*3.1.3 Micro electrical discharge machining (μEDM)*

The μEDM technology is a non-conventional electrochemical processing method. The mold insert is fabricated based on the material removal mechanism with the erosive effect of the electrical discharges that happen between electrode and workpiece. The electrode and workpiece are placed with a small enough gap so that the voltage–current system can efficiently ionize the dielectric. The shape and dimension of the processed workpiece are determined by the electrode pattern. Micro mold insert with the feature size of ~20 μm can be machined by μEDM technology but the forming accuracy and surface roughness are not able to be guaranteed. **Figure 9** demonstrates

#### **Figure 9.**

*Stainless steel mold insert fabricated by μEDM technology: graphite electrode with better geometry definition on micro-patterns (a); copper electrode with non-uniform edge finish (c); the crater size of both electrodes ((c) and (d)) [33]. Copyright (2015) with permission from IOP publishing, LTD.*

the stainless steel mold insert machined by μEDM. With the assistance of other technologies, the surface finishing issues can be solved, such as ultrasonic-assisted μEDM. Overall, μEDM is a competitive technology, which has non-contact mechanical force, heat, and stress generation for machining the mold insert for microfluidic applications.
