Electrical Discharge Machining (EDM)

Electrical Discharge Machining (EDM) shapes conductive materials with controlled sparks, achieving intricate geometries, sharp corners, and tight tolerances regardless of material hardness.

Overview

Electrical Discharge Machining (EDM) removes material using rapid electrical discharges between an electrode and a conductive workpiece submerged in dielectric fluid. Common sub-processes include sinker EDM for cavities, wire EDM for precision profiles, and EDM drilling for very small, deep holes. The process introduces no cutting forces, allowing stable machining of delicate, hard, or thin-walled parts with minimal distortion.

Choose EDM for features that are difficult or impossible to cut with traditional tools: very tight internal radii, deep narrow slots, complex die and mold geometry, and micro-holes in hard alloys. EDM excels on hardened tool steels, carbides, and high-temperature alloys without annealing or softening. Tradeoffs include slower material removal rates, higher hourly machine cost, and the need for conductive materials only. EDM may leave a recast layer, so critical surfaces sometimes require extra skim passes or post-processing. For low-to-medium volumes of high-value precision parts, EDM is often the most reliable and repeatable option.

Common Materials

  • Tool steel H13
  • Stainless steel 17-4
  • Carbide
  • Titanium Ti-6Al-4V
  • Inconel 718

Tolerances

±0.0002" to ±0.001"

Applications

  • Injection mold cavities and cores
  • Extrusion and stamping dies
  • Turbine blade root forms and fir-tree slots
  • Precision gear and spline profiles
  • Micro cooling or fuel injector holes
  • Sharp internal keyways and slots

When to Choose Electrical Discharge Machining (EDM)

Use EDM when you need precise features in conductive materials that are hard, delicate, or difficult to machine with rotating tools. It is ideal for tight-tolerance profiles, sharp internal corners, deep narrow slots, and micro-holes on low-to-medium volume, high-value parts. EDM is especially useful after heat treatment, avoiding distortion from secondary machining steps.

vs Milling

Choose EDM over milling when you need sharp internal corners, very small internal radii, deep narrow slots, or features in hardened materials that would require tiny, fragile end mills. EDM is also preferred when tool reach or rigidity makes milling unstable or when avoiding cutting forces is critical for thin walls.

vs Turning

Choose EDM instead of turning for intricate profiles on parts that cannot be held or rotated easily, or when you need internal forms that a lathe tool cannot reach. EDM is useful for hardened shafts or forms requiring precise non-cylindrical features, such as keyways and spline forms, after heat treat.

vs Drilling

Use EDM drilling when you need very small diameter, high-aspect-ratio holes in hard or heat-treated materials that conventional drills cannot handle reliably. It is also preferred for angled or intersecting holes that risk drill walk, or for starting holes for wire EDM threading in thick sections.

vs Grinding

Select EDM instead of grinding when you need complex 3D cavities, non-linear profiles, or features that are difficult to fixture for a grinding wheel. EDM is also advantageous for intricate die details, deep slots, and internal geometries where wheel access or form dressing would be problematic.

vs Broaching

Choose EDM over broaching for low-volume internal forms such as keyways, splines, and polygons where dedicated broach tooling is not economical. EDM handles harder materials and more complex or variable profiles without the cost and lead time of custom broach tools.

Design Considerations

  • Keep overall cut height and part thickness as low as feasible; tall cuts greatly increase EDM cycle time
  • Design features so flushing holes or clearances can be added; good dielectric flushing improves speed and accuracy
  • Specify the minimum material removal or stock for EDM so the shop can minimize roughing and reduce burn time
  • Call out which surfaces truly require tight tolerances or fine surface finishes; each extra skim pass adds cost
  • Avoid unnecessary extreme aspect ratio slots or holes; if required, clearly define depth, width, and access for fixturing
  • Ensure all features to be EDM’d are on datums that can be reliably located after heat treatment or prior machining steps