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Wire & Sinker EDM Machining

Six sinker EDM machines in our own shop, and wire EDM — slow, medium and fast wire — at a partner plant we have worked with for years. Hardened tool steel, sharp internal corners, blind cavities and the features a cutter cannot reach. Electrodes made in-house, every first article measured on our CMM before the run continues.

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Wire EDM cut motor stator lamination rings in three sizes – GY Machining — Motor stator lamination rings, wire cut

6Sinker EDM machines, in-house

2 / 2 / 3Slow / medium / fast wire EDM at our partner

60+ HRCHardness is no limit

16 hQuote turnaround

Wire vs sinker

Through the part, or into it

The rule is simple. If the feature goes all the way through the part, it is wire EDM. If it has a floor — a pocket, a cavity, a deep rib — it is sinker EDM. You do not need to decide: send the drawing and our engineer picks the process. This is how the two compare.

	Wire EDM	Sinker EDM
How it works	A thin wire erodes a through-profile with a spark. No cutting force, no tool pressure.	A shaped copper or graphite electrode is sunk into the part under dielectric fluid. The cavity is the negative of the electrode.
Best for	Punches, dies, gears, thin profiles, sharp internal corners in plate, hardened parts	Blind cavities, square internal corners, deep ribs and slots, mould cores, engraving in hardened steel
Machines	7 at our partner plant: 2 slow-wire, 2 medium-wire, 3 fast-wire	6, in our own shop
Max workpiece	400 × 300 × 200 mm	500 × 350 × 250 mm
Achievable tolerance	±0.005 mm on slow-wire with skim cuts; medium and fast wire hold less — see the wire-type table below	±0.01 mm
Internal corner	Radius from 0.1 mm	Square — no radius at all
Surface finish	Ra 0.4 – 3.2 µm depending on wire type and number of cuts	Ra 0.4 – 3.2 µm, set to the drawing
Depth / taper	Taper cutting up to 15°	Cavities up to 150 mm deep
Consumable	Brass wire on slow-wire machines; molybdenum wire on medium and fast wire	Copper and graphite electrodes, designed and milled in-house
Material hardness	No limit — any conductive material, cut or sunk after heat treatment so nothing moves afterwards

Wire EDM · partner plant

Cutting with a wire, not a cutter

Wire EDM erodes material with a thin wire and an electrical spark, so there is no cutting force and no tool pressure on the part. Hardness does not matter — tool steel at 60 HRC cuts the same way as annealed stock. That makes it the right process for parts that have already been heat treated, for internal corners smaller than any end mill, and for thin, delicate profiles that would deflect under a milling cutter.

Wire EDM is not done under our roof. It is done at a partner plant we have used for years, on seven machines across the three wire-EDM types. We program, fixture and inspect; they cut. You deal with one supplier and one invoice, and the finished part is measured on our CMM before it ships.

Wire EDM brass wire cutting a steel plate under dielectric fluid

Three kinds of wire EDM — and why the price differs

“Wire EDM” covers three different machine types. Anyone who buys wire-cut parts should know which one is quoting, because the wire, the number of cuts and the achievable accuracy are not the same — and neither is the price.

	Slow-wire EDM	Medium-wire EDM	Fast-wire EDM
Machines at our partner	2	2	3
Wire	Brass wire, fed once and discarded	Molybdenum wire, reused	Molybdenum wire, reused
Cuts	Main cut plus several skim cuts	Main cut plus one to three skim cuts	Single cut
Accuracy and finish	Finest — this is where the ±0.005 mm figure comes from	Between the two	Coarsest; visible cut lines
Cost per part	Highest	Middle	Lowest
We use it for	Punches, dies, gauges, tight fits, small radii, fine finish	General precision parts, fixtures, most production work	Blanks, roughing before finishing, non-critical profiles, cost-driven jobs

Tell us the tolerance and the finish you actually need. We choose the wire type from that, and it is often the single biggest lever on the price of a wire-cut part.

Machined aluminium hex manifold with finned body and three threaded ports – GY Machining

Operator threading the wire on a wire EDM machine before cutting a machined part

What wire EDM is used for

Hardened punches and dies

Tool steel, D2, SKD11 and carbide cut after heat treatment, so nothing moves afterwards.

Sharp internal corners

Square pockets, keyways and slots with a corner radius no end mill can produce.

Thin profiles and lamination stacks

Fine features in thin plate that would deflect or burr under a cutter.

Gears, ratchets and cams

Profiles cut straight from plate, with the tooth form held to the drawing.

Extrusion and blanking dies

Land and relief cut in one setup, with taper where the drawing calls for it.

Rework and salvage

Opening a bore, adding a slot or removing a broken tap in a finished part.

Sinker EDM · six machines, in-house

Burning a shape, not cutting it

Sinker EDM — also called die sinking or ram EDM — pushes a shaped copper or graphite electrode into the workpiece under a dielectric fluid. The spark erodes the exact negative of the electrode. Because nothing rotates and nothing touches, we can produce a square internal corner with no radius at all, sink a cavity into fully hardened steel, and reach into places where no cutter has clearance. Electrodes are designed and milled here, on the same machining centres that cut your part, so lead time does not depend on anyone else.

Row of wire and sinker EDM machines on the GY Machining shop floor in Dongguan

What customers use our sinker EDM for

Blind cavities

Pockets with a closed bottom, where a wire has no way in and a cutter cannot reach the corner.

Square internal corners

Keyways, hex and square broach forms, and splines with no corner radius.

Injection mould cores and cavities

Detail sunk into hardened tool steel after heat treatment.

Deep ribs and slots

Narrow features deeper than any end mill of that diameter can cut without chatter.

Text, logos and serial marks

Engraved into hardened surfaces where laser marking will not survive the process.

Broken tap and stud removal

Eroding out a seized tool without damaging the thread around it.

Recent work

Parts that went through EDM

Sample parts from our own floor — never a customer’s job.

Graphite gear electrodes and copper ribbed electrode for sinker EDM – GY Machining — Graphite and copper electrodes for sinker EDM

Batch of wire EDM cut motor stator lamination rings and tooth segments – GY Machining — Wire-cut stator lamination rings and segments

Slotted stainless index disc with radial slots and hole pattern – GY Machining — Slotted stainless index disc

Hardened steel V-block fixture – GY Machining — Hardened steel V-block fixture

Machined finned aluminium heat-sink housing – GY Machining — Finned aluminium heat-sink housing

Batch of CNC milled aluminium X-brace brackets – GY Machining — CNC milled aluminium X-brace brackets

Machined steel guide bar and block – GY Machining — Steel guide bar and block

Machined aluminium U-shaped block with four tapped holes – GY Machining — Machined aluminium U-block with tapped holes

Materials

Materials we cut and sink

Any electrically conductive material, hardened or annealed. Tool steels are the everyday work; stainless, titanium, copper alloys and carbide are routine.

Tool steel D2 / SKD11A2H13S74140Stainless 303 / 304 / 316L17-4 PHTitanium Gr.2 / Gr.5 Aluminium 6061 / 7075 Brass C360 Copper C110Beryllium copperTungsten carbideInconel

Good to know

Before you send the drawing

Is wire EDM done in your own shop?

No, and we say so. Sinker EDM is in-house on six machines. Wire EDM goes to a partner plant we have worked with for years — seven machines across slow, medium and fast wire. Our engineer programs the cut and chooses the wire type, the partner receives the blank and the cut profile, and the finished part comes back to our measuring room before it ships. You place one order with us and get one invoice.

Wire EDM or sinker EDM — which do I need?

If the feature goes all the way through the part, wire EDM is faster and cheaper. If it is blind — a pocket with a floor, a deep rib, a cavity — it has to be sinker. Send the drawing and we will tell you which we would use and why.

How tight a tolerance can wire EDM actually hold?

On a single pass we work to about ±0.01 mm. With skim passes we hold ±0.005 mm, and on short, thin sections we have done better. Thickness matters more than most people expect — a 10 mm plate and a 120 mm block do not behave the same, so tell us the stack height along with the tolerance.

Can you cut a part that is already hardened?

Yes, and it is usually the better order of operations. Cutting after heat treatment means the profile does not move when the part is quenched. Send it hardened, or we can arrange heat treatment and then cut.

Do I need a start hole for wire EDM?

For any closed profile, yes — we drill it here, so you do not need to add it. Tell us if there is a face where a start hole would be unacceptable and we will position it somewhere harmless.

Do I need to supply the electrode for sinker EDM?

No. We design and machine copper or graphite electrodes here, on the same machining centres that cut your part. That is one less supplier in your chain and one less thing to wait for.

How square can an internal corner really be?

Truly square. The corner takes the shape of the electrode, so there is no tool radius at all. If the drawing calls out a sharp corner, we can give you one; a milling cutter never can.

What about the recast layer and surface finish?

Both processes leave a thin recast layer. For most parts it is irrelevant. If your application cannot accept it — fatigue-critical or medical parts, for example — say so and we will add skim passes or a light polish and note it on the quote. Sinker finish runs from Ra 0.4 to 3.2 µm depending on settings; a mirror-fine finish takes more machine hours, so we quote the finish your drawing asks for rather than the finest we can do.

CNC Milling

Most EDM parts are milled first and finished on the wire or in the sinker. The part and its electrodes are milled on our own floor. CNC milling →

Inspection

Every first article measured on the CMM before the rest of the run is cut. Quality and inspection →

Surface finishing

Polishing, plating and coating after the profile is cut or the cavity is sunk. Surface finishes →

Ready for a quote?

Send the drawing — price and lead time within 16 hours. STEP, IGES, X_T, DWG, DXF or PDF, metric or inch. No minimum order.

Request a quote Email Eileen