This paper presents an experimental study on rough cut, trim cut using distilled water as a dielectric fluid and Al & Si metal powders in dielectric fluid for WEDM of Nimonic-90. First, the influence of discharge energy (DE) in rough cut is evaluated for machining rate (MR) and surface roughness (SR) and compared with trim cut without any metal powder additives in dielectric fluid. The effect of Al and Si metal powders (varying concentration of 1g/L, 2g/L and 3g/L) in dielectric fluid is studied separately and comparison is also made for MR, SR, recast layer and micro hardness of machined Nimonic-90. From the results it is observed that using trim cut, a fine and uniform surface texture is obtained irrespective of the high discharge energy of rough cut. Al and Si powders additives show a significant reduction in MR for trim cutting operation whereas a remarkable modification is obtained in surface textures after trim cut using metals powder mixed dielectric. SR improves with a concentration of 1g/L and shows a little increase with high concentration of both metals powder. Using metals powder in dielectric fluid, the recast layer becomes smooth and denser and thus, micro hardness increases.

Trim cutting operation in wire electrical discharge machining (WEDM) is considered as a probable solution to improve surface characteristics and geometrical accuracy by removing very small amount of work materials from the surface obtained after a rough cutting operation. In this study, an attempt has been made to model the surface roughness and dimensional shift in trim cutting operations in WEDM process through response surface methodology (RSM). Four process parameters; namely pulse-on time (Ton), servo voltage (SV), wire depth (Wd) and Dielectric flow rate (FR) have been considered as input parameters in trim cutting operations for modelling. Desirability function has been employed to optimize multi performance characteristics. Increasing the value of Ton, Wd and FR increases the surface roughness and dimensional shift but increasing SV decreases both surface roughness and dimensional shift. Quadratic models have been proposed for both the performance characteristics. In present experimentation, thickness of recast layer was observed in the range of 6?m to 12?m for low to high value of discharge parameters.