Oil-based wire EDMs have been around for a while, but did not gain much attention because their cutting speeds were quite a bit slower when compared with water-based wire EDMs. But shops that were not so concerned about cutting speeds often used oil-based machines instead of water-based ones to eliminate the problem of corrosion buildup on parts left in machines overnight or for long periods of time.
In general, water-based wire EDMs have always delivered better cutting performance, in particular, when running small (< 0.004") wire diameters because the water cools the spark gap much faster, allowing for higher cutting currents, and thus faster cutting speeds.
Some oil-based wire EDMs, however, can now cut at the same speeds as water-based machines. "This is the result of advancements in EDM generator technology, such as that found in the AgieCharmilles IPG high-performance generator from GF Machining Solutions on the company's Cut 1000 OilTech oil-based wire EDM," said a company spokesperson. "Besides this special generator, the machine, designed for micromachining, also incorporates other proprietary advancements that further boost cutting speeds."
For shops micromachining parts for nano applications, oil-based EDMing allows them to successfully generate precise and clean part surfaces. This is critical when secondary cleaning or polishing operations are not an option on parts that are too small to handle.
In the past, EDM builders faced challenges with oil-based machines - especially those for micromachining - when it came to adapting automatic wire threading capabilities. On water-based wire EDMs for micromachining, automatically threading extremely small wire diameters is easily achieved, but trying to automatically thread them through oil's thicker viscosity took some new technology.
For example, the Cut 1000 OilTech machine quipped with the only dual wire system can use wire that is 0.0008" in diameter, and GF AgieCharmilles had to design an automatic wire threader specifically for it. This threader allows that size wire to pierce the oil's surface, and the system provides reliable automatic wire-threading cycles.
When comparing the operating costs of a water-based wire EDM to those of an oil-based machine, operating costs of the oil-based machine may be a bit higher in the first year of operation. However, in the years following, those costs are measurably less than with a water-based machine.
In the first year of operation, oil-based EDMs involve initial cost outlays for dielectric tank oil and, as recommended by most EDM builders, fire extinguishing systems, such as those used on die sinking EDMs.
What makes oil-based wire EDMs less expensive to operate after the initial year of operation is the fact that they eliminate the need for deionization resin bottles because oil does not break down like dielectric water does. Frequently changing deionization resins can be costly, especially for shops that must maintain low water conductivity levels essential to achieving superior surface finishes. Keeping conductivity levels low (5µS) requires frequent resin changes.
Similar to water-based wire EDMs, oil-based wire EDMs also require filtering of dielectric fluid. Oil-based machine filters are the same as those used on die sinking EDMs. But, the wire EDM filters typically last longer than die sinker filters due to the fact that the micromachining wire EDM process generates fewer particles and material removal rates are lower.
Shrinking part sizes as well as other new and existing industry requirements continue to drive the use of oil-based wire EDMs. In fact, such technology has quickly caught on in Asia and Europe.
Many EDM builders believe that the emergence of today's technologically advanced oil-based wire EDMs is an opportunity for the average U.S. shop to set themselves apart from the competition because, in the United States, few shops have adopted the technology.
For instance, oil-based wire EDMing allows mold and die shops to machine additional features into finished mold components without affecting the parts' polished surfaces, unlike with water-based wire EDMing. These shops can also cut fine mesh-type mold materials using oil EDM without having those parts absorb water during the machining process or when left on the machine for extended periods of time, as is the case with water-based wire EDMing.
Oil-based wire EDM also benefits those shops cutting tiny carbide parts and facing similar water absorption issues as shops cutting fine mesh materials. Water-based EDMing can result in adverse surface conditions caused by the water in the dielectric tank, so carbide parts must be dried as soon as the part is completed to prevent corrosion. An oil-filled dielectric tank eliminates these problems.
When carbide parts are left in dielectric water, the amount of water the parts absorb depends on the particular type of carbide's density level. Once water is absorbed, corrosion can occur deep inside certain carbide types. This corrosion permeates way beyond an EDMed or ground part surface and is undetectable with simple visual inspection. As this corrosion grows, it jeopardizes the integrity of the finished part.
"Companies such as GF Machining Solutions continue to advance oil-based wire-EDM technology," said the spokesperson. "And as they do, more shops are discovering the benefits, especially those doing micromachining and cutting materials that can be adversely affected by water-based EDM operations."
Authored by: Gisbert Ledvon, Director of Business Development, GF Machining Solutions
For more information contact:
Gisbert Ledvon
GF Machining Solutions
560 Bond St.
Lincolnshire, IL 60069-4224
800-CTC-1EDM
gisbert.ledvon@us.gfac.com
www.gfac.com/us