Tungsten carbide is one of the best materials you can put through an EDM machine, as long as the process respects the grade. Wire EDM is the standard choice for through-profiles such as punches and die openings. Sinker EDM handles blind cavities and formed features. In both cases, the result depends less on the carbide's hardness and more on how well you control discharge energy, dielectric exposure and the finishing passes that protect the cobalt binder.

That matters because carbide tooling is expensive to make and even more expensive to replace early. A roughing burn that leaves microcracks or a binder-depleted skin can take months off a punch's life before it ever sees production. This guide walks through process choice, electrodes, grades and parameters for carbide work in forging, stamping and mold tooling.

Why Carbide Behaves Differently Under EDM

Cemented carbide is a composite: hard tungsten carbide grains held together by a softer metal binder, usually cobalt. EDM only needs the workpiece to conduct electricity, so hardness never slows the burn the way it slows a cutting tool. That is why carbide and EDM are such a natural pairing. The composite structure is also why carbide needs more care than tool steel.

The binder goes first

Cobalt melts at a much lower temperature than the carbide grains around it. Each spark tends to remove binder before it removes grain, so too much energy leaves a surface with loose or poorly supported grains. In practice, aggressive settings show up as:

• Binder depletion in a thin surface layer
• Grain pullout that weakens sharp edges and punch lands
• Microcracks from rapid heating and cooling in a brittle material

None of these are visible at a glance, and all of them shorten tool life. Lower energy on the finishing passes keeps the affected layer thin enough to remove.

Expect slower removal than steel

Carbide conducts less evenly than steel because the grains and binder respond to current differently. Removal rates are lower than you would see on mold steel, so quote cycle times accordingly and resist the urge to make up time with higher current.

Pure tungsten is a different material

Pure tungsten has no binder and erodes slowly and evenly. Settings that work on tungsten or heavy alloy do not carry over to a cobalt-bonded die. Start from the carbide grade's own data and run a test coupon before burning the production part.

Choosing Wire or Sinker EDM for the Geometry

Use wire EDM when a feature passes all the way through the block. Use sinker EDM when a feature stops inside the block or has a 3D form. Many carbide tools need both.

Wire EDM for punches and die openings

Wire EDM is the usual process for carbide punches, die openings and stripper profiles. The wire follows a path through a start hole or from an open edge and holds tight corners without any cutting force on brittle edges. A good carbide wire job includes a roughing cut followed by several skim cuts at progressively lower energy, plus clamping that supports the slug so it cannot drop and chip the edge on the way out.

Sinker EDM for blind forms

Sinker EDM reaches what the wire cannot: blind pockets, formed cavities, coining details, embossing and undercuts. It is the standard route for forging die impressions and carbide mold inserts. A stable sinker with a well-tuned power supply makes a large difference here, because carbide punishes arcing and inconsistent gap control far more than steel does. EDM Zap's Advantage series EDM power supplies include automatic arc detection that adjusts power before an unstable discharge can mark the workpiece.

Electrodes and polarity

Copper tungsten is a strong electrode choice for carbide because it resists wear and holds fine detail. Graphite is practical for larger forms, though it wears faster on carbide than on steel. Whichever you use, run a short test burn, measure electrode wear and cavity size, and confirm polarity before committing the production block.

Picking a Carbide Grade That Suits EDM

Choose the grade for the job the tool will do, then confirm it suits the EDM process you plan to use.

Finer grains and lower cobalt content give more hardness and wear resistance but less toughness. Coarser grains and higher cobalt give better impact strength, which suits heavy stamping and forging. For EDM, more cobalt means more binder available to leach, so higher-cobalt grades need extra care on the finishing passes.

If a tool will spend long hours in a wire EDM tank, ask your carbide supplier about corrosion-resistant binder grades. These alloy or replace some of the cobalt so the binder holds up better in deionized water. Order dense, stress-relieved blocks with ground faces, and leave stock on working surfaces for grinding or lapping after EDM.

Planning carbide die work on an older sinker? Our engineers can look at your grade, electrode and power supply setup and tell you where the risk sits. Talk to an Engineer.

Controlling Cracks, Binder Loss and Accuracy

Every setting either thickens or thins the damaged layer you will need to remove later. Carbide rewards a patient, staged approach.

Step the energy down

Short pulse on-times and moderate current suit carbide. Long, high-energy pulses push heat deeper and raise crack risk. Stepping from roughing to finishing over several stages keeps each layer thin enough for the next pass to clean up. A single DC arc can leave a crack-prone burn mark, which is why stable gap control matters so much on this material.

Limit water exposure on wire jobs

Deionized water slowly attacks cobalt through electrolysis and corrosion, especially when a part sits in the tank for hours. Keep water conductivity in range, avoid long idle soaks and use anti-electrolysis settings if your machine offers them. Oil dielectric on a sinker avoids this problem, though steady flushing is still needed to clear debris and prevent secondary sparks.

Finish and inspect before the tool goes into service

Plan enough skim cuts or finishing burns to remove the zone left by roughing, then grind, lap or polish cutting edges and punch lands to take off the last binder-depleted skin. Measure the electrode after roughing and switch to a finishing electrode before wear shows up in the cavity. Check size against the drawing and inspect working edges under magnification for cracks and grain pullout.

Where Carbide EDM Earns Its Place

Carbide EDM is most valuable on tools that face high wear and long runs.

Stamping punches and die segments. Dies for electrical laminations, connectors and fasteners use carbide punches and sections to last through millions of hits. Sectional designs also make repairs simpler, since one worn segment can be replaced on its own.

Forging tooling. Forging dies use carbide inserts at high-wear points such as flash lands and punch tips, with sinker EDM forming the impression in the hardened insert. When those tools wear, EDM is often the cleanest way to bring them back. Our guide to EDM for forging die repair covers rework options in detail, and you can see how EDM Zap supports forging manufacturers more broadly.

Mold inserts and small precision parts. Gate inserts and core pins for glass-filled resins, along with nozzles and wire guides, rely on low-energy finishing and fine electrodes to hold size.

Build a Carbide Process You Can Repeat

Successful carbide EDM comes down to a validated process. Pick the grade for the wear and impact the tool will see, use wire EDM for through-features and sinker EDM for blind forms, step energy down with every pass and leave stock for grinding or lapping. Run a coupon from the same block lot whenever you change the grade, electrode or power supply settings, and record the settings that work.

Burning carbide dies without cracking or binder loss takes a stable machine, the right electrode and settings matched to the grade. EDM Zap has designed and built EDM equipment in the USA since 1971, and our engineers can recommend a sinker and power supply configuration for your carbide tooling. Request a Quote, or call (630) 852 1699 to talk it through.

Frequently Asked Questions

Can you wire EDM tungsten carbide?

Yes. Wire EDM cuts tungsten carbide well and is the standard method for punches and die openings. Use several skim cuts at lower energy and keep water conductivity under control to protect the binder.

Which carbide grade is best for EDM tooling?

A medium or fine grain cobalt grade suits most general dies, while a coarser grade with more cobalt is better where impact is heavy. For long wire EDM runs in water, ask your supplier about corrosion-resistant binder grades.

What electrode should I use for sinker EDM on carbide?

Copper tungsten is a common choice because it resists wear and holds fine detail. Graphite works for larger forms, but test it for wear before the production burn.

Why does deionized water damage cobalt-bonded carbide?

Electrolysis and corrosion can pull cobalt from the surface and loosen the carbide grains. Long soaks and high water conductivity make it worse, so keep cuts moving and the water within spec.