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UNIT 2.pptx
- 1. UNIT-II THERMAL ENERGY BASED PROCESSESELECTRICAL ENERGY BASED PROCESSES
- 2. EDM-Principle • A thin wire of round shape used as an electrode, which is supplied to the work area through a pair of wheels. With the aid of current a high power spark is produced between wire- electrode and work piece. Due to this high amount of heat is produced nearly to 10000 degree Celsius. This heat energy used to melt and vaporize the work material. Then with the supply of dielectric fluid the molten stage materials are flushed away, likewise the machining is carried out in the work piece.
- 3. .
- 4. Specifications Voltage = 250 V GAP = 0.005 – 0.05 mm Temperature = 10000 degree celcius Spark occur = 10 – 30 micro seconds Current density = 15 – 500 A
- 5. Dielectric Fluid Petroleum Products Paraffin White sprit Transformer oil Kerosene Mineral oil Mixture of all Dielectric Fluid Requirements •Should not be toxic •Should not be corrosive •Should not be hazardous •Should be circulate freely •Should be flushed out •Should be act as coolant • Should be filtered before use •Should be less cost
- 6. Di electric Fluid – Flushing Method 1. Pressure Flushing 2. Suction Flushing 3. Side Flushing
- 7. Pressure Flushing Di electric Fluid – Flushing Method
- 8. Suction Flushing Di electric Fluid – Flushing Method
- 9. Side Flushing Di electric Fluid – Flushing Method
- 10. Functions of Dielectric Fluid
- 11. Electrode (Tool) • Graphite ( Non Metallic) • Copper (Metallic) • Coppre - Tungsten
- 12. POWER GENERATING CIRCUITS SPARK GENERATING CIRCUITS OR AC Current DC Current Rectifier is used to convert AC to DC
- 13. Types
- 14. 1. Relaxation Circuit • Commonly used • Simplicity • Less cost
- 16. Dis-advantages
- 17. 2. R-C-L Circuit • MRR increases with the decrease of R Capacitor charging time is the problem in R-C circuit. So to overcome this , inductance (L) is introduced in the circuit
- 18. Rotary Pulse Generator • R-C and R-C-L yield low MRR • Rotary Pulse Generator over come Drawback of above to circuits • It give high MRR • It give good Surface finish • It give low tool wear • It provide better control in all Parameters
- 19. Rotary Pulse Generator • Here Capacitor is discharged through the diode during first half cycle. • In the next half cycle sum of voltages is given with charged capacitor to the circuit. • So high spark produced • It results high MRR Draw Back •Poor Surface Finish
- 20. Controlled Pulse Generator Circuit • All above three circuits not having any safety incase of Short circuit in the circuit Here in this a vacuum tube (Transistor) is provided as an automatic control
- 22. 1. Operating Parameters 2. Taper 3. Surface finish 4. Current Density PROCESS PARAMETERS
- 23. • Operating Parameters PROCESS PARAMETERS Tool Wear Rate Tooling cost Accuracy Working Time Used to calculate
- 24. • Operating Parameters PROCESS PARAMETERS Types of wear 1.End Wear 2.Corner Wear 3.Side wear
- 25. • Taper PROCESS PARAMETERS Due to High dielectric Pollution , side sparks are more than front spark. So Tapering Occur in Hole
- 26. • Surface Finish PROCESS PARAMETERS It Depend on i) Energy of Pulse ii) Frequency of operation
- 27. • Current Density PROCESS PARAMETERS Current Density (More Spark) = MRR + Surface Roughness Current Density (Less Spark) = MRR + Surface Roughness Good Surface Finish Poor Surface Finish
- 31. Wire – Cut EDM (WEDM) Travelling Wire Cut EDM (TWEDM) 0.02 – 0.03mm dia wire Wire - Brass or Molybdenum 10 – 30 micro second sparking 15 – 500 Amp / mm2 30 - 250 V 10,000 C - Temperature 10 – 30 mm/ sec wire Feed 15 – 80 mm3 / sec MRR Petroleum Based Hydrocarbon Fluids – Paraffin, white Sprit ..
- 32. Features of WCEDM i) Manufacturing Electrode ii) Electrode Wear iii) Surface Finishing – No Manual finishing needed iv) Complicated Shapes – No need of skilled operators v) Time Utilization – overall control is by NC Machine vi) Straight Holes – Feed mechanism avoid taper holes vii) Rejection – NC programmes avoid rejections viii)Economical – for Batch production (including prototypes) ix) Cycle Time – for die manufacturer is shorter x) Inspection Time – very less
- 33. Disadvantages of WEDM • High Capital cost • Cutting Rate is slow • Not suitable for large work pieces
- 34. Applications of WEDM • In the manufacturing of Gears Tools Rotors Turbine Blades Cams
- 35. Wire Cut EDM Vs EDM
- 39. PRINCIPLE Here the machining is done by usage of heat energy. The heat energy is focused on a particular portion for melt & Vaporize the work material Example : 1. Electron Beam Machining (EBM) 2. Laser Beam Machining (LBM) 3. Plasma Arc Machining (PAM)
- 40. ELECTRON BEAM MACHINING (EBM)
- 42. PRINCIPLE - EBM
- 43. TYPES OF EBM
- 49. Process parameters 1.Control of current
- 50. Process parameters 2.Control of Spot Diameter
- 54. Process parameters 3.Control of Focal Distance of magnetic lens
- 55. LASER BEAM MACHINING Photon Emission
- 56. History - Laser • The laser was successfully fired on May 16, 1960. In a July 7, 1960 press conference in Manhattan,Maiman Theodore Harold "Ted" Maiman (July 11, 1927 – May 5, 2007) was an American engineer and physicist credited with the invention of the first working laser Maiman's laser led to the subsequent development of many other types of lasers.
- 57. Differences .
- 58. PRINCIPLE OF LASER BEAM PRODUCTION
- 60. ACCURACY
- 61. TYPES OF LASER 1. Gas lasers 2. Solid lasers 3. Liquid lasers 4. Semi Conductor lasers
- 62. SOLID LASER RUBY LASER Synthetic Ruby rod made up of crystal of aluminium oxide
- 64. LASER BEAM MACHINING Flash tube filled with Xenon, argon or krypton Gases 250 – 1000 watts power Few Chromium Atoms are placed in Ruby rod for absorbing Green light
- 65. . Cooling of ruby rod is necessary – Because they are less efficient in high temperature
- 66. .
- 67. .
- 68. MACHINING APPLICATIONS OF LASER 1. Laser in Metal Cutting 2. Laser in Drilling 3. Laser in Welding 4. Laser in Surface Treatment 5. Trimming 6. Blanking 7. Micromachining applications
- 69. LASER IN METAL CUTTING • .
- 71. Laser in Surface Treatment A thin layer of cobalt alloy coating is applied on Turbine blade for heat and Wear Resistance. A thin Ceramic coating is applied on metal Surface for heat and Wear Resistance. Its also used to seal the micro cracks which are usually present in hard – Chromium electroplates
- 72. Advantages of LBM 1. All Kind of metals are machined 2. Micro holes are possible 3. Soft materials like rubber can be machined 4. No tool wear and contact with w/p 5. Automated process 6. Controlling of beam is easy
- 73. 1. High initial Cost 2. Operating cost is high 3. Required skilled labours 4. Rate of production is low 5. Need safety equipments 6. Life of flash lamp is low 7. The machined holes are not straight and round Disadvantages of LBM
- 74. PLASMA ARC MACHINING OR PLASMA JET MACHINING IONIZED GAS High velocity jet of high temp. ionized Gas
- 75. INTRODUCTION SOLID GAS or LIQUID Heated LIQUID Heated GAS GAS Heated FREE electrons and IONIZED GAS
- 76. PLASMA GAS When a gas is heated to a sufficiently high temperature of the order of 11000 – 28000 degree Celsius, it becomes partially ionized its known as PLASMA PLASMA It’s a mixture of Free electrons + Partially ionized gas and Neutral Atoms
- 79. ACCURACY
- 80. GASES USED IN PAM
- 81. TYPES OF PLASMA ARC TORCHES
- 82. Direct Arc Plasma Torch PILOT ARC A Pre arc (Pilot arc) is created b/w electrode and nozzle when this pre arc touches the work piece the current flows from work piece to electrode . This make main arc b/w electrode and work piece. So now pre –Arc is switched off
- 83. Transferred arc process Direct Arc Plasma Torch • The arc is formed between the electrode(-) and the work piece(+). • In other words, arc is transferred from the electrode to the work piece. • A transferred arc possesses high energy density and plasma jet velocity. For this reason it is employed to cut and melt metals. Besides carbon steels this process can cut stainless steel and nonferrous metals also where oxyacetylene torch does not succeed. Transferred arc can also be used for welding at high arc travel speeds. A pilot arc is established between the electrode and the nozzle. As the pilot arc touches the job main current starts flowing between electrode and job, thus igniting the transferred arc. The pilot arc initiating unit gets disconnected and pilot arc extinguishes as soon as the arc between the electrode and the job is started. The temperature of a constricted plasma arc may be of the order of 8000 - 250000C.
- 84. In-Direct Arc Plasma Torch .
- 85. Non-transferred arc process In-Direct Arc Plasma Torch • The arc is formed between the electrode(-) and the water cooled nozzle(+). • Arc plasma comes out of the nozzle as a flame. • The arc is independent of the work piece and the work piece does not form a part of the electrical circuit. Just like an arc flame (as in atomic hydrogen welding), it can be moved from one place to another and can be better controlled. The non transferred plasma arc possesses comparatively less energy density as compared to a transferred arc plasma and it is employed for welding and in applications involving ceramics or metal plating (spraying). High density metal coatings can be produced by this process. A non- transferred arc is initiated by using a high frequency unit in the circuit.