What is Electrical Discharge Machining (EDM)?
Introduction
Machining processes are becoming popular because of producing parts with desirable features. Commonly the machining processes such as CNC turning and CNC milling are used to remove material from a workpiece.
Sometimes, these processes fail to produce the desired features, which are attained using another machining process, i.e., electrical discharge machining (EDM). Joseph Priestley, an English physicist, first observed this process uses thermal energy to produce desirable complex features in a workpiece.
What is EDM?
Electrical discharge machining is a non-traditional method that utilizes thermal energy to remove material from a workpiece. No mechanical force is required during the cutting process. So, thermal energy is used for the machining process instead of mechanical force.
The cutting is done by a wire resulting from an electric discharge between the tool and the workpiece. It is especially popular in manufacturing molds and tools because of its high efficiency in cutting harder materials. Other machining processes are also used to make complex features that are not attainable.
How Does Electrical Discharge Machining Work?
EDM works by producing electrical discharge between the workpiece and the tool. The process requires the following equipment.
- Power supply
- Tool and the tool holding devices
- Flushing system and dielectric fluid supply
- Workpiece and workpiece holding devices.
It is compulsory to use an electric conductive workpiece during the process. It is because it only machined the material that allows the passage of electric current through it. The process starts by immersing the tool and workpiece in a dielectric fluid. Dielectric fluid aids in the removal of suspended particles from the workpiece because they can cause short circuits by bridge formation.
A servomechanism can maintain a small gap between the tool and the workpiece. The gap is required for the proper arc formation and is equal to the thickness of human hair.
A spark is produced between the workpiece and the tool by supplying a high-frequency current to the electrodes. It is followed by the high generation of the spark in the work cavity. As a result, the erosion and evaporation of ions occur, which causes material removal from the workpiece. EDM produces an overcut. Thus, the cavity produced is slightly larger than the electrodes.
Types of EDM
Electrical discharge machining can classify into two types.
- Wire EDM
- Conventional EDM
1- Wire EDM
Wire EDM, also called Spark EDM, uses an electrode, a thin heated wire. The desired cut is produced by moving the wire electrode through the target metal. The electrical discharge of the wire produces the cut without touching the wire to the metal. The wire smoothly cuts the metal into the desired form.
If a middle cut is required for a specific shape, then the wire EDM is used along with a hole drilling EDM which efficiently helps to make a hole in the middle of the workpiece. The wire threading attains the proper shape through the hole. In this condition, tube-shaped electrodes are used with the flow of dielectric fluid through the hole.
2- Conventional EDM
Conventional EDM is also called sinker EDM or ram EDM. It is ideal for creating complex features and shapes.
During the process, an electrode with a definite shape is created. This electrode is then sunk into a workpiece that needs machining. As a result, a mold is created by producing a negative impression of the shape of the electrode.
Advantages and Disadvantages of EDM
Here are some advantages and disadvantages of EDM:
Advantages
- It can cut all electrically conducting metals into desired shapes.
- After process completion, little or no polishing is needed.
- No burr formation occurs during the process.
- It can efficiently create small holes.
- Machining time is less compared to other machining processes.
- The process lacks mechanical stress because of the lack of connection between the workpiece and the tool.
- It can accurately machine complex shapes.
- No distortion occurs during the machining of slender and fragile workpieces.
- It helps develop the corrosion-resistant and hard surfaces of the metals.
- This process can machine the extremely hard workpieces.
- The process helps in achieving the tolerances with a range of +/-0.005.
Disadvantages
- The workpieces that are brittle at room temperature can face surface cracking.
- The major limitation of this process is that the sharp corners can reproduce.
- It cannot machine non-conductive metals.
- It is impossible to do the profile machining of the complicated contours.
- The process requires high consumption of specific power.
- There is excessive tool wear during machining operations.
- The rate of removal of metal is very low.
Applications of EDM
Electrical discharge machining offers the following applications.
1: Prototype production
EDM is a common process for mold making, extrusion dies tool manufacturing, and the manufacturing of blanking punches. This method can apply to parts fabrication and applications used in the automobile and aerospace industries. The applications requiring a low residual stress level can perform with the EDM process.
2: Small Hole Drilling
EDM is an ideal method for creating small hole drilling in various materials in less time. It helps to create small hole drilling even in the harder materials. During the process, a brass electrode tube is used to direct electrical discharge on the targeted material resulting in hole creation.
3: Disintegration of components
It is an appropriate method for the removal of those that are stuck in the work part. These stuck materials may be difficult to remove with other machining processes. The EDM process precisely removes the stuck material from the work part without causing any damage to the work part.
4: Injection Molding
EDM is a popular method used in the injection molding process. It is clear that mold having a proper shape, depth, and right dimensions is compulsory in the injection molding process. All these features are successfully achieved with the help of EDM. Moreover, the injection molding process needed complicated and best workpieces. This requirement is fulfilled with EDM.
5: Die Casting
EDM is a highly recommended process for die-making applications because high accuracy is needed to manufacture highly tailored die casting. The main features of these die-casting applications may include deep ribs and sharp internal corners. Hard steel alloys are mainly used to manufacture these die-casting applications.
The steel alloys are not only difficult to machine because of hardness but also need proper surface finishing before heat treatment. It may lessen the detail’s accuracy. So, the EDM process is employed.
Conclusion
The electrical discharge machining process uses thermal energy instead of a mechanical force to cut the conductive material and fulfill the high demand for machining applications. It can even cut hard material into complex, smooth shapes to reshape materials, which other methods cannot do.
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