Abstract
The majority of ceramic parts are made by forming a powder compact, known as a green body, which is subsequently sintered i.e. heated to a temperature at which diffusion takes place to densify the body which causes considerable shrinkage of the body. If the part is undersized then it must be scrapped; if it is significantly oversized then there are extra costs associated with machining. Hence, the accurate prediction of shrinkages is important. Although various models and simulation techniques have been proposed, these are not particularly accurate and/or easy to use. Thus, the purpose of this study is to provide a numerically based model that is better suited to the needs of industry i.e. one that is relatively simple and predicts the shrinkage reliably. A general structure for sintering simulation was constructed by comparing different constitutive laws and densification equations proposed by various authors with experimental measurements. A finite element computer code was developed that could accommodate various constitutive laws for different sintering processes. Master sintering curves are a new concept in the representation of sintering data. A new method of constructing such a curve was developed, based on the finite element concept of dividing a region into sub-elements. This approach is more flexible than the standard technique and allows data which cannot be fitted using a constant activation energy to be analysed. A similar technique was then used to give a new method for the general representation of various constitutive laws. This method facilitates the modification of bulk/shears viscosities and also prevents a sudden change in these functions, thus providing smooth transitions during different sintering stages. Finally, a new empirical finite element method for the analysis of sinter shrinkage was developed which does not require a constitutive law. The new method uses only density as a function of time as input data; this can be obtained from a few simple sintering experiments or by using the data provided by a master sintering curve. Using this method eliminates the need for bulk and shear viscosity expressions. This method is limited to pressureless sintering but is applicable to variety of different sintering mechanism. The validity of method has been tested by comparing the results with various constitutive models and experimental data. The results are comparable with predictions from models using full constitutive laws and requiring more difficult to obtain input data. Thus, it offers significant advantages over previous models.