As highlighted in the first lesson, there are three main types of EDM machines: Wire EDM, Sinker EDM, and EDM Drilling. In this segment, we’ll focus our attention on EDM Drilling.
EDM Drilling Machine Basics
EDM Drilling machines, which are commonly referred to as EDM hole poppers or small-hole EDM, create small diameter holes in parts faster than conventional mechanical drilling and will achieve higher L:D (length to diameter) depth ratios. EDM Drilling will not typically achieve the same level of tolerance or surface finish as Sinker or Wire EDM, but the process is commonly utilized to prep parts with start holes for the Wire EDM process. These machines can range from simple toolroom type machines on up to dedicated and highly specialized machines for high-volume production applications.
EDM Drilling machines use hollow tubes made from brass alloys or copper as electrodes to burn holes that have a depth-to-diameter ratio up to 100-to-1 or greater. Electrodes can be a simple tube or a multi-channel tube. The multi-channel tubes are preferred to eliminate the creation of a core or slug on the inside of the tube. The electrode tube is rotated during machine operation, allowing the multi-channel tube to remove all material during erosion.
The main criteria of EDM Drilling is speed. Typical hole sizes range from 0.125” down to 0.020” Ø using a single roughing process (most EDM Drill machines cannot orbit or perform any additional finishing operations), and commonly achieve tolerances in the +/-0.002” range. EDM Drills can be simple manual machines or CNCs that include electrode tool changers and automation. EDM Drilling machines use pressurized water flushing through the electrode with a secondary external waterline hose for debris evacuation. Most machines operate non-submerged and utilize external flush lines. However, more advanced machines provide fully submerged operations that improve cycle time, part stability, and electrode break-thru machining.
There is a specialized subset category of EDM Drilling machines called fine hole EDM Drilling which provide high accuracy hole size, surface finish, and circularity. Hole diameters can range in size from 0.125” down to below 0.001” while achieving ±0.0001” accuracy. Machining is performed with high-pressure flushing through the rotating electrode and is usually fully submerged in an oil dielectric. Machining speed is slower than the water-based EDM Drilling, but accuracy and metallurgical characteristics are vastly improved. These machines often have the capability to perform both EDM Drilling and standard Sinker EDM operations on a single machine platform.
Most EDM Drill machines use deionized water as the insulating dielectric fluid because it’s 10-times faster than machining in dielectric oil. That said, small-hole EDMing in oil is 10-times more accurate. Small-hole EDM Drilling can be run non-submerged, but the process is significantly faster under dielectric fluid, especially during electrode break-thru.
Production EDM Drilling applications can be found in the medical and aerospace industries. Medical applications have focused more on producing smaller diameter holes with high accuracy, whereas the aerospace industry pushes the speed envelope. The aerospace industry uses EDM Drilling to produce the cooling-film holes for turbine blades and vane details for jet engines. These details include both holes and shaped diffuser profiles (tapered funneled hole).
Stay Tuned for More!
If you’ve enjoyed this fifth lesson in our 6-part Back to Basics series, be sure to stay tuned for future lessons as we reflect on our industry and celebrate the building blocks that have led us to the fascinating EDM advancements that we encounter each day.
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