A Guide to Designing for EDM After CNC Machining

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In the world of precision manufacturing, combining processes often yields the best results. CNC machining excels at creating complex geometries with excellent surface finishes, but it has limitations when it comes to sharp internal corners, deep cavities, or extremely hard materials. This is where Electrical Discharge Machining (EDM) comes in as a powerful secondary operation. Designing with this sequence in mind is crucial for optimizing part functionality, cost, and lead time.


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Understanding the EDM Process After CNC

EDM, particularly sinker EDM, uses electrical sparks to erode material. An electrode, shaped inversely to the desired feature, is plunged into the premachined CNC part. This is ideal for creating intricate details that CNC tools cannot access or form.

A common application is creating precision injection molds. The CNC machine creates the main mold cavity and external features efficiently. The EDM then burns in delicate text, logos, undercuts, or perfectly sharp corners on the mold core. Similarly, in aerospace and medical components, EDM is used to machine small, highprecision holes or slots in turbine blades or surgical instruments that have been preformed by CNC.

Key Design Considerations for a Seamless Workflow

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To leverage the CNC+EDM combination effectively, incorporate these design principles:

1. Strategic Stock Allowance: When designing your CNC model, leave a small amount of excess material (e.g., 0.10.5mm) in areas designated for EDM. This "EDM stock" ensures a clean, predictable burn and protects the CNCmachined surface.



2. Electrode Accessibility and Design: Always consider how the electrode will access the burn area. Design open passages for the electrode to travel without obstruction. Simpler electrode shapes are cheaper and faster to produce. Avoid designing deep, narrow cavities that require long, fragile electrodes.

3. Start Holes and Fixturing: For internal features, the CNC process should predrill a "start hole" for the EDM wire or electrode. This eliminates the need for the EDM to burn through a large volume of material, drastically reducing machining time. Also, design in fixturing points or datums during CNC machining to ensure the part can be accurately and securely relocated for the EDM operation.

4. Material Selection: While EDM can machine hardened materials, specifying a uniform, highquality material for your part ensures consistent sparking and a superior final surface finish.

Business Growth Through Integrated Manufacturing

Offering a seamless CNCtoEDM workflow positions your company as a true solutions provider. It demonstrates deep technical expertise and allows you to tackle more complex, highvalue projects that competitors might refuse. By educating your clients on these designformanufacturability (DFM) principles, you build stronger partnerships, reduce costly design revisions, and deliver superior, readytouse components. This integrated approach not only enhances part quality but also becomes a significant driver for business growth, attracting clients who need sophisticated, precisionengineered parts.