![Relaxation Circuit
Energy Released per spark = E = ½ C.Vd 2
Where
C= Capacitor Value
Vd= Discharge Voltage
= Vo [1-exp[-t/Rc]]
Vo = D.C source voltage](https://image.slidesharecdn.com/unit3electricalenergybasedprocess-200523134439/85/ELECTRICAL-ENERGY-BASED-PROCESSES-19-320.jpg)
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ELECTRICAL ENERGY BASED PROCESSES
- 1. RAMCO INSTITUTE OF TECHNOLOGY Mr.M.LAKSHMANAN Assistant Professor (Senior Grade) Department of Mechanical Engineering
- 2. UNIT III ELECTRICAL ENERGY BASED PROCESSES
- 3. Principle The heat energy available in the electric spark is used to remove the material from the workpiece. Whenever a spark is developed between two electrical contacts a small amount of material is removed from each contact. • Electrical Discharge Machining (EDM) • Wire cut Electrical Discharge Machining (WC EDM)
- 4. Electrical Discharge Machining (EDM) PRINCIPLE: EDM / spark erosion machining / Electro erosion machining , metal is removed by producing powerful electric spark discharge between the tool(Cathode) and the work piece (Anode).
- 7. Characteristics • Voltage – Greater than 250V • Spark Interval – 10 to 30 Microseconds • Current Density – 15 to 500A/mm2 (1000 spark discharge occurs per seconds.) • Temperature during process – 10,000˚C. • Dielectric Fluid – Petroleum based Hydrogen fluids, paraffin, white spirit, Transformer oil, Kerosene, Mineral oil, etc.,
- 8. DIELECTRIC FLUID • It’s a medium that does not conduct electricity. • Its must circulate freely between tool and work piece. • The eroded particles should be flushed out at the earliest since it reduces the further metal removal rate.
- 9. Types of Flushing 1. Pressure Flushing:
- 12. Function of Dielectric Medium • Its acts as an insulating medium. • It cool the spark region and helps in keeping the tool and work piece cool. • It carries away the eroded metal particles along with it. • It maintains a constant resistance across the gap. • It remains electrically non conducting until the required breakdown voltage has been reached.
- 14. Tool Material (Electrode) and Tool Wear • Metallic Materials – Copper, Brass, copper- Tungsten • Non metallic materials – Graphite • Combination of Metallic & Non metallic – Copper-Graphite Wear Ratio = Volume of work material removed Volume of electrode consumed
- 15. • Brass Electrode – 1:1 • Copper – 2:1 • Copper Tungsten – 8:1 • Non Metallic (graphite) – 5:1 to 50:1
- 16. MRR and Surface Finish • MRR up to 80mm3/s. • Surface Finish 0.25micro meter • Rough Process = +/- 0.05 to 0.13mm • Fine Process = +/- 0.003 to 0.013mm
- 17. Factors Affecting MRR • MRR increases with forced circulation of dielectric fluid. • It increases up to optimum value of work – tool gap, after that it drops suddenly. • MRR is maximum when the pressure is below the atmospheric pressure.
- 18. Power Generation Circuits / Spark Generating Circuits • Resistance – Capacitance Circuit (RC Circuit) or Relaxation Circuit • R-C-L Circuit • Rotary Pulse Generator Circuit • Controlled Pulse Generator Circuit
- 19. Relaxation Circuit Energy Released per spark = E = ½ C.Vd 2 Where C= Capacitor Value Vd= Discharge Voltage = Vo [1-exp[-t/Rc]] Vo = D.C source voltage
- 21. R-C-L Circuit
- 23. Controlled Pulse Generator Circuit
- 24. Process parameters • Operating Parameters • Taper • Surface Finish • Current Density
- 25. 1.Operating Parameters • MRR = ɸ(E) f = ɸ ʃvi dt Where ɸ - Function E – Electrical Energy V – Voltage i – Instantaneous current dt – Time interval f – Torque ῑp – Pulse width Tool Wear rate (TWR) = Ѱ (E)f = Ѱ ʃvi dt ῑp
- 26. MRR and TWR Based on • Energy content of the pulse • Rate of energy supplied • Servo sensitivity • Gap width • Dielectric parameters
- 27. Types of Wear in Tool • End Wear • Corner Wear • Side Wear
- 29. 2.Taper
- 31. 3.Surface Finish Surface finish of the material depends upon the following factors i. Energy of the pulse ii. Frequency of operation
- 32. 4.Current Density • It is affected by either changing current or changing the electrode (tool) – work piece gap. • When the current is increased, each individual spark removes a larger piece of metal from the work piece. But its also increases surface Roughness.
- 34. • Electrical Discharge Machining https://www.youtube.com/watch?v=L1D5DLW WMp8 • Electro discharge machine (EDM) https://www.youtube.com/watch?v=2W4xZYRk WGo • Electrical Discharge Machining EDM https://www.youtube.com/watch?v=k646HE6M xE4
- 35. Advantages of EDM Process • It can be used for machining various materials like, Tungsten Carbides, Electrically conductive materials and other hard materials. • It gives good surface finish. • Machining of very thin section is possible. • It is well suited for complicated components. • There is no cutting forces act on the job.
- 36. • High accuracy is obtained. • Fine holes can be easily drilled. • Its quicker process. • The process once setup does not need constant operators attention.
- 37. Disadvantages • Its only used for machining electrically conductive materials. • Its suitable only for machining small work pieces. • Electrode wear and over cut are serious problems. • Perfectly square corners cannot be made by EDM process. • Power requirement is very high.
- 38. Applications • Production of complicated and irregular shaped profiles. • Thread cutting in jobs. • Drilling of micro holes. • Helical profile drilling. • Curved hole drilling. • Re sharpening of cutting tools.
- 40. • Electrical discharge machining - Video Learning - WizScience.com https://www.youtube.com/watch?v=7Ln_l5bXx6 U
- 41. WIRE CUT ELECTRO DISCHARGE MACHINING (WCEDM) or TWEDM • A very thin wire (0.02 to 0.3mm) made of brass or molybdenum having circular cross section is used as a electrode (Tool). • The wire is stretched and moved between two rollers. • The part of wire is eroded by the spark. • Complicated cutout can easily machined.
- 42. Construction of WCEDM It consist of, i. Work piece movement control unit. ii. Work piece mounting Table iii. Wire drive section iv. Dielectric fluid supply v. Power supply unit
- 44. Characteristics of WCEDM • Material Removal Technique: By using Powerful electric spark • Work material : Electrically conductive materials and alloys • Tool Material : Copper, Yellow Brass, Alloy of Zinc, Copper Tungsten, molybdenum • MRR : 15 to 80 mm3/s (2 to 400mm3/min) • Spark Gap : 0.005 to 0.05mm
- 45. • Spark Frequency : 200 to 500 KHz • Spark interval : 10 to 30 microseconds • Volts : 30 to 250 V • Current : 5 to 60A • Current density : 15 to 500A/mm2 • Temperature : 10,000˚C • Dielectric Fluid : Petroleum based hydrocarbon fluids, Parafin, White spirit, etc., (Distilled water) • Wire feed : 10 to 30mm/s • Surface Finish : 0.05 to 12.5 microns
- 46. Process parameters • Spark on time • Spark off time • Spark Gap • Discharge current • Voltage
- 47. S. No. Wire cut EDM EDM 1. Very thin wire made of molybdenum or brass is used as the electrode (tool). Alloy of silver and Tungsten is used as the electrode (tool). 2 Whole workpiece is not submerged in dielectric medium. Whole workpiece is submerged in dielectric medium. 3 Its easy to machine complex two dimensional profiles. Its difficult to cut complex two dimensional profiles.
- 48. • Wire EDM NC test cutting a cat, part 2 https://www.youtube.com/watch?v=vYiPRm- HBWM • How Wire EDM Works https://www.youtube.com/watch?v=pBueWfzb7P0 • Wire EDM Animation.flv https://www.youtube.com/watch?v=RFm9V-NtC3w • Wire EDM https://www.youtube.com/watch?v=IewSHORZTJ8