Technical Reference
Edm Heat Affected Zone Guide
The EDM heat-affected zone includes thermal changes beneath or around the recast layer and must be considered separately from Ra. A narrow heat-affected or thermally altered zone can be hidden beneath an acceptable roughness reading.
Quick Answer
The EDM heat-affected zone includes thermal changes beneath or around the recast layer and must be considered separately from Ra.
Key Surface Points
What the Surface Requirement Means
A visually smooth surface can still contain thermal change below the measurable roughness profile. The consequence changes fit, function, or service performance for the Heat-Affected Zone decision; it is not only a change in surface appearance.
How to Control It
Identify fatigue, hardness, corrosion, seal, or wear faces and define whether microhardness, metallography, or post-process verification is needed. When planning Heat-Affected Zone, apply the requirement only to the dimensions and faces that control fit, function, service life, or documented release.
What Gets Missed
A narrow heat-affected or thermally altered zone can be hidden beneath an acceptable roughness reading. Fatigue, hardness, corrosion, or coating performance may still fail unless the affected layer and inspection method are defined.
Technical Context
Below the resolidified surface, the thermal cycle can alter hardness, residual stress, or microstructure without fully melting the material. The depth and significance of this heat-affected zone depend on energy, pulse duration, material, and finishing passes. This mechanism explains the limits and behavior that matter when planning Heat-Affected Zone.
EDM Heat-Affected Zone Guide Reference
| What you're asking | What you can expect |
|---|---|
| Acceptance item | Define separately |
| Roughness | Ra and measurement method |
| Recast/white layer | limit or removal on named face |
| Microcracks | method, magnification, and acceptance |
| Edge | radius, break, chipping, or rollover |
| Post-process | polish, lap, grind, stress relief, or passivation |
Inspection and Post-Process
Use hardness traverse, metallography, or another agreed method when the sub-surface thermal zone matters. The drawing should identify the functional face and service risk rather than applying one blanket HAZ statement to every surface. For Heat-Affected Zone, tie the accepted condition to the feature and inspection method named in the drawing.
Heat-Affected Zone Drawing and Release Checkpoints
- Identify the controlled feature, material condition, access direction, and functional datum for this Heat-Affected Zone decision.
- Separate dimensional requirements from texture, edge, recast, corrosion, fatigue, or post-process acceptance.
- State the inspection method, sampling or first-article requirement, drawing revision, quantity, and any documentation needed for release.
Limits and Better Alternatives
Main Limit
For EDM Heat-Affected Zone Guide, one Ra value cannot approve recast, micro-cracks, edge damage, corrosion response, fatigue risk, or post-processing. When that boundary dominates, use lower-energy finishing, selective polishing/lapping/grinding, or a process redesign where the functional surface cannot accept the EDM-affected condition.
Consider Another Route When
Use lower-energy finishing, selective polishing/lapping/grinding, or a process redesign where the functional surface cannot accept the EDM-affected condition.
Practical Next Step
Use hardness traverse, metallography, or another agreed method when the sub-surface thermal zone matters. Identify fatigue, hardness, corrosion, seal, or wear faces and define whether microhardness, metallography, or post-process verification is needed.
What to Remember
The EDM heat-affected zone includes thermal changes beneath or around the recast layer and must be considered separately from Ra. Release roughness, recast, cracks, edge condition, and post-processing as separate requirements wherever function demands it.
Technical Reference
Use the values as planning references and define the functional requirement on the controlled drawing.
Use This Guide to Prepare Your RFQ
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Frequently Asked Questions
Is Ra enough to approve the surface?
No. Roughness and metallurgical/edge condition are separate.
Which faces need detailed control?
Fatigue, seal, wear, corrosion, contact, cutting, and medical surfaces.
Can finishing reduce the affected layer?
Yes, but the pass or removal method and inspection must be defined.
Should every surface use the same requirement?
No. Restrict detailed acceptance to functional faces.