Ceramic Injection Research Articles

Analysis of Shrinkage & Warpage in Ceramic Injection Molding of HPT Vane Leading Edge Core of a Gas Turbine Casting

Gas Turbines in Aerospace applications operate at extreme conditions of temperatures and stresses. The Blade/Vane components of these turbines have sculpted, twisted and hollow aerofoil geometry made using Nickel based super alloys through the investment casting process. Hollow wax patterns produced with use of ceramic cores are the first input to the investment casting process. The quantification and prediction of dimensional deviations due to shrinkage & warpage, which are dependent on injection parameters, shape of part and gating system adopted, is mandatory to arrive at acceptable tooling and castings. The insight of flow pattern in the die cavity imparts knowledge of possible weld lines, air-trap, jetting etc. The gating system may be designed, based on simulation results, to minimise such defect. The effects of injection molding parameters such as holding time, packing pressure and melt temperature on shrinkage and warpage of green part using moldex3D software are studied in this paper

Powder modification mechanism, effects of binder compositions on the thermal behavior, and the mechanical properties of the ceramic injection molded system

In this study, a systematic research has been conducted into the powder modification mechanism, the effects of binder compositions on the thermal behavior, and the mechanical properties of the ceramic injection molded system. SA is adopted to modify the as-received ceramic powder for the ceramic injection molding system. The TGA results demonstrate that the mass loss in SA occurs at 200–300°C while the loss in SA-modified zirconia is mainly located at 300–400°C, which is believed that SA reacts with zirconia through an esterification reaction, causing the exothermic peak to shift to a higher temperature. TGA analysis at different locations on the green bodies can effectively evaluate the CIM binder segregation and it is observed that, for feedstock B30, there are four data points in the defined sensitivity range, which could be proved to be the most homogeneous. And it has the best mechanical performance, with three-point flexural strength of 825.7MPa and the relative density of 98.8%. Feedstock B60 has the maximum pores and the minimum mechanical strength, with the relative density of 95.1% and the three-point flexural strength of 541.4MPa. The Weibull modulus for Feedstock B30 is greater than 10, signifying the most concentrated strength distribution, which further verifies that feedstock B30 is the most homogeneous formula.

Effects of the binder compositions on the homogeneity of ceramic injection molded compacts

In this study, the effects of different binder compositions on the homogeneity of injection molded ceramic compacts are discussed from the standpoint of the rheological properties of the feedstocks, density, density deviation, and flexural strength of the as-prepared compacts, and the microstructures of the as-prepared compacts, compacts after solvent debinding, and compacts after thermal debinding. Also the pore size distribution of the compact after thermal debinding was characterized to examine the distribution of the binders in the as-prepare compacts. The feedstock with 30% macromolecular binders attains the minimum power-law index n value at 160°C, hence it is the most appropriate feedstock for injection molding. The optimal composition is feedstock B30, which is the most homogeneous at an injection temperature of 160°C. The macromolecular binder-to-PW weight ratio of 3:7 allows best mixing of feedstock and more homogeneous binder distribution. B30 has the highest density, the lowest density deviation and the lowest deviations in flexural strength of the as-prepared compact. Compacts prepared with B30 have the most homogenous pore size distribution after thermal debinding, as determined from the sharp, narrow peaks on the pore size distribution curves.

Effects of PVP incorporation on the properties of injection-molded high-performance ceramics with PEG-based binders

PEG/PMMA binder systems are among the most widely used water-soluble binders for ceramic injection molding. Binder-induced binder segregation in PEG/PMMA systems is mainly caused by the difference between crystallization temperature of PEG (below 50°C) and glass transition temperature of PMMA (~120°C). In this study, we have adopted the method of introduction of appropriate amount of PVP to reduce the binder-induced defects. A principle model was thus established for the suppression of PEG crystallization by PVP molecules. It was revealed that the mechanism by which PVP suppresses PEG crystallization is hydrogen-bonded formation between the carbonyl group of PVP and the hydroxyl groups of PEG molecules. This compresses the crystallization space of PEG molecules, and suppresses their crystallization. It was determined that the range of PVP content that can be safely removed via water debinding is 0–30wt/wt% PEGS. The incorporation of PVP could effectively enhance the homogeneity of the compact, reduce the size of pores formed after thermal debinding in the compact, promote densification, reduce defects after sintering and enhance the mechanical performance of the sintered bodies. Furthermore, the performance of the molded product was optimal when 20wt/wt% PEGS of PVP was added to the binder; the flexural strength and density of the resulting sintered body were 811MPa and 98.7%, respectively.

Characterisation of NiO-YSZ Porous Anode-Support for Solid Oxide Fuel Cells Fabricated by Ceramic Injection Moulding

Ceramic injection moulding (CIM) has advantages for a cost effective fabrication of large-scale, near-net-shape products. In this work, CIM is carried out to prepare porous anode-support for solid oxide fuel cells (SOFC) applications. The CIM process started with a preparation of feedstocks by mixing powder with binder. The feedstock is then injected into the mould of desired shapes. The mouldings were subsequently undergo the removal of the binder (debinding) and, finally, sintering. It is shown that porous nickel oxide-yttria stabilized zirconia (NiO-YSZ) anode-support for SOFC were successfully prepared by CIM technique. In addition, a water-soluble based binder system, consisted mainly of polyethylene glycol (PEG), has been used in this work. This is to avoid the use of organic solvents when wax-based binder was used. Therefore, it can promote more environmentally friendly process. The removal of binder was carried out using water debinding technique. The porous anode for SOFC was subjected to systematic characterisation. The effect of processing parameters, such as powder characteristics and powder/binder ratio has been investigated. Rate of binder removal was also studied. The porous anode specimens were characterised for their properties and microstructure. It was also found that the porosity of the specimens can be controlled by adjusting the sintering temperatures and holding times.

Development of a ceramic injection molding process for liquid jet nozzles to be applied for X-ray free-electron lasers

Serial crystallography experiments at X-ray free-electron lasers can utilize specially designed ceramic nozzles to generate a strongly focused liquid jet of sample. Several nozzle design options have been evaluated and a concept using a sharpened glass capillary mounted in a self-centering ceramic nozzles is detailed. Filling simulations and tool construction are given for micro ceramic injection molding manufacture of the nozzles. Produced parts are found to meet the specifications for nozzle dimensions and bearing features. Functionality tests show superior performance with respect to liquid jet straightness and reproducibility compared to flame polished glass nozzles.

Process Development for the Ceramic Injection Molding of Oxide Chopped Fiber Reinforced Aluminum Oxide

In this study, it was tried to develop a process chain for ceramic injection molding of Al2O3-chopped-fiber reinforced oxide-ceramic-matrix-composite. The feedstocks are compounded at 50 Vol. % filling degree of solid (Al2O3 μ-powder (Taimei Chemicals Co. Ltd.) and 3,2 mm chopped fibers (3M)), in which fiber content varies from 0 Vol. % to 100 Vol. %. As binder system, PE + Paraffin Wax + Stearic Acid are used. The ingredients are compounded in a kneader (Brabender) at 125°C and after the viscosity measurement in the high pressure capillary rheometer at 160°C and certain shear rates, the feedstock is injection molded (Battenfeld) at 160°C, which is followed by debinding process, including chemical (in n-Hexane) and thermal steps, and 2h sintering at different temperatures. Flow paths in the machinery parts, rheological properties of binding system, fiber content and the fiber orientation have significant effect on the flow behavior of the feedstock, fiber -orientation, -distribution & -length, which are crucial to understand the properties of end-parts like mechanical reinforcement of the fibers. The fibers in the sintered parts are ca. 200 μm in average length. The fibers in the feedstock show different orientations depending on the part-geometry and the green bodies have different densities depending on sintering temperature, amount of dispersant and fiber orientation.

Effect of backbone binders on rheological performance of ceramic injection molding feedstocks

In a novel binder system, carnauba wax (CW), and acrawax (AW) (N,N′‐Ethylene Bis‐stearamide) were considered to replace the synthetic backbone polymers (polyolefins) in aluminum oxide (Al2O3) Ceramic Injection Molding feedstocks. For both proposed substitutes there is a significant reduction in viscosity in comparison to polyolefin based binder and also commercially available one, and in case of CW based feedstock also in processing temperature, which is essential for injection molding of reactive powders. For all ceramic feedstocks studied, there is a nonmonotonous dependence of viscosity on shear rate/stress, whose fitting requires eight‐parameter model. At the processing‐relevant shear conditions, polyolefin based feedstocks show dilatant cause, whereas both CW and AW compounds have a pseudoplastic manner. Thermal characterization was used to evaluate i(miscibility) of the neat binder components, their mixtures and mixtures with Al2O3. The presence of powder lowered melting temperatures of all tested binders except of polyolefin. Further depression in melting point of poly(ethylene glycol) is observed in combination with polyolefin in the presence of powder, and it is related to changes in size of the crystalline domains. POLYM. ENG. SCI., 57:739–745, 2017. © 2017 Society of Plastics Engineers

Use of Ceramic Injection Molding Technology to Increase Biogas Burners Efficiency

The article gives considerations to issues relating to organization of biogas combustion process. A new design of biogas burner is suggested. It differs from existing analogues by more complete combustion of air and gas mixture and high efficiency. Feasibility of greater burners' effectiveness due to the use of ceramic injection molding technology is demonstrated here.

Tribology study of hydroxyapatite (HAp) scaffold blended single based binder via rheology and mechanical properties

PurposeThis paper aims to investigate the vital characteristic of an innovative ceramic injection molding (CIM) process for orthopedic application with controlled porosity and improved tribological and mechanical properties which were affected by complex tribological interactions, whether lubricated like hip implants and other artificial prostheses. The main objective is to maximize the usage of palm stearin as a single based binder as the function of flow properties during injection molding process.Design/methodology/approachThe binder used in this present study consists of 100 per cent palm stearin manufactured by Kempas Oil Sdn Bhd and supplied by Vistec Technology Sdn Bhd. The feedstock was prepared by using a Z-blade mixer (Thermo Haake Rheomix OS) and Brabender mixer model R2400. The feedstock prepared was injection molded using a manually operated vertical benchtop machine with an average pressure of about 5-7 bars. The firing step included the temporary holds at intermediate temperatures to burn out organic binders. At this stage, the green molded specimen was de-bound using a single-step wick-debinding method.FindingsThe maximum content of ceramic material is applied to investigate the efficiencies of net formulation that can be achieved by ceramic materials. The longer the viscosity will change with shear rate, the higher the value of n obtained instead. From the slope of the curves obtained in Figure 3, the value of n for the feedstock was determined to be less than 1, which indicates a pseudoplastic behavior and suitability for the molding process. Moreover, high shear sensitivity is important in producing complex and intrinsic specimens which are leading products in the CIM industry.Originality/valueThe feedstock containing HAp powder and palm stearin binder was successfully prepared at very low temperature of 70°C, which promoting a required pseudo-plastic behavior during rheological test. The single binder palm stearin should be optimized in other research works carried out, as palm stearin is most preferred compared to other polymeric materials that provided high energy consumption when subjected to the sintering process. Besides the binder is widely available in Malaysia, low cost and harmless effect during debinding process.

Multiphysic coupling and full cycle simulation of microwave sintering applied to a ceramic compact obtained by ceramic injection moulding

ABSTRACTMicrowave sintering represents the coupling of multiple physical phenomena. It involves the distribution of electromagnetic fields, heat generation by electromagnetic effects, heat conduction in the material, and evolution of the densification in the sintered components. This paper describes the mathematical models and the numerical methods used to simulate the complex sintering process. Simulation results are provided for the prediction of shrinkage and evolution of the relative density of the sintered materials. A full cycle simulation of the microwave sintering process have been realized on the COMSOL Multiphysics finite element software platform. This work provides an important approach to studying the process of microwave sintering. The simulation results for sintering submicron zirconia powders are compared with experimental results in terms of the relative densities of the sintered material.

Rheological Behavior of Yttria Stabilized Zirconia (YSZ) Feedstock for Ceramic Injection Moulding (CIM) Process

The characterization of CIM feedstock consisting 58, 59, 60vol% of YSZ powder with binder system comprising a palm stearin (PS) and low density polyethylene (LDPE) were studied. The effects of powder loading and temperature (°C) on the rheological behavior of the YSZ were investigated by using Rosand RH2000 Capillary Rheometer. The results showed all the feedstock achieved desirable injection moulding characteristics such as pseudoplastic behavior, flow behavior index (n) less than 1 and low activation energy (E). The rectangular parts were successfully injected moulded at optimum temperature of 170°C with the highest green strength was 12.7 N, obtained from 60 vol% powder loading which correspond to greater density and low porosity of the samples.

Effects of different backbone binders on the characteristics of zirconia parts using wax-based binder system via ceramic injection molding

In this work, various backbone binders were used in wax-based binder system to formulate zirconia parts by ceramic injection molding (CIM). The effect of different backbone binders on the molding, debinding, and sintering behaviors was investigated. After blending process, the feedstock using multi-polymer components exhibited more homogeneous structure compared with that using the mono-polymer ones due to the synergistic effect of multi-polymers. During solvent debinding, some defects such as “slumping” and “peeling” appeared in the parts containing ethylene-vinyl acetate copolymer (EVA), but they were not found in the parts with other thermal polymers. Also, as for the parts after sintering, the one using low density polyethylene (LDPE) and high density polyethylene (HDPE) as backbone binders presented a more uniform microstructure with finer zirconia grains among all the investigated compositions, and thus obtained the highest flexural strength (~949 MPa) and relative density (~98.9%).

Influence of Carbon Content on Ceramic Injection Molding of Reaction‐Bonded Silicon Carbide

Reaction‐bonded silicon carbide (RBSC) was prepared by ceramic injection molding (CIM) technique with feedstocks containing silicon carbide (SiC), a wax‐based organic system and different amounts of carbon black. As a critical effect of the reaction sintering process, carbon was introduced from the carbon black and the decomposition product of the organic polymers, respectively. This study described the influence of carbon content on the mixing and injection process firstly and then emphasized the debinding process since it played a large role in the process of the pyrolysis of organic. Results indicated that the preferable thermal debinding was performed in N2 and the optimal performance was obtained for RBSC with 7 wt.% of carbon black, with the density of 2.98 g/cm3, apparent porosity of 0.24%, bending strength of 301.59 MPa and fracture toughness of 4.18 MPa·m1/2.

Novel fabrication of more homogeneous water-soluble binder system feedstock by surface modification of oleic acid

Compared to conventional debinding process of wax-based binders used in ceramic injection molding, polyethylene glycol-based binders (water-soluble binders) with its high efficiency and environmental acceptability have appeared as a good alternative. However, water-soluble binder feedstock still presents some problems such as powder–binder separation or particle segregation which limits injected parts’ final properties. In the present work, we have successfully prepared the more homogeneous water-soluble feedstock with lower shear viscosity by a prior ball milling treatment to induce a small quantity of oleic acid to the surface of zirconia powders before the mixing process. Also, the surface modification mechanism of oleic acid to zirconia powders has been systematically discussed. With the modified powder, as-leached part with less agglomeration and phase separation has been fabricated, which suggests a novel modification method for fabricating injection molded ceramic parts by using water-soluble binders.

Experimental Investigation of Comparative Process Capabilities of Metal and Ceramic Injection Molding for Precision Applications

The purpose of this paper is to make a comparative study on the process capabilities of the two branches of the powder injection molding (PIM) process—metal injection molding (MIM) and ceramic injection molding (CIM), for high-end precision applications. The state-of-the-art literature does not make a clear comparative picture of the process capabilities of MIM and CIM. The current paper systematically characterizes the MIM and CIM processes and presents the process capabilities in terms of part shrinkage, surface replication, tolerance capability, and morphological fidelity. The results and discussion presented in the paper will be useful for thorough understanding of the MIM and CIM processes and to select the right material and process for the right application or even to combine metal and ceramic materials by molding to produce metal–ceramic hybrid components.

RETRACTED ARTICLE: Optimisation of compositions of PEG/PMMA binder system in ceramic injection moulding via water debinding

In this study, we have made a comprehensive investigation on the optimisation of the compositions of polyethylene glycol (PEG)/polymethyl methacrylate (PMMA) binder system for water debinding. An orthogonal test was designed, and L9(33) table was chosen to investigate the influence of the molecular weight of low molecular PEG (L-PEG), high molecular PEG (H-PEG) and the percentage of L-PEG in PEGs on flaws of the injection moulded compacts after water debinding. In addition, the ratio of PMMA content to PEG content on flaws is also investigated. Four regions were defined as high stress region, safe debinding region, low binder removal rate region and unavailable injection region respectively. It is believed that our work could provide comprehensive and convincing principles for the manufacturing of injection moulded ceramic parts via water debinding.

The Effect of Fused Silica Crystallization on Flexural Strength and Shrinkage of Ceramic Cores for Investment Casting

Complex designed silica-based ceramic cores were fabricated by ceramic injection molding. Slow heating rate (0.2K/min) for debinding restrained bloating on the surface of ceramic cores. To investigate effect of sintering conditions on mechanical properties of ceramic cores, green bodies were sintered at temperatures in a range from 1150°C to 1400°C for various dwelling times (6h to 48 h). Sintering above 1300°C for 12 h and dwelling time over 24 h at 1200°C reduce the flexural strength and increase the linear shrinkage of ceramic cores. Cristobalite, formed by high sintering temperature or long dwelling time, induces reduction of mechanical properties due to its phase transformation, which is accompanied by volume contraction and microcracking. Ceramic core sintered at 1200°C for 12 h endured wax patterning and shell molding, and was manufactured successfully.

Investigation into Paraffin Wax and Ethylene Vinyl Acetate Blends for Use as a Carrier Vehicle in Ceramic Injection Molding

ABSTRACTAn experimental study into paraffin wax and ethylene vinyl acetate-28 blends has been undertaken to investigate the potential for their use as carrier vehicles for ceramic injection molding applications. Carrier systems are critical for the fabrication of this type of molded component, making their properties at all stages of the process of great importance. Paraffin wax and ethylene vinyl acetate-28, in most circumstances, combine to form stable homogeneous blends, which experience relatively small changes in the melting and solidification phase transition behavior. However, these blends exhibit notable viscosity shifts and flexural strength performance changes with increasing ethylene vinyl acetate-28 content. The melt flow behavior of the blends at shear rates of 100 s−1 varies from 0.01 Pa.s for paraffin wax to 10 Pa.s for the composition by weight of 50% paraffin wax and 50% ethylene vinyl acetate-28, which suggests the upper viscosity limit for successful carrier systems. All paraffin wax/ethylene vinyl acetate-28 blends experience shear thinning behavior with increasing shear rate, which can be modeled with reasonable accuracy using the Cross and Carreau models. Increasing the ethylene vinyl acetate-28 content in a blend causes the initiation of shear thinning at progressively lower shear rates and also forms a blend with an increasing elastic character at typical injection temperature. Yield stress is not developed for blends containing less than 50 wt% ethylene vinyl acetate-28. The addition of ethylene vinyl acetate-28 significantly alters the mechanical properties of the blends, modifying the brittle nature of paraffin wax to develop increasing flexible and plastic properties. Although with less than 25 wt% ethylene vinyl acetate-28 in a blend fracture failure still results, greater ethylene vinyl acetate-28 content represses the failure mechanisms, developing the increasing degrees of plastic deformation.

The Influence of Single Based Binder of Palm Stearin in HAP Feedstock on Rheological Properties Used for Ceramic Injection Moulding (CIM)

Development of binder system based on natural resources is one the main interest among researchers in ceramic injection moulding (CIM) with the main aim of processibility of complex biomedical implant. In this paper, the influence of single binder comprised of palm stearin mixed with HAP powder was investigated. The powder and binder mixture, generally known as feedstock was analyzed for its flowability in order to get some insight for injection moulding purposes. Two different mixing temperatures were investigated for preparing the feedstock; 160°C and 70°C. The feedstocks viscosity was then evaluated using a capillary rheometer at temperature range from 70°C to 90°C. The results clearly showed that the use of 100% palm stearin was promising in providing required pseudoplastic flow for injection molding. The injection molding process can be carried out at relatively low temperature in comparison with the conventional binder systems used.