Sinker EDM for blind cavities and 3D contours.
Argent provides aerospace sinker EDM — also called ram EDM or die-sinking EDM — for blind cavities, internal features, and 3D contoured geometries that wire EDM and conventional machining can't reach. Inconel, Hastelloy, hardened tool steel, and refractory metals at the hardness and complexity aerospace and defense programs demand.
How sinker EDM produces features other processes can't.
Sinker EDM (also known as ram EDM, die-sinking EDM, or plunge EDM) uses a shaped electrode — typically graphite or copper — that is plunged into the workpiece in a dielectric fluid bath. Electrical discharges between the electrode and the part erode material in the exact shape of the electrode, producing blind cavities, internal features, sharp inside corners, and 3D contours that no other process can economically produce.
Where wire EDM only cuts through, sinker EDM can produce features that terminate inside the material. That's the difference between cutting a profile (wire) and machining a pocket (sinker).
What sinker EDM does best
- Blind cavities and pockets. A sinker electrode can plunge into a part to create a pocket of any depth, with vertical walls, sharp inside corners, and 3D contoured bottoms.
- Internal geometries unreachable by tools. Splines, gears, keyways, and complex internal cavities inside hardened parts.
- Sharp inside corners on hardened parts. Sinker EDM can produce nearly-zero-radius inside corners after the part is heat-treated to final hardness. Conventional machining requires re-finishing after heat treatment.
- Mold and die cavities. Forging dies, plastic injection mold cores, and casting tooling are routinely sunk into hardened tool steel.
- 3D contoured surfaces. Turbine blade airfoil dies, impeller forming tooling, and any complex 3D surface that needs to be replicated into hardened material.
Aerospace sinker EDM specifications.
Typical aerospace sinker EDM applications
- Turbine blade airfoil tooling — forging dies, casting cores, finishing fixtures in hardened tool steel
- Forging dies for high-temperature aerospace parts — Inconel and titanium forging tooling
- Injection mold cavities — composite layup tooling, plastic component molds
- Internal splines and gear forms — inside hardened aerospace shafts and couplings
- Blind pockets in heat-treated parts — pockets that have to be machined AFTER heat treatment to avoid distortion
- Aerospace test fixtures — complex 3D contoured holding tooling
Materials we sink most often
- Inconel 718 and 625 — hot-section parts, forging dies
- Hardened tool steel (D2, A2, H13, S7) — dies, molds, fixtures
- Titanium 6Al-4V — aerospace structural fittings, fasteners
- 17-4 PH and 15-5 PH stainless — aerospace landing gear, structural parts
- Refractory metals (tungsten, molybdenum) — defense and space applications
Electrode design and burn strategy.
The quality of a sinker EDM part is determined in the electrode design phase, not the burn. A poorly designed electrode produces poor parts even on the best machine. A well-designed electrode produces parts that hit aerospace tolerances on the first burn.
What goes into electrode design
- Spark gap compensation. The electrode must be undersized by the spark gap (typically 0.001-0.005 in per side) so the burned cavity matches drawing dimension.
- Roughing vs finishing electrodes. Production parts typically use a roughing electrode (removes bulk material fast) followed by 1-3 finishing electrodes (refine surface finish and final dimension).
- Electrode material choice. Graphite for general work, copper for fine-detail or low-roughness work. Copper-tungsten for the most demanding electrode wear ratios.
- Flushing. Dielectric fluid must be flushed through the spark gap to clear eroded debris. Electrode designs include flushing holes, side flushing fixtures, or pulsed retraction strategies.
Argent's sinker EDM partners do their own electrode design in-house. We work from your final part drawing — you don't need to provide electrode geometry. The complexity of going from a part drawing to a finished sunk feature stays on our side.
Pairs well with.
Argent customers typically combine multiple capabilities on the same program. These are the most common pairings with this work.