Experimental investigation of electric discharge parameters in correlation with peak pressure at industrial electrohydraulic forming

Abstract

The paper shows the investigation results of correlating electric discharge and pressure field parameters aimed to improvements in the electrohydraulic impact forming (EHF) technology at industrial application. The experimental research was performed by using a conical discharge chamber equipped with a set of two electrodes in semi-industrial EHF installation. Pressure fields along round flat area were measured by applying the multi-point membrane pressure gauge methodology. The conditions of the tests include a wide range of spark gaps with four levels of charge voltage and energy. Measurements of discharge voltage and current are performed with voltage divider, Rogovsky coil and electronic oscilloscope. Other electric discharge parameters were calculated from the recorded voltage and current curves. The essence of investigation is to analyse energy parameters for peak pressure of shock wave generated by these discharge energy parameters. Though these dependencies were earlier analysed theoretically and tested in electrohydraulic plants under laboratory conditions, the practical interest in this experimental investigation is to reveal influence of conditions of real semi-industrial EHF press designed for batch production of sheet parts. Conducted experimental investigation has shown that industrial applications of high-voltage non-initiated discharges can significantly deviate from the theoretical and laboratory results. Dependencies of peak pressure from maximum power during the first semi-period of discharge current and slope of power curve appeared to be not so strong. These deviations in peak pressure can reach 20–30%. Among the assumed additional factors influencing energy and pressure parameters are: condition of current-conductive rod of electrode (erosion, rust, radius); condition (wear) of electrode insulator (increase of naked area of current-conductive rod); variations in shape, position and length of discharge channel relative to spark gap; “shadowing” effect of electrodes at some positions of discharge channel relative to electrode;, several discharge channels at small spark gap and other. To reveal effect of these factors the authors plan to carry-out tests with wire-initiated discharges to check the variations in shape, position and length of discharge channel relative to spark gap in the same discharge chamber configuration.