Finite element analysis and experimental validation of incremental sheet metal analysis forming process

Abstract

In this thesis, the main focus was on development and enhancement of a non conventional metal forming process called dieless forming or incremental sheet forming that needs further investigations. Incremental sheet forming (ISF) is an emerging metal-forming technology in which the tool motion is controlled numerically. A review of the present state-of-the-art technologies and the potential applications of incremental sheet metal forming are presented to address the approaches and methods that are prevalently applied and to be a guide to identify inadequacies of the current approaches and potential for valuable contributions. Before conducting the experiments, numerical simulation was done to test the capabilities and limitations of the finite element method at simulating the ISF process. The numerical simulations were carried out with regard to the overstretching in depth phenomena, the forming strategy and the evolution of temperature during the process. ISF is complex due to the number of variables involved. Thus, it is not possible to consider that the process has been well assessed; several remaining aspects need to be clarified. Therefore, the effects of some relevant process parameters on thickness and surface roughness variation have been studied experimentally and statistically in order to optimize and enhance the process quality. In terms of sheet thickness, several forming passes were investigated, which has not been done before, by using Taguchi method. It was found according to the characteristic parameters that part slope plays a great role. In terms of surface roughness, investigations have shown that the most important factors influencing the surface roughness are the tool size and the step size. These two studies have led to the derivation of two predictive models that could be used to estimate the final quality of the formed part in terms of thickness distribution and surface roughness, respectively. Furthermore, a new forming strategy was developed to enable ISF to form a cylindrical cup with a higher depth like in deep drawing. In this research, a cup with height more than half of its diameter has been formed. In the conventional processes, temperature is a significant factor while forming. Thus, heat and maximum temperature were investigated in every ISF forming step in order to compare it to the conventional forming processes by using infrared/thermo-graphic camera. It was found that the temperature effect could be neglected due to the very low temperature values measured during the process. The numerical results in terms of sheet thickness distribution and temperature were in close agreement with the experimental results. Thus, the developed simulation module can be used as a design tool which can save time and cost when making prototypes using ISF.