Electrical Discharge Machining (EDM) for Precision Superalloy Parts Fabrication

EDM Techniques for Superalloy Fabrication

EDM uses electrical discharge between a tool and workpiece in a dielectric fluid to erode material without mechanical force.

• Wire EDM for profile cutting, slots, and thin-walled structures

• Sinker EDM for cavities, tip restoration, and sharp corners

• Micro-hole EDM for holes ≤0.3 mm diameter at depth-to-diameter ratios >20×D

• Orbital and multi-axis EDM for angled channels and internal feature finishing

EDM enables machining of hardened alloys up to 60 HRC without inducing tool deflection or heat-affected distortion.

Superalloys Commonly Processed via EDM

EDM supports the manufacture and repair of parts with internal contours, intersecting passages, and thin-wall cross sections.

Case Study: Micro-Hole EDM on CMSX-4 Cooling Airfoil

Project Background

A turbine customer required 0.3 mm diameter holes in CMSX-4 airfoils for film cooling. Holes had a depth of 6 mm and tolerance of ±0.008 mm. Hole EDM was used after rough machining. Final recast layer was ≤2 μm, and roundness deviation remained under 5 μm.

Typical EDM Applications and Industries

EDM is particularly effective where fine tolerances and low thermal deformation are required.

Challenges in EDM Machining of Superalloy Parts

1. Recast layer >3 μm leads to fatigue crack initiation—requires finishing pass or post-EDM polish

2. Dielectric breakdown at high energy can cause microcracks in thin sections

3. Electrode wear rate >1% per operation affects dimensional control in deep cavities

4. Taper deviation in deep holes exceeding 0.02 mm must be corrected with orbital paths

5. Heat-affected zone (HAZ) requires control below 0.5 mm in turbine hardware

EDM Solutions for Superalloy Fabrication and Repair

• Low-energy finishing cycles to reduce recast layer to ≤1.5 μm for fatigue-sensitive parts

• Multi-pass orbital EDM for precision angle drilling in CMSX and Rene blades

• Electrode compensation algorithms for dimensional repeatability within ±0.005 mm

• Post-EDM heat treatment and surface passivation to restore grain boundaries

• CMM and SEM inspection to verify geometry and microstructure

Results and Verification

Process Execution

EDM was performed on fully heat-treated superalloy substrates. Pulse energy, feed rate, and dielectric were controlled via adaptive feedback. Geometry verified using in-process sensors.

Finishing and Accuracy

Final hole diameters held to ±0.008 mm. Surface finish Ra 0.3–0.5 μm achieved. Recast layer removed via brushing or low-energy finish passes.

Post-Processing

EDMed parts underwent heat treatment for residual stress relief. Surface cleaned and passivated where corrosion resistance was required.

Inspection

CMM confirmed dimensional targets. X-ray verified bore straightness. SEM confirmed crack-free microstructure and HAZ quality.

FAQs

1. What EDM processes are best for Inconel and CMSX parts?

2. How is the recast layer removed after EDM machining?

3. Can EDM be used to repair turbine blade tips or airfoils?

4. What is the typical positional tolerance of EDM-machined holes?

5. How are EDM components inspected for quality assurance?