Dimensional Control and Formability in Impact Forming

Abstract

Electromagnetic forming (EMF) is a high speed forming technique that can be used for embossing fine surface features onto sheet metals. Here two coupled experimental and analytical studies show how interface conditions including rebound and friction affect the ability to create a component in impact forming. In the first part of this work high velocity is generated with the Uniform Pressure Actuator (UPA) and impact with a die emboss fine features in a nominally flat component. The primary objective of this work is to develop a modelling facility that guides experimental design nominally flat grooved components. Both shape fidelity and formability aspects are presently considered. In a second short study expansion of a round tube into a square hole is considered. Traditional modelling techniques solve a coupled system of equations with spatially varying electromagnetic fluxes controlling the dynamics of the plastic deformation. Because the magnetic pressure is spatially uniform, the flux equations are obviated from the coupled system rendering them computationally efficient. The calibration of contact mechanics that influence the rebound behaviour of the sheet metal remains as a difficult issue. The interfaces between various sheet metals and the metal die play a critical role in controlling the shape of the final product. The characterization of such an interface using appropriate calibrated friction coefficients is assessed. The role of magnetic pressure in reducing the sheet metal rebound is demonstrated via a comparison between results from mechanical and electromagnetic simulations. The influence of the channel geometry on final shape is illustrated through simulation and experiments.