Sparks vs cutters. Any hardness. Complementary processes.

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.