Electron Beam Welding

Electron beam welding

Electron Beam Welding

Electron beam welding (EBW) is one another form of the fusion welding process or power beam processes, in which the melting and joining of metals is done by heating them with an high velocity electron beam. In electron beam welding, the kinetic energy of the electrons is converted into heat as they strike the workpiece. 

Electron beam welding process is required the typically vacuum environment to focus the electron beam on the workpiece. The higher the vacuum, the more the beam penetrates to the workpiece, and the greater is the depth-to-width ratio; thus, the methods are called Electron Beam Welding  of high vacuum or EBW-HV (for “high vacuum”) and Electron Beam Welding  of medium vacuum EBW-MV (for “medium vacuum”); it has some speicla features too that some materials also may be welded by Electron Beam Welding  of no vacuum or EBW-NV (for “no vacuum”).

Electron beam welding is mostly used in joining of refractory materials like columbium, tungsten, ceramics. In electron beam welding the power density of electrons are much higher compared to the laser beam welding.

Sometimes in arc welding processes, weld joints and penetration are not good so at that time electron beam process comes into picture where both arc heat source and laser heat source can be utilised simulataneously to get the deeper penetration and weld joints.

How Electron Beam Welding is better than Laser Beam Welding?

We can achieve extremely narrow weld zone using electron beam welding compared to laser beam welding because laser absorption capacity of the material is very low. For example, aluminium does not absorb any laser lights and steel absorbs maximum 30% of laser lights in case of laser beam welding processes. Whereas the absorption of the electrons to material are much higher especially in alloys. So the efficiency of the electron beam welding is much higher about 90-95%.

Other Applications of Electron Beam Welding

  1. High Precision Welding of electronics components. 
  2. High precision welding of nuclear fuel elements.
  3. Special alloy components of jet engines.
  4. Pressure vessels for rocket.
  5. Joining of Dis similar metals.
  6. Welding of Titanium medical implants.

Also read: Submerged arc welding

Principle of Operation of Electron Beam Welding

source:- ASM Welding handbook
Figure (a)-Schematic of Electron beam welding set up.
Figure-keyhole formed during Electron beam welding process.

The electron beam is formed (under high-vacuum conditions) by employing a triodestyle electron gun consisting of a cathode, a heated source (emitter) of electrons that is maintained at some high negative potential; a grid cup, a specially shaped electrode that can be negatively biased with respect to the hot cathode emitter (filament); and an anode, a ground potential electrode through which the electron flow passes in the form of a collimated (parallel) beam.

The hot cathode emitter (filament) is made from a high-emission material, such as tungsten or tantalum. This emitter material, usually available in wire, ribbon, or sheet form, is fabricated into the desired shape for being either directly or indirectly heated to the required emitting temperature of about 2500 °C (4500 °F).

Process

  1. The cathode of the electron beam gun is a negatively charged filament.
  2. When heated up to its thermionic emission temperature, this filament emits electrons.
  3. These electrons are accelerated by the electric field between a negatively charged bias electrode (located slightly below the cathode) and the anode.
  4. They pass through the hole in the anode and are focused by an electromagnetic coil to a point at the workpiece surface.
  5. The beam currents and the accelerating voltages employed for typical EBW vary over the ranges of 50–1000mA and 30–175kV, respectively.
  6. An electron beam of very high intensity can vaporize the metal and form a vapor hole during welding, that is, a keyhole, as depicted in Figure (b).

Advantages of Electron Beam Welding

  1. Electron beam welding proess has the ability to make welds that are deeper and narrower than arc welds.
  2. EBW has the ability to achieve a high weld depth-to-width ratio.
  3. Due to lower heat input results in a narrow workpiece heat-affected zone (HAZ)
  4. Permits welding of refractory metals, reactive metals, and combinations of many dissimilar metals that are not joinable by arc welding processes.
  5. Welding of most hardened or work-strengthened metals can be done using EBW.
  6. Using EBW, distortion and shrinkage  can be minimized during welding.

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