Electrical Discharge Machining (EDM)

EDM removes metal with controlled electrical sparks in a dielectric, producing precise features in any conductive material with no cutting forces.

Overview

Electrical Discharge Machining (EDM) is a non-contact machining process that erodes conductive materials using electrical discharges between an electrode and the workpiece in a dielectric fluid. Common sub-processes include sinker EDM for cavities and complex 3D shapes, wire EDM for precise through-cuts and profiles, and EDM drilling for small, deep holes.

Choose EDM when hardness, thin walls, or delicate features make conventional cutting risky, and when you need sharp internal corners, fine details, or deep, narrow features with high accuracy. Typical tradeoffs are slower cycle times, higher cost per part, and practical limits on non-conductive materials.

Expect a recast/heat-affected layer and surface finish that depends heavily on rough/skim pass strategy; critical sealing or fatigue surfaces may need secondary finishing. Electrode design (sinker) and wire start holes (wire) drive both lead time and cost.

Common Materials

  • Tool steel D2
  • Hardened H13
  • Stainless steel 17-4 PH
  • Inconel 718
  • Titanium Ti-6Al-4V
  • Carbide

Tolerances

±0.0005" to ±0.002"

Applications

  • Punches and dies
  • Injection mold cores and cavities
  • Extrusion dies
  • Carbide wear components
  • Keyways and splines in hardened parts
  • Fuel injector and nozzle micro-holes

When to Choose Electrical Discharge Machining (EDM)

EDM fits low-to-medium volume work where feature precision matters more than removal rate, especially in hardened or tough alloys. It’s a strong choice for thin sections, deep narrow cavities/slots, sharp internal corners, and small deep holes where cutting forces would distort the part. Plan for longer lead times and validate surface integrity needs early.

vs Milling

Choose EDM when you need sharp internal corners, deep narrow pockets, or hardened materials that would require slow milling and frequent tool wear. EDM also avoids cutting forces that can deflect thin ribs and webs, improving geometric stability on delicate features.

vs Turning

Choose EDM for non-axisymmetric features on turned parts—keyways, splines, vents, and intricate profiles—especially after heat treat. EDM is also useful when the part is too hard or too thin-walled to hold tolerances under cutting loads.

vs Drilling

Choose EDM drilling for very small diameters, extreme depth-to-diameter ratios, or hard materials that rapidly wear drills. EDM can produce starter holes for wire EDM and holes in locations where chip evacuation and tool breakage are major risks.

vs Grinding

Choose EDM for complex internal geometries, deep slots, or enclosed features that grinding can’t access. EDM can hold tight tolerances without wheel dressing constraints and can create shapes beyond simple flats and cylinders.

vs Broaching

Choose EDM when volumes don’t justify broach tooling or when features are in hardened material after heat treat. EDM also handles one-off or changing profiles without dedicated broach design and lead time.

Design Considerations

  • Call out which EDM method is intended (wire, sinker, or EDM drilling) and identify surfaces that cannot tolerate recast or micro-cracking
  • For wire EDM, provide a start-hole location/size or allow a tab/lead-in area so the shop can initiate the cut cleanly
  • Avoid unnecessarily tight corner radii requirements in sinker EDM; specify minimum internal radii only where function demands it
  • Define datum scheme and inspection surfaces clearly; thin parts may need dedicated fixturing to control flatness and taper
  • Dimension deep narrow features with realistic aspect ratios and indicate acceptable taper on tall walls if applicable
  • Specify surface finish requirements by functional surface; skim passes improve finish but add time and cost