallic and ceramic items using forming method for thermoplastics. This technique allows the large-number production of relatively small (corresponding to a weight of around 100 grams) parts of complex shapes with reduced cost comparing to traditional metallurgy and increased efficiency by avoiding the use of extra processes. On the other hand, the number of process variables is very high, and their interactions are only partially understood. The knowledge of the flow properties is the key factor for successful injection molding. Its novelty consists in the polymer physics aspects of the problem, considering the compounds obtained in PIM process as polymer melts highly filled with powder particles.

Limits and challenges of manufacturing micro moulds

Due to the ongoing miniaturisation in industrial sectors like automotive, electronics or medical, the development of new manufacturing processes which are suitable for micro system technologies gains more and more importance. The miniaturisation of components leads to challenges in the manufacturing of micro parts. One application area is the manufacturing of moulds for the micro powder injection moulding (μPIM) process. This process requires good surface qualities and a sufficient demoulding behaviour of the moulds. Micro milling, micro electrical discharge machining (μEDM) and micro laser beam machining (μLBM) are appropriate processes for the manufacturing of micro structures in different materials. Abrasive micro peening can be used for further precision treatment. Depending on the desired structure a single process or the combination of several processes has to be chosen to obtain superior surface qualities of the moulds. This paper deals with challenges and limits of the manufacturing processes among others exemplified on a gearwheel mould.

Application of powder injection molding process to manufacturing of Ni-ZrO2 anodes in Solid Oxide Fuel Cells

1Solid oxide fuel cells (SOFC) are a promising high-efficient power generating system that can directly convert chemical fuel to electrical power. Cost reduction of materials and processing is one of the key issues for commercialization of SOFCs. SOFCs, as the electrochemical devices consist of anode and cathode, separated by the ion conducting material called electrolyte. The main SOFC element is anode, whose function, apart from oxidation the hydrogen, is to carry the mechanical loads which occur in the whole cell. Anode features the cell skeleton supporting electrolyte and cathode. Due to the rising interest in SOFC a high demand for them in future is expected, therefore, one should use the powder forming method applicable for mass production of such elements. Powder injection molding is the best solutions in this case. This method offers the possibility of fabricating tubes or plates which can be assembled into packets making increase of the SOFC power possible. Powder injection molding (PIM) is a manufacturing technology for the net-shape production of small, intricate, and precise metal or ceramic components. The PIM process includes mixing of either metal or ceramic powders with a binder to produce a feedstock, injection molding to form a green part with the desired shape by making the feedstock flow into and fill a mold under pressure, debinding to form a brown part by removing the binder components, and sintering to near full density. The powders (NiO and ZrO2) were mixed with a binder system which consists of stearic acid (SA), polypropylene (PP) and paraffin wax (PW). Mixing of components was done using two blades at the temperature of 170 o C at the speed of 40 rpm. Five selected mixtures of powders with binder are studied. Rheological characterization of all type of feedstocks were performed in a Rheoflixer capillary rheometer at 170, 180 and 190oC over a range of shear rates from 10 to 10000 s -1 . Feedstocks were injected on the injection molding machine to make the test pieces. The debinding process of green samples was made by two different steps. First the injected samples were debound in a bath with the heptanol and next by thermal debinding. The sintering process took place immediately after the debinding. Debound pieces were sintered by heating from 1150 to 1450oC and by soaking at these temperatures for one hour. Results of the rheological and torque investigations have essential importance for further search of the optimum feedstock to injection molding machines making forming possible of shapes for fuel cells anodes, which require in addition debinding of the binder and sintering. High viscosity of the feedstock in which there are hard ceramic particles cause fast wear of screws, dies, heads, and cylinders of injection molding machines and extruders, therefore binder portion increase is required. One may state based on bending strength tests and density examinations of the sintered and reduced anodes that the sintering temperature should not be lower than 1250 o C. Lower sintering temperature deteriorates significantly mechanical properties of anodes which perform also the mechanical load carrying function for the whole fuel cell.

PIMSIM: optimisation of powder injection moulding using advanced moulding simulations

(2009). PIMSIM: optimisation of powder injection moulding using advanced moulding simulations. Powder Metallurgy: Vol. 52, No. 4, pp. 279-281.

In situ Studies and Simulations of Mould Filling with a Model System for PIM

Abstract The processing conditions and the mould design are important parts of the powder injection moulding (PIM) process. In the present work, the mould filling phase of the process has been studied in situ with a special mould equipped with a sight glass using a high speed camera. Effects of features such as the mould temperature, the melt temperature, the surface roughness of the mould cavity, the gate dimensions, the mould design and the flow rate on the filling behaviour were demonstrated. In particular it was noted that a rougher mould surface to some extent facilitated the filling of the mould. The mould temperature, the nominal melt temperature and the flow rate affected the position of weld lines via the cooling of the feedstock and the corresponding change of the melt viscosity. The experimentally determined weld-line positions were compared with predictions from numerical simulations performed with the commercial software Moldex3D. The agreement between the experiment and the prediction was in most cases quite fair or good. The in situ observation of the mould filling also provided the possibility to study how the gate dimensions and the flow rate influenced the jetting behaviour.

Powder injection moulding of an Al–AlN metal matrix composite

A powder injection moulding process for producing fine AlN particle reinforced aluminium matrix composites was developed. The process is a promising low-cost technique for net shape production of complex aluminium metal matrix composite components. Net shape parts of near full density with good strength and ductility were produced. The AlN reinforcement particles exhibited good compatibility and were uniformly distributed throughout the AA6061 matrix. An Al–AlN composite/Al hybrid was also successfully produced. The hybrid parts exhibited good interfacial adhesion and were free of distortion.

The Study of Prototypes of Dental Implants Obtained by the Titanium Powder Injection Molding Process: <i>In Vivo</i> Study

The production of titanium parts from powder metallurgy is one of the tendencies of modern metallurgy, since it allows obtaining structures with complex geometries and controlled porosity. The purpose of this study was to produce two types of dental implant prototype, and compare them biologically. Smooth surface prototypes were obtained, by the conventional turning process and porous surface prototypes using Metal Injection Molding (MIM). The prototypes were implanted in rats that were euthanized after 3 weeks, and the bone/implant interface was analyzed. The results showed that all prototypes were clinically stable at the end of the healing period, but those produced by the MIM process presented a significantly higher percentage of osseointegration (bone/implant contact) than the milled prototypes in the same healing period. It is concluded that the bone tissue grew independent of type of implant, enabling quick, rigid fixation already in the third week of the healing process.

Sequential and global optimization in powder injection molding processing

The work is focused on the overall optimization associated to powder injection molding (PIM). The PIM process includes four main stages, from the mixture of the powders and binders to the final sintering stage. Injection and sintering stages are considered to be the most important for optimization, as they mostly affect the final quality of the produced components. The injection stage shapes the green parts but initiates powders segregation that will be inherited and amplified by the sintering stage to finally appear in the resulting products. One first introduces an optimization loop based on the surfaces response method to minimize the powder segregation. Then the results are transferred to a sintering optimization loop applied through an experimentally calibrated thermo-mechanical creep model to predict the shrinkage and density contours on the final parts. The overall optimization combines both optimizers based on the developed simulation tools to provide a realistic way to improve the PIM process design accounting the different processing stages.

Two-material powder injection molding of functionally graded WC–Co components

Abstract Functionally graded cemented tungsten carbide (WC–Co) components with graded cobalt concentrations have been developed to offer solutions to the tradeoff between wear resistance and fracture toughness. However, the problem of cobalt homogenization during liquid phase sintering is currently still a challenge. This paper presents the two-material powder injection molding (PIM) of functionally graded WC–Co components without cobalt concentration gradients. The powder compositions of the outer layer and core layer of the molded ring are WC–0.5 wt%Co–0.5 wt%VC–4.5 wt%W and WC–0.6 wt%Co respectively. The PIM process facilitates abnormal grain growth as a result of the loose powder structure that is present after debinding. The loose powder compact facilitates rearrangement and grain boundary formation and consequently facilitates abnormal grain growth during sintering process. The abnormal grains serve to toughen the core layer of the component. VC diffusion generates a graded microstructure in terms of the density of abnormal grains varying radially from the initial boundary to the core layer. The graded microstructure results in a gradual decrease in hardness from the outer layer to the core layer.

Net-shape production of graphite parts via powder injection moulding of carbon mesophase

In the present study the feasibility of the net-shape production of graphite components via powder injection moulding (PIM) of carbon mesophase is demonstrated. The difficulty in the PIM process lies in the selection of an appropriate binder system. If conventional binders are used, problems arise because the sintering temperature of carbon mesophase is below the thermal degradation temperature of most organic binders. One promising alternative is the use of partially water-soluble binder systems. These can be easily removed by solvent debinding in water. Binder selection and debinding process were adapted to avoid crack formation. Special attention has been paid to the influence of thermal treatment. The elastic modulus improved from 2.1 to 7.2 GPa while the open porosity was reduced from 32.6 to 23.7% by an adjusted temperature ramp in the thermal-debinding step. The second approach is to use a water-based binder system. This has the advantage that the water can be removed by drying at room temperature. Under optimized drying conditions, crack-free parts were produced with a very homogeneous distribution of small pores which has a positive influence on the mechanical properties. An average pore diameter of 0.32 μm was obtained with this binder system compared to 1.03 and 0.69 μm of the samples produced with the water-soluble binder system. With the water-based binder system an elastic modulus of 9.0 GPa was achieved.

Sequential and global optimization in powder injection molding processing

The work is focused on the overall optimization associated to powder injection molding (PIM). The PIM process includes four main stages, from the mixture of the powders and binders to the final sintering stage. Injection and sintering stages are considered to be the most important for optimization, as they mostly affect the final quality of the produced components. The injection stage shapes the green parts but initiates powders segregation that will be inherited and amplified by the sintering stage to finally appear in the resulting products. One first introduces an optimization loop based on the surfaces response method to minimize the powder segregation. Then the results are transferred to a sintering optimization loop applied through an experimentally calibrated thermo-mechanical creep model to predict the shrinkage and density contours on the final parts. The overall optimization combines both optimizers based on the developed simulation tools to provide a realistic way to improve the PIM process des...

Production of micro-porous austenitic stainless steel by powder injection molding

The powder space holder (PSH) and powder injection molding (PIM) methods have an industrial competitive advantage that is capable of net-shape production of the micro-sized porous parts. In this study, a micro-porous austenitic stainless steel part was produced by the PSH–PIM process. Spherical poly(methyl methacrylate) (PMMA) particles were used as a space holder material. The effects of fraction and average size of PMMA on properties of sintered micro-porous austenitic stainless steel samples were investigated. It was shown that the fraction and average size of PMMA could be controlled properties.

Application of PEG/PMMA Binder for Powder Injection Moulding of Hardmetals

Powder injection moulding (PIM) is a cost effective powder metallurgical process for the fabrication of small, complex-shaped components for high performance applications. A binder system, which comprises a major fraction of polyethylene glycol (PEG) and a minor fraction of a very finely dispersed polymethyl methacrylate (PMMA), has been applied for tungsten carbide (WC) – cobalt (Co) hardmetal powders. PEG can be removed rapidly by water leaching and PMMA is removed by subsequent pyrolysis when the components are ramped up to the sintering temperature. In this work, the development of feedstock formulations and of the processing parameters for a successful injection moulding and to achieve high density has been investigated. The present study has demonstrated that the binder can be employed for the production of WC-Co hardmetal components by PIM process. The maximum density achieved thus far is 97% of the theoretical value.

Studies on the fabrication of tool steel components with micro-features by PIM

Fabrication of structures with fine features has been a challenge and has required sophisticated equipment. In the current work, the use of a cost-effective method, PIM (powder injection molding) was evaluated to fabricate structures with fine features such as sharp edges with dimension in microns. The selected component consisted of micro features of two steps having a cross-section dimension of 0.6×0.07 mm and 0.6×0.06 mm. In order to achieve good mechanical properties coupled with wear resistance, an M2 tool steel material was selected. The mould tip region with two-step micro features was fabricated using into multi-mould pieces to ensure the edge sharpness of the two-step micro features in the mould cavity and to create an air vent to release the entrapped gas at the moulding stage. The moulded samples were first debound and then sintered at different temperatures. The results of actual sintering at 1,244, 1,252, 1,260, and 1,280°C were analyzed, since transition to liquid phase sintering occurs in this region. Visual observation, microstructural analysis and hardness distribution were carried out on the samples sintering at different temperatures. Incomplete sintering occurred at 1,244°C while at 1,252°C distortion of the samples was identified. Sintering at 1,260°C yielded parts with good integrity and strength and a further increase of sintering temperature deteriorated the characteristics. Five samples were chosen randomly from three batches of 100 pieces for a pilot production scale. Their dimensional flatness was measured and the result showed that flatness less than ±0.3% can be achieved under optimized sintering temperature of 1,260°C ± 0.3°C. This means that the M2 tool steel component with micro features can be possibly produced by PIM process in mass production.

Development of Dental Scaler Tip Mold with Powder Injection Molding Process

With the capability of net shaping for complex 3D geometry, powder injection molding (PIM) is widely used for automotive parts, electronics and medical industry. In this study, an ultrasonic dental scaler tip produced by machining process was redesigned for the PIM process. An injection mold was designed and machined to produce the dental scaler tip by the PIM process. The mold design was aided by CAE analysis. A PIM feedstock was made of SUS316L powder and a wax based binder. The filling balance in the mold was checked by a short shot test with LDPE and the PIM feedstock. Production capability of the PIM process for the dental scaler tip was examined with the mold. Although there were minor problems such as a discoloration around the gate and a flashing at the air vent, the PIM process turned out to be an excellent substitute for machining process to manufacture the ultrasonic dental scaler tip.