The effects of machining settings on the behavior of pulse trains in the WEDM process

A pulse discrimination system has been developed to study the characteristics of pulse trains in the WEDM process under various machining conditions. The effects of on-time, off-time and feed on the variations of the proportions of short sparks, arc sparks, and normal sparks in the total sparks (defined as short ratio, arc ratio, and normal ratio, respectively); the distribution of the ignition delay time of the normal sparks; the average ignition delay time; and the proportion of machining time in a specific sampling period were investigated. An approximate method for estimating the variation of the average gap width is also introduced. It is found that a short on-time, or a long off-time, or a large feed, results in the decrease of both normal ratio and average ignition delay time, and an increase of short ratio. On-time has the largest effect on the arc ratio, whilst off-time has the least effect. The ignition delay time of the normal sparks displays a reverse J-shape distribution. On-time is the most prominent factor amongst all of the machining settings under consideration affecting this distribution. In addition, the distribution becomes more left skew with a higher peak and a shorter tail under the condition of a shorter on-time setting. Based on the analysis results, the instability during the WEDM process can be attributed to an apparent increase of either arc sparks, short sparks, or both. A strategy to improve machining stability with respect to each case is proposed accordingly. © 1997 Elsevier Science S.A.