An on-line pulse trains analysis system of the wire-EDM process

Ignition delay time (Td) has been widely used to distinguish the abnormal discharges from the normal ones in wire electrical discharge machining (WEDM) process. In this paper an on-line analysis system for the causality of the Td data sequences was developed to evaluate the machining performance of WEDM process. The system is composed of a stand-alone Td processing circuitry and a user-friendly computer program for data analysis. The Td processing circuitry calculates and records the Td of every single electrical discharge in the first place, and then transmits the Td data via an embedded communication port to a desktop or notebook computer. The computer program, after performing the analysis tasks, will display the result in a graphic way. Two mathematical algorithms were employed for the analysis: autocorrelation function and Fourier transform. Through experiments under different working conditions, it was found that the autocorrelation function could be used to detect if arc or short circuit discharges take place consecutively, and to distinguish the WEDM process with similar Td distributions. On the other hand, the spectral analysis revealed that several factors were identified to be able to induce certain periodic patterns of Td data. These factors include the length of wire electrode, the water pressure, etc.