The importance of the EDM filters
EDM Machine Types
Sinker EDM
Sinker EDM, also called cavity type EDM or volume EDM, consists of an electrode and workpiece submerged in an insulating liquid such as, more typically, oil or, less frequently, other dielectric fluids. The electrode and workpiece are connected to a suitable power supply. The power supply generates an electrical potential between the two parts. As the electrode approaches the workpiece, dielectric breakdown occurs in the fluid, forming a plasma channel, and a small spark jumps.
These sparks usually strike one at a time because it is very unlikely that different locations in the inter-electrode space have the identical local electrical characteristics which would enable a spark to occur simultaneously in all such locations. These sparks happen in huge numbers at seemingly random locations between the electrode and the workpiece. As the base metal is eroded, and the spark gap subsequently increased, the electrode is lowered automatically by the machine so that the process can continue uninterrupted. Several hundred thousand sparks occur per second, with the actual duty cycle carefully controlled by the setup parameters. These controlling cycles are sometimes known as “on time” and “off time”, which are more formally defined in the literature.
The on time setting determines the length or duration of the spark. Hence, a longer on time produces a deeper cavity for that spark and all subsequent sparks for that cycle, creating a rougher finish on the workpiece. The reverse is true for a shorter on time. Off time is the period of time that one spark is replaced by another. A longer off time, for example, allows the flushing of dielectric fluid through a nozzle to clean out the eroded debris, thereby avoiding a short circuit. These settings can be maintained in micro seconds. The typical part geometry is a complex 3D shape, often with small or odd shaped angles. Vertical, orbital, vectorial, directional, helical, conical, rotational, spin and indexing machining cycles are also used.
Wire EDM
In wire electrical discharge machining (WEDM), also known as wire-cut EDM and wire cutting, a thin single-strand metal wire, usually brass, is fed through the workpiece, submerged in a tank of dielectric fluid, typically deionized water. Wire-cut EDM is typically used to cut plates as thick as 300mm and to make punches, tools, and dies from hard metals that are difficult to machine with other methods.
The wire, which is constantly fed from a spool, is held between upper and lower diamond guides. The guides, usually CNC-controlled, move in the x–y plane. On most machines, the upper guide can also move independently in the z–u–v axis, giving rise to the ability to cut tapered and transitioning shapes (circle on the bottom square at the top for example). The upper guide can control axis movements in x–y–u–v–i–j–k–l–. This allows the wire-cut EDM to be programmed to cut very intricate and delicate shapes.
The upper and lower diamond guides are usually accurate to 0.004 mm, and can have a cutting path or kerf as small as 0.021 mm using Ø 0.02 mm wire, though the average cutting kerf that achieves the best economic cost and machining time is 0.335 mm using Ø 0.25 brass wire. The reason that the cutting width is greater than the width of the wire is because sparking occurs from the sides of the wire to the work piece, causing erosion. This “overcut” is necessary, for many applications it is adequately predictable and therefore can be compensated for (for instance in micro-EDM this is not often the case). Spools of wire are long—an 8 kg spool of 0.25 mm wire is just over 19 kilometers in length. Wire diameter can be as small as 20 microns and the geometry precision is not far from +/- 1 microns.
EDM filtering
Benefits
One of the most important aspects of EDM performance is flushing. TAGUTI stresses the importance of providing dielectric filtered to a continuous and five microns for flushing. Fewer and smaller particles result in a predictable environment where the following EDM benefits can be achieved.
Reduced Machining Time=Faster Cuts
Without clean dielectric, microscopic particles present in the oil can interfere with effective machining of the workpiece. If present in sufficient quantities, the frequency of discharge will be reduced and the electrode will back away from the cut. TAGUTI’s five microns filtration helps to eliminate this contamination contributing to efficient performance at optimum machining speed.
Improved Accuracy
Geometric shapes may be deformed and tolerances not achieved when dielectric is contaminated by conductive particles. Again, TAGUTI’s five microns filtration capabilities minimize these particles which interfere with the controlled discharge machining of the sidewalls of the cavity. Clean dielectric is essential to achieve the repeatability and close tolerance requirements of production and multi-cavity mold applications.
Reduced Pitting=Reduced Polishing
Particles bridging the gap between the electrode and workpiece convert the AC current used in EDM to DC current. This causes a concentrated discharge, resulting in arcing and pitting that damages the electrode or the workpiece. With dielectric filtered to five micron, more consistent current allows finer surface finishes that reduce polishing time.
So we can find that a good EDM filters or Wire EDM Filter is very important to the EDM machine. Choose TAGUTI, Manufacturing better!
