Sinker EDM

Sinker EDM (also known as Ram EDM or Die Sinking) is a manufacturing process that uses a custom-machined electrode (made of copper or graphite) to erode a specific shape into a workpiece. Unlike Wire EDM which cuts through the part, Sinker EDM can create blind cavities, sharp internal corners, and intricate 3D contours in hardened materials.

At Jucheng Precision, we utilize high-performance Sodick Sinker EDM machines capable of achieving mirror-like surface finishes (down to Ra 0.2µm) without hand polishing. This process is indispensable for our Mold Making department, allowing us to produce precision injection molds and die-casting dies that require complex internal geometries impossible to machine with traditional CNC milling.

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Sinker EDM

Key Specifications

Specification Technical Range Note
Max Part Size 800 mm x 500 mm x 400 mm Tank size dependent
Machining Tolerance +/- 0.005 mm (5 microns) High precision
Surface Roughness (Ra) 0.2 µm – 3.2 µm (VDI 0 – 24) Can achieve mirror finish
Electrode Materials Oxygen-Free Copper, Graphite, Tungsten Copper CNC machined in-house
Min. Corner Radius 0.03 mm Sharp internal corners
Compatible Materials Hardened Steel, Carbide, Titanium, Hastelloy Any conductive metal
Standard Lead Time 3 – 7 Days Includes electrode machining

EDM Process Strategies

Strategy Description Key Benefits & Applications
Roughing EDM Using high amperage and graphite electrodes to remove bulk material quickly. Leaves a rougher “pitted” surface. Benefit: Fast material removal in hardened steel.
App: Opening up large mold cavities, creating rough textures.
Finishing EDM Low amperage, high frequency passes using copper electrodes. Erodes very small amounts to size the part perfectly. Benefit: Tight tolerances and smooth surfaces.
App: Final sizing of die inserts, precision holes.
Mirror Finishing A specialized finishing cycle using specific power settings to create a highly reflective surface directly in the machine. Benefit: Eliminates manual polishing, maintains sharp edges.
App: Cosmetic plastic injection molds (lens molds).

Design Guidelines for Sinker EDM

Sharp Internal Corners:
Sinker EDM is the only way to create sharp internal corners in a blind pocket (milling tools are round). However, the electrode itself will wear slightly on the corner. Tip: Allow for a very small radius (0.03mm) if absolute sharp is not required to reduce cost.

Electrode Wear:
The electrode degrades during cutting. For deep or precise cavities, we often machine multiple electrodes (Rougher, Semi-Finisher, Finisher). Tip: This adds cost/time compared to CNC milling. Use EDM only when milling is impossible.

Surface Texture (VDI):
EDM naturally leaves a non-directional matte texture. In mold making, this is often desirable (VDI texture). Tip: Specify the desired VDI number (e.g., VDI 24) on your drawing.

Blind Keyways & Ribs:
Deep, narrow ribs or blind keyways are perfect candidates for Sinker EDM as cutting tools would deflect or break in these geometries.

Industry Applications

Injection Mold Making
Creating complex cavities, ribs, and text/logos inside hardened steel molds (P20, H13) that cannot be milled.

Aerospace
Machining blind keyways, splines, and hexagonal sockets in high-temp superalloys (Inconel, Titanium) for engine components.

Die Casting
Producing heat-resistant dies for aluminum and zinc casting, requiring rugged surface finishes and deep pockets.

Medical Manufacturing
Creating micro-features on surgical tool handles or shaping difficult-to-machine biocompatible alloys.