Electrical Discharge Machining: Construction, Application, Pros

Electrical discharge machining, also is called spark machining, is a process very different from most of the conventional machining processes like CNC turning and milling. In the latter processes, sharp cutting tools are required to be able to subtract material from the work part being machined. Unlike turning and milling, the EDM process takes advantage of the erosion of metal through a series of electrical discharges.

Read on below and learn more about the fundamental concepts involved in EDM manufacturing.

How does EDM work?

Electrical discharge machining uses electric sparks on the edm machine to erode some parts of the workpiece. These “electric sparks” are actually electric arcs formed between two current-carrying conductors brought in close proximity with each other. The electric arcs are the ones responsible for generating extreme heat that causes the electrically conductive materials to melt and evaporate. Inside the system of an EDM process, the workpiece is connected to the positive terminal or the anode, while the tool responsible for eroding materials is connected to the negative terminal or the cathode.

Basic Construction of an EDM System

To further elaborate on the working principle, below is a breakdown of the basic construction of an electrical discharge machining (EDM) system.

1.   DC Pulse Generator

This component converts the AC power supply to a pulsating DC supply high enough to generate a spark between the eroding tool and the work part.

2.   Electrode Tool

This part of the system is connected to the cathode of the power supply while being mounted on a tool post. The profile of your tool will be the exact same profile left on your work part. During the process, a very tiny gap called the arc gap (identified by manufacturing engineers) is maintained between the electrode tool and the work part. The most common materials used for electrodes are Copper, Tungsten alloy, graphite, steel, and cast iron.

3.   Servo Motor Mechanism

This mechanism controls the feed and movement of the tool in the EDM machine. The arc gap, previously mentioned above, is critically controlled by a programmed servo motor mechanism.

4.   Spark generator

This component supplies the right amount of voltage needed for spark generation and discharge maintenance. The generation of one hundred thousand sparks per second makes it possible to create a significant subtraction of material from the work part.

5.   Di-electric fluid

Both the electrode tool and the work part are submerged in a dielectric fluid while having the fluid supplied at the gap between the tool and the work part. Moreover, the dielectric fluid should be set to circulate at a constant pressure to flash away metal parts that have eroded from the work part. Too much fluid pressure may cause the metal chips to be removed quickly resulting in a slower cutting action. Too weak fluid pressure might cause a short circuit in the system due to the unevacuated chips during the erosion process.

The most common dielectric fluids used in this process are deionized water, glycol, and silicone oil.

6.   Workpiece

This completes the EDM machine ecosystem because the work part is connected to the anode. To make the process possible, the work part should be a good electric conductor.

Type of EDM processes

The EDM process is classified into different types depending on the shape and approach of the tool used. The three common types of electrical discharge in the industry include hole drilling EDM, wire EDM and sinker EDM.

1.  Wire EDM

As the name implies, EDM wire cutting uses a very thin wire(copper or brass alloy usually ranging from .004 inches to .0006 inches thin) that is held by diamond guides to precisely cut a two-dimensional shape on a 3D workpiece. The path is controlled by a CNC program which allows complex shapes to be easily cut. The cutting may be likened to the cutting feed of a bandsaw and a cheese cutter. This process is typically used for cutting metal extrusion dies, punches, and plates.

2.  Sinker EDM

Also called ram EDM, this type of EDM process uses graphite or copper electrodes formed in a reverse shape to cut a cavity on the work part. The tool to be used is machined in a reverse form of the desired shape to be left on the workpiece.

Sinker EDM makes it perfect for machining molds to be used for casting and injection molding where complex cavity shapes are needed.

3.  Hole Drilling EDM

In this type of EDM process, the electrode tool is used to cut extremely thin and deep holes that a conventional drill may not be capable of. The tool for this process is designed in such a way that the dielectric liquid is fed directly through the hole, hence a hollow electrode. Since hole drilling EDM is not made through the conventional machining method, no burrs are formed in the work part. Hole drilling EDM is used for machining tiny relief holes on various turbine blades, dies, and molds.

What are the Applications of EDM Machining?

EDM machining is highly capable of producing intricate shapes and geometries.

That is why generally, electric discharge machining is used for highly precise applications where conventional machining isn’t capable. Below are the most common applications of EDM machining:

Small hole drilling

Many manufacturers choose to use EDM machining in drilling extremely tiny holes because it lessens the risk of having deflected and damaged tools. EDM machined holes can be very small in structure and can be seen on the edges of turbine blades, microscopic orifices for fuel system components, and many more.

Mold and Die Making

EDM machining is often used as a complementary process in addition to conventional machining in the fabrication of molds and dies. As mentioned above, the wire cut type is typically used for forming blanks for the molds, the sinker type may be used to form complex shapes of the cavities, and the hole drilling may be used for creating pressure release holes.

Components disintegration

The EDM machine is also used to remove stuck metals within a work part that can’t be removed in any ordinary way. Disintegrating the stuck components means destructing or removing the material. Some circumstances include sheared bolts on threaded holes, suck toolings on a machined part, or a pin stuck on a very precious part. By disintegrating the components, you get to remove the stuck metal without causing damage to the part to be reclaimed.

Medical components

EDM machined products do not form burrs when being manufactured, that is why these are perfect for creating various medical implant components.

Aerospace components

There are a lot of features on an aerospace part that cannot be made by some standard cutting tools, and that is where the EDM machining comes in. EDM machining is capable of producing challenging features with foremost, turbine rotor disc, thin slots, sharply squared holes, and very tight deep hole requirements.

Why EDM is Preferred?

Highly capable of machining complex profiles

The freedom of cutting for EDM is less constrained than that of conventional machining operations. In this process, various features that are almost impossible to be achieved through the use of end mills and drills can be cut with ease. These features include intricate pockets, fine deep holes, thin walls, and other irregularly shaped geometries.

High accuracy

EDM technology machined parts can be precise to up to the smallest tolerances used in the metals manufacturing industry. This is possible because the ecosystem of EDM machining does not introduce high stress on the work part and does not have aggressive vibrations. Aside from this, a skimming process may also be done to increase its precision and accuracy.

Burr-free surface finish

The work part produced from EDM machining comes out burr-free because of the nature of the process wherein the eroded metal from the work part almost disintegrates into microparticles that are then flushed out. Most importantly,  EDM cutting does not involve sharp cutting tools like endmills, saws, and drills, that is why this process does not cause any burrs on the work part.

Can cut hard metals

EDM machining is capable of cutting hard metals with low force and minimal effort as long as they are conductive. The hardness of the material being cut does not affect the overall process.

Low Stress

The tools used in an EDM process do not touch the workpiece, unlike other machining methods where the cutting tools contact with the surface being cut. This explains the minimal stress being introduced into the workpiece.

Highly Scalable Manufacturing

EDM machining processes are very versatile when it comes to production scale, it is suited for low to high-volume manufacturing. These processes are highly repeatable, meaning multiple parts can be made with consistent quality.

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What are the Limitations of the EDM Process?

Only Applicable to Conductive Materials

The heat responsible for eroding the material on the work part relies on the introduction of electrical discharges, which makes edm machining not compatible on non conductive materials like composites, plastics, and other dielectric materials.

Low Material Removal Rate

As mentioned, EDM machining gradually erodes the material. That makes its material removal rate much slower than that of the conventional machining processes like milling and turning.

Expensive Production cost

The cost for producing parts using EDM involves different factors like high power consumption, excessive tool wear, and long machining time.

Summary

Electrical discharge machining is a very useful addition to various conventional CNC machining processes. It plays to its strength where it is capable of producing special features that are hard to achieve through milling and turning. In addition to this, the EDM process has exceptional accuracy even when cutting extremely hard electrically conductive metals, plus it posts low strain during processing.