Abstract:In order to study the influence of preformed shapes on the thickness distribution of double-pass incremental forming, based on the double-pass incremental forming of straight-wall part, three double-pass strategies with arc and straight line profile preformed shapes were designed. A finite element method (FEM) model of double-pass incremental forming was then established and experimentally verified. It is found that the double-pass strategy with a curved profile of curvature radius of 80 mm is expected to achieve less thickness reduction,equivalent plastic strain and larger minimum thickness. Additionally, the increased plastic deformation region does not always lead to larger thickness,and the final thickness is mostly related to the actual deformation area during the second pass that depends on the specific design of the preformed shape. Finally, a linear relationship between the curvature radius of the preformed shape and the final thickness distribution is not observed. When the tangential angle(θ) is around 40°,it has the most uniform thickness distribution.

Abstract:In order to solve the fracture defects in incremental forming， the Oyane criterion was introduced into numerical simulation， and the forming limit of sheet metal in incremental forming was effectively predicted. Firstly， based on DC56D+Z plate and its material constants of the Oyane criterion， the critical value of fracture integral （I=4） was determined by experiment and numerical simulation. Afterwards， by using response surface methodology， a nonlinear model between the process parameters （forming angel α， interlayer spacing Δz and diameter of tool head d） and I was established， and the effectiveness of the model was verified by a parametric analysis. It is found that the value of I can be effectively predicted by the numerical model. The value of I increases with the increase of α， Δz and d. The influence of α， Δz and d on I value gradually decreases in sequence. In addition， the relative large interaction effects of α&Δz and α&d are found.