Flow and Filling Characteristics in Plane Strain and Axisymmetrical Deformation in Forging

Abstract

The flow and filling characteristics of a forging process are important because they are related to the study of the forgeability of metal which is the cornerstone of forging technology. The usual conception of forgeability is the extent to which the metal being deformed without failure. The old criterion of failure is the appearance of cracks, whereas this criterion is now found to be inadequate by the fact that cracks can appear anywhere in the forging. Furthermore, a non-homogeneously deformed or incompletely filled forging can also be called a failure. Since it is for strength that the forging is to serve, any damage to the strength through deformation of the forging can be considered as failure. It is on the study of the deterioration of strength through deformation that this project is based. The deformation from point to point in the forging is not only non-uniform but very large as compared with the small deformations commonly analysed in the analysis of small strain. So a new mathematical tool, namely, the analysis of large deformation, has been developed in Part A of this thesis. This method is a combination of the work by Professor Hsü and the mathematical method of Truesdell and other mathematical physicists. The objective of this project is to use this mathematical tool to analyse the deformation in upsetting processes, and consequently explore the implications to the loss of strength of the forging through deformation. With the use of this analytical tool, a scalar value called the deformation intensity value ⌈,  is developed to represent the extent of the deformation of an element. Subsequently, contour maps with varying deformation intensity values of the forging are produced to represent the distribution of the various levels of damage due to deformation. Such contour maps are essential tools for forging designers in deciding the shape of the forging. Deformation is so non-uniformly distributed in a forging that a homogeneity value has been developed to indicate how much the most damaged part deviates from the least damaged part in the forging. It has been revealed that the initial filling of the die cavity which is also one of the criteria included in the study of forgeability, is dominated by the folding of metal from the side face of the forging. The analysis presented in this thesis cannot claim to be the solution to all the problems in the study of forgeability, but a proper route has been found to further this study.