EDM vs CNC

Sparks vs cutters.
Any hardness.
Complementary processes.

Q: EDM surface quality?

EDM leaves "recast layer" — 0.01-0.05 mm of resolidified material with altered structure. For most applications, adequate. For fatigue-critical parts: recast layer can be crack initiation site — polishing or grinding after EDM may be required. Wire EDM: better surface than sinker EDM (finer finishing passes possible). For aerospace: EDM specifications often require surface integrity verification.

Q: Mold making workflow?

Standard injection mold workflow: (1) CNC mill bulk features — fastest material removal. (2) Sinker EDM for features CNC cannot produce (sharp internal corners, complex cavity details, deep features). (3) Wire EDM for ejector pin holes and precise slots. (4) Polish and texture as needed. EDM handles 10-30% of mold features that CNC cannot — essential complement, not replacement.

Q: Small hole EDM?

Small hole EDM (also "hole popping" or "fast-hole EDM"): rotating thin tube electrode drills small deep holes (0.1-6 mm diameter, 100+ mm deep). Used for: cooling holes in turbine blades, start holes for wire EDM, small diameter deep holes. Speed: 20-100 mm/minute drilling rate. Often faster than conventional micro-drilling for deep small holes. Specialty process we coordinate for specific applications.

Q: Surface texture options?

EDM surface texture adjustable by electrode selection and discharge parameters. Fine finish: Ra 0.2 µm achievable with final passes. Coarse/textured: Ra 6.3+ µm deliberately produced for friction, bonding, cosmetic applications (injection mold texture). VDI surface texture series (VDI 9-45) commonly specified for mold cavities — produces specific matte to leather-grain textures. Common spec on consumer product molds.

EDM removes material by electrical sparks, not mechanical cutting. Can machine hardened steel, sharp internal corners, and features no milling tool can reach. But slower and more expensive than CNC for most features. Used together, they produce features impossible with either alone.

Get a Quote DFM guide

01 · At a glance

Side-by-side summary.

Option A

EDM (Electrical Discharge)

Material removal by controlled electrical sparks. Works on any electrically conductive material at any hardness. Can produce sharp internal corners, deep narrow slots, complex profiles. Slower than cutting.

Option B

CNC Machining (Milling/Turning)

Material removal by mechanical cutting. Fast, versatile, economical for most features. Limited by tool reach, tool geometry (can't produce sharp internal corners), and material hardness (practical limit ~50 HRC).

02 · Detailed comparison

Feature-by-feature breakdown.

Attribute	EDM	CNC Machining
Material hardness	Any (0-70+ HRC)	Practical limit ~50 HRC
Sharp internal corners	Yes (easily)	Limited (tool radius)
Speed (typical features)	Slow	Fast
Surface finish	Ra 0.2-6.3 µm	Ra 0.4-3.2 µm
Tolerance	±0.005-0.02 mm	±0.025-0.1 mm
Setup time	Fast (wire EDM)	Moderate
Tool/electrode cost	Consumable electrodes	Consumable tools
Max material removal	Low (0.1-5 cm³/min)	High (100+ cm³/min)
Surface integrity	Recast layer (0.01-0.05 mm)	No recast
Cost per feature	Higher	Lower
Application	Specialized features	Most features
Typical use	Sharp corners, hardened parts	Primary machining

03 · Decision guide

When to choose each.

Choose EDM (Electrical Discharge) when:

Sharp internal corners (< tool radius)
Hardened material (> 50 HRC)
Deep narrow slots
Specialty dies and molds
Features impossible with milling
Complex 2D profiles (wire EDM)

Choose CNC Machining (Milling/Turning) when:

General material removal
External features and pockets
Standard holes and slots
Production quantities
Cost-sensitive features
Most mechanical parts

FAQ

Common questions.

Wire EDM: thin wire (0.1-0.3 mm) traverses like a bandsaw. Cuts 2D profiles through part thickness. Used for: punches, dies, gears, complex 2D profiles. Sinker EDM (Die Sinking): shaped electrode plunges into work. Used for: mold cavities, internal features, blind pockets with complex shape. Two processes, different capabilities. For most mold work, both used in sequence.

EDM costs 2-10× CNC for equivalent material removal. Justified when: (1) Feature impossible with CNC (sharp internal corners in hardened part). (2) Hardened material machining would require specialty tooling beyond EDM cost. (3) Very small features (< 2 mm) where milling is impractical. (4) Deep narrow features. Hybrid workflow: CNC bulk material removal, EDM specialty features only.

EDM leaves "recast layer" — 0.01-0.05 mm of resolidified material with altered structure. For most applications, adequate. For fatigue-critical parts: recast layer can be crack initiation site — polishing or grinding after EDM may be required. Wire EDM: better surface than sinker EDM (finer finishing passes possible). For aerospace: EDM specifications often require surface integrity verification.

Standard injection mold workflow: (1) CNC mill bulk features — fastest material removal. (2) Sinker EDM for features CNC cannot produce (sharp internal corners, complex cavity details, deep features). (3) Wire EDM for ejector pin holes and precise slots. (4) Polish and texture as needed. EDM handles 10-30% of mold features that CNC cannot — essential complement, not replacement.

Small hole EDM (also "hole popping" or "fast-hole EDM"): rotating thin tube electrode drills small deep holes (0.1-6 mm diameter, 100+ mm deep). Used for: cooling holes in turbine blades, start holes for wire EDM, small diameter deep holes. Speed: 20-100 mm/minute drilling rate. Often faster than conventional micro-drilling for deep small holes. Specialty process we coordinate for specific applications.

EDM surface texture adjustable by electrode selection and discharge parameters. Fine finish: Ra 0.2 µm achievable with final passes. Coarse/textured: Ra 6.3+ µm deliberately produced for friction, bonding, cosmetic applications (injection mold texture). VDI surface texture series (VDI 9-45) commonly specified for mold cavities — produces specific matte to leather-grain textures. Common spec on consumer product molds.