Abstract
Micro-drills have been widely used in the micro-hole machining of printed circuit boards. The helical flutes are the key feature of the micro-drills, and play an important role in chip discharge. Precision grinding is the most popular technology for machining the spiral flutes in micro-drills. Grinding is a contact machining technology, which means that a grinding force is inevitably generated during the process. When the diameter of the micro-drill is minimal (Φ ≤ 100 µm), the grinding force can easily cause deformation or even fracture of the micro-drill, leading to a decreased yield. Focusing on the above problem, this paper proposed to apply micro-EDM for machine the helical flute structure on the surface of micro-drill using a beryllium-copper-tin composite disc foil electrode (CDFE). Micro-EDM is a kind of non-contact machining, which can effectively avoid the disadvantage of grinding the helical flute of micro-drill. Through an orthogonal experiment, the effect of the rotation velocity of the CDFE, machining voltage and pulse duration ratio on the machining quality of the helical flute was analyzed in detail. Finally, with 4000 r/min CDFE rotation velocity, 24 V machining voltage, 1 µs pulse duration and 3 µs pulse interval, a helical flute structure with a surface roughness Ra of 0.381 µm was successfully machined on the surface of micro-drill with a diameter of 70 µm.