The need to create small, precise holes with high depth-to-diameter ratios in hardened materials is on the rise. Such holes are used as start holes for micro wire EDM work for machining miniature molds and stamping dies. They may also be found on small vacuum plates, turbine blades, and miniature medical and electronics components that require tiny, burr-free holes.
Small holes have commonly been produced on dedicated, fast-hole EDM equipment. These machines operate in much the same fashion as ram EDM equipment, with a few differences. Fast-hole EDM feeds a rotating, small-diameter electrode tube into the workpiece on a programmable Z axis. The dielectric fluid is pumped through the hollow center of the tube at high pressure to provide flushing as the hole is produced.
Makino (Mason, Ohio) brings the two EDM techniques together on the same machine platform with the Fine-Hole option on its Edge2 ram EDM unit. According to Jeff Kiszonas, Makino’s EDM product manager, the machine can switch from ram to fine-hole mode in a matter of minutes once the Fine-Hole option is accurately installed. A change of the oil-based dielectric fluid is not required. The Edge2 is said to be the only machine that can operate in both fast-hole and ram EDM modes.
In Fine-Hole mode, the machine can produce holes ranging in diameter from 0.03 mm to 0.51 mm. Edge2 machines with the Fine-Hole option are fitted with all the hardware required for the W axis, which holds the middle guide, die guide plate, die guides and electrode tubes. Fine-Hole programming macros are also provided. In addition, a workpiece reversing device allows the machining of very deep holes by allowing the operator to begin drilling from one side of a thick workpiece, flip the workpiece 180 degrees while maintaining positioning accuracy and finish drilling the hole from the other side.
The dielectric system is oil-based, rather than water-based, to allow fine spark gap control for a quality surface finish and hole accuracy. In ram mode, the Edge2 is capable of standard EDM functions, which include 60-amp burning with full orbiting capabilities.