After rough or semi EDM
- Thicker recast and visible pitting on the eroded surface
- Corners and lands may be out of spec for gloss until skim or hand work
- Faster metal removal when electrode wear is acceptable
Glossary
EDM Recast Layer on Injection Mold Steel: White Layer & Polish
Recast layer forms on every EDM surface. Plan skim burns and polish when shutoffs or Class A lands must seal or gloss.
Definition
What Is the EDM Recast Layer?
The EDM recast layer is a heat affected zone left on eroded steel after sparks remove material. Mold shops often call it white layer.
Recast is not parent tool steel. It is harder, brittle, and can hold stress at the surface after sinker EDM, wire EDM, or hole-drilling EDM.
Rough burns leave thicker recast. Skim passes, stoning, and polish reduce it before plastic touches the land or before shutoffs must seal.
Recast affects whether as cut EDM is acceptable on vents, shutoffs, and Class A cavity faces.
See theEDM overviewfor process context and theEDM finishspoke for part surface planning.
Finish
Recast layer after every EDM spark
White layer management on shutoffs and Class A lands.
- Rough burns leave thicker recast; skim passes reduce it before polish.
- Sinker, wire, and hole-drilling EDM all leave recast on the eroded surface.
- SPI gloss and texture specs belong on the RFQ when plastic touches burned steel.
Processes
Recast on sinker, wire, and hole drilling
Every EDM discharge leaves some recast. Finish plan depends on which face sees plastic or air.
Sinker EDM recast on ribs, pockets, logos, and shutoffs burned with shaped electrodes
Wire EDM recast on through slots, insert walls, and pin holes after rough and skim cuts
Hole-drilling EDM recast at wire start holes and vent mouths where burr or white layer narrows flow
RFQ
What to specify on tooling prints
State acceptable surface when EDM is the final steel step before texture or polish.
Mark cosmetic lands that need recast removal before SPI gloss or high gloss polish
Functional vents may tolerate thin recast if effective area still meets vent rules
Shutoff faces may need skim EDM plus stoning when flash or seal is sensitive
Reference SPI, VDI, or MoldTech only after recast is managed on the underlying steel
Management
Rough EDM versus skim and polish
Geometry comes first. Recast management is a separate line item on many mold quotes.
After skim EDM and planned finish
- Thinner recast before stoning or diamond polish
- Shutoffs and cosmetics closer to SPI targets when labor is scoped
- More electrode or wire time explicitly on the quote
Go deeper
EDM and finish links
Each link covers a different step after sparks erode the steel.
EDM overview
Three EDM processes in one hub.
EDM overviewSinker EDM
Blind burns and electrode sequence.
Sinker EDMWire EDM
Through cuts and skim passes.
Wire EDMHole-drilling EDM
Start holes and vent mouths.
Hole-drilling EDMEDM finish
Part surface after mold steel is cut.
EDM finishSPI A1 finish
Gloss target after recast is removed.
SPI A1 finishVisual reference
Photos from molding and tooling programs
Images are selected from the NetProto Forge media library for this topic.
EDM recast layer white layer on mold steel surface close up
EDM recast layer white layer on mold steel surface close up
Skim pass sinker EDM surface before mold polish
Skim pass sinker EDM surface before mold polish
Stoned mold land after EDM recast removal
Stoned mold land after EDM recast removal
FAQ
Frequently Asked Questions About EDM Recast Layer
What is EDM recast layer on injection molds?
A heat affected layer left by EDM sparks on cavity or core steel. It must be managed when cosmetics, seal, or fatigue matter.
Does wire EDM leave recast layer?
Yes. Wire paths leave recast on cut walls. Skim passes and polish reduce it on visible or shutoff faces.
Must recast layer be removed before molding?
Not always. Functional vents and hidden steel may tolerate it. Class A gloss and tight shutoffs usually need skim EDM and/or stoning.
Is recast layer the same as SPI finish?
No. SPI labels describe final mold polish or texture. Recast is an intermediate EDM condition removed before those targets.
How do I call out recast on an RFQ?
State which faces are cosmetic, which are shutoffs, and whether as cut EDM is acceptable or post EDM polish is required.
Next step
Quote tooling with finish targets
Upload CAD with cosmetic faces, shutoffs, and SPI or texture notes so recast management and polish time quote correctly.