Micro Electro Discharge milling of freeform micro-features with High Aspect Ratio

Micro Electrical Discharge Machining (liEDM) technology is widely used to process conductive materials, regardless to their hardness and strength, and realize micro-sized feature components for industrial application. liEDM proves to be a very competitive fabrication technology since micro-sized features within 1 Lim of accuracy and with high surface quality (<0.1 Lim Ra) can be attained. When High Aspect Ratio (HAR) micro-features are machined via liEDM milling, the main problem is to identify the technological parameters and settings mainly affecting the process performance. In the present study the influence of the adjustment factor and flushing conditions are investigated and discussed for the machining of HAR cavities with different Fill Factor (FF). Material Removal Rate (MRR) and Tool Wear Ratio (TWR) are evaluated when deep cavities having variable square sections are machined on Ni-Cr-Mo steel workpiece. All tests are performed using a state of the art micro-EDM milling machine, with a Tungsten Carbide electrode tool and a dielectric oil for flushing. The experimental results presented here highlight different trends in the machining performance in dependence of AR and FF. In particular, MRR exhibits a decreasing trend where the curve slopes are strictly related to the FF and the initial adjustment factor. On the contrary,TWR, for higher FF, displays two distinct trends characterized by opposite slopes in each curve. Finally a nozzle for micro-injection with varying Aspect Ratio and Fill Factor is machined and presented as demonstrator.