Electrical discharge machining (EDM), which may also be referred to as spark machining or spark eroding, is a non-traditional process of fabricating metal in which electric discharges or sparks are used to cut out any desired shapes. By using thermal energy, material is removed from the workpiece through a series of recurring discharges between two electrodes. It does not require mechanical force to achieve material removal, a fact that has made it quite popular for use on hard materials and complex shapes which may otherwise be difficult to achieve using traditional cutting processes like milling.
Generally, every conductive material like metals and metal alloys like titanium, composites, and hardened steel can be machined with electrical discharge machining. A high level of accuracy can also be achieved using this method.
Types of Electrical Discharge Machining
Although the focus of this article is on Sinker EDM, there are two other types. We will look at the description of all three types below.
This is also called die sinking, traditional EDM, and so on. This type allows a user to produce complex shapes. It requires electrodes which are often made of either copper or graphite and are pre-machined to have the required shape. It is these electrodes that are inserted into a material which then creates a negative version of the shape. What influences the choice of the electrode material to use is its conductivity and resistance to erosion. While graphite is easier to work with, copper is strong and highly conductive.
This can also be called wire burning, wire erosion, or spark EDM. In this type, a thin wire, rather than an electrode, is used to cut into the workpiece with the wire replacing the electrode. During the process, the wire will constantly come from an automated feed. If the cut is required in the middle of the material instead of outside of it, a hole is made into the workpiece using small hole drilling EDM and from here, the wire is threaded. The wire, which is usually made from copper or brass, is held with diamond guides and the liquid used is deionized water.
The wire used in this type does not need to have good resistance because during the cutting process, new wire is constantly introduced. Common wire types used are zinc and brass.
Hole Drilling EDM
This, as the name suggests, is used to drill holes. It can be used to make pretty small and deep holes that do not need deburring. It also employs the use of tubular electrodes.
Advantages of Using Electrical Discharge Machining
The major advantage of this cutting method is that it can be used with any material as long as the material is conductive. This makes it useful for working with materials that are hard to machine using traditional methods.
Its other advantages include the following:
- Increased ease with making fragile outlines as there is no force applied.
- Making shapes and reaching depths that may be impossible with cutting tools.
- Better surface finish with high precision.
You will find more on the pros and cons here.
How the Sinker EDM Process Work
The principle behind EDM is the capacity of controlled electrical discharges or sparks to erode material. The two electrodes in an EDM, one called a tool electrode or simply tool and the other a workpiece electrode or simply workpiece, are separated by a dielectric liquid and do not make physical contact. By applying or increasing the electric voltage between these two electrodes, there is increased intensity in the electric field and this causes a dielectric breakdown of the liquid present between the two electrodes producing an electric arc. This results in material being removed from the electrode through melting based on the specification set on the controller.
The space between the two materials is a fraction of an inch and the amount of material removed with a single spark is small but the discharges occur as many as 100,000 times in one second. These sparks do not occur simultaneously but one after the other. Excess material is removed through a steady flow of dielectric fluid which is useful for cooling and also for controlling the sparks.
You can find a rich explanation of the whole process in this article here: https://www.engineering.com/AdvancedManufacturing/ArticleID/10100/EDM-101-Electrical-Discharge-Machining-Basics.aspx.
Application of Sinker EDM
Electrical discharge machining is suitable for small-volume productions and it can be used for different purposes including milling, turning, grinding, etc. Some common application of the process include:
- Making prototypes and molds.
- Drilling small holes
- Coinage die making such as in badges, jewelry, etc.
Popular industries where it is applicable include aeronautic, automobile, and medical industries especially for the production of electronic components and engines.
When you desire to make complex shapes or work with hard materials, traditional machining will not be effective. Electrical discharge machining offers you many advantages in this regard. With bit, you can do seemingly impossible things, work with small pieces, be precise and at the same time get good finishing.