What is EDM Machining? Process, Pros, and Cons

Conventional machining methods, such as lathe, turning, milling, and drilling, struggle to create micro-geometrical features like sharp corners, internal channels, long cavities, etc. In such situations, manufacturers and engineers prefer Electrical Discharge Machining (EDM) methods. 

Wirecut, sinker, and hole-drilling EDM options are available to micro-machine diverse types of workpieces. Furthermore, we will discuss the EDM machining process, its advantages, and application examples. 

What is EDM Machining?

Electrical discharge machining creates the desired cuts, features, and patterns using an electrical spark between the cutting electrode( or wire) and the conductive workpiece within a dielectric medium. Let’s look at the EDM setup to understand its working mechanism;

EDM setup 

The key components of the EDM machining setup are the power supply, servo motor control, EDM tank, and movable electrodes. They work together to shape the workpiece inside the dielectric fluid.

Once power is supplied, the rectifier converts the AC supply into DC. Meanwhile, the current control device regulates the electric flow between the electrode and the work. It can adjust the discharge intensity, which influences the EDM precision, material removal speed, and accuracy. 

Furthermore, the servo motor integrated with the control unit dictates the electrode movement as desired for the material removal. How deep the machined cavity or features is decided depends on the potential difference between the electrode and workpiece inside the medium. This difference can be controlled by adjusting the gap between them. 

Deionized water, kerosene, and other different dielectric mediums can be used based on the work material properties and desired machining characteristics. 

Localized Heating and Material Erosion 

After the current flows through the EDM machining circuit, the voltage( electric field) causes the electron movement from the tool to the workpiece. This moving electron collision generates ions build-up, and ultimately a concentrated plasma ( spark) with a temperature beyond 10,000°C.

The intense heat erodes the material from the workpiece in a controlled manner through melting and vaporizing. Next, the plasma collapses when the voltage is cut off. Then, the shock waves further remove the material and clean the cuts.

Three Types of EDM 

Die sinker EDM

There are three types of EDM; Wire EDM, Die-sinker EDM, and Hole Drilling EDM. Each of them has different capabilities and application preferences.

The wire electrodes are suitable for the 2D- features or cuts. Die sinker for tool and dies. Consequently, hole drilling is ideal for deep holes and pockets. 

• Wire EDM: It uses a thin wire as an electrode to cut intricate shapes with high precision and complex profiles, such as prototype parts and medical devices
• Die-Sinking EDM: Sinker EDM uses custom-shaped electrodes to create detailed cavities. 
• Hole-Drilling EDM: As the name suggested, it is ideal for small and deep holes at specific angles. 

Advantages of EDM Machining 

The first benefit of EDM is the non-contact machining process and its capability to create micro-features. For instance, drilling holes of diameter less than 1 mm in hard materials. Other advantages of EDM are precision, no machining stress, clean cuts, and a finely machined surface.

Here are the

• Dimensional Accuracy 

The EDM process can achieve tight tolerances, as low as  ±0.0001 inches. This accuracy is valuable in the production of dies, molds, and other tooling.

• Design Flexibility 

You can create highly complicated geometrical features that are impossible with conventional machining. EDM process is compatible with deep cavities, pockets, channels, etc.

• Hard Workpieces

Since EDM does not involve direct contact between the tool (electrode) and work, it can cut any hard materials or steel, that are electrically conductive. For example, tool steel, titanium alloys, and hardened steel. 

•  As-machined Surface Finish

Furthermore, the EDM machined surfaces are smooth and burrs-free. Often, the roughness level (Ra = 0.1 to 7   μm) is easily achievable with this. 

Disadvantages of EDM

The EDM also has some drawbacks regarding work material options and machining cycle time. 

• Material Limitations 

The EDM process is only compatible with electrically conductive materials like metal and alloys. It can not machine materials like plastics and ceramics that can't generate electrical discharges with electrical fields. 

• Lower Production Speed

Although EDM machines can be integrated with the CNC system, the machining speed is slower compared to CNC milling, drilling, and other processes.

• Not Suitable for Large-scale Projects

Large-sized geometrical features are not feasible due to the slower material removal rate is the size limitation of EDM electrodes.

What Are the EDM Applications?

One of the main uses of EDM is tool and die-making. It can create intricate features on injection molds, casting dies, compression molds, fixtures, etc. Use of electrode with the shape of the required cavity of features is used for this. Additionally, other industries also use EDM precision manufacturing for different components. The table below shows some common application examples across industries.