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Electron beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. The workpieces melt and flow together as the kinetic energy of the electrons is transformed into heat upon impact. EBW is often performed under vacuum conditions to prevent dissipation of the electron beam. == History == Electron beam welding was developed by the German physicist Karl-Heinz Steigerwald, who was at the time working on various electron beam applications. Steigerwald conceived and developed the first practical electron beam welding machine, which began operation in 1958. American inventor James T. Russell has also been credited with designing and building the first electron-beam welder.〔(【引用サイトリンク】title=Inventor of the Week - James T. Russell - The Compact Disc )〕 ==Physics of electron beam heating== Electrons are elementary particles possessing a mass ''m'' = 9.1 · 10−31 kg and a negative electrical charge ''e'' = 1.6 · 10−19 C. They exist either bound to an atomic nucleus, as conduction electrons in the atomic lattice of metals, or as free electrons in vacuum. Free electrons in vacuum can be accelerated, with their orbits controlled by electric and magnetic fields. In this way narrow beams of electrons carrying high kinetic energy can be formed, which upon collision with atoms in solids transform their kinetic energy into heat. Electron beam welding provides excellent welding conditions because it involves: *Strong electric fields, which can accelerate electrons to a very high speed. Thus, the electron beam can carry high power, equal to the product of beam current and accelerating voltage. By increasing the beam current and the accelerating voltage, the beam power can be increased to practically any desired value. *Using magnetic lenses, by which the beam can be shaped into a narrow cone and focused to a very small diameter. This allows for a very high surface power density on the surface to be welded. Values of power density in the crossover (focus) of the beam can be as high as 104 – 106 W/mm2. *Shallow penetration depths in the order of hundredths of a millimeter. This allows for a very high volumetric power density, which can reach values of the order 105 – 107 W/mm3. Consequently, the temperature in this volume increases extremely rapidly, 108 – 1010 K/s. The effectiveness of the electron beam depends on many factors. The most important are the physical properties of the materials to be welded, especially the ease with which they can be melted or vaporize under low-pressure conditions. Electron beam welding can be so intense that loss of material due to evaporation or boiling during the process must be taken into account when welding. At lower values of surface power density (in the range of about 103 W/mm2) the loss of material by evaporation is negligible for most metals, which is favorable for welding. At higher power density, the material affected by the beam can totally evaporate in a very short time; this is no longer electron beam welding; it is electron beam machining. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Electron beam welding」の詳細全文を読む スポンサード リンク
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