Academic literature on the topic 'Ceramic powder injection moulding'

The literature concerning the injection moulding of engineering ceramics has been reviewed. This indicated that a number of claims had been made for the successful use of different organic binders during moulding and their removal prior to sintering. However, many of the claims were not supported by detailed/exact eScperimental evidence as to powder-binder compositions, moulding conditions, moulded properties, debinding times/cycles, or details of the structure and properties of the solid ceramic bodies produced. From the available information it was clear that there were few systematic and scientific investigations concerning the understanding of each stage of the injection moulding process. The present research programme has been carried out in two phases as follows. The first phase was concerned with the reinvestigation and re-evaluation of binder systems claimed to be successful for the injection moulding of alumina ceramics. The binders re-investigated included the thermoplastic-based binders such as polystyrene, polyacetal and atactic polypropylene and the water-based methylcellulose (Rivers) binder system. Alumina was chosen as the main powder to be investigated due to its simple handling and, highest applications amongst ceramic materials and on the basis that there is incomplete published work for almost every step of the injection moulding process. During the first stage of this work the optimum properties such as powder-binder compositions, mixing and moulding conditions, debinding properties, green and sintered densities provided by each binder system were determined. The results of these investigations showed that all the previous (re-evaluated) binder systems had major limitations and disadvantages. These included low volume loading (64 % maximum) of the alumina powder resulting in rather low sintered densities (96 % maximum-of theoretical density) and very long debinding times in the case of the thermoplastic-based binders. it ry low alumina volume loading (55 % maximum resulting in a 94 % . sintered theoretical density) and long moulding cycle time (- 5 min) along with adhesion and distortion problems during demoulding occurred in the case of the water-based methylcellulose binder system. Further work did not appear worthwhile. The newly developed binder systems have been used with a number of other powders such as zirconia, silicon nitride, silicon carbide, tungsten carbide-6 weight % cobalt and iron-2 weight % nickel, to establish- whether injection moulding is feasible. Optimum properties such as powder volume loadings, mixing, moulding, demoulding, moulded densities, debinding and some sintered density results showed that these new binder systems can also be used successfully for the injection moulding of other ceramic and metallic powders, although a fuller evaluation of the properties such as optimum sintered densities and mechanical properties is required.

no<br>Real-time diagnostics of ceramic powder injection molding using a commercial micromolding machine was performed using ultrasound. Miniature ultrasonic sensors were integrated onto the mold insert. Melt front, solidification, temperature variation and part detachment of the feedstock inside the mold cavity were observed. It has been demonstrated that ultrasonic velocity in feedstock inside the mold cavity, the ultrasonic contact duration during which the part and mold are in contact, and holding pressure can be used to assist with optimization of injection and cooling parameters to minimize energy consumption and maximize process efficiency.Real-time diagnostics of ceramic powder injection molding using a commercial micromolding machine was performed using ultrasound. Miniature ultrasonic sensors were integrated onto the mold insert. Melt front, solidification, temperature variation and part detachment of the feedstock inside the mold cavity were observed. It has been demonstrated that ultrasonic velocity in feedstock inside the mold cavity, the ultrasonic contact duration during which the part and mold are in contact, and holding pressure can be used to assist with optimization of injection and cooling parameters to minimize energy consumption and maximize process efficiency.

A novel powder processing technique has been developed by combining conventional powder injection moulding with polymer co-injection moulding, to permit the in-situ surface engineering of metal or ceramic components as an integral step within the processing cycle. The new technique has been used to produce surface engineered iron based components with either corrosion resistant or wear resistant surfaces, and to produce alumina based components with toughened surfaces. The most critical factor for the feasibility of surface engineered components is that the sintering profiles of the skin and core materials must be well matched or differential shrinkage or delamination will result. A particular requirement of surface engineering is the ability to control the surface engineered skin profile. Polymer injection moulding modelling software was applied to predict the surface engineered skin profiles of the surface engineered metal/ceramic components. Successful skin profile prediction is dependent on the characterisation of the feedstock materials being injection moulded. Several feedstocks have been characterised for their material properties and first pass models developed to predict the feedstock material properties as a function of their individual material properties and mass or volume ratios. It has been demonstrated that the design of the feedstock composition and injection moulding process conditions can be optimised by the use of computer-based injection moulding modelling software to achieve the desired surface engineered skin profile. A methodology has been developed that outlines all the stages necessary for successful powder co-injection moulding.

Ceramic injection moulding is already established as a production technique for complex shaped ceramic components. However the process is limited to thin section mouldings generally not exceeding a wall thickness of 10 mm. The global objective of this work is to describe and understand the aetiology of defects which preferentially appear in thick injection moulded ceramics, and to find ways to overcome these problems. The following stages are examined mould-filling, solidification, binder removal and sintering. Different moulding techniques; conventional moulding, modulated pressure moulding, insulated sprue moulding and low hold pressure moulding were applied. Moulding thicknessw as systematicallyv aried (15,20,25, and 35 mm).. Hold pressures and times were closely controlled and found to be decisive processing parameters for defect creation. The use of insulated sprue moulding prevented void formation in 25 nun thick mouldings and the application of low and constant hold pressures (>5 MPa) led to a reduction of residuals tressesin the mouldings. An intensive study was carried out on the binder removal stage in which the catalytic removal of the polyacetal binder enabled removal of the binder from sections of 35 nun thickness. The reaction and transport kinetics during binder removal were studied and close observations were made out on various defects which could appear during interrupted binder removal. Differential shrinkage of the ceramic components during sintering was studied and could be tracked back to flow-induced particle alignment during mould filling. The sintering behaviour of the alumina feedstock used in this study was compared with an equiaxed zirconia powder injection moulding suspension. The phenomenon of jetting in large section mouldings and the creation of spherulites during solidification of the polymer were found to influence moulding structure.

Die in der vorliegenden Arbeit untersuchten Metall-Keramik-Verbunde wurden mittels Pulverspritzgießen hergestellt. Unter Anwendung der teilautomatisierten Verfahrensoptionen Mehrkomponentenspritzgießen und Inmould-Labelling, welches u. a. die Verwendung tiefgezogener Grünfolien beinhaltete, wurden hierzu 2K-Prüfkörpergeometrien (Zugstab, Biegebruchstab, Ringverbund) und 2K-Demonstratoren (Innenzahnrad, Fadenführer, Greifer) jeweils bestehend aus Stahl 17-4PH und ZrO2 (3%Y2O3), im Co-Sinterverfahren unter H2-Atmosphäre bei 1350°C, entwickelt. Schlüssel zur Darstellung schwindungskonformer ZrO2- und Stahl 17-4PH-Formgebungsmassen war der Angleich der Pulverpackungsdichte. Untersucht wurde neben der Werkstoff- und Gefügeausbildung das sich während dem Formgebungs- und Sinterprozess ausbildende Metall-Keramik-Interface sowie die sich bevorzugt in diesem Bereich manifestierenden Verbundeigenspannungen. Neben der stoffschlüssigen Versinterung beider Partner konnte eine Steigerung der Verbundfestigkeit durch Legierungsmodifikation unter Ausschluss technologischer Fehlerquellen erreicht und spezifiziert werden.

Les contributions de cette thèse de doctorat sont focalisées sur les développements de formulations à base de polymères bio sourcés et déliantable à l’eau basés sur l’emploi d’acétate butyrate de cellulose (CAB) et de polyéthylène glycol (PEG). Ces nouvelles formulations ont été appliquées sur différentes nuances de poudres métalliques (invar) et céramiques (zircones). Ces matériaux possèdent une bonne stabilité dimensionnelle sous une large gamme de température imposée et possèdent de très bas coefficients d’expansion thermique.L’objective est l’étude et la compréhension du comportement des liants à base de CAB et PEG quand ils sont utilisés dans les variantes du procédé MIP (étapes de moulage avec ou sans pression, conditions particulières liées à la micro-injection, …) réalisées avec différentes nuances de poudres et différentes granulométries.Les caractéristiques intrinsèques de chaque CAB, leurs interactions avec le PEG et les poudres, l’influence de la nuance de poudre employée, ainsi que la granulométrie et la morphologie des poudres employées ont été étudiées et analysées en fonction du comportement final de la formulation développé et des taux de charges obtenues.L’homogénéité des mélanges développés, leurs taux de charge critique et maximal, ainsi que leurs comportements mécaniques, thermiques et rhéologiques ont été analysés et investigués par différentes études mécaniques, thermo et physico-chimiques. De nouvelles analyses chimiques et physiques ont été introduites par accroitre les connaissances sur les formulations développées. Les formulations optimales ont été validées pour différentes applications et avec l’emploi de différentes variantes du procédé MIP conduisant à l’élaboration de composants et de micro-composants PIM obtenus sans défauts et possédant d’excellentes propriétés fonctionnelles. L’étape de déliantage ainsi que l’étape de densification ont été optimisées en termes de cinétique et d’atmosphère aboutissant aux propriétés physiques et mécaniques escomptées pour l’ensemble des nuances de poudres considérées dans cette étude.En conclusion, les formulations développés des liants basées sur l’emploie de CAB et PEG sont exploitable au niveau de la recherche et au niveau industriel dans le procédé MIP. Elles apportent des améliorations par rapport aux liants conventionnels grâce à un procédé plus écologique. Cette première contribution représente une avancée significative dans l’émergence d’un procédé MIP plus écologique mais d’autres travaux futurs sont encore possibles<br>This PhD Thesis studied the use of binders based on cellulose acetate butyrate (CAB) andpoly(ethylene glycol) (PEG) in different type of materials, including a ceramic, the zirconiumsilicate, and a metallic alloy, the Invar 36. These materials share their low dimensionalstability with temperature with low coefficients of thermal expansion.The scope of this work is the study and comprehension of the behaviour of the mentionedbinder systems when they are employed in different PIM processes and under differentconditions and powder-types. With regard to this matter, different formulations were designedwith several types of PEG and CAB. These formulations were compared with commercialones. The intrinsic characteristics of each CAB were linked with the behaviour of the differentfeedstock also containing PEG and powder particles. The mixtures homogeneity, the optimumand critical solid loading and its flowability were assessed by torque and capillary rheology.Other complementary techniques such as electronic and light microscopy or the measurementof the mixtures densities by pycnometry were carried out to contrast rheology results. Thecompatibility between the feedstocks’ components and their thermal behaviour were analysedby calorimetry and thermogravimetry techniques. These methods were employed by the firsttime to determine the optimal solid loading.The optimal compositions were injected by using low or high pressures or by a micro injectionmoulding process. The debinding and sintering stages were optimised using severalatmospheres. Finally, the physical and mechanical properties of the final consolidated partswere measured.It could be concluded that the studied binder systems based on PEG and CAB presentedsuitable characteristics for PIM, providing improvements with respect to conventional bindersystems and by a more environmental friendly processing. However, that doctoral work wasjust a first approach to the use of these types of binder systems in PIM. Along this workseveral issues were detected and some topics regarding the processing should be furtherinvestigated to obtain the best of these binder systems

The application of a powder injection moulding process to the production of fully sintered hardmetal components has been studied. Salient, highly interdependent process variables investigated include; powder and binder characteristics, mixing techniques, feedstock rheological characteristics, mould design features, moulding parameters, debinding and sintering parameters. Fundamental studies were conducted to determine the effect of powder and binder characteristics on the powder loading capacity of feedstocks. Various methods of mixing were investigated. The most favourable methods were identified from the rheological response of their respective feedstocks as determined by capillary rheometry. Thermogravimetric analyses were used to; (a) identify binders and feedstocks essig beneficial debinding kinetics, (b) in the study of suitable debinding atmospheres and (c) to develop thermal debinding profiles for selected feedstocks. A spiral mould was used to assess the mouldability and optimum moulding parameters of selected feedstocks. Feedstock properties and mould design features which promoted moulding defects were identified and solutions developed. It was found that the maximum hardmetal powder loading achievable in a given feedstock was dependent on the powder size, size distribution and level of agglomeration. Low viscosity binders with high dielectric permittivities were found to promote highly loaded feedstocks. Feedstock viscosity increased with powder concentration. This relationship was modelled by a simple exponential power function over a narrow range of shear and powder concentration. Compounding methods utilising high shear melt mixing principles were found most effective in producing low viscosity feedstocks of consistent rheological response. Feedstock compositions of high powder concentrations and based on single, crystalline, wax binder systems were found to exhibit a high thermal dependence of viscosity, high activation energies of viscous flow, a high shear sensitivity and tended to segregate when subjected to shear. Such propensities were found detrimental to moulding behaviour. Spiral mould analysis revealed feedstock compositions were sensitive to changes in thermal parameters. Compositions based on multi-component binder systems were found most preferential in producing defect free mouldings of sound integrity and offered favourable debinding characteristics. Thermal debinding of mouldings was only completely effective by careful control of heating rates and when performed in hydrogen rich atmospheres. The reaction order and activation energy of the binder volatilisation was found to be dependent on the level of binder decomposition. Melt wicking was most effective using a hydrated magnesium aluminium silicate substrate. Sintered engineering components were produced by an injection moulding process with near theoretical densities and acceptable microstructures.