A guide to choosing EDM filtration equipment

Poor part quality clearly is a pressing issue, but particulate buildup in the dielectric fluid also has detrimental, and even more costly, effects on key mechanisms of EDMs.

Clean dielectric fluid is fundamental to producing quality parts with any kind of electrical discharge machine (EDM).

This is primarily because the fluid is what transfers the charge from the wire or electrode to the metal (electrodes and wires do not actually make contact with parts). This fluid also flushes the micron-sized particulate that breaks away from the part or electrode from the spark gap.

Numerous factors affect the size, shape, and quantity of these particles, including the type of power supply, material, and the precision of the work being done (roughing or finishing). For example, larger wire size, like 0.3 mm dia. as opposed to 0.15 mm dia., is known to remove larger “chunks” of metal.

Metals like aluminum, INCONEL® alloy, and some coppers have a gummy characteristic; not only do they break off in larger pieces, but they also tend to stick together, making them more difficult to filter out of the fluid. Regular tool steels, on the other hand, tend to break up in smaller pieces that can elude filtration media that has large pores.

When talking about big and small particles, it’s still a matter of just a few microns, in most cases less than the common filter rating of 5. Over time, however, as these particulates accumulate without being properly filtered out of the liquid, they act more and more like sand in the system.

Impact of poor filtration

These tiny pieces of metal not only disturb a burn in the moment they are generated if they are not flushed properly, but as they build up in system fluid, they also can find their way into the spark gap and disturb future work. They also affect the conducting qualities of the liquid. These particulates in the spark gap lead to little explosions that damage both the part and the wire or electrode. Pits then form, weakening the part or requiring time-consuming secondary finishing operations.

Poor part quality clearly is a pressing issue, but particulate buildup in the dielectric fluid also has detrimental, and even more costly, effects on key mechanisms of EDMs. Roller bearings that perform key functions like moving the table and feeding wire can wear prematurely. The delicate—and expensive—solenoids that power the pumps that move the fluid through the system do not get along well with particulate buildup either. And finally, resin life is reduced because it acts as the primary filter instead of the filter itself, resulting in unnecessary accrued costs.

Speed is another factor that is costly over time because of the impact poorly filtered liquid has on cutting speed. It’s difficult for an operator to diagnose, because it’s not something that changes overnight; just as material builds up in the liquid, slowing can happen gradually and feel normal. In reality, muddied liquid interferes with the clear transmission and lessens the intensity of the charge to the part.

Not all filters are created equal

Filtration equipment is the heart of any EDM. When machines aren’t working correctly, further inspection of the filters often makes it clear that the fix is much simpler than taking a machine offline for repair—or at least it could have been.

Filter media, which is where the rubber meets the road in filtration, generally are either a natural material or a synthetic, polyester-style sheet. Regardless of the material, each filter media has a swell factor; when wet, the pores can shrink and actually deliver more filtration than what they are rated for. Similarly, some filters don’t always perform as promised out of the box. The truth is that it takes time for buildup in the form of tiny mountains and valleys to accrue and essentially supplement the actual media’s filtration performance.

Filter media, which is where the rubber meets the road in filtration, generally are either a natural material or a synthetic, polyester-style sheet.

When new filters are installed but shops can’t run their sheeting for a few hours, the chemicals and glues that are sometimes applied to media aren’t getting along with the water. Even regional water differences can have an impact on the effectiveness of the media.

If the only way to make filtration happen is to rely on resin initially, the resin’s life is shortened and there’s probably a better filter option for the work being done or for your liquid’s characteristics. It’s often overlooked, but resin is a cost, too, and it is time-consuming to replace. Resin levels also tell you a lot about how the filtration system is working and the quality of the media you’re using. In a perfect world, a new batch of resin and new filter media should always have about the same effective lifespan.

Resin really is one of the most overlooked factors in proper filtration. EDMs can’t run without it.

In addition to the burn remnants, all kinds of elements naturally occur in tap water that can ultimately affect a burn and the machine’s mechanics. An EDM needs 100 per cent pure water. Many geographic regions have a high concentration of iron in the soil, and if shops replace evaporated water in the tank from the tap, a hard metal like that is clearly going to affect the burn, unless the resin is fully functional.

There are also some gimmicks out there in filter design that get the buzz but may not be all that’s promised. Some are sold as taller, “life-extending” filters, but liquid still has to run through the media regardless of its height. There are even some filters in which the media is replaceable inside the cage, but these don’t deliver the levels of filtration that they should.

6 tips for maintaining well-filtered EDM liquid

Different wires, electrodes, and materials burn differently. When softer metals burn off, their particles can stick together, clogging filters faster. Larger-diameter wires and roughing operations can have the same result.

Not all EDMs do the same work. Knowing the differences and how they’ll affect filtration provides a chance to optimize cutting and machinery performance.

Many shops say that they get 400 to 450 hours out of their filters. Be skeptical about this. The media often misses materials until the precoat is completed. Micron ratings of a media change as a precoat occurs, and small peaks and valleys form on the screen. Also, not all materials and liquids interact the same with a filter over time, and different media cake at different rates.

This is the most overlooked factor of filtration. Water is different everywhere, and different filters can have different chemicals and glues. This means that they don’t always filter as they should when first installed. The filter itself and resin work hand-in-hand to deliver complete filtration, so don’t opt for filters with higher micron ratings and lean too heavily on resin to do the heavy lifting.

Sight glasses, solenoids, valves, and plumbing all suffer when filtration is poor. Knowing this in advance helps prevent machine and part problems. Spending a few extra dollars on a filter is much easier to swallow than spending thousands to replace a part.

Some filters are ready to perform as advertised right out of the box. I call this honest filtration. Others perform as stated only for the better part of their life because of variables like swell rate and chemicals, making it difficult to track if and when filtration begins to suffer. This generally means opting for synthetic media over cellulose-based alternatives.

Most people who buy a Mercedes opt to go to a Mercedes dealership for service, and wisely so. The same goes for EDM filtration. OEM EDM manufacturers usually test the filtration they offer to make sure it performs as advertised right away and for a life cycle that’s intended. Factors like chemicals, glues, media materials, caking, and swell rates are all tested and accounted for upfront.

Consumables like filters often are afterthoughts in the machining or fabrication shop, but that is a risky game to play, especially when it comes to the world of EDM. It may take a shift in mindset and budget planning, but whatever short-term discomfort this may cause will be far outweighed by the long-term benefits and savings.