Choosing between EDM graphite electrode grades comes down to one question: how fine is the detail you need to burn, and in what workpiece material? A general-purpose grade like ISO-88 handles most semi-finishing and multi-cavity die work, while ultra-fine grades such as TTK-8 exist specifically for mirror-finish and micro-detail electrodes. This guide compares the four grades Expo machines most often — ISO-88, SF/EDM-3, IG-430U and TTK-8 — by grain structure, distinguishing strength and best-fit application, so you can match the grade to the job before you request a quote.
Expo Advanced Materials Pvt. Ltd. (Expo Graphite & Composites) is an authorised machining partner of TOYO TANSO CO., LTD., Japan, and machines EDM electrodes to drawing from certified isostatic graphite on graphite-dedicated CNC centres in Noida, India.
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EDM graphite electrode grades at a glance
Graphite's grain size is the property that decides how it behaves as an electrode. Finer grain resolves sharper detail, produces a smoother EDM surface and wears more evenly; coarser grain removes metal faster on roughing but cannot hold crisp edges. The four grades below span that range from all-round workhorse to ultra-fine detail.
| Grade | Grain structure | Distinguishing strength | Best-fit EDM work |
|---|---|---|---|
| ISO-88 | Fine grain (<20 µm), 1.82 g/cm³ | All-round workhorse — speed, edge holding and cost balanced | Semi-finishing, medium and multi-cavity dies |
| SF / EDM-3 | Fine grain | Clean fine-finish detail on intricate geometry | Fine-finishing, micro-EDM, complex profiles |
| IG-430U | Ultra-fine grain | Ultra-high purity (<5 ppm ash) | Exotic alloys — titanium, Inconel, carbide |
| TTK-8 | Ultra-fine grain | Highest detail resolution and surface finish | Mirror-finish EDM, ultra-fine detail electrodes |
All four are machined to the same shop standard: ±0.02 mm on cavity features, ±0.005 mm repeat accuracy on multi-cavity sets, and Ra 0.8 µm surface finish as standard (finer on request). Every order ships with an ISO 9001:2015 dimensional inspection report and full material traceability. Round-rod stock — the Graphite Electrode Rod — is also available for wire EDM and spark-erosion work where a standard cylindrical geometry is enough.
Graphite is preferred over copper for most of this work because it machines 3–5× faster, does not burr, and weighs far less — an advantage that compounds on large or multi-cavity electrodes. For the full material trade-off, see our guide to EDM graphite vs copper electrodes.
How to choose an EDM graphite grade
Short answer: pick the coarsest grade that still resolves your finest feature and finish. Coarser grain gives faster, cheaper burning; finer grain gives detail and surface quality. Move up the fineness ladder only as far as the cavity demands, then choose a higher-purity grade if the workpiece is an exotic alloy. The four grades below map to that logic.
ISO-88 — the semi-finishing workhorse
ISO-88 is the most popular EDM grade and the right default for the majority of die-sink work. It is a fine-grain isostatic graphite (grain below 20 µm, density 1.82 g/cm³) that balances machining speed, edge definition and electrode wear. Use it for semi-finishing, medium cavities and multi-cavity electrode sets in steel and carbide tooling, where you need dependable results without paying for ultra-fine grain you will not use. This is also the grade to start from when you are unsure — it covers the widest span of jobs. See the full EDM graphite electrode product page for machining formats (DXF, STEP, IGES, PDF drawing).
SF / EDM-3 — fine-finishing and micro-EDM
SF (also sold as EDM-3) steps up the fineness for detail work. Its finer, more uniform grain holds crisp edges on intricate profiles — thin ribs, sharp internal corners, small slots and lettering — and produces a cleaner finish than ISO-88 at the same settings. Choose SF/EDM-3 for fine-finishing passes, micro-EDM and complex profile electrodes where feature definition matters more than raw removal rate.
IG-430U — exotic alloys and ultra-high purity
IG-430U is an ultra-fine-grain, ultra-high-purity grade at under 5 ppm ash (isostatic graphite grades). Purity is the reason to specify it: when you are burning titanium, Inconel or cemented carbide, a low-ash electrode reduces the risk of contamination and gives more stable, predictable erosion on those difficult workpieces. It is the same grade family Expo supplies for semiconductor CVD/MOCVD work, so material cleanliness is tightly controlled. Reach for IG-430U when the workpiece — not just the finish — is demanding.
TTK-8 — mirror finish and ultra-fine detail
TTK-8 is the fine end of the range. Its ultra-fine, highly homogeneous grain resolves the smallest features and produces the smoothest EDM surface of the four, which is what makes it the mirror-finish grade. Use it for ultra-fine detail electrodes and mould cavities that must come off the machine close to a polished finish, reducing downstream hand-polishing. It is the grade you specify when detail resolution and surface quality are the whole point of the job. Grade-level specifications for TTK-8 and IG-430U are listed on the TOYO TANSO graphite grades page.
Grade selection by application
If you prefer to work from the job rather than the grade, this maps the most common EDM tasks to a starting grade:
- General die-sink, medium cavities, multi-cavity sets → ISO-88
- Fine-finish detail, thin ribs, micro-EDM, complex profiles → SF / EDM-3
- Titanium, Inconel or carbide workpieces → IG-430U (low ash matters more than finish)
- Mirror-finish cavities, ultra-fine detail → TTK-8
- Wire EDM and spark-erosion rods → Graphite Electrode Rod (round stock)
The site also stocks additional isostatic grades for specialised electrode work — including SCD-40, R850N, R8510, ISCM-8, ISO-63, SCD-65 and SCD-70. If your drawing calls out a grade not listed above, send it with your enquiry and Expo will match or advise an equivalent.
Why grain size and ash content decide the grade
Two properties do most of the work in an EDM electrode, and they map to two different problems.
Grain size governs detail and finish. In electrical discharge machining, the electrode's form is mirrored into the workpiece by controlled spark erosion, so the electrode's own surface and edge quality set the ceiling on the cavity you can produce (how EDM works — Wikipedia). A finer, more uniform grain erodes more evenly and holds sharper edges, which is why the fineness ladder above runs from ISO-88 up to TTK-8. Isostatic graphite is used for all four grades because the isostatic pressing process gives an isotropic, homogeneous block — the electrode behaves the same in every direction, unlike extruded graphite.
Ash content governs contamination, and it is expressed in parts per million (ppm), not vague labels. For most tool-steel EDM the ash level is not the deciding factor; grain size is. It becomes decisive on reactive or high-value workpieces — titanium, Inconel, carbide — where a low-ash grade such as IG-430U (<5 ppm) protects the burn. Matching purity to the workpiece, rather than over-specifying it everywhere, is how you avoid paying for cleanliness the job does not need. Graphite's stability at the temperatures generated in the spark gap — it does not melt but sublimes near 3,650 °C — is what lets all of these grades hold their form as electrodes (graphite material properties — Wikipedia).
Graphite or copper first?
Before grade selection, some shops still weigh graphite against copper. In short: graphite machines 3–5× faster, will not burr, and is far lighter for large or multi-cavity electrodes, while copper is chosen mainly for the very finest mirror finishes or where no dust extraction is available. This article assumes you have already chosen graphite; if that decision is still open, our dedicated comparison covers it in full — see EDM graphite vs copper electrodes.
FAQ — choosing an EDM graphite grade
Which EDM graphite grade should I use for general die-sink work?
ISO-88 is the standard choice for general and semi-finishing die-sink EDM. It is a fine-grain grade (below 20 µm, 1.82 g/cm³) that balances machining speed, edge definition and cost, and it covers the widest range of medium and multi-cavity jobs. Start here unless the cavity needs finer detail or the workpiece is an exotic alloy.
What is the difference between ISO-88, SF/EDM-3, IG-430U and TTK-8?
They differ mainly by grain fineness and purity. ISO-88 is the all-round workhorse; SF/EDM-3 has finer grain for fine-finishing and micro-EDM; IG-430U is an ultra-high-purity grade (<5 ppm ash) for exotic alloys like titanium and Inconel; TTK-8 is ultra-fine for mirror-finish and the highest-detail electrodes. Pick the coarsest grade that still resolves your finest feature.
Which graphite grade gives a mirror finish in EDM?
TTK-8 is the mirror-finish grade. Its ultra-fine, homogeneous grain produces the smoothest EDM surface of the common grades and resolves the finest detail, which reduces downstream hand-polishing on mould cavities.
Which grade should I use for titanium or Inconel?
IG-430U. When the workpiece is a reactive or high-value alloy such as titanium, Inconel or carbide, its ultra-high purity (under 5 ppm ash) gives more stable, contamination-free erosion — purity matters more than finish on these materials.
Do I need a different grade for wire EDM?
Wire EDM typically uses round Graphite Electrode Rod (cylindrical stock) rather than a machined-to-drawing die-sink electrode. Specify the rod diameter and grade with your enquiry.
Can Expo match a grade specified on my drawing?
Yes. Expo machines to DXF, STEP, IGES or PDF drawings and supplies a range of isostatic grades (including ISO-88, SF/EDM-3, IG-430U, TTK-8, ISO-63 and others). If your drawing calls out a grade not stocked, send it and Expo will match or advise a certified equivalent with material traceability.
Source EDM graphite electrodes from India
Expo machines all of these grades to drawing at 30–45% below European equivalent pricing, on a quote basis, with no minimum order — from a single prototype electrode to production multi-cavity sets. As an authorised machining partner of TOYO TANSO CO., LTD., Expo supplies certified isostatic graphite with full material traceability and an ISO 9001:2015 dimensional inspection report on every order, dispatched from Noida to customers across India and 16+ export countries.
Not sure which grade fits your job? Send your drawing (DXF, STEP, IGES or PDF) and workpiece material, and Expo will recommend a grade and quote it. Explore the full EDM graphite electrode range or request a quote:
query@eapl.tech · +91 98919 24639