Sinker EDM (Die Sinking): Blind Cavities, Electrodes & Specs

Sinker EDM (Die-Sinking EDM): Blind Cavities & Sharp Corners

Sinker EDM (Ram EDM) utilizes custom-machined 3D graphite or copper electrodes immersed in dielectric hydrocarbon fluid to spark-erode complex blind cavities, sharp internal corners, and deep ribs.

Engineering Specifications & Parameters

Cavity Type	Blind 3D Cavities, Undercuts, Sharp Ribs
Surface Finish	VDI 12 to VDI 30 Spark Texture
Dielectric Fluid	Synthetic Dielectric Hydrocarbon Oil
Electrode Materials	High-Density Isostatic Graphite, Copper-Tungsten, Copper
Tolerance Capability	+/-0.005 mm (+/-0.0002 in)

Sinker EDM Principles

Unlike Wire EDM which cuts completely through workpieces, Sinker EDM plunges a reverse-shaped 3D electrode into raw metal, creating blind features with zero cutting force.

Major Capabilities

Sharp Internal 90 Degree Corners: Replaces circular milled corners with near-zero radius internal corners.
Deep Ribs & Keyways: Machines narrow slots (down to 0.2 mm width) with 20:1 aspect ratios impossible with rotary end mills.
Hardened Steels: Easily erodes hardened carbide, Stellite, and 65 HRC tool steels.

Electrode Materials: Copper vs Graphite

Graphite electrodes provide 3x faster spark removal rates and low wear; fine-grain copper electrodes deliver mirror surface finishes on mold cavities.

Frequently Asked Questions

When is Sinker EDM chosen over high-speed CNC milling?

For deep internal sharp square corners, complex textured injection mold cavities, and small intricate keyway slots in hardened steels.

Why are multiple electrodes (rough and finish) used in Sinker EDM?

Spark erosion causes slight electrode wear; a roughing electrode removes 90% of stock, followed by 1 or 2 finish electrodes to achieve exact final dimensions.