The most frequently overlooked factor in the EDM process is the filtration method used to maintain the dielectric fluid. 

A typical tool and die operation had 12 EDM's, each with its own standard paper cartridge filter or diatomaceous earth filtering system. "The fluid was as black as coal," recalled the foreman. "Forget about being able to see the bottom of the work tank. Two inches under the surface everything disappeared." 

Late in 1994, several Charmilles CNC (computer numerical control) EDM’s were installed and integrated with the existing Elox, Sodick and LeBlond Makino units. The project team also recommended installing better EDM filtration systems to cut labor hours and disposal costs. "All filling and draining of the machines is now via the filter and the fluid is filtered to one micron. Even after six months of heavy use, including applications where we pull up to 200 Amps in roughing mode, the oil is absolutely crystal clean." 

Their EDM processing showed marked improvements in machining times and finish as well. One operator, who had relocated with his machine from another facility, found that a wrench die that took nine hours using EDM at his previous shop now took only seven hours at the new shop on the exact same machine. On other applications, typical EDM times dropped more than 20% and some as much as 40%.