A ‘virtual sensing’ framework for µECM/hybrid laser- µECM for monitoring interelectrode gap conditions

Abstract

Micro-ECM (µECM) has capability to process wide class of conductive materials ranging from metals, cermets to bulk metallic glasses and shape memory alloys. The process efficiency and speed is further enhanced by hybridization of micro-ECM process with laser which can act as a localized heat source or a cutting energy source depending on the fluence on the workpiece surface. The hybridization of micro-ECM with laser facilitates machining of materials/alloys with conductivity variations and promotes their uniform dissolution. The process mechanism involves several multiphysics phenomena occurring in the interelectrode gap (IEG) which is of the order of 20-50 µm. The technological limitations of putting sensors in this small IEG limits the monitoring of physical quantities (such as temperature, hydrogen and oxygen gas volume fraction, electrolyte conductivity, current density on workpiece surface) during the process. However, these physical quantities can be effectively estimated by multiphysics simulations.At first, the experimental experience with different sensors (temperature sensor, current sensor, high speed imaging and particle image velocimetry (PIV)) is presented for µECM/hybrid laser-µECM process and their limitations are discussed. Subsequently, this work proposes a ‘virtual sensing’ approach enabled by multiphysics simulations. A detailed multiphysics model is developed in Comsol® software which models several phenomena occurring in µECM/hybrid laser-µECM process such as temperature-dependent electrolyte properties, hydrogen and oxygen gas generation, heat generation due to joule heating and laser heating, laminar fluid flow and electric currents. The properties are evaluated at 5 different (virtual sensor) locations inside the IEG, more specifically on the workpiece surface, tool surface, in the center of IEG, just at the exit of IEG and at a specified location. These virtual sensors are implemented in the Comsol® software by employing a dynamic point probe which probes the model-solution at a defined point in a moving geometry. The evolution of the aforementioned parameters in the IEG is monitored and supported by fundamental explanations as well as observational experiments. This research is a first step towards facilitating predictive sensing of ECM and allied multiphysics processes thereby supporting process design and minimizing experimental efforts by virtual process monitoring.