Guides / Process
Wire and Sinker EDM for Tungsten and Tungsten Carbide Parts
September 21, 2026 · Reviewed September 26, 2026
Electrical discharge machining, EDM, removes material by controlled electrical sparks rather than by cutting with a tool, which makes it useful for tungsten and tungsten carbide features that milling and turning struggle with. This guide covers what EDM does, how wire and sinker EDM differ, and when to specify it for a tungsten part.
How EDM works, briefly
EDM erodes material from an electrically conductive workpiece using a series of electrical discharges between the workpiece and an electrode, submerged in or flushed with a dielectric fluid that controls the sparks and flushes away eroded material. Because it removes material electrically rather than mechanically, the process does not depend on the tool being harder than the workpiece, which is why it works on sintered tungsten carbide, one of the hardest commonly machined materials, as readily as it works on pure tungsten or steel.
Two variants matter for tungsten parts:
- Wire EDM uses a thin, continuously fed wire electrode, typically brass or coated wire, to cut a profile through the workpiece the way a coping saw cuts a shape from a sheet, following a programmed path. It is used for through-cutting slots, apertures, gears and other profile shapes.
- Sinker EDM, also called ram EDM, uses a shaped electrode that is sunk into the workpiece to form a cavity matching the electrode’s shape. It is used for blind features, such as a pocket or cavity that does not go all the way through the part.
What EDM does that milling and turning cannot
Milling and turning remove material by cutting, which requires the tool to physically contact and shear the workpiece. Several situations push past what that can do reliably on tungsten materials:
- Small, deep holes in brittle pure tungsten. A small-diameter hole with a high depth-to-diameter ratio is prone to tool deflection and breakage when drilled conventionally, and pure tungsten’s brittleness raises the risk of chipping around the hole entrance and exit. Wire EDM cuts these without mechanical cutting force on the surrounding material.
- Fine apertures in collimators. Collimator apertures with tight straightness requirements, discussed in more detail in the collimator sourcing guide, sometimes need wire EDM rather than drilling or boring, particularly at small diameters where a drill’s inherent wander becomes significant relative to the tolerance.
- Shaping sintered tungsten carbide. As covered in the grinding guide, sintered carbide is too hard for conventional milling. EDM, alongside diamond grinding, is one of the two practical ways to add or modify features on carbide after sintering, and it reaches internal shapes grinding wheels cannot access.
- Fine slots and internal profiles. A narrow slot or an internal profile with sharp internal corners is difficult or impossible to mill with a rotating cutter, which cannot produce a true sharp internal corner, but is straightforward for wire EDM to cut to the programmed path.
Trade-offs against conventional machining
EDM is slower than milling per feature and generally more expensive as a result, so it is chosen for what it makes possible rather than as a default process. A part that mills successfully with conventional tooling should be milled; EDM enters the process plan specifically where a feature’s geometry, the material’s hardness, or its brittleness rules out conventional cutting.
Tolerances achievable by wire EDM are often comparable to precision milling and grinding on these materials, commonly in the ±0.01 mm range or tighter on straightforward profiles, though the achievable number depends on wire diameter, part thickness and the specific geometry involved. Surface finish from EDM has a distinct texture from a milled or ground surface, which occasionally matters for parts with a finish callout tied to a specific process.
| Process | Best suited to | Limitation |
|---|---|---|
| Milling and turning | Most heavy alloy parts, most pure tungsten features | Cannot cut sintered carbide; struggles with small deep holes and sharp internal corners |
| Wire EDM | Through-cut profiles, slots, apertures, carbide shapes | Slower and more expensive per feature than milling |
| Sinker EDM | Blind cavities and pockets, especially in carbide | Needs a custom shaped electrode, adding setup cost |
| Diamond grinding | Tight tolerance and fine finish, carbide surfaces | Limited to accessible external and some internal surfaces |
Recognizing when your drawing needs EDM
A few signals on a drawing point toward EDM before the shop even quotes it:
- Material is sintered tungsten carbide with any feature beyond a simple ground surface.
- A hole or slot with a depth-to-diameter ratio high enough that conventional drilling risks deflection or breakage, particularly on pure tungsten.
- Sharp internal corners specified on a pocket or slot, which a rotating end mill cannot physically produce.
- Very tight straightness or position tolerance on a small feature, such as a collimator aperture, where drilling’s inherent wander would exceed the allowed tolerance.
If you are unsure whether your part needs EDM, conventional milling, or grinding, providing a complete drawing with all tolerances and finish requirements clearly called out lets the shop identify the right process mix rather than requiring you to specify the manufacturing method yourself.
Sourcing a part that needs EDM
State the material and the features you expect to be difficult, along with the full tolerance and finish requirements, in your RFQ. Shops that offer wire or sinker EDM alongside milling and turning can quote the full part as one job rather than requiring you to split it across separate suppliers.
EDM is one of the finishing routes in our guide on how to machine tungsten.
When your drawing is ready, send your RFQ and we match it with shops equipped for EDM work on tungsten and carbide. For when grinding is the better alternative, see grinding tungsten carbide versus machining. For general tolerance expectations across processes, see tungsten machining tolerances and finish.
Frequently asked questions
Does wire EDM work on tungsten heavy alloy the same way it works on pure tungsten?
Both are electrically conductive enough to EDM, but heavy alloy is more often milled and turned instead, since it machines well by conventional cutting and EDM is slower. Pure tungsten and sintered carbide reach for EDM more often because their brittleness or hardness limits what milling can do, particularly on small or deep features.
Is EDM more expensive than milling for the same feature?
Generally yes, per feature, since EDM removes material more slowly than milling. It is chosen not because it is cheaper but because it can produce a feature, such as a small deep hole in brittle pure tungsten or a fine slot in sintered carbide, that milling cannot produce reliably or at all.
What tolerance can wire EDM hold on a tungsten part?
Wire EDM commonly holds tolerances in the same range as precision milling and grinding on these materials, often ±0.01 mm or tighter on straightforward profiles, with the achievable tolerance depending on wire diameter, part thickness and the specific feature geometry. Confirm the tolerance a shop can hold on your specific feature rather than assuming a single number applies across all EDM work.
Sources
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