EDM for Cavity Molds: Three Electrode Strategies Compared

Cavity molds—including forging, die-casting, extrusion, and plastic injection molds—are difficult to machine by EDM. They involve blind cavities where fluid circulation is poor, debris is hard to flush, and electrode wear cannot be fully compensated.

Three main EDM strategies are used to overcome these challenges.

Single‑Electrode Planetary Machining

This is the most common method. One electrode does everything—roughing, semi‑finishing, and finishing.

A planetary head moves the electrode in a circular orbit. As machining progresses, the orbital radius increases to compensate for the changing discharge gap and surface roughness.

• Pros: Only one electrode, one setup, and accuracy down to 0.05 mm.

• Cons: Cannot produce sharp corners—every corner gets a radius. The electrode may also develop a carbonized layer during roughing, affecting surface finish. Polishing the electrode between stages helps.

Multiple‑Electrode Change Machining

This method uses two or more electrodes, changed sequentially, to machine the same cavity.

Each electrode is sized for its specific stage. Roughing removes the bulk, finishing removes the marks left by roughing.

• Pros: High contour accuracy—ideal for sharp corners and narrow slots.

• Cons: Requires multiple electrodes with consistent geometry and precise re‑positioning during changes.

• Best for: Precision cavities where accuracy is the priority.

Decomposed Electrode Machining

This combines the two methods above. The cavity is split into a main cavity and secondary features (like sharp corners and narrow slots). A separate electrode machines each part.

• Pros: Different parameters can be used for each area, improving speed and surface quality. Electrode manufacturing is simpler.

• Cons: Precise alignment between main and secondary electrodes is challenging.