Powder Injection Molding Process Research Articles

Effect of ball milling on the rheology and particle characteristics of Fe–50%Ni powder injection molding feedstock

Fe–50%Ni soft magnetic alloys were produced by powder injection molding (PIM) using carbonyl iron and carbonyl nickel as raw materials. The effect of mixing technique of metal powders on the characteristics of mixed powders and PIM process was studied. It was found that the branched chain of carbonyl nickel was broken and the mixture was homogeneous with a good dispersion by ball milling. Due to the improvement of the powder characteristics, the tap density increased from 3.21g/cm3 for mixed powders without ball milling to 4.86g/cm3 for ball mixed powders. Additionally, the critical powder loading of the feedstock was raised from 52% for the mixed powders without ball mixing to 62% for the ball milled powders, which benefited dimension precision. As the degreased specimen sintered at 1360°C in a flowing hydrogen gas, the high magnetic property Fe–50%Ni alloy with maximum permeability of 43541, saturation induction of 1.48T, coercive force of 6.8A/m and relative density of 97% was obtained.

Development of non-eroding rocket nozzle throat for ultra-high temperature environment

The powder processing methods including powder metallurgy (P/M) and powder injection molding (PIM) techniques for tungsten (W)–rhenium (Re) were employed to produce a W–Re rocket nozzle. The composition of W–Re was determined by 25wt.% of Re to avoid the formatting brittle sigma (σ) phase. The samples for analysis of the densification behavior on sintering were prepared by die pressing and cold isostatic pressing (CIP). The feedstock for the PIM process was produced by mixing the W–25wt.% Re powder and binder system based on a wax-polymer with an optimum solid loading through the twin-extruder mixer. The injection molded specimens were debound to extract and decompose the binders via the solvent and thermal debindings. The debound samples were sintered in a hydrogen atmosphere. After sintering, hot isostatic pressing (HIP) was carried out in an argon atmosphere to enhance the density.The dilatometry experiments were performed to analyze and predict a densification behavior during sintering. The master sintering curve (MSC) model was used to characterize the densification behavior with a minimal set of preliminary experiments. The mechanical properties were evaluated through microstructure and chemical composition measured by EDX–SEM and X-ray diffraction (XRD).Finally, the eroding test was conducted using the W–25wt.% Re rocket nozzle produced by PIM under the high temperature. After carrying out erosion tests, the erosion rate, hardness and microstructure were evaluated.

Water soluble Invar 36 feedstock development for μPIM

A water soluble binder system based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) is proposed and investigated to carry out a micro powder injection moulding (μPIM) process with an Invar 36 alloy powders. The overall process was optimised with an emphasis on the determination of the optimal solid loading. Several methodologies were evaluated and compared to determine this parameter. A full μPIM was performed with different powder content feedstocks. Dog bone-type micro test parts were fabricated thereof and their mechanical properties were evaluated. Solid loadings up to 65vol.% resulted to have the most equilibrated properties to successfully fabricate Invar 36 micro parts with the selected powder and binder system.

Powder Injection Molding of Ceria-Stabilized, Zirconia-Toughened Mullite Parts for UAV Engine Components

Powder injection molding (PIM) of ceria-stabilized, zirconia-toughened mullite composites were investigated in the present article with the goal of obtaining performance enhancement in complex geometries for energy and transportation applications. A powder-polymer mixture (feedstock) was developed and characterized to determine its suitability for fabricating complex components using the PIM process. Test specimens were injection molded and subsequently debound and sintered. The sintered properties indicated suitable properties for engine component applications used in unmanned aerial vehicles (UAVs). The measured feedstock properties were used in computer simulations to assess the mold-filling behavior for a miniature turbine stator. The results from the measurements of rheological and thermal properties of the feedstock combined with the sintered properties of the ceria-stabilized, zirconia-toughened mullite strongly indicate the potential for enhancing the performance of complex geometries used in demanding operating conditions in UAV engines.

Thermal stability and degradation kinetics of feedstocks for powder injection moulding – A new way to determine optimal solid loading?

Degradation kinetics and the thermal stability of zircon powder injection moulding feedstocks (PIM) based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) binders were investigated using simultaneous thermogravimetric analysis (STA). The initial decomposition temperature (IDT) and the integral procedure decomposition temperature (IPDT) were used to analyse the thermal stability of the binder system as a function of the solid loading content. The degradation kinetics was studied, and the degradation activation energy was assessed for varying zircon powder contents using isoconversional methods. All the methodologies revealed changes in the thermal degradation behaviours of the feedstocks for solid loadings that were previously determined to correspond to optimal solid loadings using other experimental procedures. These results may promote the proposal of thermodynamic degradation studies of feedstocks as an alternative or complementary technique to determine optimal solid loading contents in powder injection moulding (PIM). The studies in this paper also examined PIM process operation temperatures for zircon feedstocks.

Injection Moulding of Tungsten Carbide-Nickel Powders Prepared by Electroless Deposition

Tungsten carbide with nickel (WC-Ni) is generally used in applications in which high wear and corrosion resistance are required. In most cases, WC is mixed with Ni powder through a powder-processing route. In the present study, an electroless deposition technique was employed in order to prepare Ni coated WC particles prior to forming specimens by powder injection moulding method. The starting WC powders were subjected to surface activation followed by electroless Ni coating. The effects of a variety of processing parameters, including coating time and powder to electrolyte content ratio, were examined. The characteristics of the prepared powders were assessed by scanning electron microscopy and laser particle size analysis. It has been found that the fabrication of WC powder coated with Ni can be achieved through the electroless deposition technique. The amount of Ni introduced to the WC particles can be controlled by the powder to electrolyte content ratio and the deposition duration. The use of small particle loadings can ensure relatively large deposition and uniformity of the coatings. It is widely known that powder injection moulding (PIM) is an effective process for fabrication of small and complex shaped components of high performance materials. The PIM process includes 4 main steps: feedstock preparation, injection moulding, debinding and sintering. In this work, the WC-Ni powders were mixed with polyethylene glycol (PEG) and polymethyl methacrylate (PMMA) binder to form feedstock for injection moulding. The injection moulding process was carried out by a laboratory scaled, plunger-type machine. The mouldings were subjected to debinding and sintering. It was found that the PEG could be removed by water leaching. Specimens retained their shapes during and after leaching of the PEG. The remaining binder could be removed through pyrolysis. The mouldings were sintered under vacuum at 1400 °C for 1 hour. The sintered density achieved was at 88% of the theoretical value due to the low powder loading employed in the study.

Optimization of the Powder Injection Molding Process Parameters Using the Sequential Simplex Algorithm and Sensitivity Analysis

In this work, the minimization of warpage was investigated using the “moldflow” software and sequential simplex algorithm based on feedstock properties. Also, the sensitivity analysis was implemented to determine the degree of impact of each parameter on the warpage. This study is divided into two portions: experimental analysis and numerical analysis. First, for the experimental study, four kinds of feedstock with different alumina powder loadings were prepared to investigate the rheological properties. This investigation showed that the feedstock with 60 vol. % alumina powder was the optimum feedstock for the injection molding. Also, the results indicated that the viscosity of feedstock decreases by increasing both the shear rate and temperature. Next, the thermal conductivity of this feedstock was measured at different temperatures and it was found that the change of temperature can greatly influence the thermal conductivity of feedstock. In the numerical study, the injection molding parameters were divided into three categories. Based on the feedstock properties obtained form the first portion, and in order to minimize the warpage, the values of these parameters were sequentially acquired by moldflow and used in the sequential simplex algorithm for gradual convergence to the optimum level. To show the accuracy of numerical results, several samples were injection molded using the injection molding conditions for each vertex; results showed a close correlation between the values obtained by the numerical simulation and by the actual case. After determining the optimum parameter values, the sensitivity analysis was performed to identify the level of influence of each parameter on warpage. The obtained results showed that the most effective parameters on warpage are the mold temperature, packing pressure, and the holding time. Generally, it is demonstrated that the experimental and numerical analysis, performed via the moldflow software and sequential simplex algorithm, together with the sensitivity analysis can be useful in achieving success in the powder injection molding (PIM) technique.

Powder injection moulding: processing of small parts of complex shape

Powder Injection Moulding (PIM), Metal Injection Moulding (MIM) when is limited to metals, is a fabrication route of parts with the final shape desired. This process combines the high capability of polymer injection moulding to produce complex shapes with the advantages of a powder route to process metallic, ceramic or composites materials. The process has some limitations that comes from different technological steps involved in the production of the part (feedstock production, injection, debinding and sintering). All of these different steps can be industrially controlled, being the PIM process a real alternative to produce complex parts in a high rate production method that can compete with many other processing methods to produce materials. In this work, we will go through the different steps of this manufacturing process, making special emphasis on the solutions provided by the powder technology group of the University Carlos III of Madrid (UC3M).

Investigations on thermal debinding process for fine 316L stainless steel feedstocks and identification of kinetic parameters from coupling experiments and finite element simulations

Abstract Thermal debinding is one of the most important steps in powder injection moulding process. Thermogravimetric analysis (TGA) was employed to analyze thermal debinding behaviour under argon atmosphere. Thermal debinding kinetics with different heating rates have been compared using 316L stainless steel feedstocks loaded typically at 60, 62, 64 and 66 vol.% for fine metallic powders D50 = 3.4 μm. The Kissinger and Ozawa methods have been used to estimate the kinetic parameters from thermogravimetric experiments. To set up the numerical simulations of thermal debinding stage using finite element methods, a coupled mathematical model for mass diffusion and heat transfer in deformable porous media have been developed. The basic steps of the proposed model consist of solving the following coupled problems: thermal degradation of binder coupled with heat transfer and deformation phenomena by finite element methods using Comsol Multiphysics® software. The obtained numerical simulation results are in proper agreement with experimental data. The proposed numerical simulations allow the determination of remaining binder distribution, temperature distribution and deformation fields in the component during the whole thermal debinding process at any time.

Prediction of Powder Injection Molding Process Parameters Using Artificial Neural Networks

The parameters of Powder Injection Molding (PIM) process were modeled by artificial neural networks (ANNs). The feed-forward multilayer perceptron was utilized and trained by back-propagation algorithm. Particle size, particle morphology, debinding time, and sintering temperature were taken into account and regarded as inputs of the ANN model. The outputs included relative density, wax loss, shrinkage, and hardness. The results obtained using the ANN model were in good agreement with the experimental data. In fact, they displayed an average R-value of 0.95 versus the experimental values. The optimum architecture of ANN was 7-4-1, in which the network was trained with Levenberg–Marquardt training algorithm. Thus, the ANN model can be used to evaluate, calculate, and forecast PIM process parameters.

Advantages and Limitations of Using Nano Sized Powders for Powder Injection Molding Process: A Review

Powder injection molding (PIM) is among the most known forming techniques that use material powders. This technique has been widely evaluated for the production of large scale and small components using metal and ceramic powders. Nano particles have larger surface-to-volume ratio compared with large-sized particles, thus they display high surface area. Some merits in the application of nano-sized particles in the PIM process includes increasing its comparative density at a low sintering temperature, decreasing sintering temperature, decreasing grain size of sintered bodies, increasing hardness value, and improving surface properties. However, it also has several disadvantages, which include increasing the viscosity behaviour of feedstock, oxidation, and agglomeration. This article reviews current studies on the effects of nano-sized particles on the PIM process and finding solutions to address its disadvantages.

Effect of nano-sized powders on powder injection molding: a review

This review presents a thorough survey of academic work on the analysis and application of the usage of nano-sized powders in powder injection molding (PIM). The PIM process has become well-established in the fabrication of micro parts or microstructured parts in recent years. Given their unique inherent properties, nano-sized powders are widely used over micro-sized powders in all high-volume PIM methods of fabricating metal and ceramic components. Current critical issues are discussed, such as the effect of nano-sized powders on the mixing, injection, debinding, and sintering processes, as well as the effects on the feedstock and final properties of the components. Based on this survey, the current study proposes improvement on the limitations caused by applying nano-sized powders in the PIM process by utilizing new binder systems, milling, new deagglomeration methods, and new sintering procedures. Fields and topics that require further research are identified, and prospects for future industrial implementation of the process are given. This study is the first to aims at providing insights into the effects of using nano-sized powders in the PIM process. Moreover, this paper shows the great potential for further investigations and innovation in the field of powder injection molding using nano-sized powders.

Defect Analysis of 316LSS during the Powder Injection Moulding Process

Austenitic Stainless Steel Has a FCC Structure at Room Temperature and the Temperature Range of the Austenite Phase Depends upon its Composition. 316L SS Is Widely Used in Medical, Marine, Industrial, Sporting and Aerospace Applications due to its Excellent Combination of Mechanical Properties and Corrosion Resistance. this Study Presents the Defects Observed during Optimization of the Processing Parameters for the Fabrication of Powder Injection Molding (PIM) of 316L SS Parts. in this Study, Five Formulations of Feedstock Containing 60-71vol% of Metal Powder Were Prepared Using a Wax-Based Binder. Green Samples Were Injection-Moulded, Followed by Binder Removal by Solvent and Thermal Means. Paraffin Wax (major Binder) Was Extracted at Various Temperatures in Order to Determine the Solvent Extraction Temperature. the Thermal De-Binding Was Performed Successfully at a Temperature of 450°C by Varying the Heating Rate from 1°C/min -10°C/min. SEM Results Showed Complete Removal of the Plastic Binder. Test Samples Were Sintered at Various Temperatures and Atmospheres. the Defects Observed during Solvent Extraction Were Swelling, Cracks and, at the Thermal De-Binding Step, Collection of Binder, Swelling and Holes. Sintered Samples Showed a Loss of Dimensional Control. these Types of Defect Were Considered to Be due to Inappropriate Heating Rates, Temperature and Dwell Time at each Process Step.

Properties of Porous Alumina Fabricated by Ceramic Injection Moulding Using Environmentally Friendly Binder

Porous alumina (Al2O3) ceramics were fabricated by powder injection moulding process. The feedstocks, composed of 44 50 vol% of Al2O3 powder, could be prepared using a composite binder, consisting of polyethylene glycol (PEG) and polyvinyl butyral (PVB). Debindings were carried out using a combination of water leaching of the PEG and thermal debinding of the PVB. It was observed that the removal of the PEG was fast at the initial stage and more than 90 wt% of the PEG could be removed within 4 hours. Sintering was performed in argon atmosphere at 1600 °C. The sintered specimens had apparent porosity in range of 26-32 %, depending on the feedstock compositions. The flexural strength values were in range of 90-140 MPa while the hardness values were in range of 5-9 GPa. It was found that both the strength and hardness of the specimens were increased with increasing powder loading.

Holding Pressure and Its Influence on Quality in PIM Technology

The PIM (powder injection molding) process consists of several steps in which faults can occur. The quality of the part that is produced usually cannot be seen until the end of the process. It is therefore necessary to find a way to discover the fault earlier in the process. The cause of defects is very often “phase separation” (inhomogeneity in powder distribution), which can also be influenced by the holding pressure. This paper evaluates the powder distribution with a new method based on density measurement. Measurements were made using various holding pressure values.

Fretting behaviour of 316L stainless steel produced by powder injection moulding

The biocompatible metals made available for powder injection moulding (PIM) are increasing, and as a result, the PIM process is becoming attractive for manufacturers of medical implants and surgical instruments. In addition, friction and wear properties play an important role in biomaterial applications. This study aimed to systematically investigate the fretting wear properties of 316L stainless steel parts produced by PIM under dry contact conditions. The fretting experiments were performed under gross-slip regime. The influence of a number of fretting test parameters on the friction and wear behaviour was investigated, as the contact frequency, the normal load, and number of reciprocating sliding cycles. Fretting tests were performed against corundum counter bodies. After the tests, the wear scars were examined by laser surface profilometry, scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis. The results indicate that wear occurred predominantly by abrasion, plastic deformation, and cracking. K e y w o r d s : fretting, stainless steel, powder injection moulding, biomaterials

Influence of microstructure and processing on mechanical properties of advanced Nb-silicide alloys

ABSTRACTIn this study different powder metallurgical processing routes, commonly used for refractory metal based materials, were evaluated on their impact on mechanical properties of a multi-component Nb-20Si-23Ti-6Al-3Cr-4Hf (at.%) alloy. Powder was produced by gas-atomization or high energy mechanical alloying of elemental powders and then consolidated either by HIPing or powder injection molding (PIM). The PIM process requires fine particles. In this investigation powder batches of gas-atomized powder (< 25 μm) and mechanically alloyed powder (< 25 μm) were compacted via PIM. Fine (< 25 μm) and coarser (106-225 μm) particle fractions of gas-atomized powder were compacted via HIPing for comparison. Quantitative analysis of the resulting microstructures regarding porosity, phase formation, phase distribution, and grain size was carried out in order to correlate them with the ensuing mechanical properties such as compressive strength at various temperatures.

금속분말사출성형법으로 제조된 WC-10Co계 초경합금 소결체의 탄소첨가량에 따른 특성변화

In order to investigate the microstructure and mechanical properties of WC-10 wt% Co insert tool alloy fabricated by PIM (Powder Injection Molding) process, the feedstock of WC-10 wt% and wax used as a kind of binder were mixed together by two blade mixer. After injection molding, the debinding process was carried out by two-steps. First, solvent extraction, in which the binder was eliminated by putting the specimen into normal hexane for 24 hrs at , and subsequently thermal debinding which was conducted at and for 6 hrs in the mixed gas of , respectively. Meantime, in order to compensate the decarburization due to hydrogen, 1.2~1.8% of carbon was added to ensure the integrity of the phase. Finally, the specimens were sintered in vacuum under different temperatures, and the relative density of 99.8% and hardness of 2100 Hv can be achieved when sintered at , even the TRS is lower than the conventional sintering process.

New methacrylate-based feedstock systems for micro powder injection moulding

New methacrylate-based feedstocks have been developed according to fulfil the requirements of the micro powder injection moulding process chain, consisting of compounding, moulding and thermal post-processing for the realization of dense and warpage-free ceramic or metal parts. The different feedstock systems, consisting of polymethylmethacrylate (PMMA) as major binder component and microsized zirconia or stainless steel filler, were prepared by reactive compounding. The individual components—PMMA, solved in its monomer methylmethacrylate (MMA), additives and fillers—were mixed in a dissolver stirrer under ambient conditions and subsequently polymerized to a thermoplastic feedstock. Prior to injection moulding the mixtures’ flow properties were characterized by high pressure capillary rheometry as function of the composition, solid load and shear rate. After replication the obtained test specimen were debinded and sintered using optimized temperature programs. The achieved specimen densities reach 99% of the theoretical possible value for zirconia and 98.7% in case of stainless steel 17-4PH.

Powder Injection Molding – An innovative manufacturing method for He-cooled DEMO divertor components

At Karlsruhe Institute of Technology (KIT), a He-cooled divertor design for future fusion power plants has been developed. This concept is based on the use of modular cooling fingers made from tungsten and tungsten alloy, which are presently considered the most promising divertor materials to withstand the specific heat load of 10 MW/m 2. Since a large number of the finger modules ( n > 250,000) are needed for the whole reactor, developing a mass-oriented manufacturing method is indispensable. In this regard, an innovative manufacturing technology, Powder Injection Molding (PIM), has been adapted to W processing at KIT since a couple of years. This production method is deemed promising in view of large-scale production of tungsten parts with high near-net-shape precision, hence, offering an advantage of cost-saving process compared to conventional machining. The complete technological PIM process for tungsten materials and its application on manufacturing of real divertor components, including the design of a new PIM tool is outlined and, results of the examination of the finished product after heat-treatment are discussed. A binary tungsten powder feedstock with a solid load of 50 vol.% was developed and successfully tested in molding experiments. After design, simulation and manufacturing of a new PIM tool, real divertor parts are produced. After heat-treatment (pre-sintering and HIP) the successful finished samples showed a sintered density of approximately 99%, a hardness of 457 HV0.1, a grain size of approximately 5 μm and a microstructure without cracks and porosity.