Electron beam welding
Basic information about the technology
Electron beam welding is one of the fusion welding methods that uses a focused beam of high energy electrons to heat the materials being joined. On impact, the kinetic energy of the electrons is converted into heat, which is used to heat the parts being welded. Welding is generally carried out without additional material. Thanks to the so-called depth effect, depending on the parameters of the welder, considerable thicknesses of material can be welded in a single pass – over 10 cm in stainless steel.
The electron source is the so-called electron nozzle (see popular presentation). Here, electrons are extracted from a thermoemission cathode, accelerated by an electrical voltage of 30 kV to 200 kV and focused into the weld spot by electron optics. The entire welding process takes place in a vacuum (10-2 to 10-3 Pa) as the electron beam is scattered by air molecules. The size of the weldment is thus limited by the size of the vacuum working chamber, the loss times necessary for its exhaustion are incurred and metals with high vapour tension such as Zn, Cd, Mg cannot be welded. On the other hand, the vacuum acts as a “protective atmosphere” and allows welding even reactive metals such as Ti. In practice, arrangements where welding is carried out under low vacuum or in air are also being promoted. More detailed information on the technology can be obtained from e.g. monographs.
In spite of its high cost, electron beam welding has gained a firm foothold in many important industries, such as automotive, nuclear, aerospace and aviation, due to its distinctive and unique properties. Its main advantages include:
- high weld depth/width ratio (up to 25/1 according to parameters) with a characteristic knife-edge cross-section (see images below)
- deep through-holes per pass (due to the depth effect)
- welding of metallic materials regardless of their melting temperature
- minimum heat affected area
- minimum deformation
- high welding productivity
- weld purity, vacuum metal remelting
Principles for welded joint design
Welding is carried out without additional material. In order to achieve fusion of the fused metals at the welding point, the parts to be welded must adhere tightly to each other with clean (free of contamination by cutting fluid, abrasive, etc.) and smooth surfaces. In order to ensure that the material of both parts to be welded is heated evenly, it is better if they have the same thickness at the weld point.