Comparative Analysis of Dry-EDM and Conventional EDM for the Manufacturing of Micro Holes in Si3N4-TiN

The importance of Electrical Discharge Machining (EDM) process is increasing, especially for the machining of electric conductive ceramic materials within the field of micro production technology. Due to its thermal working principle, EDM is particularly suitable because it allows almost force free machining independent of the material's mechanical properties [1]. High aspect ratios and precise micro holes with diameters D ≤ 0.3 mm leads manufactures to more complex processes, which reduce the flushing in the working gap and therefore the stability of the process. Enabling the increase of flushing by gaseous dielectrics, dry-EDM technology represents an alternative solution.This paper presents a comparative analysis of dry-EDM with two different gases as dielectric (oxygen and argon) and conventional EDM (deionized water) to manufacture micro holes in Si3N4-TiN ceramic. The results show that the axis displacement y, voltage u0, and current iL differ for the processes. It can be observed that dry-EDM has higher effective pulse frequency fe and shorter relative motions between workpiece and tool electrode than the conventional EDM process [2].The differences observed in the discharge flow and relative motions between workpiece and tool electrode are related to the dielectric fluid properties. As for example, deionized water as a dielectric has a higher viscosity ηwa = 89·10-5 Pa·s than oxygen ηo2 = 2,1·10-5 Pa·s and argon ηar = 2,3·10-5 Pa·s. Thus, with the same flushing pressure of p = 80 bar it is possible to achieve higher flow speed for faster removal of particles in dry-EDM. Furthermore, deionized water has a higher breakdown resistance ED_wa = 650 kV/cm than oxygen ED_o2 = 29 kV/cm and argon ED_ar = 6,5 kV/cm. The better flushing condition enables the increase of the effective pulse frequency fe for oxygen and a decrease of the electrode relative wear ϑ.