Electrical discharge machining (EDM) has become popular in the manufacturing industry. What sets this non-conventional machining method apart from manufacturers is the fact that it can be used on any material, especially the hard ones.
EDM can be used to machine even complex designs on materials irrespective of their hardness. The process entails the use of a workpiece and electrode whereby the two are submerged in a dielectric fluid to allow electric currents to flow between the two. The repeated flow of electrical current creates plasma zones or electrical sparks which melt and erode the material instantaneously.
To perform the EDM process, you can use various types of electrodes. For instance, Ram EDM machines (die sinkers), make use of electrodes that are custom machined on 3D shapes. On the other hand, Wire EDM machines make use of a thin wire to cut into the material.
Additionally, there is a hole popper or rather a small-hole EDM machine that works just like the ram EDM machine. However, this machine makes use of a cylindrical electrode that is used to machine holes in the part.
In this article, we will explore everything you need to know about electrical discharge machining. We will explore the principles, processes, and applications to leave you well-informed.
EDM Machining (Image Source: Istockphoto)
The EDM Process
The EDM process, which was invented in the 1940s has been around for quite some time. This process applies a certain principle where thermoelectric energy is used to erode a workpiece by automatically repeating an electrical spark caused when the workpiece and electrode are submerged in a dielectric electrolyte.
Repetition of the spark between the workpiece and the non-contact electrode allows for erosion on the workpiece surface as desired. To achieve optimal results in this process, the operator has to choose the gap between the workpiece and the electrode carefully so as to ensure that the voltage is strong enough to ionize the dielectric fluid.
The electric sparks produced between the electrode and workpiece further generate high temperatures on the plasma channel where thermal dissipation happens. This high heat generated melts both the electrode and workpiece.
After erosion, the eroded material solidifies to form debris. This debris is then carried away when the dielectric fluid is flushed during the machining process. The flushing process helps to restore the sparks in the gap and prevents short-circuiting.
Nonetheless, there is no cutting force between the workpiece and the electrode since there is no contact between the two. Doing so helps minimize vibrations and stress that might occur in the process.
EDM Vs Traditional Machining Methods
Unlike traditional machining methods which can only be used to create parts that require less complex machining, you can use electrical discharge machining to make sophisticated machine cutting tools even up to 5-axis. The EDM machines perform the job efficiently and accurately to create parts that are of high quality.
That said, the main difference between EDM and traditional machining methods is the fact that in traditional methods, you need to have physical contact between the electrode and the workpiece. On the other hand, EDM performs the subtractive work without contact with the conductive material. EDM uses electric current to create sparks that erode the workpiece without deforming it.
Types of EDM
There are three main types of EDM which include Wire EDM, Sinker EDM, and Hole Drilling EDM. Below, we will look at the three in detail!
1. Wire EDM
Wire EDM is also known as wire-cut EDM. This EDM method, just like the name suggests, uses a thin brass or copper wire to cut the workpiece.
Normally, the cutting process involves the use of a computer to control the cutting of the piece as per set geometry. This wire erodes the workpiece using the electrical sparks created.
The wire EDM method is widely used to produce circular saws, punch units, and other complex shapes. This method is also a fan-favorite when it comes to aesthetically appealing products as it is very precise in cutting the workpiece.
2. Die Sinking EDM
Die sinking EDM possesses various names including sinker EDM, ram EDM, or plunge EDM. This variant of EDM was the first type of EDM and it uses graphite, copper, or tungsten as the electrode.
The ram EMD process usually entails the use of an electrode with a mirror shape or negative shape of the intended part. While this type of EDM can be used to make deep holes, their primary use is to make complex cavities.
This makes the method suitable for turbine blades, gear wheels, and air compressors. These components can be used in heavy industrial, automotive, energy, and aerospace sectors.
3. Hole Drilling EDM
The hole-drilling variant of EDM is majorly used to make holes in the workpiece. This method utilizes a rotating tool electrode to make accurate and tiny holes. Additionally, while using this technique, the expert does not need to perform deburring once done drilling the holes.
When trying to achieve deep holes, this method comes in handy to form holes even as deep as 250 times the diameter of the tool electrode. Bear in mind that the tool electrode typically has a diameter anywhere between 0.255m to 4.7mm
Hole drilling EDM uses a tubular tool electrode to remove the debris from the formed hole. These particles are then flushed out using the dielectric fluid. This process is highly used in the medical and aerospace industries.
Hole Drilling EDM (Image Source: Istockphoto)
Advantages of EDM
Electrical Discharge Machining (EDM) offers several advantages that make it a popular choice for precision machining. They include:
1. High Precision
EDM allows for exceptional precision and accuracy in machining operations. It can achieve tight tolerances and produce complex shapes and features with excellent repeatability.
2. Material Versatility
EDM is suitable for a wide range of materials, including metals, alloys, ceramics, and even non-conductive materials like graphite and composites. This versatility allows for the machining of diverse workpiece materials.
3. Design Freedom
EDM is particularly effective for machining complex designs and even utilizing materials with high hardness and difficult-to-cut properties, such as hardened tool steels and exotic alloys.
4. Distortion-Free Machining
EDM is a non-contact machining process. The material removal occurs through controlled electrical discharges, eliminating the need for direct physical contact between the tool and the workpiece. This reduces the risk of tool wear, deflection, and damage to delicate workpieces.
5. High Quality Surface Finish
EDM produces excellent surface finishes, often eliminating the need for additional post-machining operations. The non-contact nature of the process minimizes the formation of burrs, resulting in smooth and burr-free surfaces.
Considerations for Using EDM
To have a successful EDM process, you need to consider various factors such as material removal rate, wear resistance, machinability, material cost, and surface finish.
Material Removal Rate (MRR)
The material removal rate is usually expressed as cubic inches per hour (in3/hr), but in fact, could just as realistically be expressed as $/hr.
Achieving an efficient MRR is not simply a matter of the right machine settings. It also involves direct energy dissipated in the EDM process.
MRR is influenced by the physical properties of the workpiece material such as melting point and thermal conductivity.
Wear Resistance
There are four different types of wear: volumetric, corner, end, and side (figure 6-3). Corner wear is usually the most important since it will determine the degree of accuracy of the final cut.
If an electrode can successfully resist erosion at its most vulnerable points, then overall wear will be minimized and maximum electrode life achieved.
Machinability
Materials with high hardness values can cause machining problems. The fabricating time is influenced by the particle size and strength of the material along with the desired electrode detail.
The maximum detail that may be obtained in graphite is limited by the material strength, particle, and pore size. Machining time can be wasted by trying to machine in more detail than the material can handle.
Material Cost
Electrode fabrication, wear, and redressing costs should be weighed to determine the best electrode material and machine settings. The actual material cost represents only a small part of the total EDM job cost.
Many of the commonly encountered graphite sold as EDM electrode materials are very cost-effective performers for roughing out cavities where finish and detail are not important.
Surface Finish
Surface finish can be controlled by a combination of factors, such as on-time, peak current, the electrode material, and the workpiece material.
Short on-times and low peak current settings produce the best finish, as these conditions produce smaller craters in the work metal. Until these conditions are met, no electrode material will produce a fine surface finish.
EDM Machines and Their Components
Electrical discharge machining entails various components which are vital for the process. These components include:
- Workpiece
- Tool electrode
- Power supply
- Dielectric fluid
EDM Machine in Action (Image Source: Shutterstock)
Workpiece
The workpiece is the most important component of the EDM process. Basically, this piece of material is known as a blank and it is the material that is machined in the process.
However, the workpiece has to have certain properties. For instance, an EDM workpiece must possess electrical conductivity properties. While traditional machining methods require easier-to-machine materials, EDM machining can utilize even the hardest metals.
Tool Electrode
Electrode, or rather the tool electrode is the component that is used to create sparks as it gets into contact with the workpiece. Graphite, tungsten, copper, and brass are the most common types of tool electrode.
Your choice of electrode varies based on the EDM technique. For instance, copper or brass electrodes are used in wire EDM while a tubular electrode is used in hole drilling EDM. A servo motor controls the tool electrode thus moving it precisely along CNC pathways making sure that it does not touch the workpiece in the process.
Power Supply
In EDM, the power supply serves to control the production of electrical sparks which tune the strength and the frequency of the electric current based on the job being performed.
Normally, the electric current passes through the electrode thus reacting with the workpiece. The reaction between the two produces sparks which erode the workpiece as desired.
Dielectric Fluid
Electrical discharge machining is performed in a tank of dielectric fluid. Deionized water and non-conductive lubricating oil are some of the most common dielectric fluids used.
Typically, the fluid helps to cool the particles removed from the workpiece and also move them away from the workpiece thus preventing them from being pulled to the electrode which would disrupt the process. This liquid also controls the electrical discharge produced between the electrode and the workpiece.
Applications and Advantages
One of the major advantages of EDM is that you can use it to machine complex shapes precisely. This method can also be used on small workpieces where other methods might damage due to too much pressure. These capabilities of EDM have seen it get adopted in various industries. Let’s explore its applications below!
1. Aerospace Industry
Electrical discharge machining is widely applied in making parts for use in the aerospace industry. This method, powered by precision and the ability to produce intricate parts makes it suitable for making plane and spaceship parts. EDM is essentially used for aerospace metal works vital for complex engines and other plane parts.
2. Military Industry
The military sector requires slightly different technologies. For instance, etch circuit boards are used in military vehicles and weapon systems. These complex designs call for EDM since achieving the desired metallic parts may require precision which may not be achieved via other machining methods
3. Automotive Industry
Electrical discharge machining has been used in the automotive industry since the 1960s. This technology is used to make parts such as intake manifolds, intake valves, and cylinder heads which are quite difficult to make using other methods. The main reason why EDM is suitable for the automotive industry is the fact that this machining method can be used to produce high-tolerance, low-cost, and complex parts.
4. Jewelry Manufacturing
Due to its capability to produce smooth surfaces that have no burrs affecting tolerance, EDM machines are used to make jewelry. The technique is also used to machine shapes into silver or gold whereby it removes tiny amounts of materials at a go. This results in components with mirror-like finishes and high material density thus ideal for rings and earrings with precious stones set into them.
Benefits of EDM
- Creates complex shapes that would otherwise be difficult to perform with traditional cutting tools.
- It is a great solution for cutting extremely hard, demanding, and non-template materials.
- Has great prospects for machining very small workpieces, which other methods can damage by pressing them with cutting tools.
- There is no contact between the tool and the workpiece. For this reason, delicate areas and weak materials can be processed without distortion.
- There is no polishing of the workpiece required after processing
Die Sinking EDM (Image Source: Shutterstock)
Conclusion
The EDM machining method is a powerful fabrication process that complements other manufacturing and conventional machining processes. The electrical, no-contact nature of EDM creates opportunities that traditional machining cannot achieve, especially when it comes to extremely tight tolerances for hard metals, precise holes, thin-walled parts, and complex cavities.
Additionally, EDM-machined surface finishes are typically superior to what can be achieved using traditional machining methods and cutting tools. This makes this form of machining ideal for making parts for use in various industries including automotive, military, aerospace, medical/pharmaceutical, among others.
