Electrical discharge machining

Machines use sparks to cut metal.

Two metal pieces stay close. They do not touch. A special liquid sits between them.

Sparks jump through the liquid. These sparks make tiny holes. The holes change the shape of the metal.

This works on very hard metals. It can even shape metal that is hard to cut.

New liquid flows in to clean the area. This helps the machine keep working. It is a clever way to make tools.

Some machines use sparks to cut metal. This way is called electrical discharge machining, or EDM. It is great for very hard metals. These metals are often too tough for normal tools.

To work, the machine uses two metal parts called electrodes. One electrode is the tool. The other is the workpiece, which is the metal being shaped. They stay very close but never touch. A special liquid sits between them. We call this a dielectric liquid.

When the voltage goes up, sparks jump through the liquid. These sparks make tiny craters on the metal. This removes small bits of material to make a shape. After each spark, new liquid flows in. This is called flushing. It carries away tiny bits of metal debris.

There are different kinds of EDM. In wire EDM, the tool is a thin wire. It can cut very thin paths. In die-sinking EDM, a shaped block is used. It sinks into the metal to make a cavity.

Electrical discharge machining, or EDM, is a special way to shape metal. It is often called spark machining or spark eroding. This method is very helpful for working with extremely hard materials. Some metals, like titanium alloys or carbides, are too tough for regular cutting tools. EDM can also shape ceramics and even polycrystalline diamond tools. It is part of a group called "non-traditional" machining. This group includes other methods like laser cutting and water jet cutting.

The way EDM works is like a repeating cycle of sparks. The machine uses two metal parts called electrodes. One is the tool electrode, and the other is the workpiece electrode. These two parts stay very close but never actually touch. A special liquid called a dielectric liquid sits between them. When the voltage increases, an electric arc or spark jumps through the liquid. This spark creates tiny craters on the metal surfaces. These tiny craters remove small bits of material to create a shape.

After each spark, the machine must clean the area. This step is called flushing. New dielectric liquid flows into the gap between the electrodes. This liquid carries away tiny bits of metal debris. The liquid also restores its ability to act as an insulator. Once the liquid is fresh, the voltage builds up again. This allows a new spark to happen. The cycle then repeats many times to finish the job.

People have been studying sparks for a long time. An English physicist named Joseph Priestley first noted spark erosion in 1770. In 1943, two Soviet scientists, B. R. Lazarenko and N. I. Lazarenko, worked on this. They wanted to stop sparks from wearing down tungsten contacts. They found that using a dielectric fluid helped control the erosion. At the same time, an American team also made EDM machines. Harold Stark, Victor Harding, and Jack Beaver built machines to remove broken drills. Their early machines produced 60 sparks every second.

There are different types of EDM machines for different tasks. Wire EDM uses a thin wire as the tool electrode. This is great for cutting thin paths in hardened steel. The wire moves between two spools so it does not wear out. In the 1960s, new wire-cut machines were developed. One of the first commercial ones was made in the USSR in 1967. Another type is die-sinking EDM. This uses a shaped block to sink into the metal. It makes deep cavities or complex shapes in the workpiece.

Electrical discharge machining, often called EDM, is a specialized metal cutting process. It is also known as spark machining or spark eroding. This method uses electrical discharges, which are essentially sparks, to shape a workpiece. EDM is classified as a "non-traditional" machining method. This means it does not rely on mechanical forces like drilling or milling. Instead, it uses electricity to remove material. It is especially useful for shaping extremely hard materials. These include carbides, ceramics, titanium alloys, and heat-treated tool steels.

The mechanism of EDM relies on a repeating cycle of electrical breakdown and restoration. The process requires two electrodes that must not make physical contact. One is the tool electrode, and the other is the workpiece electrode. A dielectric liquid sits in the space between these two electrodes. As the voltage between the electrodes increases, the electric field becomes stronger. This causes a dielectric breakdown of the liquid, creating an electric arc or spark. This spark removes small amounts of material from both electrodes by forming tiny craters.

Once the current stops, the machine must prepare for the next spark. This stage is called flushing. New dielectric liquid is conveyed into the space between the electrodes. This fresh liquid carries away solid particles, which are known as debris. The flushing also restores the insulating properties of the dielectric liquid. After this, the voltage is restored to its original level. This allows a new dielectric breakdown to occur, repeating the entire cycle.

There are several distinct types of EDM based on the tool used. In wire EDM, the tool electrode is a thin wire. This is ideal for cutting thin paths, or kerfs, in hardened steel. To prevent the wire from breaking due to erosion, it is wound between two spools. This ensures the active part of the wire is constantly changing. Another type is die-sinking EDM, also called conventional or ram EDM. This uses a tool electrode shaped like a block with a specific cavity cut into it. The tool is then "sunk" into the workpiece to create complex shapes.

The history of EDM involves several important discoveries and inventors. English physicist Joseph Priestley first noted the erosive effects of electrical discharges in 1770. In 1943, Soviet scientists B. R. Lazarenko and N. I. Lazarenko investigated how to prevent erosion in tungsten contacts. They discovered that immersing electrodes in dielectric fluid allowed for precise control of erosion. Their design is known as an R-C-type machine because it uses a resistor–capacitor (RC) circuit. Simultaneously, an American team consisting of Harold Stark, Victor Harding, and Jack Beaver developed machines to remove broken drills from aluminum.

Early EDM technology saw rapid improvements in speed and control. The American machines initially produced only 60 sparks per second. Later designs used vacuum tube circuits to produce thousands of sparks per second. In the 1960s, wire-cut EDM emerged for making tools from hardened steel. The first commercial numerical controlled (NC) wire-cut machine was manufactured in the USSR in 1967. Later, David H. Dulebohn’s group developed machines that could optically follow lines on master drawings. By 1976, the first computer numerical controlled (CNC) EDM machine was produced.

Managing the process requires careful control of several technical parameters. One major challenge is electrode wear, which is the gradual erosion of the tool. In micro-EDM, or μ-EDM, parameters are set such that wear is particularly severe. To fight this, engineers use various strategies. One method involves continuously replacing the tool, as seen in wire EDM. Another method uses a multiple electrode strategy, where different shaped electrodes are used in one operation. Some advanced circuits even reverse polarity to deposit eroded graphite back onto the electrode.