Electron Beam Machining (EBM) and Laser Beam Machining (LBM) are thermal processes considering the mechanisms of material removal. However electrical. Although NV system can increase productivity dramatically, they are somewhat limited since the interaction of the electron beam with air spreads and diffuses. ELECTRON BEAM MACHINING (EBM).  HISTORY. Discovery that a Beam of Electrons has Ability to Melt Materials Coincided with the Discovery.
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Today we will learn about electron beam machining principle, working, equipment's, application, advantages and disadvantages with its. Electron Beam Machining(EBM) - Free download as Powerpoint Presentation . ppt), PDF File .pdf), Text File .txt) or view presentation slides online. Electron. The earliest work of material removal utilizing an electron beam was attributed to Steigerwald Electron beam machining has been used in industry since the s, initially in nuclear and . pdf>.
Holes as small as 0. Disadvantages of Electron Beam Machining Method The equipment costs high and operator of high skill is required for carrying out operations. The power consumption is exceedingly high It is not very suitable for sinking deep holes if the sides must be parallel. In other words, it is not possible to have perfectly cylindrical deep holes by this method. Unless special care is taken the bottom of a through hole would become cone-shaped.
It is most suitable for machining operation where much less material is to be removed.
The material removal rate being of the order of a fraction of a milligram per sec. This whole process takes place in vacuum chamber.
It is mostly used to drill holes in any shape. Electron Beam Machining: Principle: This machining process works on basic principle of conversion of kinetic energy of electron into heat energy. When a high speed electron impinges on a work piece, they convert its kinetic energy into heat energy.
This heat energy used to vaporize material at contact surface. This process is carried out in vacuum otherwise the electron will collide with air particle and loses its energy before impinging on work material.
This is basic principle of EBM machining. It is used to generate electron. It is simply a cathode ray tube which generates electron, accelerate them to sufficient velocity and focus them at small spot size.
In this gun cathode is made by tungsten or tantalum. This cathode filament heated upto degree centigrade which accelerate to electron emission by thermionic reaction. It is just after the electron gun. It is a anode which is connected by the negative bias so the electron generated by the cathode do not diverge from its path and approach to the next element.
When the electrons leave this section, the velocity of electron is almost half the velocity of light.
Magnetic Lenses: After the anode, magnetic lenses are provided which shape the beam and does not allow to diverge electron or reduce the divergence of beam.
They can be positioned rapidly and accurately in space and time, and are very suitable for use in completely automated processes.
MECHANISM Electron beam is generated in an electron beam gun, which is basically a triode consisted of a cathode, a grid cup negatively biased with the respect to the cathode, and an anode at ground potential McGeough, Due to being dependent on the using of high velocity electrons, the whole process of this machining has to be performed under vacuum condition, including the placement of the workpiece to be machined.
Else, the electrons would interact with the air molecules of which condition they can lose their energy and cutting ability. As the beam strikes the surface of the work material, the kinetic energy of the high velocity electrons is converted to heat energy. This will make the spot gradually getting bigger and deeper due to the melting and vaporization of material caused by the high power density.
This process will be carried out until the desirable depth is created. The molten material, as the product of the material removal process, will be casted out from the cutting zone by the high vapor pressure at the lower part. Figure 1.
Parts of electron beam gun are divided into two categories, which are Leonard, The field-shaping elements necessary for the production of a useful beam; the various electrodes such as the cathode electrode, anode, and grids or modulating electrodes. Figure 2. A measure of this effect is the emission current, the magnitude of which varies between 25 and mA.
However, this quantity is determined by some factors, such as the type of cathode material, its temperature, and the voltage applied McGeough, Just after the cathode, there is a grid cup which functions to focus the accelerated electrons so that they travel through a hole in the anode. The grid cup is set up in high negative bias condition to prevent the electrons from divergence.
A magnetic lens is placed under the anode. This lens has the jobs of re-focusing the electron beam by shaping it and reducing the divergence.
This way, the quality of the beam can be improved and its direction towards the workpiece is kept under control. The last section to go through is deflection coils.
Deflection coils can direct the electron beam, although only for a small amount, to further improve shape of the machined holes.
Another advancement applied on electron beam guns is the installment of illumination facility and telescope for alignment of the beam with the workpiece. During the process, both the electron beam gun and the workpiece must be placed in a vacuum chamber so that electrons do not lose their energy and a significant life of the cathode is obtained. Beam current Beam current is continuously adjustable from approximately GA to 1 A.
As the setting of beam current is increased, the amount of energy per pulse delivered to the workpiece is also increased. Pulse duration Pulse duration affects both the depth and diameter of the hole. The longer the pulse duration, the wider the diameter and the deeper the drilling depth capability will be. Typically, electron beam systems can generate pulses as short as 50 tisec or as long as 10 msec.
Lens current Lens current is used as the parameter to determine the working distance as well as the spot size of the beam on the workpiece should be. Almost all materials can be machined using this process, ranging from metals such as steel, stainless steel, titanium and nickel super alloys, and aluminium to non- metals like plastics, ceramics, and leathers.