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In the mold manufacturing workshop, you often witness such a scene: A complex copper electrode is slowly submerged into a working tank filled with liquid, approaching a hard mold steel. Instantly, sparks flash beneath the liquid surface, emitting a "zing zing" sound, and metal debris is quietly washed away.

This is EDM machining (Electrical Discharge Machining). It is an indispensable process in modern mold manufacturing and is also the "magical operation" that many people are curious about.

1. How does EDM work? — The "Carving Art" of Micro Lightning

The principle of EDM sounds simple: Using the electric sparks generated by electricity, like miniature lightning, to "burn" the metal away.

The entire process can be understood through four steps:

1. Electrode preparation: First, make an electrode with a shape opposite to the final mold cavity. It is usually made of copper or graphite. For example, if you want to machine a square depression on the mold, make a slightly smaller square protruding electrode.

2. Positioning the electrode and the workpiece: The electrode is clamped onto the machine spindle, and the workpiece (mold steel) is immersed in the working fluid. They maintain a very small gap (about 0.01 to 0.5 millimeters, equivalent to the thickness of a hair strand).

3. Pulse discharge: The machine applies high-frequency pulse voltage. When the gap is the smallest, the working fluid is broken down, and a spark discharge occurs instantly. The center temperature of the spark can reach 8000°C to 12000°C (higher than the surface temperature of the sun!), and the metal is instantly melted or vaporized, "exploding" a small depression.

4. Cyclic processing: The working fluid continuously washes away the molten metal particles and heat. Then the electrode continues to descend, and the next spark discharges in the adjacent position again. Hundreds of thousands to tens of thousands of such discharges occur per second, and countless tiny depressions are superimposed, ultimately the shape of the electrode is precisely "copied" onto the mold steel.

2. What is the "water" that is immersed during mold processing?

Answer: It is usually not water, but a special "electrical discharge oil".

In rare cases, deionized water is used. However, "mold EDM processing" (especially forming processing), the liquid inside is almost all oil, not ordinary tap water.

Why must oil be used instead of water?

The EDM working fluid (dielectric fluid) has four indispensable functions, which ordinary water cannot fulfill.

First is insulation, controlling the spark. Oil is an excellent insulator. Voltage only breaks down and discharges when the gap between the electrode and the workpiece is sufficient. The spark is precisely controllable. Ordinary water contains a large number of ions and has strong conductivity. The current will run wild and cannot form a stable spark, and cannot perform precise processing.

Second is cooling, preventing overheating. Each spark discharge generates an over 10,000-degree Celsius temperature, and the oil removes a large amount of heat through circulation, preventing the mold surface from annealing or cracking due to overheating. The cooling performance of water is inferior to that of oil, and it is prone to boiling and generating bubbles, which interfere with the stability of the processing.

Third is chip removal, clearing debris. Each discharge "explodes" tiny metal particles, and the oil flows and sweeps the particles away, keeping the discharge gap clean. If using ordinary water, metal debris is likely to accumulate in the gap, causing short circuits or arc burns, directly destroying the mold.

Fourth is rust prevention, protecting precision. The oil wraps the metal surface, and the mold steel will not rust even after being immersed in it for a long time. While the mold steel is immersed in ordinary water for a few hours, it will rust completely and the processing surface will be completely ruined.

3. Safety Reminder

Electric spark oil, especially kerosene, is flammable. During the machining process, sparks fly everywhere and the oil temperature rises, which poses a fire risk. A regular EDM machine must be equipped with an automatic fire extinguishing system. Smoking or using open flames is strictly prohibited near the machine during operation, and the effectiveness of the fire extinguishing devices must be checked regularly.