EDM Electrical Discharge Machining

EDM, Electrical Discharge Machining is one of the most accurate manufacturing processes available for creating complex or simple shapes and geometries within parts and assemblies. EDM works by eroding material in the path of electrical discharges that form an arc between an electrode tool and the work piece. EDM manufacturing is quite affordable and a very desirable manufacturing process when low counts or high accuracy is required.Turn around time can be fast and depends on manufacturer back log.

The EDM system consists of a shaped tool or wire electrode, and the part. The part is connected to a power supply. Sometimes to create a potential difference between the work piece and tool, the work piece is immersed in a dielectric electrically nonconducting) fluid which is circulated to flush away debris.

The cutting pattern is usually CNC controlled. Many EDM machine electrodes can rotate about two-three axis allowing for cutting of internal cavities. This makes EDM a highly capable manufacturing process.

EDM comes in two basic types: wire and probe (die sinker). Wire EDM is used primarily for shapes cut shapes through a selected part or assembly. With a wire EDM machine, if a cutout needs to be created, an initial hole must first be drilled in the material, then the wire can be fed through the hole to complete the machining. Sinker (diesinking) EDMs are generally used for complex geometries where the EDM machine uses a machined graphite or copper electrode to erode the desired shape into the part or assembly. Sinker EDM can cut a hole into the part without having a hole pre-drilled for the electrode.

Design Considerations

Relax the Surface-finish for the part, if feasible. This allows the manufacturer to produce the part with fewer passes, at a higher current level and a higher metal-removal rate.
Design or prepare the part such that the amount of stock removed by EDM is relatively small. Use traditional machining techniques to remove the bulk of the stock with the finishing operations performed by EDM. This significantly reduces the amount of time and cost for each part.
The EDM manufacturer should consider fixtures such that several parts can be stacked and machined simultaneously or a single part can have several EDM operations performed simultaneously.
When existing holes are to be enlarged or reshaped by EDM, through holes are preferred to blind holes as they permit easier flow of dielectric fluid past the area being machined

Dimensional Accuracy (+/- 0.0005 inches per inch)
Feature Profile accuracy of .0003 is obtainable with cutting path
Features to feature true position of .002 is reasonable and down to .001 is possible when geometry requires removal and reattachment of wire.

Surface Finish (microinches) Features created by EDM have an "orange peal" appearance.
16 Ra is achievable, 64 or higher Ra is typical and less expensive.

Wall Thickness
Min Wall Thickness (inches): 0.01 (over a 5" inch span)

As always, consult with EDM vendor for specific capabilities.