Electrical Discharge Machining (EDM) is a non-traditional machining process that erodes conductive materials through spark erosion generated by pulsed electrical discharges between two electrodes immersed in a dielectric fluid. It is also known as spark machining or electro-erosion machining. EDM is capable of machining materials that are difficult to cut with conventional machining methods, as well as molds and parts with complex-shaped holes and cavities: Materials: It machines various hard and brittle materials such as cemented carbide and hardened steel. Structures & Shapes: It produces deep and slender holes, irregular holes, deep grooves, narrow slots, thin slices, and molds including hot forging dies, die-casting dies, extrusion dies, plastic molds and bakelite molds.

Electrode Fabrication
Graphite and pure copper electrodes are commonly used.Graphite electrodes have excellent machinability and can be easily formed into complex shapes. Its cutting resistance is only 1/5 that of copper, and machining efficiency is twice as high. It features high strength, high temperature resistance and extremely low thermal expansion, so it resists deformation when machining ultra-high (50–90mm) and ultra-thin (0.2–0.5mm) electrodes. Graphite has good electrical conductivity, which greatly saves machining time in EDM, especially in roughing. Graphite electrodes offer faster discharge speed than copper but higher wear. Copper electrodes are typically used for precision mold finishing, though their machined surfaces often require polishing to improve surface quality.

Carbon Slag and Debris Removal
EDM proceeds smoothly only when the generation and removal of carbon slag are balanced. In practice, machining speed is often reduced to ensure effective debris flushing. Another obstacle to slag removal is complex workpiece geometry, which blocks chip evacuation paths. Good flushing conditions must be actively established with targeted solutions. Dielectric fluid with certain insulation acts as the discharge medium, and also provides cooling and chip removal during machining. Common dielectrics include low-viscosity, high-flashpoint, stable media such as kerosene, deionized water and emulsions.

Electrode and Workpiece Wear
Long discharge pulse duration helps reduce electrode wear. Roughing EDM generally uses long pulses and high current, achieving fast material removal with low electrode wear. In finishing, small current must be paired with shorter pulse duration, which increases electrode wear and significantly reduces machining speed. Part of the discharge energy is consumed on the tool electrode, causing wear that affects forming accuracy. The cross-sectional profile of the tool electrode must be uniformly smaller than the target hole dimension by a machining gap. Its dimensional accuracy must be one grade higher than the workpiece, and its surface roughness must be lower. Typically, EDM can achieve a dimensional tolerance of IT7 and surface roughness Ra 1.25 μm. When machining relatively large holes, a pre-drilled hole is usually made with a proper allowance (approximately 0.5–1mm per side). Excessive allowance reduces productivity and makes positioning difficult during EDM. Cavity machining is mostly blind-hole machining with complex geometry, which hinders dielectric circulation and debris removal, making it more difficult than through-hole machining.To improve machining conditions, oil flushing holes are sometimes drilled in the tool electrode for cooling and ejecting machining byproducts.