Determination of the gas generation during precise electrochemical machining

In addition to anodic dissolution there are secondary reactions during electrochemical machining (ECM) of metal materials. Among others the secondary reactions include the generation of hydrogen and oxygen. These gases are present in the working gap in form of bubbles and influence the local conductivity of the electrolyte, and thus also the local current density. During machining the working gap is flushed with fresh electrolyte and so a distribution of gas bubbles in flush direction has to be expected. The described influence of the gas generation is one significant challenge in ECM process design. [1,2] In this study the generation of gas during pulsed electrochemical machining (PECM) will be examined. Therefore a device is created to analyse the amount of generated gas in a PECM process. The device realises a quantitative ascertainment of the generated gas volume and was implemented into a commercial PECM setup. The generated gas is directed into a measuring cylinder. This enables the analysis of the gas amount through the displacement principle [3]. The gas collector is implemented at the electrolyte outlet of the flushing chamber. In this connection the diameter from the electrolyte outlet to the measuring cylinder becomes bigger and the electrolyte-gas-mixture slows down. Thereby the gas bubbles up in the measuring cylinder and is gathered in the upper part. For correct measuring during a machining process the gas level is measured before and after the machining process. The determination of gas generation is shown on selected removal experiments by variation of the current density and pulse duration.