Mumbai University > Mechanical Engineering > Sem 5 > production process 3

Marks: 10M

Year: Dec 2015

Electron Beam Machining:

• Principle: EBM process is used for machining of material using very high velocity beam of electrons. The component to be machined is held in vacuum chamber and beam of electrons is focused on to it magnetically.
• When electrons strike the work piece their kinetic energy is converted into heat energy and raises the temperature, a small amount of work piece material vaporizes that means there is removal of metal from the work piece.

• Construction:

  • Above figure shows the setup for electron beam machining. The complete setup is enclosed in a vacuum chamber having vacuum of order 10-5 mm of Hg.
  • The vacuum chamber carries a door, through which the component to be machined is placed on the table. After placing the component the door is sealed.
  • The electron gun which is the cause of emission of electrons consist of three main parts:
    • Tungsten filament.
    • Grid Cup.
    • Arode.
  • Tungsten filament acts as a cathode, as it connected to negative terminal of DC Supply and positive terminal is connected to anode as shown in figure.
• Working:
  • As the current supply starts, the filaments wire is heated to a temperature upto 2500o C in the vacuum. Due to this, electrons are emitted by filaments, which are directed by the grid cup to travel downward.
  • A potential difference of 50-150 KV is maintained between anode and filaments. The velocity passing through anode is z/3 of light.
  • The high velocity electrons streams after passing through anode passes through the tungsten diaphragm and then through the electromagnetic focusssing coil.
  • After passing through focusing coil, (focusing lens) it precisely focus on the desired area of the component.
  • The workpiece is kept on the table which can be transverse as per the requirement.
  • When the high velocity beam of electrons impact on the workpiece, its kinetic energy is converted into heat energy.
  • Due to high temperature, generated materials from the work piece are removed by vaporization.
  • Melting and Vaporizing of the metal takes only a fraction of second and turning off of the beam is necessary to conduct away the heat from the workpiece.

Need of Vacuum:

• The electron beam should not collide with the molecules of gas and should not scatter.
• Electron can travel from cathode to anode easily.
• There should be no loss of heat from cathode.
• To maintain high velocity of electron beam i.e. 2/3 of light.

Advantages of EBM:

• Accurate and precise holes can be machined.
• It is quicker process.
• Small diameter, narrow slots can be easily machined.
• It can machine any material i.e..metal or non-metal.

Disadvantages of EBM:

• Perfectly cylindrical deep holes cannot be produced.
• High power consumption.
• MRR is low.
• Initial Investment is high.

Applications of EBM:

• EBM is used for producing precise holes in wire drawing dies.
• Used for machining operations like cutting, drilling or milling on varieties of materials, irrespective of hardness.
• Also used for synthetic jewels drilling in watch industry.