THE BASICS OF HIGH-SPEED EDM HOLE DRILLING

High-speed EDM hole drilling was designed especially for fast, accurate small- and deep-hole drilling applications. Small holes that were once almost impossible to drill by conventional machine tools are now being performed with ease. With the capability of drilling through virtually any conductive material, the use of this technology is continually expanding.

Initially shops were using this technology specifically for start holes in wire EDM jobs. Because of this technology, workpiece materials are being sent out for heat treating prior to drilling the start hole. This removed two major problems: having to program, locate and drill the holes by conventional machine methods in the “soft” workpiece prior to heat treat and by heat treat the workpiece before drilling, all the stresses are being removed prior to the drilling process. As this process became more widely known, test burns were being done in more than just hardened tool steel; tungsten carbide, aluminium, stainless, titanium, brass and inconel were being tested. High-speed EDM hole drilling applications began to expand to mould and part manufacturing-injection nozzles, oil drain holes, hydraulic cylinders and dowel pins, as well as turbine blades, ball bearings and safety wire holes in hex nuts, to name a few.

The EDM Drilling Process

The process consists of using a precision tubular electrode (generally brass or copper) mounted into the drill chuck located on the “Z” axis and held in location on top of the workpiece by the ceramic guide. The top of the workpiece is located and the drilling depth is set. The electrode rotation is turned on and the deionized water solution, which is pressurized between 30 and 120 kg/cm2, is sent through the tubular electrode as a flushing agent. The power supply parameters are set-which normally consist of on-time, off-time, peak current and amount of capacitance. At this point, the discharge is turned on to begin the drilling cycle. At the end of the drilling cycle, the discharge is turned off and the “Z” axis is retracted above the workpiece.

Drilling Times

Drilling times are based on the hole size and type of material.

A few samples of possible speeds for reference:

  
MaterialElectrode Dia.Drill DepthMachining Time
Alloy Tool Steel0,5mm12,5mm25 to 35 seconds
 0,5mm25mm50 to 60 seconds
 1,0mm25mm55 to 65 seconds
Tungsten Carbide0,5mm12,5mm4 to 5 minutes
 0,5mm25mm8 to 9 minutes
Aluminum0,5mm12,5mm40 to 50 seconds
 0,5mm25mm90 to 100 seconds
 1mm70mm3 minutes

 

Observing the mentioned times explains why high-speed EDM hole drilling has become an alternate method to conventional machining in mould manufacturing. In addition, this method of drilling produces burr-free holes, which results in the elimination of secondary deburring processes.

Today, Novidrill 400-II can use distilled water/tap water as the flushing agent, which opens new and very economically application possibilities in the medical field. With continued improvement in this technology, more and more applications are being seen on the horizon-it has become a whole new method of manufacturing moulds and parts.