Modeling and validation of forming by vaporizing foil actuators

Abstract

Sheet metal forming by means of vaporizing actuators attempts to utilize the explosion-like expansion of a cheap and simple aluminum foil, which occurs when a high capacitor discharge current heats it up to the gas phase within a very short time. Until now, mainly basic experimental investigations of this flexible, relatively young manufacturing process exist. In this work, the modeling of the complete forming process, i.e. including the expanding actuator, is conducted for the first time. A crucial parameter is the energy deposition until the so-called burst point, eventually representing an initial equation of state condition for the actuator in the forming simulation. The actuator is modeled using Smoothed Particle Hydrodynamics (SPH), while deformable solid bodies interacting with it are modeled by the Finite Element Method (FEM). The dynamic character of the process especially necessitates the incorporation of the strain rate-dependent constitutive behavior of the solids, which are a steel sheet and a protective polyurethane interlayer. Free forming histories of circular DC01 blanks are recorded with a Photon Doppler Velocimetry (PDV) system. The resulting curves validate the adopted modeling approach for three different, experimentally measured electrical energy depositions. Further aspects of the established numerical model are addressed: It is found, i.a., that the impulse of the bursting actuator is transferred to the blank through the elastomeric interlayer principally without changing the amplitude and effective area. The maximum free kinetic particle energy, however, restricts the possible energy available for deforming solids, and therefore expresses an upper bound for the process efficiency.