Sinker EDM vs Wire EDM: How to Choose for a Specific Part

Rule out wire EDM if the part has a blind cavity or 3D internal form

Start with geometry, because it eliminates a process before tolerance or price is worth discussing. Wire EDM cuts with a continuously fed wire that must travel all the way through the workpiece to the lower guide, so a pocket that stops halfway into a block is physically unreachable^17,19.

Sinker EDM forms the same feature with a shaped electrode that descends into the workpiece, which is why closed cavities, blind pockets and 3D internal forms are sinker work^1,8,9,15.

If your drawing shows a through-cut, an open profile or a taper, wire EDM is the candidate; if it shows a cavity with a floor, sinker EDM is the only EDM process that applies^1,15.

Check this on the drawing before you send anything out — no tolerance callout or cost negotiation changes what the wire can reach.

Confirm the workpiece is electrically conductive

Both EDM processes remove material by controlled electrical discharges between an electrode or wire and the workpiece, so a non-conductive workpiece cannot be machined by either one^6,21,22. That rules out plastics, ceramics and other insulators regardless of how well the geometry suits the process.

On the conductive side, the process is not limited to soft stock: it erodes hardened tool steels, conductive carbides and titanium alloys. And it does so without cutting force, so thin or fragile sections are not deflected during the burn^21,22.

If your material is conductive and hard, EDM is feasible on material grounds; if it is not conductive, stop here and look at a different process.

Match the required finish and tolerance to the process, and budget for finishing passes

Wire EDM typically produces a smoother surface finish than sinker EDM, which leaves a matte EDM texture whose quality depends on how many burn passes are run^1,15. Both processes leave a recast layer and heat-affected zone that finishing passes refine, and those repeat passes are what carry the part to a high-precision tolerance^6,10,19.

The practical consequence for your quote is that a tighter finish or tolerance is not a free callout — it adds passes, and passes add machine time.

Decide which surfaces actually need the fine finish and which can carry the as-burned texture, then state that on the drawing rather than applying one blanket finish note to the whole part.

Compare the cost and time drivers that differ between the two processes

The two quotes are not built from the same inputs, so comparing a sinker price against a wire price line by line will not tell you which is cheaper. Sinker EDM cost sits in electrode design and fabrication plus burn time, and the electrode is a custom tool shaped like the cavity you want^1,15.

Wire EDM cost sits in machine time plus wire consumption, and the wire is not reusable after one pass, so it is replenished continuously^1,19. On speed, sinker EDM is slow, especially for large volumes, while wire EDM is moderate and faster than sinker for cuts^1,15.

When you interrogate a quote, ask which of those line items dominates it — electrode count and burn hours on the sinker side, wire hours and consumable wire on the wire side.

Tolerance figures the sources give, and the conditions attached to them

The tolerance numbers below come from different sources under different stated conditions, so treat them as a range to discuss with the shop rather than a guaranteed value for your part. Actual tolerance depends on machine capability, part size, geometry and process parameters^1,6,10.

Check the shop's machine envelope, wire or electrode capacity, and certification

A process being technically right for the part does not mean the shop you are talking to can run it. Wire diameter sets the smallest internal corner the wire can cut, and electrode size and positioning set which sinker features are reachable at all^1,31.

Certification is a separate gate: ISO 9001 covers most industrial work, while AS9100D is required for flight hardware^13,33.

• ✓Ask which specific machine will run your job, not which machines the shop owns.
• ✓For wire work, confirm the wire diameter range available and whether your internal corner radius clears it.
• ✓For sinker work, confirm the shop can design and position an electrode for your cavity geometry.
• ✓Confirm the shop holds the certification your industry requires — ISO 9001 for most industrial work, AS9100D for flight hardware.
• ✓Verify the certification scope statement, not just the logo.

Questions to put to the shop before you issue the RFQ

The sources settle the geometry rule and the cost structure, but they do not publish the quantitative figures you need to compare quotes. Ask for those directly rather than inferring them from the process descriptions.

• ✓Ask for the machining time the shop expects on your specific feature, in hours — the sources publish no removal-rate data for either process.
• ✓Ask for a per-part price at your quantity, since no source gives a one-off or per-part cost comparison between the two processes.
• ✓Ask how many electrodes the sinker job needs and what they add to the price.
• ✓Ask whether the shop runs both processes in-house or will subcontract one of them.
• ✓Ask what inspection evidence you will receive with the parts.

What the sources do not establish

• No quantitative machining speed data (mm²/min or in²/hr) for either process on comparable features.
• No per-part or one-off cost comparison between sinker and wire EDM.
• No material-specific removal rate, electrode wear, or wire breakage data for hardened tool steel, carbide, titanium, superalloys, or PCD.
• No maximum workpiece dimensions, travels, electrode size or weight capacity, or required power supply specifications for either process.
• No specific certification requirements for EDM shops in medical, aerospace, or other regulated industries.
• No comparison of the skill levels required for electrode design (sinker) versus wire programming.
• No data on typical outsourcing options or on how often both processes are available in-house.