Modeling of shell forming by line heating

Abstract

Metal forming by a moving heat source is an efficient and economical method for forming flat metal plates into doubly curved shapes. This thesis proposes an FEM model for three dimensional thermo-mechanical simulation of the process of shell forming by line heating. Since the heat flux is focused on a small area under the heat source, a rezoning technique is developed to reduce computation time in three-dimensional numerical simulation. This involves dynamic remeshing of the metal plate so that the area directly under the heat source is densely meshed while other areas are sparsely meshed. A simplified model is also developed which is based on semi-analytical thermal analysis and idealization of plastic zone during line heating. This simplified model is useful in real-time control of the forming process since the computation time can be greatly reduced. The two thermo-mechanical models lead to a better understanding of the line heating mechanism and more accurate and efficient prediction of the deformation of metal plates. Based on these two models, parametric studies of the edge effects, heat input, heat source velocity, spot size, heat loss coefficients, etc. are performed, and nondimensional parameters which control the bending angle are derived. Finally, an algorithm for surface development for heating path planning is developed. This algorithm minimizes the strains from the doubly curved surface to its planar development. Compared with conventional surface development methods, this algorithm takes into account the characteristics of the process of forming by line heating. This surface development algorithm lays the basis for heating path determination. Based on the developed algorithms and models, we will be able to not only determine the heating paths, but also determine the heating conditions which are necessary to form an initial flat plate into a doubly curved plate. These are critical for automation of the metal forming process.