Study on gap variation in multi-stage planetary EDM

Tooling costs, machining time and surface finish in an EDM operation can be improved by using multi-stage planetary EDM strategies. However, the technological tables provided by machine manufacturers do not always adequately fit to the specific user application, especially in the case of gap values. In this work, a methodology for the calculation of gap variation between two consecutive stages that can be applied both in roughing and in finishing regimes is described. The methodology defined requires the realization of a number of EDM tests, in which the surface finish of each intermediate stage must be assured. It is shown in the paper that this is optimally done by using the strategy based on the complete removal of RtRt. Results also show that gap variation is dependent upon the radius of the first orbit until a limit value is reached. It is observed from the experiments that larger gap variations are related to the use of smaller electrodes and copper electrodes. Finally, it is shown that the steepest decreases in gap variation occur at the regimes at which both discharge current and pulse time decrease.