1. Electric Discharge Machining (EDM)

2. Introduction
EDM is a method for producing holes and slots, or other shapes. It is also called spark erosion.
EDM, is especially well-suited for cutting intricate contours or delicate cavities that would be difficult to produce with a grinder, an end mill or other cutting tools.
EDM removes metal by producing a rapid series of repetitive electrical discharges. These electrical discharges are passed between an electrode and the piece of metal being machined. The small amount of material that is removed from the work piece is flushed away with a continuously flowing fluid. The repetitive discharges create a set of successively deeper craters in the work piece until the final shape is produced.

3. Materials
Materials must be electrically conductive. so it does not work on materials such as glass or ceramic, or most plastics.
EDM is primarily used for hard metals or those that would be impossible to machine with traditional techniques. Metals that can be machined with EDM include hastelloy, hardened tool-steel, titanium, carbide, inconel and Kovar

4. Ram EDM
In a typical ram EDM application, a graphite electrode is machined with traditional tools. The new specially-shaped electrode is connected to the power source, attached to a ram, and slowly fed into the workpiece. The entire machining operation is usually performed while submerged in a fluid bath. The fluid serves the following three purposes:
flushes material away
serves as a coolant to minimize the heat affected zone (thereby preventing potential damage to the workpiece)
acts as a conductor for the current to pass between the electrode and the workpiece.

5. Wire EDM
In wire EDM a very thin wire serves as the electrode. Special brass wires are typically used; the wire is slowly fed through the material and the electrical discharges actually cut the workpiece. Wire EDM is usually performed in a bath of water.
The wire itself does not actually touch the metal to be cut; the electrical discharges actually remove small amounts of material and allow the wire to be moved through the workpiece.

6. Electrical-Discharge-Machining Process
FIGURE Schematic illustration of the electrical-discharge-machining process.

7. Cavities made with electrical-discharge-machining process
FIGURE (a) Examples of cavities produced by the electrical-discharge-machining process, using shaped electrodes. The two round parts (rear) are the set of dies for extruding the aluminum piece shown in front. Source: Courtesy of AGIE USA Ltd. (b) A spiral cavity produced by a rotating electrode. Source: American Machinist. (c) Holes in a fuel-injection nozzle made by electrical-discharge machining. Material: Heat-treated steel.

8. Stepped Cavities
FIGURE Stepped cavities produced with a square electrode by EDM. The workpiece moves in the two principal horizontal directions, and its motion is synchronized with the downward movement of the electrode to produce various cavities. Also shown is a round electrode capable of producing round or eliptical cavities. Source: Courtesy of AGIE USA Ltd.

9. Wire EDM Process
FIGURE Schematic illustration of the wire EDM process. As much as 50 hours of machining can be performed with one reel of wire, which is then discarded.

10. Fundamentals of wire EDM

11. Super precision band saw
To better understand the wire EDM process, visualize the wire EDM machine as a super precision band saw with accuracies capable up to +/-0.001’’ (0.0025mm), and under certain circumstances even closer.

12. The step by step EDM process
Deionized water surrounds the wire electrodes as the power supply generates voltages and amps to produce the spark

13. The generated spark precisely melts and vaporizes the material

14. During the off cycle, the pressurized dielectric fluid immediately cools the material and flushes out the eroded particles

15. New wire is constantly fed, while the eroded particles are removed and separated by a filter system

16. Three types of wire EDM
Two Axis
Simultaneous Four Axis

17. Different shapes can be produced on top and bottom of a workpiece
Independent four axes
The top profile can be independent from the bottom profile. This is particularly useful for extrusion molds and flow openings, injection molds and many others.
Different shapes can be produced on top and bottom of a workpiece
Produced Parts

18. Machine is capable of cutting up to 15
Machine is capable of cutting up to in(400 mm) with independent angles up to 30

19. Our EDM Machine in Hess Lab

20. Wire EDM Example

21. Program
N10 G1X0.394 Y0.Z0.
N20 X0.399 Y0.005
N30 G3 X Y I J-0.005
N40 G1 X Y0.3103
N50 X Y0.3483
N60 X Y0.3231
N70 X Y0.3615
N80 X Y0.3345
N90 X Y0.3722
N100 X Y0.3434
N110 X Y0.3803
N120 X Y0.3498
N130 X Y0.3857
N140 X Y0.3537
N150 X Y0.3884
N160 X0. Y0.355
N160 X0. Y0.355
N170 X Y0.3884
N180 X Y0.3537
N190 X Y0.3857
N200 X Y0.3498
N210 X Y0.3803
N220 X Y0.3434
N230 X Y0.3722
N240 X Y0.3345
N250 X Y0.3615
N260 X Y0.3231
N270 X Y0.3483
N280 X Y0.3122
N290 X Y0.3362
N300 G3 X0.399 Y0.I J
M02

22. Project-2: Wire EDM Programming and Machining
In the programming, the part should be composed of lines, coded in G01 G02 and G03 CNC codes. Choose a part and begin by drawing in AutoCAD or Pro-e, then get all necessary coordinates for cutter move programming. Include dimensions on your final hand-in drawing. Submit program codes a week before your lab so the code can be verified. Keep the parts simple and for complexity reasons use straight lines only. Keep them smaller than 2”x2”. Below you will find some examples of parts you can do. Feel free to be creative.
In Week-6 you need to go to Machine shop, type in the codes, operate the machine and make the part you designed.

23. Flower – Team 1

24. Crown – Team 2

25. Jet Plane (top view outline) – Team 3

26. Tree - Team 4

27. Irregular star - Team 5

28. Snow Flake