Evaluation and simulation on deformation instability mechanism in laminated sheet incremental forming

Abstract

Abstract Incremental sheet forming is a flexible and die-less manufacturing technology, which leads to a significant increase in predicted formability. Laminates combine the characteristics of different metal materials to promote the effect of comprehensive service. Thus, it has been highly valued to improve the forming limit of laminates by employing the incremental sheet forming technology. In this paper, two kinds of stress status, the plane strain and equi-biaxial stretching cases, are presumed based on large quantities of previous studies. The simplified quasi-static stress state and resulting strain of the micro-elements in incremental sheet forming of laminated plates are analyzed by employing the force border conditions and compatibility deformation of connection layer, and the trend of stress and strain changes of the micro-elements with process parameters is established. A new analytical instability model is developed by utilizing Marciniak and Kuczynski model according to the fracture behavior of material. The instability model contains the influence of through-thickness stress and finally turns into a 2D stress solution with the neglect of hydrostatic stress, which is validated and calibrated by mathematical method and a series of simulation experiments. The comparison between mathematical model and simulation results is clearly represented in failure limited diagram.