Wire EDM vs Milling: When a Part Needs Each

Written by: Carl Erickson

Carl EricksonLast Updated: Nov 12, 2026

5 min read

Machined and anodised components arranged on a black ground.

Wire electrical discharge machining (EDM) suits parts milling cannot reach: hardened material, sharp internal corners, thin sections, and anything that must not take cutting force. Milling is faster and cheaper everywhere else.

Both are among the main processes Vector Components uses for customer-designed parts, alongside computer numerical control (CNC) lathe work and casting. The default assumption on a drawing should be milling, with wire EDM called for when one of four specific reasons applies.

What Does Wire EDM Do That Milling Cannot?

Wire EDM cuts with sparks instead of a rotating tool.

A thin brass wire travels continuously through the workpiece while a controlled electrical discharge erodes material at the gap. The wire never touches the part, and it never pushes against it.

Four consequences follow, and they are the four reasons to use the process:

Hardness stops mattering. Erosion does not care how hard the material is.

Internal corners get sharp. The corner left behind is the wire's radius, not a cutter's.

No cutting force. Nothing deflects a thin wall or a fragile feature.

Geometry opens up. A profile that no tool could reach into becomes a path the wire follows.

Outside those four, milling removes material far faster and the comparison does not apply.

Why Does Hardness Stop Mattering?

Because the wire erodes rather than cuts, so a hardened surface is no harder to remove than a soft one.

That reverses the usual order of operations. Normally a part is machined soft, then hardened, and the hardening distorts it, so it needs finishing afterwards in a hardened state that tools dislike.

With wire EDM the part can be hardened first and cut to final dimension afterwards. The distortion happens before the dimensions are established, which removes the problem instead of correcting it.

This is why tool and die work leans on the process so heavily. A punch or a die is hardened by definition, and cutting it after heat treatment is the only way to hold the fit.

Where Does the Sharp Corner Come In?

Wherever a drawing calls for an internal corner that no standard tool can produce.

A milled internal corner carries the radius of the cutter that made it. The smallest cutter that fits a pocket sets the smallest radius available, and small cutters run slowly because they deflect.

A wire leaves a corner equal to the wire's own radius, which is far smaller than any practical milling cutter. For a part where a mating component has to seat fully into a corner, that is not a cost question but a feasibility one.

It is often the only reason a part needs the process at all. A drawing with one sharp internal corner and nothing else unusual is a drawing asking for wire EDM in one feature, which is worth saying explicitly so the whole part is not quoted that way.

Internal corner radius also appears as a cost driver on milled parts, covered in 6 Cost Drivers on a Machined Part That Are Not the Material.

What Are the Limits?

Three, and they rule the process out more often than people expect.

Conductive materials only. The process depends on an electrical discharge through the workpiece, so engineering plastics are out entirely. The materials Vector machines include aluminium, steel, stainless steel, zinc alloy, copper alloy and engineering plastics, and only the metals among those can be wire cut.

Slower than milling. Material removal is measured against a mill's and loses. On any part a mill can make, the mill makes it sooner.

The wire needs somewhere to start. An internal feature needs a drilled start hole before the wire can be threaded, and an external profile needs an edge to enter from. Both are ordinary, both have to be allowed for in the design.

There is also a recast layer: a thin re-solidified skin left by the discharge. Where it matters, it is removed, which is another operation.

Which Process Should the Drawing Assume?

Milling, unless one of the four reasons applies, and then say which.

That is a more useful instruction than it sounds. A drawing that assumes wire EDM throughout gets quoted as a wire EDM part, which is slow and expensive for the features that did not need it.

A drawing that names the one feature requiring it, and leaves the rest to milling, gets the part made on the right machine for each operation. Vector selects the manufacturer for each part and process, and coordinates the transfer of parts between factories when a part needs both.

Parts are made by the partner factories Vector represents. Send computer-aided design (CAD) drawings and specifications with the material condition stated, because whether the part arrives hardened or soft changes the route entirely.

A quotation follows within one business day, and quotations are free.

Send the drawing and the material condition.

FAQs

When should a part be cut by wire EDM instead of milled?

When the material is already hardened, when the design needs a sharp internal corner, when the section is too thin or fragile to take cutting force, or when the geometry is beyond tool access. Outside those cases milling is faster and cheaper, so the drawing should assume milling by default.

Can wire EDM cut hardened steel?

Yes, and that is one of its main uses. Because the wire erodes material electrically rather than cutting mechanically, hardness has little effect on the process. This allows heat treatment before final machining, which removes the distortion that hardening a finish-machined part would otherwise introduce.

Why can wire EDM make a sharp internal corner?

Because the corner it leaves is set by the wire's own radius rather than by a rotating tool's. A milled internal corner can never be sharper than the smallest tool that fits the pocket, so a drawing calling for a genuinely sharp internal corner is calling for this process whether it says so or not.

What are the limitations of wire EDM?

It only cuts electrically conductive material, so plastics are out. It is slower than milling for the same amount of material removed. The wire also needs somewhere to start, either a drilled hole for an internal feature or an edge to enter from, which has to be allowed for in the design.

Is wire EDM more expensive than milling?

Per unit of material removed, generally, because the process is slower. The useful comparison is not cost per part but whether milling can make the part at all: where it can, it usually should, and where it cannot, the comparison does not apply.