Electron beam machining (ebm)

Introduction and details about electron Beam Machining

1. Electron Beam Machining Er . Mohit Ostwal Assistant Professor Department of Mechanical Engineering Jodhpur Institute of Engineering and Technology, Jodhpur 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 1

2. Content Introduction Equipment/Setup Process Mechanism of material removal How vacuum is created? Process capabilities Advantages Disadvantages Application 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 2

3. Introduction - EBM Electron beam machining (EBM) is a thermal material removal process that utilizes a focused beam of high-velocity electrons to perform high-speed drilling and cutting . Used with high power density to machine materials. The mechanism of material removal is primarily by melting and rapid vaporization due to intense heating by the electrons Also known as “Electro-optical-thermal process”. Very high drilling rates are achievable. Can machine almost any material. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 3

4. Equipment/Setup High voltage supply to cathode Cathode Cartridge Bias grid Anode Port for vacuum gauge Diffusion pump Magnetic Lens Illuminating system Aperture Telescope Electromagnetic coils Deflector coils Slotted Disc 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 4

5. Equipment/Setup Cathode Cartridge Tungsten/Tantalum High voltage is applied 2500’C Thermo-ionic emission of electrons (Vacuum)- thermally induced flow of electrons from surface. Negatively biased – repel the electrons 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 5

6. Equipment/Setup Bias Grid Highly negatively biased Controls the flow of electrons. To avoid the divergence of the electrons and send them as a beam to the next step (anode) 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 6

7. Equipment/Setup Anode Positively biased terminal Due to the potential difference b/w cathode and anode the electrons accelerates. Velocity is approx. half the velocity of light – passing through anode. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 7

8. Equipment/Setup Magnetic Lens Same function as that of any lens. Concentrates the beam of electrons. Shape the beam. Reduce the divergence of the beam. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 8

9. Equipment/Setup Aperture Capture the stray electrons present near the frame. (Diverged low energy electrons.) Captured electrons are then set for obtaining a concentrated beam of electrons. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 9

10. Equipment/Setup Electromagnetic Lens Focuses the electron beam onto the workpiece. On a particular spot. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 10

11. Equipment/Setup Deflector coils Deflect the electron beam by small amount. Correct the beam in case of not getting proper hold-ship. Improve the shape of the machined holes. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 11

12. Equipment/Setup Illuminating system & Telescope Both are used simultaneously to align the electron beam with the workpiece. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 12

13. Equipment/Setup Slotted Disc To avoid obstruction of vapor of metal into the optical window of EBM. Allow Electron beam to pass but not the vapors/metal fumes to pass through it. Synchronized with the pulsed beam. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 13

14. How vacuum is created ? DIFFUSION PUMP Heater Backing Pump Boiler Nozzle Cooling Coils 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 14

15. How vacuum is created ? Main element for creating the vacuum is DIFFUSION PUMP. The oil diffusion pump is operated with an oil of low vapor pressure. Its purpose is to achieve higher vacuum. Diffusion pump is essentially an oil heater. As the oil is heated the oil vapour rushes upward where gradually converging structure. The nozzles change the direction of motion of the oil vapour and the oil vapour starts moving downward at a high velocity as jet. Such high velocity jets of oil vapour entrain any air molecules present within the gun. (Due to the high momentum of oil jet air is removed) This oil is evacuated by a rotary pump via the backing line . Level of vacuum – 10 -4 to 10 -6 Torr 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 15

16. Mechanism of material removal As high voltage is applied across the Cathode filament , thermo-ionic emission of electrons takes place. These Thermo-ionic electrons are replied by the cathode and attracted by anode through the bias grid, electrons are accelerated to the half of the velocity of the light. These electron/beam of electron is shaped and focused with the help of series of magnetic and electromagnetic lenses. Finally the electron beam impinges the workpiece. Upon impingement the kinetic energy of the electron is absorbed by the workpiece which will result into heating, melting and vaporization – drilling. Spot size – 10 to 100 microns – high energy density 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 16

17. Mechanism of material removal Localized heating by focused electron beam Gradual formation of hole Auxiliary workpiece Auxiliary workpiece W/P W/P 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 17

18. Mechanism of material removal Penetration till the auxiliary support Removal due to high vapour pressure Auxiliary workpiece W/P Auxiliary workpiece W/P 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 18

19. Process Parameters Accelerating Voltage ( V a )– 100 KV Beam current ( I b )– 250 μ A to 1 A Pulse duration (t on ) – 50 μ s to 50 ms Energy per pulse – 100 J/Pulse Spot size - 10 μ m to 500 μ m Power Density 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 19

20. Process capabilities EBM can provide holes of diameter in the range of 100 μm to 2 mm with a depth upto 15 mm, i.e., with a l/d ratio of around 10. The hole can be tapered along the depth or barrel shaped. By focusing the beam below the surface a reverse taper can also be obtained. Generally burr formation does not occur in EBM. A wide range of materials such as steel, stainless steel, Ti and Ni super-alloys, aluminium as well as plastics, ceramics, leathers can be machined successfully using electron beam. Typically the heat-affected zone is around 20 to 30 μm . Some of the materials like Al and Ti alloys are more readily machined compared to steel. EBM does not apply any cutting force on the workpieces . Thus very simple work holding is required. This enables machining of fragile and brittle materials by EBM. Holes can also be drilled at a very shallow angle of as less as 20 to 30 . 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 20

21. Advantages EBM provides very high drilling rates when small holes with large aspect ratio are to be drilled. Moreover it can machine almost any material irrespective of their mechanical properties . As it applies no mechanical cutting force, work holding and fixturing cost is very less . Further for the same reason fragile and brittle materials can also be processed . The heat affected zone in EBM is rather less due to shorter pulses. 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 21

22. Disadvantages The primary limitations are the high capital cost of the equipment and necessary regular maintenance applicable for any equipment using vacuum system. Moreover in EBM there is significant amount of non-productive pump down period for attaining desired vacuum . 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 22

23. Application Drilling Perforating of sheet Pattern generation (associated with integrated circuit fabrication ) 3/28/2016 Er. Mohit Ostwal Asst. Prof. JIET-Jodhpur 23