Submarine Gate vs. Pin-Point Gate Electrodes: Selection Guide

Electrode Geometry Comparison

Submarine Gate Electrodes

Submarine gate electrodes are used to EDM-machine the tunnel-shaped gate channel that runs from the runner (at or above the parting line) down into the cavity at an angle below the parting line. This tunnel geometry allows the gate to shear automatically during mold opening — the part pulls away from the fixed angled channel, breaking the gate at the thinnest point.

Critical dimensions for submarine gate electrodes:

• Entry diameter — The largest end of the tunnel, connecting to the runner (typically 1.5–3.0 mm)
• Exit diameter — The smallest end, where the gate meets the part surface (typically 0.8–2.0 mm)
• Taper angle — 15–30° per side. Too shallow and the gate won't shear; too steep and the tunnel is hard to fill
• Tunnel length — 5–15 mm, depending on how far below the parting line the gate entry is positioned

According to ScienceDirect's EDM reference, electrode overcut (the gap between electrode and workpiece during EDM) must be accounted for in the electrode dimensions — typically 0.01–0.05 mm per side, depending on the EDM energy settings.

Pin-Point Gate Electrodes

Pin-point gate electrodes create the small-diameter gate orifice in the gate bushing or directly in the cavity plate. Unlike submarine electrodes, the geometry is simple — a thin cylindrical or slightly tapered tip that burns a straight-through hole at the exact gate diameter.

Key requirements:

• Tip diameter accuracy — Must produce the specified gate orifice diameter within ±0.01 mm after accounting for EDM overcut
• Tip concentricity — The tip must be perfectly concentric with the electrode body to ensure the gate orifice aligns with the bushing bore
• Surface finish — The gate orifice surface must be smooth (Ra ≤ 0.4) to prevent material hang-up. This requires finishing passes with low EDM energy.

Material Selection: Copper vs Tungsten Copper

For gate electrodes that will be used to process multiple cavities (8+ gates from one electrode), tungsten copper is strongly recommended. The electrode tip erodes progressively with each cavity processed — copper electrodes may need replacement after 4–6 cavities, while tungsten copper can process 15–20 cavities with acceptable dimensional accuracy. According to AZoM's tungsten copper data sheet, WCu70/30 (70% W, 30% Cu) offers the best balance of wear resistance and electrical conductivity for EDM electrode applications.