Electrical discharge machining (EDM) services remove metal by burning instead of cutting or grinding. This is accomplished by submerging the workpiece in a dielectric fluid and sending rapid electrical discharges through a wire or electrode (the cutting tool). EDM is one of the most accurate and versatile machining techniques; it can be used on any metal that conducts electricity, and on some ceramics. It has the advantage of being able to cut fragile or hardened parts because it does not cause the deformation induced by mechanical cutting processes.

Since EDM is a very specialized process that requires special equipment, many machining companies do not have in house EDM capability. EDM service providers supply this capability and capacity to those that need it. Part design dimensions and features are forwarded to the EDM shop or "house". Parts are machined or cut from provided or internally purchased stock. When requirements are met the parts are returned to the client.

Types of EDM

EDM is also called "spark machining" because repetitive electrical discharges (sparks) are used to remove metal. The electrical discharges are passed between the metal part and the electrode through a dielectric liquid. This continuously flowing liquid (typically oil or deionized water) is responsible for multiple tasks: 1) providing an inert atmosphere for discharge to take place; 2) removing metal remnants produced during the process; 3) keeping the temperature of the process stable.

There are three basic types of electrical discharge machining (EDM) operations: sinker EDM, wire EDM, and small-hole EDM. These processes differ based on the type of electrode used.

Sinker EDM

A sinker, die-sinker, ram, or electrode EDM uses an electrode that is fabricated into a specific shape. The inverse of this shape is imprinted on the part as the electrode "sinks" itself into the workpiece, eroding away the material. A servo control mechanism is used to monitor the gap voltage and maintain continuous sparking during the process. Oil is typically used as the dielectric fluid.

Sinker EDMs are extremely accurate and create fine finishes. They are used when parts need tight tolerances or when a tight corner radius is required. The sinker EDM process is versatile, allowing parts of many different sizes to be machined. They are commonly used to burn mold cavities for part fabrication and for internal holes and recesses.

Sinker EDM. Video Credit: EDM Technologies / CC BY 3.0

Wire EDM

A wire EDM burns the workpiece using a very thin (typically brass) wire as the electrode. The wire is spun between two reels during machining and travels vertically through the workpiece. The cutting is done in a bath of deionized water. Computer software controls all the operations of the process, including the path of the wire.

Wire EDM machines excel at cutting very intricate and delicate shapes efficiently. They are used to machine contours, sharp corners, and tapers either internally or externally. Wire EDM is the most accurate EDM process, capable of achieving tolerances well under .0001 inches for most cuts.

Introduction to wire EDM (how it works). Video Credit: Xact Wire EDM / CC BY 3.0

Small-hole EDM

A small-hole EDM uses a small, hollow tube electrode which spins about a spindle much like a drill and drill bit. The discharge process is more aggressive than sinker EDM, and blasts small holes in workpieces very quickly. Dielectric fluid is flushed through the electrode to provide an effective "sparking" environment.

Small-hole EDM is similar to drilling, but creates very little machining residue. The process was originally used for putting in pilot holes (starting points) for wire EDM machines. They are ideal for blasting and drilling small holes in various types of parts, including those with curved or angled surfaces and those made of hardened materials.

Small-hole EDM drilling. Video Credit: EDM Technologies / CC BY 3.0

Sizing

EDM machining services differ in terms of size capabilities. Sizing specifically refers to the lengths of the parts being machined. If the service company is limited to a range of part sizes, they will often specify that range. Most parts will be in a range from 48" to less than 1". Services that specify micro machining have the ability to machine very small parts using EDM processes.

Materials

EDM services typically indicate what types of materials they specialize in and are capable of machining. Unlike other machining companies, EDM service companies are less limited by the mechanical properties (e.g. hardness, machinability) of the materials. The only limitation of electrical discharge machines is that the materials must be electrically conductive. Some materials commonly machined by EDMs include:

• Aluminum
• Brass
• Bronze
• Copper
• Nickel
• Stainless steel
• Steel
• Titanium

Service Features

EDM machining service companies may offer a number of features that correspond to the services they offer.

CAD / CAM support - Since most EDM machines are automated by computer numeric control (CNC), service companies often have the ability to take sold-model design files electronically and use them for part creation. Clients should consult the suppliers for details on the computer aided design (CAD) and computer aided manufacturing (CAM) software they use and support.

• Design assistance - The supplier may offer assistance with concepts, manufacturing costs, manufacturing techniques, and material considerations. Suppliers may also be able to assist in upgrading or redesigning, re-evaluating or modernizing existing products to increase performance and/or reduce manufacturing costs.
• Prototype services - Suppliers may provide services for building small quantities of representative parts for use in presentations and functional testing.
• Low volume production - Suppliers may specify that they offer low volume production, meaning they can cost-effectively produce low quantities of parts for their clients.
• High volume production - Suppliers may specify that they are capable of high volume production, meaning they are able to produce large quantities of parts in a reasonable time.
• Reverse engineering - Some EDM machining services can offer reverse-engineering of parts in order to provide part replication or duplication services.

Applications

The EDM process is most widely used by the mold-making tool and die industries, but is increasingly applied to make prototype and production parts, especially in the aerospace and electronics industries in which production requirements are relatively low. EDM is particularly well suited for parts which are made from materials that are difficult to machine and/or contain small or odd-shaped angles, intricate cavities or intricate contours.

Other Considerations

Once all of the service criteria for part production have been met, factors such as cost and location need to be considered.

Cost

The cost of a service is important to consider in any application. Quotes (cost estimates) for part manufacturing orders are given to the customer after he or she provides the supplier with the part specifications or a description of the requirements. Cost typically correlates to the time spent producing the product and the expense of the materials used (when purchased by the service company). Additional costs include transportation or shipment costs of the parts once they have been made.

Location

The location of the service provider is important to consider both for logistical reasons and expenses. Operations located farther away from the customer will have higher associated shipping costs, especially for large production volumes. In addition, there may be additional logistical complications when dealing with suppliers from different countries.

References

EDM Technologies - EDM Services

PolCraft Inc. - What is EDM?