In advanced manufacturing sectors such as precision mold production, aerospace component machining, and semiconductor fabrication, Electrical Discharge Machining (EDM) remains an indispensable process.
A critical factor determining the performance and reliability of EDM operations is the EDM oil, which functions far beyond a simple coolant or lubricant.

EDM oil must simultaneously provide insulation, cooling, and flushing while maintaining chemical and thermal stability under extreme operating conditions.
This article examines three fundamental physical properties — viscosity, flash point, and dielectric strength — and how their balance directly affects EDM quality and process efficiency.

1. Viscosity: Balancing Cooling and Flushing Performance

Viscosity represents the internal resistance of a fluid to flow, and in EDM oil, it dictates how efficiently the oil cools and removes debris during discharge.

▪ When viscosity is too high:

• Cooling efficiency decreases, causing localized overheating.
• Sludge removal becomes slower, and carbon residues tend to remain between the electrode and the workpiece.
  → This leads to rougher surface finishes and reduced machining speed.

▪ When viscosity is too low:

• The spark gap may lose its insulation prematurely, leading to unstable discharges.
• The oil vaporizes more easily, increasing odor and mist generation in the work area.

In general, a moderate viscosity range of approximately 2–4 mm²/s at 40°C provides optimal performance — ensuring both stable discharge control and effective heat dissipation.

2. Flash Point: A Critical Parameter for Safety

The flash point is the lowest temperature at which oil vapors can ignite in air.
Because EDM continuously generates high-voltage sparks, the flash point directly affects operational safety and thermal stability.

▪ If the flash point is low:

• The oil is more prone to vaporization and ignition during machining.
• This increases the risk of fire and operator exposure to harmful fumes.

▪ If the flash point is high:

• The oil remains stable under prolonged exposure to heat.
• Oxidative degradation and vapor loss are significantly reduced.

For industrial EDM applications, oils with flash points above 100°C are considered safe, while premium-grade fluids exceeding 150°C are preferred for high-load or continuous operations, offering both safety and durability.

3. Dielectric Strength: The Core of Discharge Control

In EDM, the dielectric strength of the oil defines its ability to withstand electric fields without breakdown.
This property determines the precision and stability of each discharge event between the electrode and the workpiece.

▪ When dielectric strength is too low:

• Unwanted discharges (short circuits, arcs) can occur.
• The surface becomes rough, and electrode wear accelerates.

▪ When dielectric strength is too high:

• Discharges may occur less frequently or with delay, lowering machining speed.

Typically, a dielectric breakdown voltage of 15–30 kV or higher is required to ensure consistent spark formation while maintaining insulation stability throughout the process.

4. Achieving Balance: The Key to Optimal EDM Performance

Each physical property serves a distinct role:

• Viscosity governs heat dissipation and debris removal.
• Flash point ensures safety and thermal endurance.
• Dielectric strength enables precise control of electrical discharge.

However, these characteristics are interdependent — improving one can often compromise another.

For instance:

A high-viscosity, high-flash-point oil may offer superior safety but slower cooling.
A low-viscosity oil enhances flushing but can reduce insulation stability.

Thus, the optimal EDM oil formulation is a carefully engineered balance that matches both the work material (e.g., steel, copper, aluminum) and the machining mode (roughing vs. finishing).

🏁 Conclusion

The performance of EDM oil cannot be defined by a single property or specification.
Only when viscosity, flash point, and dielectric strength are properly balanced can the oil deliver:

• Stable and consistent discharges,
• High-quality surface finishes,
• Extended electrode life, and
• Safe, low-maintenance operation.

In essence, understanding and controlling the physical properties of EDM oil is the foundation of superior machining quality and process stability in modern precision manufacturing.

Dyna Co., Ltd.
Industrial Lubricant Solution
E-Mail : dyna@dynachem.co.kr
Web : dyna.co.kr/en/