Radio Frequency (RF) based process signature of micro-EDM process: Process considerations and involved mechanisms

Micro electrical discharge machining (micro-EDM) process relies primarily on spark discharge to remove the material. The phenomenon of spark discharge radiates electromagnetic waves in radio frequency (RF) regime to the surrounding space and, the analysis of RF radiation offers a possibility to perform non-invasive process monitoring for the micro-EDM. Therefore, this work focuses on the preliminary investigations on the analysis of RF characteristics in micro-EDM. Firstly, the RF radiation mechanism in EDM is studied by exploring the monitored RF signal for different stages of the discharge process. Secondly, the influence of machining status and monitoring equipment on RF signal are examined from the perspectives of time domain and time-frequency domain. The results show that there are obvious differences in the amplitude and spectrum of RF radiation caused by different discharge types. Among them, the RF signal generated by normal discharge has the largest intensity and the widest bandwidth. For monitoring equipment, using coaxial cable can effectively avoid signal attenuation and spectrum loss. Furthermore, despite the different types of antennas, the relative amplitude variation trends of RF signals induced by different discharge statuses are similar, while much discrepancy can be observed in the maximum frequency monitoring range.