Electrohydraulic trimming of advanced and ultra high strength steels

Electrohydraulic trimming (EHT) is a novel method of trimming sheet metal panels and is based upon the electro-hydraulic effect: a complex phenomenon related to the discharge of high voltage electrical current through a liquid. In EHT, electrical energy is stored in a bank of capacitors and is converted into kinetic energy within the liquid and the sheet metal blank by rapidly discharging the stored energy across a pair of electrodes submerged in a fluid. The objective of this paper is to describe the newly developed EHT process, to report the results of early proof-of-concept experiments, and to provide an explanation for the observed results through the use of a numerical modeling technique developed as a part of this work. The key innovation behind the EHT concept is the chamber design, which consists of a narrow fluid channel positioned directly below a sharp trim steel. The narrow channel can transmit fluid pressure very efficiently, and the design has enough inherent flexibility such that it can be used to cut straight lines and can also be applied to more complex curvature. The new, channel chamber design concept was successfully demonstrated for electrohydraulic trimming of Advanced and Ultra High Strength Steels, including DP500 at 0.65 mm thick, DP590 at 1.0 mm thick, DP980 at 1.0 mm and 1.4 mm thick, and AISI 4130 steel at 2.0 mm thick. Separation of the offal from the part initiates in the area of the blank directly above the discharge channel. Further separation along the remainder of the trim line is influenced by a number of factors, including the strength and thickness of the sheet material, the mass density of the sheet material, and the propagation of pressure waves along the fluid channel and their reflection from the walls at the ends of the fluid channel. A numerical model was developed which is able to predict the offal separation mechanism and the sequence of offal separation during electrohydraulic trimming. The developed model incorporates several individual models into one integrated simulation, including models for the plasma channel, the liquid within the fluid channel, the steel chamber and trim blade, and the deformable blank. (C) 2013 Elsevier B.V. All rights reserved.