Ceramic Injection Moulding Research Articles

Improving the homogeneity and reliability of ceramic parts with complex shapes by pressure-assisted gel-casting

Forming process plays an important role in the homogeneity and reliability of advanced ceramic products. Inspired by the surprising observation of pressure-induced solidification in colloidal forming processes, the authors have developed a new ceramics forming process, colloidal injection moulding, with the potential of forming large ceramic parts of complex shapes such as engine turbines and biomedical implants. This process combines the advantages of the conventional injection moulding and gel-casting processes of ceramics. Not only the efficiency but also the homogeneity of the green body is greatly improved owing to the pressure-induced solidification. It is also found that the inner stress generated by non-uniform solidification due to temperature gradient is responsible for the origination of microstructural defects in green body during colloidal-forming processes. A new strategy is taken to reduce the inner stress by adjusting the stiffness of the green body using a moderator additive. Ceramic products with complex shape such as engine turbines have successfully been fabricated with reduced defects.

Polymer coating on the surface of zirconia nanoparticles by inductively coupled plasma polymerization

Polymer coating on the surface of inorganic ceramic nanoparticles is beneficial to decrease agglomeration and improve dispersion in organic solvent in ceramic injection moulding technology. A layer of thin polymer film on zirconia nanoparticles is deposited by inductively coupled ethylene/nitrogen plasma. Transmission electron microscopy photographs indicate the presence of uniform polymer coatings and the thickness of the polymer layer is estimated as several nanometers. The chemical structure of the film is revealed as quasi-polyethylene long hydrocarbon chain by x-ray photoelectron spectroscopy examination.

Ceramic injection moulding: influence of specimen dimensions and temperature on solvent debinding kinetics

Ceramic injection moulding (CIM) has been the process selected for the production of complex ceramic components in recent years. In this process, binder removal is one of the most critical steps due to the possible appearance of defects. In this study, the influence of specimen geometry and temperature on the solvent debinding step of an as-moulded specimen was investigated. Green specimens with different bulk surface area to volume ratios ( A s/ V) were maintained in hexane at 20, 40 and 60 °C, and the weight losses were evaluated as a function of time. The kinetic study showed an increase in weight loss rate with increasing A s/ V ratio and solvent temperature. A mathematical model was proposed to predict debinding kinetics of specimens with known A s/ V ratios at different temperatures. Specimens were also submitted to porosity analysis and electronic microscopy to evaluate their characteristics during and after solvent debinding.

Shrinkage properties of ceramic injection moulding part with a step-contracted cross-section in the filling direction

The need for ceramic materials in microelectromechanical systems (MEMS) is increasing quickly. A typical form of designed ceramic micro parts involves the structuring of several micro columns and/or thin walls on a substrate. This work considers the use of a model mould with a straight mould cavity and a step-contracted cross-section in the filling direction. The injection moulding of such of ceramic micro part is experimentally simulated. The effect of the mould cavity contraction ratio, moulding conditions, and the solid loading of the ceramic/binder mixture on the distribution of the transverse shrinkage of the moulding parts at moulded, debinded, and sintered stages, respectively, are examined. Experimental results reveal that transverse shrinkage of the region downstream from the step-contracted cross-section clearly exceeds that of the region upstream in all three stages. Furthermore, transverse shrinkage varies greatly in the plane of the step-contracted cross-section. The magnitude of the variation in transverse shrinkage in the step-contracted cross-section increases with the contraction ratio of the mould cavity. Appropriately increasing either the holding pressure or the filling pressure of the mould cavity reduces the variation in the transverse shrinkage of the step-contracted cross-section. Moreover, using the ceramic/binder mixture with a composition similar to that of critical solid loading can lower the internal stress caused by sintering in the vicinity of the step-contracted cross-section.

Solvent debinding mechanism for alumina injection molded compacts with water-soluble binders

The solvent debinding process has been widely accepted in the ceramic injection molding (CIM) industry process due to its short debinding cycle. However, the organic solvents most adopted in solvent debinding now are flammable, carcinogenic and not environmentally acceptable. For eliminating the use of unsound solvents, water-soluble polyethylene glycol (PEG) is used in this study to modify the pattern of debinding in CIM. The purpose of the investigation was to examine the binder behavior during solvent debinding based on water extraction for a multi-component PEG binder system. Based on the in situ evaluation results of dimensional variations, mercury intrusion data and scanning electron microscope (SEM) observations, possible solvent debinding mechanism for alumina injection molded compacts with water-soluble binders is proposed.

Reaction and transport kinetics for depolymerization within a porous body

AbstractPolyoxymethylene is used as the organic vehicle for ceramic and metal powder injection moulding. It is ideal for studies of shrinking‐core reaction kinetics in porous systems because it decomposes exclusively to monomer in the solid state in the presence of nitric acid vapor. The solid–gas reaction interface can be defined to within 3 μm by electron microscopy and about 50 μm optically. Reaction rates were measured in crowded powder assemblies containing 56 vol % alumina powder by observation of the boundary; a method that avoids the ambiguities of gravimetry. The reaction‐rate constant and the effective diffusion coefficient of gas in the porous reacted layer were calculated from the shrinking core kinetics. The diffusion coefficient was in good agreement with theoretical estimates involving counterdiffusion. The time for complete depolymerization of a moulding was estimated for different powder characteristics, geometries, and volume fractions.

Colloidal Injection Moulding of Ceramics

Colloidal Injection Moulding of Ceramics

A PRIME approach for the moulding of conduit ceramic parts

The processing of advanced materials such as refractory ceramics and metallic alloy powders has been investigated intensely over the past two decades. Ceramic injection moulding has therefore become a prime method for manufacturing complicated parts from a robust material. Typically, powder is dispersed within a thermoplastic carrier (or binder) before it is moulded at high temperatures and pressures. Further removal of the binder by thermal or solvent degradation methods yields a component that is suitable for sintering. Within industry, components have been manufactured with densities greater than 95% of theoretical. However, this processing route has its drawbacks. De-binding can take days due to slow heating rates and changes in viscosity of the polymeric carrier that can delay production and increase costs. A solution has been found by using a reactive binder that can polymerise within seconds and degrade back to a monomer within a fraction of conventional de-binding times. This technology, known as powder reaction injection moulding engineering (PRIME), has been developed using a cyanoacrylate binder that is commonly used as an adhesive, thus introducing difficulties when moulding. This paper describes the processing limitations of this binder and the method for moulding a conduit ceramic part.

Thermal removal of multicomponent binder from ceramic injection mouldings

Thermal removal of polymer binder containing low-molecular-weight components from ceramic injection mouldings was studied. The effect of the shape and size of bodies on the process of binder removal was examined. Evaporation of low-molecular-weight components represented the most important process at the beginning of binder removal. It was found that a bed of activated carbon speed up removal of low-molecular-weight components. The mechanism of binder removal in a bed of activated carbon was described. Binder redistribution and evolution of porosity in the body during binder removal was investigated. A high rate of binder removal resulted in non-uniform binder distribution in the body. The formation of defects due to non-uniform binder removal was described and requirements for their elimination were proposed.

Solidification of large section ceramic injection mouldings under low hold pressures

Many of the problems of making large ceramic injection mouldings have been identified with solidification in the cavity, particularly with the level of hold pressure applied during cooling. In this work, a wide range of hold pressures (0.1–120 MPa) was used to compensate for thermal contraction of large mouldings. A new pneumatic technique for applying pressure was designed. An insulated sprue was used to prolong solidification of the gate. These techniques provide a combination of high injection pressure during mould filling (95 MPa) with hold pressure control in a range from 0.1–1 MPa during solidification. Large (25 × 45 × 60 mm) mouldings made at these low hold pressures did not have shrinkage-related cracking and the organic vehicle could be safely removed.

Injection moulding and sintering of ceria ceramics

Ceria powder was dry-milled to sub-micrometric particle sizes and used in the preparation of ceramic mixture for injection moulding. Specimen bodies were injection moulded in the shape of rectangular bars. The sintering kinetics of these bodies was studied in air atmosphere under various sintering conditions and also by the rate-controlled sintering method. Sintering the injection moulded CeO 2 to a density of 7.08 g cm −3 (99.3% TD) was possible already at a temperature of 1400 °C, and the highest density value (99.8% TD) was obtained at a heating rate of 2 °C min −1 and a holding time of 1 h at 1500 °C. Using heating rates of over 5 °C min −1 had an adverse effect on the density obtained. Applying the rate-controlled sintering (RCS) method did not lead to any decrease in the grain size if compared with temperature-controlled sintering (TCS). No reduction of CeO 2 ceramics was observed during all sintering experiments.

Differential sintering in ceramic injection moulding: particle orientation effects

The sintering shrinkage in three orthogonal directions was measured in sections cut from large rectangular injection moulded ceramic blocks. Two powders were used: a comminuted alumina and a chemically-derived zirconia. Pronounced anisotropy of shrinkage was observed in the former whereas the equiaxed zirconia showed uniform shrinkage throughout the moulding. The pattern of shrinkage anisotropy was consistent with that observed by other investigators and indicates that slight particle anisotropy can introduce differential sintering. The sintering shrinkage in the alumina powder was found to be most pronounced perpendicular to the main flow direction.

Effect of Polymer Crystallinity on Morphology in Ceramic Injection Molding

Many ceramic injection molding vehicles include semicrystalline polymers which characteristically adopt a spherulitic growth morphology. Usually the spherulites are rendered invisible by the opacity of the ceramic powder but in this study they are clearly visible. Polyoxymethylene (POM), has been used as the vehicle. The growth of the spherulites is shown to be dependent on cooling rate and hence on position in the molding. Furthermore, migration of low molecular weight additives by syneresis is shown to occur and to influence the crack path in the as‐molded state. An unusual composite fractograph is shown in which fracture faces made after molding, after binder removal, and after sintering are contiguous. Only after molding does the crack path follow the spherulite boundaries; behavior that is also widely reported for unfilled POM.

Preparation of ceramic injection moulding feedstocks

Preparation of ceramic injection moulding feedstocks

Transient effects during catalytic binder removal in ceramic injection moulding

Abstract This work is part of a comprehensive study of the incidence and cause of defects in large section ceramic injection mouldings. In previous related work, the defects associated with mould-filling and with solidification and packing in the cavity were identified. Such defects sometimes manifest themselves only after binder removal or after sintering and so may be causally connected with those stages by mistake. In the present work, defects which do indeed arise from the binder removal stage itself as a result of minor process interruptions are isolated. These are identifiable by a pattern of defects which are distinct from those due to solidification and are independent of solidification conditions. This work reports on the systematic study of perturbations to conditions in the binder removal oven in order to track the origin of these defects and hence distinguish them from shrinkage-related defects.

Packing and solidification in ceramic injection moulding

The occupation of volume in large ceramic injection mouldings solidified under different pressures using two moulding techniques is considered. Large (60 × 45 × 25 mm) alumina injection mouldings were prepared in cavities fitted with conventional (metallic) and insulated [poly(ether ether ketone)] sprues. These provide quite distinct solidification histories which, in turn, influence the physical properties of the moulding and the extent and type of defects it contains. In the former case, the gate solidified after 26 s whereas, in the latter, the hold pressure could be applied for over 240 s. In insulated sprue moulding, the advance of the solid liquid boundary during packing and solidification was traced by fractography. Pressure was varied from 5 to 120 MPa. The interdependencies of moulding mass, apparent density, local density, polymer crystallinity, and microstructure were accounted for as a function of pressure and pressure transmission method. Changes in polymer crystallinity due to different cooling rates at different positions in the mouldings were insufficient to account for observed density differences. Systematic changes in the mass as a function of hold pressure were related to macroporosity in conventional mouldings and to microporosity in insulated sprue mouldings.

Decomposition of binder from a ceramic injection molding sample

Ceramic injection molding (CIM) has been recognized as attractive technique for the fabrication of ceramic parts. Binder systems comprise between approximately 5 and 40 vol.% of a given ceramic green body depending on the chosen forming method. In this work, the thermal decomposition behaviors of four binder systems used in CIM were investigated by thermal analysis. The decomposition kinetic parameters were also evaluated using non-isothermal DSC/TG techniques.

Process improvement in preparation of ball valves

The industrial application of ceramic injection moulding has been limited to small components because of the associated binder burnout problems. Injection moulding may improve the manufacture of alumina ball valves for the process industries by reducing costly and potentially damaging machining operations. However, these components are too large to be produced using conventional thermoplastic binders. Aqueous injection moulding allows most of the binder system to be driven off as water vapour, cutting process time, reducing burnout difficulties, and causing less environmental pollution. The manufacture of ball valve blanks from -alumina was carried out using a die cavity of 25·4 mm outside dia. Improved processing parameters were efficiently identified using orthogonal arrays as described by Taguchi. The following factors were evaluated for their influence on defects: binder content in solution, die temperature, injection velocity, injection time, barrel temperature, injection pressure, hold pressure, and residence time in the mould. Binder content in solution was found to be the most influential factor. The defects observed included cracking, poor make up, and distortion. Ball valve blanks of significantly improved quality were successfully manufactured under the preferred conditions.

New Perspectives for Ceramic Injection Molding with Gas Injection

New Perspectives for Ceramic Injection Molding with Gas Injection

New Perspectives for Ceramic Injection Molding with Gas Injection

New Perspectives for Ceramic Injection Molding with Gas Injection