EDM (Electrical Discharge Machining) is an unconventional machining technology that is based on the principle of removing or cutting material using an electrical discharge.
The principle of EDM
Electrical discharge machining is a process in which the material is machined in stages by electrical discharges generated between the tool (electrode) and the workpiece. The electrode is connected to a power source (negative pole) and positioned just above the surface of the workpiece, which is connected to the positive pole. A voltage is generated between the electrode and the workpiece, which releases an electrical discharge. These generate heat when they strike the workpiece, which causes melting or vaporisation of the work material. For the EDM process to work, the workpiece must be electrically conductive. This technology allows precise machining of even very hard metals that would be difficult to machine by other methods, without the risk of deforming the material.
The electrodes are usually made of copper or graphite. These materials are suitable for their production due to their high electrical conductivity and ability to withstand the heat generated during machining. Although erosion of the workpiece is the primary cause during machining, it is important to monitor the material removal on the electrode and replace it regularly if necessary. To ensure optimum EDM progress, the electrode and workpiece are immersed in a dielectric fluid (typically deionized water or special liquid dielectrics) that prevents direct contact and helps remove heat and eroded particles from the machining area.
With EDM machining it is possible to achieve the production of complex and precise shapes within narrow tolerance bands. Modern EDM machines are equipped with CNC controls that provide control over key process parameters such as voltage, current and pulse length.
Types of EDM
In practice, there are two machining methods that use the EDM principle. The difference between them lies in the form of the tool and its movement. If the electrode is used to produce a shape (cavity), then this process is called EDM. During EDM hollowing, the electrode creates a cavity in the workpiece that corresponds to the negative of the electrode shape. Typically, the EDM hollowing process uses a roughing electrode (to remove most of the material) and then a finishing electrode (for finer details).
If a thin brass wire (usually 0.2 mm in diameter) is used as a tool for EDM machining, we speak of EDM wire cutting. With wire cutting it is possible to achieve very precise cuts without deforming the material to be cut. The wire is gripped between two guides, with one guide below and the other above the workpiece. As the guides move, the material is gradually cut. During the cutting process, the wire is continuously moved between the guides. Special EDM punches are then used to create the starter holes for wire cutting.
Advantages and disadvantages of EDM
- Machining of difficult-to-machine materials:EDM technologies are also effective for machining materials with high hardness and strength (such as hardened steel, titanium, tungsten, etc.) that are difficult or impossible to machine using conventional methods,
- Shape complexity: With EDM it is possible to produce complex and precise geometric shapes within narrow tolerance bands,
- Specific surface: this method can leave specific surface textures on the workpieces after production, which can be useful for some applications, such as the production of injection mould cavity surfaces.
- Electrode costs: the production and maintenance of a tool electrode can be expensive and sometimes it is necessary to machine larger quantities of electrodes,
- Machining Time: Compared to traditional machining methods, EDM can be more time consuming,
- Machining of conductive materials only: EDM is only applicable to electrically conductive materials.
Our tool room has an EDM depth gauge (with punching function) with the following parameters:
- NASSOVIA/KRUPP FE 502
- travels: 760 mm(x), 450 mm(y), 300 mm(z)
- stroke: 160 mm
- OrbiCut Midi CNC 3R, 10 mm(x), 10 mm(y)
- Generator: 60 A for electrodes made of graphite or copper
Fig. 1 Our EDM depth gauge NASSOVIA/KRUPP FE 502
Our tool room also has an EDM wire machine with the following parameters:
- wire cutter CHARMILLES TECHNOLOGIES, ROBOFIL 290P
- travel: 400 mm(x), 250 mm(y), 200 mm(z), 250 mm(u), 400 mm(v)
- workpiece maximum: 850 mm(x), 500 mm(y), 200 mm(z), 500 kg
- Maximum cutting angle without jigs: 30°/200 mm
- maximum surface finish CH/Ra: 9/0,28 μm
Fig. 2 Our EDM wireline ROBOFIL 290P
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