Electrical Discharge Machining (EDM) is a non-conventional manufacturing process that removes material through controlled electrical sparks between an electrode and the workpiece submerged in dielectric fluid.
The key advantage: it can machine any electrically conductive material regardless of hardness — perfect for hardened tool steels (HRC 58-68) that cannot be CNC milled.
Temperature at spark point: 8,000-12,000°C. Spark duration: 1-500 microseconds.
1. Sinker EDM (Die Sinking EDM or Conventional EDM) — Uses a shaped electrode (copper or graphite) that mirrors the desired cavity. Best for 3D cavities in mold tooling.
2. Wire EDM (Wire-Cut EDM) — Uses a thin wire (brass, molybdenum) as the electrode. Travels through the workpiece like a band saw. Perfect for precision through-cuts, gears, and extrusions.
3. EDM Drilling (Small Hole EDM) — For drilling small holes (0.1-3mm diameter) with high depth-to-diameter ratios.
4. EDM Grinding — For precision surface finishing.
Use EDM when:
• Material hardness > HRC 55 (pre-hardened steel, carbide)
• Complex 3D cavities that cannot be reached with standard cutters
• Deep ribs, sharp internal corners, and narrow slots
• Micro-holes (diameter < 1mm) with depth-to-diameter > 10:1
• Thin sections that would deflect under cutting forces
Use CNC Milling when:
• Material is below HRC 50
• Part has large flat areas and simple contours
• Production speed matters (EDM is 10-50x slower than milling)
• Surface finish requirement is moderate
Copper — Universal material, good surface finish, moderate wear. Best for general tooling.
Graphite — 2-3x faster material removal than copper, lower electrode cost. Higher wear but excellent for roughing and pre-finishing. Best for large cavities.
Tungsten-Copper — Highest wear resistance. Best for precision finishing, deep ribs, and small corners. Expensive but long-lasting.
Copper-Tungsten — Best for small, detailed electrodes where low wear and fine finish are essential.
Roughing EDM:
• Current: 6-12A
• Pulse-on time: 100-300 μs
• Duty factor: 50-60%
• Gap: 0.2-0.5mm
• Surface finish: Ra 6.3μm
Finishing EDM:
• Current: 1-3A
• Pulse-on time: 5-20 μs
• Duty factor: 30-40%
• Gap: 0.05-0.15mm
• Surface finish: Ra 0.4-1.6μm
Wire EDM typical cutting speed: 120-300 mm²/min for 50mm thick tool steel.
China's EDM machine tool industry is centered in Suzhou, Taizhou (Jiangsu), and Chengdu (Sichuan). Domestic brands now hold over 85% of the domestic market.
Major domestic brands: Suzhou Baoma, Suzhou Hualong, Hanchuan Machine Tool, Jiangsu Sanxing
Imported brands commonly found in China: Sodick (Japan), Mitsubishi (Japan), Charmilles (Switzerland), Fanuc (Japan).
Typical EDM shop rates in China (2026):
• Wire EDM (molybdenum wire): ¥8-20/hour
• Wire EDM (brass/bronze wire): ¥15-40/hour
• Sinker EDM: ¥30-80/hour