Powder Injection Molding Research Articles

Dynamic Tensile Extrusion Behavior of Fine-Grained Copper Fabricated by Powder Injection Molding

The dynamic tensile extrusion (DTE) behavior and microstructural evolution of fine-grained (FG, ~1 μm < d < ~10 μm) Cu fabricated by powder injection molding (PIM) were investigated. The FGM Cu was fabricated by PIM with commercial micro-sized Cu powder sintering at 850 °C for 2 h, while the FGH Cu was developed by the hot isostatic pressing (HIP) of the FGM at 780 °C for 2 h under a pressure of 1000 bar. In order to compare the DTE behavior of the FG Cu manufactured using different methods, the ultrafine-grained-B (UFG, d < ~1 μm) Cu was developed by performing 16 passes of equal-channel angular pressing with route Bc, and the FG-150 Cu was fabricated by annealing the UFG-B Cu bar at 150 °C for 1 h. The DTE tests were performed with identical flyer velocities using an all-vacuum gas gun. The fragments and remnants were carefully recovered after the DTE tests and examined by electron backscattered diffraction measurement and a micro-Vickers hardness test. A strong dual <001> + <111> texture was developed during the DTE for both FGM and FGH Cu. In contrast to the outcome of the UFG-B and FG-150, little evidence of dynamic recrystallization taking place during the DTE in the FGM and FGH was found during analysis of the grain morphology and grain orientation spread. Premature failure based on void coalescence was induced at the vertex region of the FGM fragments due to pre-existing pores. The HIP treatment on the FGM Cu increased the relative density by reducing the pre-existing pores and, as a result, increased the DTE ductility of the FGH Cu.

Powder Bed Fusion, Material Extrusion and Powder Injection Molding: Mechanical and Surface Properties of 17-4ph Stainless Steel Parts

Powder Bed Fusion, Material Extrusion and Powder Injection Molding: Mechanical and Surface Properties of 17-4ph Stainless Steel Parts

Powder injection molded nano copper oxide grafted graphene reinforced copper matrix composites

The challenges associated with inhomogeneous distribution, poor interfacial interaction, and agglomeration of graphene sheets in sintered metal composites restrict its effectiveness in improving mechanical and physical properties. This study devised a grafting protocol for attachment of metal oxides on graphene nanoplatelets (GNPs) to investigate its effect on dispersion and interaction with Cu matrix. GNPs were sonicated to enhance its functionalization without a considerable change in defect ratio followed by grafting of Cu2O nanoparticles on GNPs employing a co-precipitation protocol. XPS, Raman spectroscopy, XRD, FTIR, FESEM confirmed the successful growth of homogenously distributed Cu2O nanoparticles on GNPs. Subsequently, the interaction of Cu2O grafted GNPs with copper matrix was explored using powder injection molding (PIM). Microstructural analysis showed restricted agglomeration, improved distribution of GNPs in copper matrix, and most importantly, bridged interaction between bulk copper and graphene in sintered samples. Furthermore, the densification can still be improved by optimizing the sintering process.

Binder systems for powder injection molding:A review

Regardless of high demands on properties of powder injection molding (PIM) compounds, there is still uncertainty in the role of the polymer binder in the process. To a great extent this is caused by the relatively low number of suitable direct methods to observe the interactions among binder components as well as binder-powder and binder-powder-processing tool reactions, because of the complexity of occurring interactions. In this paper the review of state-of-art in the field of binder development and characterization is reported with the special regard to methods to quantify their mutual relationship. Copyright © 2017 VBRI Press

Analysing Powder Injection Moulding of a Helix Geometry Using Soft Tooling.

Freeform injection moulding is a novel technology for powder injection moulding where a sacrificial 3D printed mould (i.e., a soft tooling) is used as an insert in the injection process. The use of 3D printed moulds enable a higher geometrical design flexibility as compared to the conventional injection moulding process. However, there is still very limited knowledge on how the sacrificial soft tooling material and powder suspension handles the increased geometrical complexity during the process. In this study, a stainless steel powder suspension is injected into a geometrically challenging sacrificial mould (viz. a helix structure) that is produced by vat photopolymerization additive manufacturing. Computed tomography is used to quantify the geometrical precision of the mould both before and after injection. In addition, a new numerical model that considers the suspension feedstock is developed to investigate the powder injection moulding process. The numerical results are found to be in qualitative good agreement with the experimental findings in terms of pinpointing critical areas of the structure, thereby highlighting a new pathway for evaluating sacrificial inserts for powder injection moulding with a high geometrical complexity.

Effect of Particle Size and Shape on Wall Slip of Highly Filled Powder Feedstocks for Material Extrusion and Powder Injection Molding.

A necessity to distinguish between the influence of powder shape and size (particle size distribution) is especially demanding for highly filled metal powder feedstocks employed in additive manufacturing and powder injection molding. As their processability is evaluated through rheological behavior, the study focuses on the effect of powder size/shape on a wall slip, which is a typical phenomenon determining flow performance of these materials. Water and gas atomized 17-4PH stainless steel powders with D 50 of about 3 and 20 μm are admixed into a binder containing low-density polyethylene, ethylene vinyl acetate, and paraffin wax. Mooney analysis to intercept the slip velocity of 55 vol. % filled compounds reveals that wall slip effect appears to vary significantly with size and shape of metal powders-round shaped and large particles are the most prone to the wall slip. However, the evaluation is affected by the type of the flow streams resulting from the geometry of the dies-conical dies reduce the slip up to 60% in case of fine and round particles.

Powder Injection Moulding and Liquid Phase Sintering of Aluminium - SiC Particulate Composite

Metal matrix composite has been increasingly appreciated by many engineering applications due it its tailored properties for specific uses. Powder injection moulding is one of the most effective composite processing essentially for small and complex parts. Moulding of feedstock is the key step determining green and sintered properties. This research investigated effects of moulding parameters which are % solid loading and moulding speed on microstructure and properties of aluminium composite. Commercial aluminium alloy powder and SiC particulate at 15 vol.% addition were formulated at 55 % and 60 % solid loading. Injection moulding were operated using a horizontal screw driven typed machine at 1600-1800 rpm speed and 280 - 300 °C moulding temperature. After sintering at 655 °C, property assessment via microstructure, density, % shrinkage, distortion and hardness were carried out. It was found that feedstock of 55 % solid loading occasionally led to flash problem while that of higher solid loading experienced higher viscosity to fulfill four-cavity mould. Moulding speed investigated did not significantly affect mould filling and overall properties. Sintered microstructures generally showed well-distributed SiC particulate in the aluminium matrix. The optimum injection moulding condition was the feedstock prepared at 60% solid loading, moulding at 1800 rpm speed, which offered theoretical density of greater than 98.5 % and micro Vickers hardness of 125.2 Hv.

Analysis of biomedical titanium implant green parts by X-Ray tomography

In this study, X-ray tomography was applied as a non-destructive test to investigate the internal defects of the green part produced with Powder injection molding (PIM). PIM is a material processing technology that combines injection molding with powder metallurgy. The determination of multiple parameters such as rheology, molding, bonding, and sintering stages in the PIM method requires a long time, energy, and high cost. Metal and ceramic injection molded parts are known to be susceptible to defects like cracks, weld lines, bubbles, or gaps. The examination and elimination of these defects are critical to the safety of the products because even a very short crack can significantly reduce the tensile and fracture strength of the parts. The internal structure analysis of the green parts after molding is very difficult. Defects (internal cracks, micropores, jetting, etc.) occurring in the green part will occur in the sintered. Therefore, it is essential to analyze the possible defects on molded parts before applying the ongoing process to save time and costs. Since the medical implants are in complex shape in general, the more internal defects can be seen at molding stage, it is needed to check the internal structure without any destruction, because there is no chance toleave them for recycle in the case of any defect. In experimental studies, it was observed that there were defects of edge, interior, and gaps in X-ray analysis for four different injection parameters. In X-ray analysis, the defects free parts were obtained for green part 4 parameters (temperature of 237 °C, flow rate of 20.11 cm3/s and pressure of 120 MPa). As a result of X-ray analysis, the difference between green part 1 and green part 4 is clearly visible in terms of defect. Injection temperatures, speeds and pressure play important role on originating of defects.

Characterization of nano / micro bimodal 316L SS powder obtained by electrical explosion of wire for feedstock application in powder injection molding

Bimodal nano / micro powders are in demand in powder injection molding (PIM) and additive manufacturing (AM) technologies. Feedstocks with bimodal powder have a higher flowability, and the resulting products have a higher density.In this work, a bimodal 316L steel powder obtained by the electric explosion of a wire (EEW) was investigated. The bimodal powder is formed directly during the explosion and does not require a mixing step. The powder was obtained at different explosion energy densities. A feedstock was obtained with a powder content of 94 wt%.The powders have a different micro: nano ratio depending on the energy density. Feedstocks with these powders have different rheological behavior. The morphology and chemical composition of the powders and the homogeneity and rheological properties of feedstock with bimodal powder were studied and discussed. A comparison of feedstock properties with bimodal and micron powder is carried out.

Rheology of Highly Concentrated Suspensions with a Bimodal Size Distribution of Solid Particles for Powder Injection Molding.

Powder injection molding (PIM) is one of the modern and prospective technologies in processing different materials. We proposed to use bimodal compositions of particles for increasing their content in the final products. A set of model suspension of Al with low-molecular-weight poly (ethylene glycol) as a binder based on theoretical arguments concerning the filling capacity of bimodal suspensions was prepared. Studying the rheological properties of these compositions showed that they demonstrate elasto-viscous behavior with significant plasticity that is favorable for the technological process. Using compositions with bimodal distributions allows for increasing the content of the solid phase up to 75 vol. % for PIM technology, which is significantly higher than the standard practical limit. This rheological approach developed for model formulations was applied to processing compositions containing aluminum oxide as typical ceramics and polyolefines as a binder widely used in technological practice. The obtained sintered ceramic samples have quite acceptable mechanical properties of the usual corundum articles.

Effect of powder particle shape and size distributions on the properties of low-viscosity iron-based feedstocks used in low-pressure powder injection moulding

ABSTRACT Low-pressure powder injection moulding (LPIM) is a cost-effective manufacturing technology used to fabricate complex-shaped parts with high mechanical properties at low- or high-volume production. This research work presents an experimental approach to investigate the debound/sintered properties of iron components produced by the LPIM process using iron-based powders exhibiting different particle shapes and size distributions. Four low-viscosity feedstocks were mixed and injected into a rectangular mould cavity before being thermally wick-debound and finally sintered using identical debinding and sintering cycles. This study confirms that both irregular and spherical iron powders can be shaped via the LPIM process. The solid loadings obtained with these two powder morphologies, varying from 58 to 62 vol.-%, represent expected values. The trend in the density values obtained with irregular (∼6.6 g/cm3) and spherical (∼7.5 g/cm3) powders was validated by metallographic observations.

Development of mechanical and visible transparency properties of spark plasma sintered spinel fabricated by powder injection molding of MgAl2O4 nanoparticles

This research aims to investigate the density, hardness, fracture toughness, and infrared and visible transmittance of spark plasma sintered (SPS) spinel discs fabricated through the powder injection molding (PIM) method. These properties were compared with the sample directly SPSed without the PIM process. For this purpose, initially, a feedstock was prepared with 80 wt% spinel nanopowder and 20 wt% binder. The results revealed that the hardness and fracture toughness of the SPSed spinel disc sintered at 1400 °C were greater than those of the spinel sample without PIM treatment. Also, for the PIMed sample and then SPSed sample, the level of infrared and visible transmittance was ~10% greater than for the SPSed spinel nanopowders.

IR Transparent Ceramic Microfluidic Chips Produced by Powder Injection Molding

IR Transparent Ceramic Microfluidic Chips Produced by Powder Injection Molding

Impact of neutron irradiation on hardening of baseline and advanced tungsten grades and its link to initial microstructure

Six tungsten grades were irradiated in the Belgian material test reactor (BR2) and characterized by Vickers hardness tests in order to investigate the irradiation-induced hardening. These tungsten grades included: Plansee (Austria) ITER specification tungsten, ALMT (Japan) ITER specification tungsten, two products from KIT (Germany) produced by powder injection molding (PIM) and strengthened by 1% TiC and 2% Y2O3 dispersed particles, and rolled tungsten strengthened by 0.5% ZrC from ISSP (China). The materials were irradiated face-to-face at three temperatures equal to 600 °C, 1000 °C, and 1200 °C to the dose of ∼1 dpa. The Vickers hardness tests under 200 gf (HV0.2) were performed at room temperature. The Vickers hardness increases as the irradiation temperature increases from 600 to 1000 °C for all materials, except for the ZrC-reinforced tungsten, for which the increase of hardness does not depend on irradiation temperature. The irradiation-induced hardness decreases after irradiation at 1200 °C. This is a result of defect annealing enhanced by thermally activated diffusion. However, even at 1200 °C, the impact of neutron irradiation on the hardness increase remains significant; the hardness increases by ∼30 to 60% compared to the non-irradiated value. In the case of TiC-strengthened material, the irradiation hardening progressively raises with irradiation temperature, which cannot be explained by the accumulation of neutron irradiation defects solely.

РЕОЛОГИЧЕСКОЕ ПОВЕДЕНИЕ ПОРОШОК-ПОЛИМЕРНЫХ СМЕСЕЙ И МОДЕЛЬНОЕ ОПИСАНИЕ ВЯЗКОСТИ ФИДСТОКА ДЛЯ ЧИСЛЕННОГО МОДЕЛИРОВАНИЯ ПРОЦЕССА ИНЖЕКЦИОННОГО ФОРМОВАНИЯ

The rheological behavior of the powder-polymer composition prepared for the application in the powder injection molding (PIM) technology has been studied. A review of models used to describe the rheological behavior of powder slips is presented. A viscosity study of MIM-4140 feedstock with a wax-polyolefin binder was carried out on a capillary rheometer with different capillary diameters. Empirical coefficients of viscosity models were determined. Verification of calculated viscosity values and experimental data for the studied feedstock is presented.

Structure and Properties of Co-Cr-Mo Alloy Manufactured by Powder Injection Molding Method.

Cobalt–chromium–molybdenum alloys samples were obtained by the powder injection molding method (PIM). PIM is dedicated to the mass production of components and can manufacture several grades of dental screws, bolts, stabilizers, or implants. As a skeleton component, ethylene–vinyl acetate (EVA copolymer) with a low temperature of processing and softening point was used. The choice of a low-temperature binder made it necessary to use a coarse ceramic powder as a mechanical support of the green sample during sintering. The injection-molded materials were thermally degraded in N2 or Ar-5%H2 and further sintered in N2-5%H2 or Ar-5%H2 at 1300 or 1350 °C for 30 min. The structure of the obtained samples was characterized by X-ray diffraction and electron microscopy. Mechanical properties, including hardness and three-point bending tests, confirmed that a nitrogen-rich atmosphere significantly increases the bending strength compared to the material manufactured in Ar-5%H2. This is due to the precipitation of numerous fine nitrides and intermetallic phases that strengthen the ductile γ-phase matrix.

Effects of Bonding Treatment and Ball Milling on W-20 wt.% Cu Composite Powder for Injection Molding.

W-20 wt.% Cu pseudo-alloys were produced via powder injection molding (PIM) with powders prepared thermochemically. Bonding treatment and ball milling (BTBM) were used, and the effects of BTBM on the characteristics of the powders, rheological properties of the feedstock, shrinkage and properties of the sintered samples were studied. The morphology of the powder changed from extremely agglomerated small particles to pebble-shaped smooth large particles which were composed of several small particles combined tightly. The tap density increased from 3.25 g/cm3 to 7.22 g/cm3, and the specific surface area decreased from 0.86 m2/g to 0.45 m2/g. The critical powder loading of the feedstock increased from 45 vol.% to 56 vol.% due to the change in powder characteristics, thereby improving densification and dimension precision. For the PIM samples sintered at 1290 °C for 120 min in a hydrogen gas, the oversizing factor decreased from 1.297 to 1.216, and the dimension fluctuation ratio decreased from ±0.61% to ±0.33%. At the same time, the relative density increased from 97.8% to 98.6%, the thermal conductivity increased from 218 W/(m·K) to 233 W/(m·K), and the average coefficients of thermal expansion were roughly similar, within the range of 8.43–8.52 × 10−6/K.

New insights on the porous network created during solvent debinding of powder injection-molded (PIM) parts, and its influence on the thermal debinding efficiency

Mn-Zn ferrite components were successfully produced using Powder Injection Molding (PIM) from a binder system (11.5 wt%) made of paraffin wax (PW), linear low density polyethylene (LLDPE) and stearic acid. Solvent debinding kinetics of the molded parts depended on n-hexane temperature, on immersion duration and on part’s geometry. The volume to surface ratio of the considered parts were comprised between 1.3 and 4.0. The primary binder (PW) removal created a porous network having a narrow average pores distribution centered on a diameter of about 50 nm. We highlighted by using Archimedes’ principle and mercury intrusion porosimetries that the parts achieved a maximal open porosity disregarding their volume to surface ratio, while it was still possible to remove additionnal PW. This maximal porosity (12.6 %) has proved to be the most relevant parameter for the definition of an optimal solvent debinding duration (∼15−20 h at 40 °C). Using this chemical debinding step, it was possible to reduce our thermal debinding duration by 62.5 % (80 h–30 h) while avoiding the occurrence of structural defects as cracking or deformations on the parts. The sintered PIM parts had a density of about 4.84 g/cm3 (94.9 % of relative density) and a magnetic saturation polarization of about 500 mT what is very similar to parts produced using the conventional fabrication techniques. These results should be useful to understand how to improve the production rate of ferrites fabricated by PIM technology.

Effects of materials and microstructures on pool boiling of saturated water from metallic surfaces

Pool boiling experiments using horizontal, flat, and upwards facing aluminum, stainless steel, and copper, heating surfaces are conducted in distilled water. The wettability, measured by the static contact angle (CA), and the critical heat flux (CHF) are found to vary significantly among the three surfaces. The Boehmite treated aluminum, stainless steel, and copper surfaces have a CHF of 1850, 1375, and 1015 kW/m2, respectively. Powder Injection Molding (PIM) and High-Temperature Conductive Microporous Coating (Cu-HTCMC) are also applied on the copper heating surface to create various microstructures, and their pool boiling performances are compared to that of a plain copper surface. The PIM and Cu-HTCMC reduce the contact angle and increase the CHF value. However, the Cu-HTCMC causes an increase in CHF well beyond the expected value, and it is believed to be due to the porous coating structures and reentrant type cavities within the microporous coating.

Application of sodium chloride as space holder for powder injection molding of alloy Titanium–Hydroxyapatite composites

The development of porous metal structures, especially for the use of titanium alloys in bone implant applications, has attracted the attention of researchers. However, forming porous structures in titanium composites via powder injection molding (PIM) remains in the early stages of analysis, allowing the determination of processing parameters to be studied in greater detail. In this study, the critical PIM parameters for processing porous alloy titanium–hydroxyapatite composites were identified via the space holder method. Titanium alloy (Ti6Al4V) was mixed with hydroxyapatite (HA) at a weight percentage ratio of 9:1 with 20 wt.% sodium chloride (NaCl) as the space holder. Feedstock was prepared by combining the powder with a binder system. Pseudoplastic flow activity, which was the desired rheological property needed for PIM, in the feedstock was determined. A tensile bar specimen was successfully injected with a green strength of 2.92 MPa. The space holder was then removed via water leaching, whereas the binders were removed by a debinding step before being sintered in a high-vacuum condition for 3 h at 1350 °C. The sintered parts were interconnected and had a porosity level of 37.03%. Energy dispersive X-ray mapping revealed that the porous titanium–hydroxyapatite composite contained titanium (Ti), calcium (Ca), phosphorus (P), and oxygen (O) components. This study indicated that the combination of PIM and the space holder method is a promising technique for manufacturing near net-shaped porous titanium–hydroxyapatite composites.