EDM often wins when
- Steel is already hardened after heat treatment
- Features need internal corners tighter than standard cutter radius
- Depth to width ratio exceeds typical end mill reach
- Blind ribs, pockets, or shutoffs have no open face for a cutter
Decision guide
EDM vs CNC Milling for Injection Mold Steel
CNC milling hogs out most mold steel. EDM finishes blind ribs, tight corners, and hardened detail where cutters cannot reach safely. Most tools use both.
Mold steel
EDM versus CNC on the tool, not the plastic part
This guide is for cavity, core, and plate steel. Part-level CNC versus molding lives on a separate compare page.
Electrical discharge machining erodes conductive steel with sparks. CNC milling cuts with rotating tools.
Buyers see EDM on quotes when deep ribs, blind pockets, sharp internal corners, or quenched steel block safe milling.
EDM is rarely a full replacement for CNC roughing. Shops CNC soft steel, heat treat, then EDM or finish mill critical land.
For injection molded parts versus CNC machined parts, seeinjection molding vs CNC machining. For the three EDM processes, see theEDM glossary overview.
Side by side
When EDM wins versus when CNC wins
Process choice follows steel hardness, geometry access, and finish plan.
CNC often wins when
- Steel is still soft before heat treatment
- Features are open with generous corner radii
- Large volume removal is faster with high feed milling
- High surface finish is needed without heavy post EDM polish on that face
Routing table
Signals for EDM versus milling on mold steel
Qualitative routing only. Geometry on CAD still drives the final quote.
| Signal | Lean EDM | Lean CNC milling |
|---|---|---|
| Steel condition | Quenched cavity or core detail | Pre heat treat roughing |
| Geometry | Blind pocket, deep narrow rib | Open pocket with tool access |
| Corners | Sharp internal corners | Radii at or above cutter size |
| Finish | As cut EDM acceptable or skim plus polish scoped | Milled finish meets spec without EDM |
Typical sequence
CNC roughing then EDM finish
Most production molds combine both processes on the same plate or insert.
CNC roughs soft steel to leave stock on ribs, shutoffs, and pockets
Heat treat hardens the tool steel to production hardness
Sinker or wire EDM finishes detail milling cannot hold in hardened steel
Skim EDM, stoning, or polish closes the gap when cosmetics or seal matter
Quote inputs
Send this with mold CAD
These flags help scope EDM hours on the tooling quote.
Deep ribs, blind pockets, and zero draft shutoffs on cavity or core
Hardened steel notes and which operations happen before versus after heat treat
Minimum internal corner radius and cosmetic face map
SPI, VDI, or texture targets when EDM land must be polished after burning
Continue exploring
Related comparisons and glossary links
Decision guides and deeper process pages.
Compare hub
All comparison guides.
Compare hubSinker EDM glossary
Blind ribs and shaped electrodes.
Sinker EDM glossaryWire EDM glossary
Through cuts and insert profiles.
Wire EDM glossaryInjection molding tooling
Tooling hub and mold build context.
Injection molding toolingDesign for manufacturing
DFM before steel is cut.
Design for manufacturingFAQ
Common questions
Should my mold use EDM or CNC milling?
Use CNC for open soft steel roughing. Use EDM for hardened blind detail, tight corners, and features cutters cannot reach. Most molds use both.
Is EDM vs CNC milling the same as injection molding vs CNC machining?
No. This page is mold tool steel. The injection molding vs CNC machining compare page is about producing plastic parts versus machined parts.
Does EDM replace CNC on every deep rib?
Not always. Some ribs are milled in soft steel before heat treat. EDM is specified when hardened steel or geometry blocks milling.
Why is EDM slower on quotes?
Electrode or wire time, skim passes, and recast management add shop hours beyond hogging with a mill.
Can I avoid EDM on a cosmetic mold?
Design generous radii, open access for milling, and pre heat treat finishing where steel hardness allows. Class A gloss may still need polish after any EDM that touches cosmetic land.
Next step
Quote tooling with ribs and hardened steel notes
Upload CAD so EDM versus milling scope is visible on the tool quote. NetProto manufacturing is ISO 9001 certified.