CNC EDM (ELECTRIC DECHARGE MACHINE) pptx

Electric decharge machine working pdf

1. Electrical Discharge Machining (EDM) By Rubul Dutta

2. Electric discharge machining, also known as Spark erosion, electro-erosion or spark machining is a process of metal removal based on the principle of erosion of metals by an interrupted electric spark discharge between the electrode tool (Cathode) and the work (anode). The workpiece and the tool are electrically connected to a D.C electric power supply. The

3. work piece is connected to the positive terminal of the electric source, so that it becomes the anode. The tool is the cathode. A gap, known as the spark gape in the range of 0.005 to 0.05 mm is maintained between the workpiece and the tool, and suitable dielectric fluid, which is non conductor of electricity is forced through this gap at pressure of 2 kgf /cm 2 or less.

4. Spark Gap The EDM process involves a controlled erosion of electrically conductive materials by the initiation of rapid and repetitive spark discharge between the electrode tool and workpiece separated by a small gap of about 0.01-0.05 mm known as the spark gap .

5. overcut The shape of the area of the cavity produced in the workpiece should theoretically be the same as that of the tool. Overcut is the distance, the spark will penetrate the workpiece from the tool and remove metal from the workpiece . Theoretically, it is slightly larger then the gap between the end of the tool and the workpiece .

6. Dielectric fluid Dielectric fluid is flushed through the spark gap and is supplied through a hole in the tool or from external jets. Properties of dielectric fluid. The dielectric fluid should have sufficient and stable dielectric strength to serve as insulation between the electrode and the tool. It should deionize rapidly after the spark discharge has taken place.

7. 3. It should have low viscosity and a good wetting capacity. 4. It should be chemically neutral so as not attack the electrode, the workpiece , the table or the working container. 5. Its flash point must be sufficiently high to avoid any fire hazards. 6. It should not emit any toxic vapours or have unpleasant odours.

8. Function of dielectric fluid Formation of barriers (insulation) between electrode and workpiece . Fluid ionises to allow good conduction of spark. Act as a coolant for eroded particles from spark gap. Flushers away eroded particles from spark gap. Prevents oxidation of work piece.

9. Types of dielectric fluid 1. Hydrocarbon oils. 2. Kerosene, 3. Silicon oils, 4. Deionized water, 5. Polar liquid. (aqueous solution of ethylene glycol) The choice of any particular dielectric depends on the workpiece size, complexity of shape, tolerance, surface finish and material removal rates.

10. Application of EDM The development of EDM has been rapid and provides another method of machining metals in the tool room. It can be used to machine cavities or intricate shapes in very hard materials, thus it becomes especially useful for machining blind cavities in dies used in die casting, stamping, forging and injecting moulding. It makes possible the machining of intricate cavities and holes in hardened steel or special alloy steel without the need of sectioning the cavity.

11. Types of Electrode Material The electrode materials generally used can be classified as metallic materials (copper), Non-metallic materials(graphite), and combination of metallic and non-metallic materials (copper graphite). Copper, yellow brass, zinc, graphite and some other materials are used for tools. Low wearing tools include silver tungsten, copper tungsten, and metalized graphite. For commercial applications, copper is best suited

12. for fine machining. One of the advantages of EDM is due to the fact that a tool made of a material softer than the workpiece material and which is good conductor of electricity can be used to machine a material of any hardness.

13. Advantages of EDM 1. Any complicated shape that can be made on the tool can be reproduces on the workpiece . 2. EDM can be employed for extremely hardened workpiece . 3. Highly complicated shapes can be made by fabricating the tool with split sectioned shapes, by welding, brazing or by applying quick setting conductive epoxy adhesives.

14. Disadvantages 1. Machining time are too long. 2. Excessive tool wear. 3. High specific power consumption.

15. Principles of EDM Electrical Discharge Machining (EDM) is a controlled metal removal process that is used to remove metal by means of electric spark erosion. In this process an electric spark is used as the cutting tool to cut (erode) the workpiece to produce the finished part to the desired shape. The metal-removal process is performed by applying a pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to the workpiece . This removes (erodes) very tiny pieces of metal from the workpiece at a contrlled rate.

16. EDM Process EDM spark erosion is the same as having a electrical short that burns a small hole in a piece of metal it contacts, with the EDM process both the workpiece material and the electrode material must be conductor of electricity. The EDM process can be used in two different ways.

17. 1. A preshaped or formed electrode usually made from graphite or copper is shaped to the form of the cavity it is to reproduce. The formed electrode is fed vertically down and the reverse shape of the electrode is eroded in to the solid workpiece . 2. A continuous travelling vertical wire electrode, the diameter of a small needle or less , is controlled by the computer to follow a programmed path to erode or cut a narrow slot through the workpiece to produce the required shape.

18. What is the function of dielectric fluids. During the EDM process the workpiece and the electrode are submerged in the dielectric oil, which is an electrical insulator that helps to control the arc discharge . The dielectric oil, that provides a means of flushing, is pumped through the arc gap. This removes suspended particles of workpiece material and electrode from the work cavity.

19. Flushing The most important factor in EDM is to have proper flushing, because eroded particles must be removed from the gap from efficient cutting. Flushing also brings fresh dielectric oil into the gap and cools the electrode and the workpiece .

20. Types of flushing: Pressure flushing. Suction flushing, Combined Pressure and Suction Flushing. Jet Flushing, Pulse Flushing.

21. Pressure flushing This is the most common preferred method of flushing. It is also referred to as injection flushing. It can be performed through the tool or through the workpiece . Pressure flushing done by forcing the dielectric fluid through the workpiece mounted over a flushing pot. The advantage of this method is that it eliminates the need for holes in the electrode.

22. Pressure Flushing Through the Tool

23. Pressure Flushing Through the Work piece

24. Suction Flushing Suction Flushing also known as vacuum flushing, has the capability of removing the eroded gap particles. It can be done through the electrode or through the workpiece .

25. Suction Flushing

26. Jet Flushing Jet or side flushing is done by tubes or flushing nozzles which direct the dielectric fluid in to the gap, pulse flushing is usually used along with get flushing.

27. Wire cut EDM The wire cut EDM is a discharge machine that uses CNC movement to produce the desired contour or shape. It does not require a special shaped electrode, instead it uses a continuous travelling vertical wire under tension as the electrode. The electrode in wire cut EDM is about as thick as a small diameter needle whose path is controlled by the machine computer to produce the shape required.