A Brief Guide To Electrical Discharge Machining

Electrical Discharge Machining or EDM as it is often abbreviated to is a process that involves the use of large amounts of thermal energy in order to get rid of material from the piece being worked on, rather than through mechanical force. Where the more traditional techniques, such as turning or CNC milling, do not work, then engineers will turn to using fanuc edm’s in order to get the cut that they require. An example of this is when there is the need to cut a sharp corner internally or in order to create a very deep cavity.

The Different Types Of Electrical Discharge Machining

This technique can be separated into 3 different types, which includes hole drilling electrical discharge machining, wire electrical discharge machining, and die sinking electrical discharge machining.

Hole Drilling Electrical Discharge Machining

As is suggested by the name, this process is used for the purpose of drilling holes. What differentiates it from other traditional drilling methods is that deep and small holes can be drilled without the need to deburr. The cut that is made is done via a pulsing cylindrical electrode that makes its way deeper down into the workpiece upon removal of the material. It is used for the purpose of manufacturing turbine blades that are high temperature, due to the fact that it is able to produce small cooling channels inside each of the blades of the turbine. 

Wire Electrical Discharge Machining

Also sometimes referred to as wire erosion, Wire Electrical Discharge Machining is mainly used in the manufacturing of extrusion dies. The process is very similar to that of a cheese cutter, whereby a 2 dimensional cut is made into a part that is 3 dimensional via an electrically charged wire. Because this wire is burnt as part of the machining process, there is the need for the wire to be continuously replaced via a fully automated spool in order to ensure that the cutting remains precise. The thickness of the wire used usually ranges from anywhere between 0.05mm and 0.35mm.

Die Sinking Electrical Discharge Machining

Ram EDM as it is also known as is used in those instances where there is the need for a complex cavity to be machined. The process begins with a graphite electrode being produced that is in a shape reverse to the cavity, in order to form a die. Voltage is then built up between the die and the workpiece (which is electrically conductive), all whilst they are being put into a fluid that is dielectric. Doing this causes an electrical breakdown which sees a spark jump across the spark gap. In doing this, the material is melted / vapourised, with the particles that were ejected being carried away by the dielectric fluid. The process is repeated in order to precisely cut out the required shape.

Advantages Of Electrical Discharge Machining

The reason why this manufacturing technique is so widely used is because it comes with so many benefits. Some of these are discussed below.

  • Quality Of The Surface Finish – the likes of CNC milling and other traditional machining techniques often end up leaving marks on the workpiece, resulting in further work having to be done in order to remove them. Because electrical discharge machining has no directionality in relation to the surface finish, the result is a completely smooth finish that does not require any further treatment afterwards. 
  • Freedom Of Design – depths and shapes can be made to any size or scale with electrical discharge machining. It is able to make cuts that traditional machining techniques simply would not be able to. This includes doing things like producing internal corners that are perfectly square and undercuts. Additionally, unlike other techniques, it does not create a burr.
  • Lack Of Distortion – because the tool never directly comes into contact with the piece that it is working on, there is no distortion as a result. This allows for very thin and detailed features to be produced via the process without the risk of any breakage. With there being no distortion, electrical discharge machining has tight tolerances of + / – 0.012 mm.
  • Unaffected By Hardness Of The Material – the process of electrical discharge machining can be used to cut through any material, no matter how hard it is; it just needs to be conductive. As a result, it can be used to cut through the likes of tungsten carbide and inconel with relative ease.

Disadvantages Of Electrical Discharge Machining

Despite of the many clear advantages of the electrical discharge machining process, there are also some disadvantages to using it. Some of these are discussed below.

  • Cost Of The Parts – where die sinking electrical discharge machining is used, there is the need for a custom electrode. The cost of this can be expensive, especially when it is not being frequently used. The more that it is used in the manufacturing process, the more that the cost of the electrode is spread out.
  •  Does Not Remove Much Material – the rate at which material can be removed from a workpiece during electrical discharge machining is relatively low when compared with other traditional machining techniques. The process is very power intensive, which can have an impact on overall cost.
  • Limited To What Materials Can Be Used – in order for a material to be subject to electrical discharge machining it has to be electrically conductive. The material also needs to be able to withstand a certain level of heat, as enough is given off during the process that it can affect the metallurgy of it.

Summary

Electrical discharge machining is clearly a very good manufacturing process that can be used either exclusively or in conjunction with other traditional machining techniques like CNC machining for the purpose of producing parts that have very specific geometrical requirements. Given that the process can be used to machine incredibly hard materials, it is a highly attractive solution for when working with inconel. It is important to be aware that the process is a slow one and so is not suitable for mass production.

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