Forming force prediction and process investigation for incremental sheet forming

Abstract

Incremental sheet forming (ISF) is a promising manufacturing process in which flat metal sheets are gradually formed into 3D shapes using a generic forming tool. Since the process features benefits of reduced forming forces, enhanced formability and greater process flexibility, it has a great potential to achieve economic payoff for rapid prototyping applications and for small quantity production in various applications. Although substantial research has been performed in the past decades on ISF, there is still a lack of an efficient prediction of forming force to facilitate the production design and optimization of the process. Also, unsatisfactory part quality obtained still hampers its wide use in industrial applications. Therefore, the work presented in this thesis is mainly focused on two aspects of ISF: efficient forming force prediction and process investigation and its improvement.The first research aspect of this thesis has been focused on the development of an efficient force prediction model that includes the development of both finite element (FE) and analytical models. (i) FE modelling. Two types of FE models have been established using an explicit code LS-DYNA to investigate the deformation mechanism in ISF which is the basis for developing the force prediction model as well as further improving the forming process. First, FE models with shell elements for the groove forming process were set up and the strain behaviour and thickness distribution with different tools were evaluated and compared with experimental results. The strain behaviour of elements at different positions has been studied and the maximum strain has been found near the end of the groove corresponding to the failure location. The thickness distributions of the groove formed with different sized tools were predicted and it was found that the groove formed by the 20 mm tool is thinner than that formed by the 30 mm tool. Second, to further investigate different deformation modes and their evolution history in ISF, a FE model with fine solid elements for the cone-forming process has been established. The FE model was verified by experimental work with forming forces to allow a quantitative study of deformation behaviours of stretching, bending and shearing during the process. The evolution history of all the strain components along with the effective strain was presented. Moreover, the characteristic of each strain component and its contribution to the total effective plastic strain during the cone-forming process were investigated in detail. It was confirmed from FE simulations that the deformation mechanism in the ISF process is a combination of shearing, bending and stretching though the quantitative contributions in two directions are varied. (ii) Force prediction modelling and its validation. Based on the understanding of the deformation mechanism during the forming process, an efficient analytical model for tangential force prediction has been developed. Initially, deformation modes including shear, bending and stretchin...