Electron beam welding is chosen as the method to joining components for several important reasons. EB welding is similar to laser welding in that both processes use high energy density beams. These high energy density beams produce a very localized heat input into the component being welded and allow for the deep, narrow "keyhole" welding. This deep hole welding is possible because the energy density of the beam is so intense that the material being welded is vaporized at the point of beam impact and the beam drills a hole into or even through the material being welded. Heat is transferred to the material being welded from the edge of this hole. The hole is then moved through the part and the moten material flows around the backside of the hole and resolidifies, forming the weld. Traditional welding techniques with lower energy densities rely on heat being conducted into the metal being welded. Since heat is conducted outward evenly in all directions, a single pass of a conduction mode weld is generally as wide as it is deep.
Even though an electron beam can produce a deep "keyhole" type weld it can also produce a precise conduction mode weld or even provide just enough heat to form a minimal heat input braze joint. This can be accomplished by scanning the beam quickly over the joint or by enlarging the apparent beam spot size by adjusting the focus or by using a deflection pattern to customize the heat input into the part. Precise electron beam welds of this type have been used to join thin foils less than 0.001 inches (0.025 mm) thick.
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