Measurements of Pressure Fields with Multi-Point Membrane Gauges at Electrohydraulic Forming

Abstract

Success of electrohydraulic forming (EHF) process depends on coincidence of the needed pressure field with the field generated by discharge chamber at sequent stages of sheet blank deformation. Impulse loading at high-voltage discharge has a very complicated character and involves many phenomena: direct shock waves, hydraulic flows, quasi-static pressure of gas bubble, reflected shock waves, cavitation, secondary shock waves, etc. Also internal shapes of a discharge chamber, design and location of electrodes have a great influence on pressure distribution along blank surface. Because of these features, the simulation of EHF processes is very complicated task to be solved for chambers equipped with single electrode pair. And difficulties are increased greatly for simulation of multi-electrode discharge blocks (MDB). First of all, reliable data on pressure distribution at various discharge conditions are necessary to reveal and describe influence of each factor of impulse loading. Multi-point membrane pressure gauges (MPG) give an opportunity to obtain pressure maps with high resolution at relatively low cost. By design MPG typically consists of body plate with large number of small holes and sensitive element - metallic membrane. Deformation of membrane in each point (hole) can be measured and recalculated into pressure. Totality of many pressure points allows plotting a pressure map. MPGs are better suitable for measurement of shock-waves pressure. For this purpose the holes diameter and membrane thickness should be specified in such a manner that membrane is sensitive only to shock waves. Combination of MPG measurements with piezoelectric sensors can give full information about pressure map changing in time. These data could be a good basis for simulation of impulse loading with approximation formulas and also could be used as a check data for the simulation programs based on theoretical relationships. Initially the method based on MPG application was designed for investigations and improvements of discharge chambers with various forms of internal (reflecting) surfaces, electrodes position and their shapes, influence of design features on pressure distribution. Vast experimental investigations were carried out with MPG application for typical single-electrode-pair discharge chambers (conical and parabolic) and multi-electrode discharge blocks.