Dielectric fluids for EDM wire cutting
Dec. 18, 2021
In order to maximize cutting speed and ensure perfect surface finish and part accuracy during in-line EDM cutting, it is necessary to ensure that the micro particles generated during the process are removed for optimal results, and this is where "dielectric fluids" come in.
Dielectric fluids: what are they?
A dielectric fluid is any liquid that has high dielectric strength and high electrical resistance. It is an electrical insulator, but in liquid form. Common dielectric fluids include vegetable oils and mineral oils because they are cheap and readily available. Other fluids, such as fluorocarbons and silicone resins, are sometimes used when non-flammable or high temperature fluids are required.
When performing EDM wire cutting, the dielectric fluid used is deionized water. Deionized water...
▸ acts as a flushing agent, washing away any debris generated during the cutting process.
▸ acts as a semiconductor between the workpiece and the energized wire to maintain controlled and stable conditions for ionization in the spark gap.
▸ cools to ensure that the table, workpiece, fixture and wire remain at a stable temperature; limiting the thermal growth of the machine and workpiece so they can maintain tight tolerances.
When commissioning EDM machines, deionized or distilled water with very low conductivity is used initially. Later, the operator can use tap water as soon as it passes through the deionized resin bottle, where the charged particles are neutralized and all contaminants are filtered out. The deionized water is then passed through a 3 micron to 5 micron filter paper to remove any residual particles.
Since the EDM wire cutting process produces microscopic particles, ensuring chip removal is critical to obtaining accuracy and maximizing cutting speed.
For the dielectric fluid, which is considered an effective flushing agent, it must flow freely to the point where the cut occurs. Considering that each spark melts tiny pieces of the workpiece, the fluid removes chips and prevents them from adhering to the workpiece surface and wires.
Adjustable flushing nozzles located near the bottom and top of the workpiece direct the fluid flow in opposite directions to the area where the cut is being made.
When set up correctly, the flow of water from the nozzle and the flushing pressure meet in the middle, creating what is called a "cocktail" effect. The effect can be seen in the blanks removed after the roughing pass.
If the microscopic debris is mainly from the bottom of the solid being cut, the flushing may not be balanced. When this happens, the wire ends up going through or across the surface of the workpiece, thus weakening it. This, in turn, can affect cutting conditions and lead to frequent wire breaks.
In addition, when flushing pressure is too high, it can cause wire deflection and vibration, especially when working with tall workpieces. In such cases, the conditions can affect the accuracy and surface finish of the part being cut.
Discharge processing filtration
To make the most of wire machines, users must ensure that their dielectric fluid is always clean. If it becomes too dirty, some materials will begin to rust inside the tank, affecting the surface finish. Good maintenance practices include sending deionization bottles for regeneration and regularly replacing the system's paper cartridges.
It is important to note that certain materials clog the filter paper faster than others when cutting. For example, when working with additively manufactured parts, loose un-sintered metal particles inside may seep into the system and clog the filter.
Of course, you don't have to know this when we cut for your project. We pay attention to the details and get your job done right!