High precision in-situ monitoring of electrochemical machining process using an optical fiber Fabry–Pérot interferometer sensor

Abstract

This article proposes a method to monitor the machining depth during the electrochemical machining process using an optical fiber. The fiber was inserted and fixed coaxially in the center of the tool electrode with its axis perpendicular to the surface of the workpiece, and an Fabry–Pérot cavity formed between the fiber tip and the workpiece was used to monitor the machining depth. By analyzing the reflected spectrum, the inter-electrode gap was calculated. The sensing mechanism was discussed in depth, and two different methods to obtain the inter-electrode gap was introduced. One of the methods has a theoretical precision of 4.45 nm, but a time-consuming spectrum alignment process is required. Another method can use a simple program but has a lower theoretical precision of 2.16 μm, and a precision of 11.05 μm during the experiment. Several groups of experiments with still tool electrode were implemented, and the machining depth-time curve was given. By comparing the final machining depth measured by our sensor and profilometer measurement, a difference of smaller than 4% was observed. This difference may be because of the change of the refractive index of the electrolyte during the machining process. This technique significantly improves the monitoring precision, and real-time monitoring is possible. This monitoring technique may provide a further understanding of the machining process and has a potential to increase machining accuracy to micrometer or even sub-micrometer scale.