A good example of a fine-hole drilling fixture is the Fine Drill module for GF AgieCharmilles’ Form 20 die sinking EDM. It's capable of deploying small-diameter electrodes as a System 3R high-speed rotation spindle drives them at 60-2,000 rpm, ensuring positioning and roundness accuracy. High flushing pressure up to 80 bar integrated in the diesinking machine’s dielectric circuit maintains clean spark gaps.
Current holemaking technologies may fall short of quality requirements when used to producing hole diameters down around 0.002 in. Holes as small as that are most often needed for wire EDM start holes, and the smaller the diameter wire to be used the more accurately sized must be the start hole, in terms of its location, dimension, cylindricity, straightness, and surface finish.
Most machine shops will use a hole popper machine to create start holes, but those machines have limitations with respect to their electrode sizes and overall quality of the holes they can produce. Now, the trend for these shops is to EDM small-diameter holes using diesinking EDMs equipped with fine-hole drilling modules/fixtures. These systems are basically two machines in one that allow shops to run normal diesinking work and, on the same machine, to generate extremely small, near-perfect holes with tolerances of 0.0004 in. and surface finishes as good as 0.10 Ra.
A good example of a fine-hole drilling fixture is the Fine Drill module from GF AgieCharmilles for the company’s Form 20 die sinking EDM. AgieCharmilles supplies wire EDM, CNC and manual diesinking systems, and high-speed/performance and 5-axis CNC milling machines.
The Fine Drill module’s arm and guide structures support small-diameter electrodes as a System 3R high-speed rotation spindle spins them at speeds between 60 rpm and 2,000 rpm to ensure positioning and roundness accuracy. High flushing pressure up to 80 bar integrated in the diesinking machine’s dielectric circuit maintains clean spark gaps.
The Fine Drill module can run electrode diameters measuring from 0.004 in. and smaller. And, the module is an option that can be added to the Form 20 at the customer side. GF AgieCharmilles also has integrated special software features and technology parameters for the Fine Drill module into the Form 20’s CNC.
In addition, GF AgieCharmilles offers an electrode-manufacturing accessory for the Fine Drill module. This special accessory manufactures electrodes using electroerosion and, again, does so on the same Form 20 die-sinking machine.
The accessory eliminates the need for a wire draw-off system by incorporating two spools, one of which winds up used wire. Wire can be used several times because there is limited wear.
Shops gain the flexibility to manufacture fine-hole electrodes to exact required sizes and tailored to their specific application requirements with the electrode-making accessory. The accessory offers an increased level of automation when making electrodes, and the Fine Drill module secures electrodes while they are being machined. Then, it allows shops to handle finished electrodes with diameters as small as 0.0008 in., easily and efficiently.
In one application, the Fine Drill module machined 0.004-in.-diameter holes into 0.060-in.-thick plate using a 0.003-in.-diameter carbide electrode. The module was so precise that it was possible to drill half of each hole from one side of the part, then the other half from the other side, in about four minutes per side.
In another application, the GF AgieCharilles Fine Drill module EDM'ed four 0.002-in.-diameter holes and one 0.004-in.-diameter hole into a 0.010-in.-thick plate. A 0.003-in.-diameter carbide electrode was used for the 0.004-in.-diameter hole, and then the same electrode burned the 0.002-in.-diameter holes after its diameter was reduced to 0.001 in. using a reverse erosion process. Reverse erosion involves machining an electrode against a carbide rod with inverted polarity. This electrode prep time took about four minutes.
During an in-house test, GF AgieCharmilles technicians further explored the Form 20’s fine-hole drilling capability by EDM'ing several 0.005-in.-diameter holes in a 0.040-in.-thick piece of Neodymium Iron Boron. The cuts were done without flushing through the electrode, which makes it more difficult to machine deeper holes and maintain required tolerances. The cut speed also decreases significantly the deeper the cut.
Burn times for the holes were between 100 seconds and 140 seconds with electrode wear varying from 62 percent to 75 percent, and average hole sizes measuring 0.0044 in. This average hole size includes measurements taken at the tops and bottoms of holes, and final hole sizes ended up at 0.0045 in. in diameter.
The Form 20
Constructed with an ultra rigid cast iron C-frame and cross-table design, the Form 20 guarantees stiffness and withstands the temperature fluctuations found in most workshop environments. GF AgieCharmilles designed the machine with an integrated tool capacity for 4 to 6 positions, as well as glass scales on all axes that continuously measure axis positions to ensure the highest level of positioning and cutting accuracy.
Also, the Form 20 is equipped with GF AgieCharmilles’ intuitive HMI (human-machine interface), which is built on a Windows XP platform and designed with “non-EDM experts” in mind. Machine operators with minimal experience can program a job and quickly yield desired geometrical and surface finish results.
The machine easily integrates into data networks via LAN for remote monitoring and data management. Adding to the smart design of the machine’s control is the proven performance of the Advanced Power Generator (APG), a high-efficiency, high-output 72/103 Amp generator that delivers high-speed, consistent surface finish quality, precision, low wear, and high material-removal rates.
