EDM, sometimes called Wire Cutting, is a favourite fast milling technique among Perth’s many high-end machine shops for machining very hard materials and intricate shapes. But EDM produces a conductive, sludgy swarf at a very high rate, and this is carried in the dielectric medium until removed by filtration. As the burden of cutting debris increases, the dielectric properties of the medium deteriorate, reducing the cutting speed. As EDM wire-cutting techniques have advanced, the need for clean dielectric has become greater.
The fundamental challenge for EDM wire cutting has always been to remove cut material at a sufficient rate to maintain the process at the greatest possible speed. Unlike traditional, curly-whirly swarf, debris from EDM consists of very small particles which are carried away from the arcing region by, and dispersed within the dielectric medium. The greater the burden of this swarf, the greater the likelihood that, as it passes through the arcing region a spark will be interrupted by a short. The cutting rate therefore suffers.
Cutting tapers is one of the tasks at which wire-cutting excels. Every machine has dimensional and angular limits to the tapers it can handle. However it will not live up to these promises if the quality of the dielectric medium – usually deionised water – is allowed to deteriorate through the accumulation of conductive swarf.
The Filtration Challenge
Dirty dielectric fluid means slower cutting, but that’s not the end of it – accuracy and surface finish quality also suffer. Clearly, creating an efficient filtration system has been one of the main concerns of the many manufacturers who compete in this field.
One company, Robofil, has addressed this issue. Its 240cc and 440cc models incorporate twice the usual number of filters – 4 instead of 2. The filters work as two pairs, each with its own circuit. These can run simultaneously to keep up with a high rate of work, or independently – allowing filter media to be replaced with the machine running. The filtration system is designed to run at a constant pressure, making more efficient use of the filtration medium. A new design of paper cartridge gives a 54% increase in surface area. Under like for like conditions, filters last 2.6 times longer, and extends the machine’s unattended run time by 3.8 times. Overall, filter costs are reduced by 40%.