Depending on the fluid’s type, make and age, the easiest way to check the condition of your sinker dielectric oil is to ask the fluid manufacturer to perform a dielectric strength test. If you are using a standard petroleum-based di-electric fluid, the oil’s useful life expectancy will be from 3-5 years. If you are performing larger and higher-amperage EDMing, then the fluid life can be a bit shorter.
From a machining performance standpoint, it is very important to track and evaluate the dielectric fluid, especially when using standard petroleum-based oils. Standard EDM fluids will break down over time and lose their dielectric strength properties. This means that as an oil ages, its ability to support stable EDM machining is decreased. The loss of machining speed (and a longer cycle time) and reduced surface finish quality will be the most easily observed result of aged dielectric fluid. Old, rancid oil is also much harsher on the skin and more likely to cause irritation and adverse reactions in the operator.
The loss of machining performance will be gradual as the oil ages rather than an overnight change. Many shops fail to evaluate the performance of their EDM fluid, and many do not ever consider replacing it. Is it fair to expect top performance from a car engine if its oil has not been changed for years? EDM is no different. Sinker EDM dielectric oil is a consumable, and it will not last forever.
To help track EDM performance, some shops have established a baseline test cut to evaluate machining output. This test might be performed once per year as part of an annual maintenance schedule, and is a good way to ensure that everything is working at optimum levels.
If your EDM dielectric fluid needs replacing, take a close look at the newer full synthetic dielectric fluids. The latest synthetic fluids, such as IonoPlus-3000, do not break down over time, and do not require periodic replacement. Synthetic fluids do cost more up-front, but since they don’t need to be replaced, they will provide long-term savings. Synthetics are often friendlier to work with, and they cause less skin irritation issues. Full synthetic dielectric fluids are also 100% compatible will all existing machines, so there is no need for any seal or gasket material replacement. It is wise to evaluate the age and performance of your dielectric fluid. If your oil is older than 5 years, then it is probably overdue for replacement, and is costing you valuable machining time. Replacing old or spent dielectric oil will provide gains in performance no matter the type of replacement fluid, but consider the long-term advantages provided by the latest synthetic fluids. As good practice, it is also recommended to replace the machine filters anytime the di-electric fluid is replaced to avoid contamination.