Electron beam welding - welding with a high concentration of heat, excellent protection. The essence of the process is to use the kinetic energy flux of electrons moving at high speeds in a vacuum. To reduce the loss of kinetic energy of electrons due to collisions with gas molecules of air, as well as chemical and thermal protection of the cathode electron gun in a vacuum of 10 ~ 4-10 ~ 6 mm Hg. of Art.
Advantages of electron beam welding
1) A high concentration of heat input into a product that stands out not only on the surface of the product, but at a certain depth in the volume of base metal. Focusing the electron beam spot can be heated with a diameter 0,0002-5 mm, which allows for the weld metal in one pass with a thickness of several tenths of millimeters to 200 mm. As a result, you can get the seams, in which the ratio of penetration depth to width ratio to 20: 1 and more. There is a possibility of welding of refractory metals (tungsten, tantalum, etc.), ceramics, etc. Reducing the length of the zone, "the thermal impact of reducing the likelihood of recrystallization of the base metal in the area.
2) A small amount of heat input. As a rule, for equal to the depth of penetration of electron-beam welding heat input is required is 4-5 times less than the arc. As a result of sharply reduced warpage of the product.
3) The lack of saturation of the molten metal and hot gases. On the contrary, in many cases there is degassing of the weld metal and increase in its plastic properties. The result is a high quality of welded joints on the reactive metals and alloys such as niobium, zirconium, titanium, molybdenum, etc. Good quality of electron beam welding has also been achieved in the low-carbon, stainless steels, copper and nickel, aluminum alloys. penetration in electron-beam welding is mainly due to the pressure of the flow of electrons, the nature of heat release in the volume of solid metal and the jet pressure of evaporating metal, secondary and thermal electrons, and radiation. possible continuous electron beam welding. However, when welding volatile metals (aluminum, magnesium, etc.), the efficiency of the electron beam and the amount of heat released in the product decreases due to energy loss by ionization of metal vapors. In this case it is advisable to weld a pulsed electron beam with high energy density and pulse frequency of 100-500 Hz. As a result of increased depth of penetration. When installed correctly, the pause time ratio and momentum can be welded very thin sheets. Due to the heat sink during the pauses decreases the length of the heat affected zone. However, with the possible formation of scores that can be eliminated by welding or the wavering defocused beam.
The main parameters of the regime of electron-beam welding - the current in the beam, accelerating voltage, travel speed of the beam on the surface of the product, the duration of the pulses and pauses, accurate focusing of the beam, the magnitude of the vacuum. To move the beam to the workpiece surface displacements using the product or of the beam by the deflection system. Deflection system allows for fluctuations in beam length and breadth of the seam or a more complex trajectory. Low voltage installation is used for welding metal thickness greater than 0.5 mm for joints with a ratio of depth to width ratio to 8:1. High setting is used for welding thicker metal with a ratio of depth to the width of the seam up to 25: 1.
Before welding requires precise assembly of parts (metal thickness to 5 mm gap of no more than 0.07 mm, thickness 20 mm gap to 0.1 mm) and the exact direction of the beam along the axis of the joint (the deviation does not exceed 0.2-0.3 mm). With the increased clearances (to prevent undercutting) requires an additional metal in the form of technological collars or filler wire. In the latter case it is possible metallurgical effects on the weld metal. By varying the gap and the amount of extra metal, you can increase the share of filler metal in the seam up to 50%.
Disadvantages of electron beam welding: possibility of incomplete and cavities in the root of the weld metals on high thermal conductivity and seams with a large ratio of depth to width, to create a vacuum in the chamber after loading the product takes a long time.
See also:
Electron Beam Welding Technology
Electron Beam Welding Article
Installations for Electron Beam Welding
Electron Beam Welding Gun
Work Chambers for EBW
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