Electron Beam (EB) Welding FAQ
Can you electron beam butt weld .007" thick BeCu to .025" thick BeCu continuous for reel to reel applications?”
Yes, these materials can be electron beam welded. However an EB Welding system with specialized fixturing is required in order to produce these parts.
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Can electron beam welding be used to weld A357 or A356 cast aluminum parts?”
Yes, these cast aluminum alloys can be electron beam welded. Care must be taken as to the quality of the cast material (pores, inclusions, etc) as well as any surface contamination of the aluminum from the casting process as these items will influence the quality of the weld. For a good fit-up, the cleaner the faying surfaces the better. Modern EB welding systems have 5-axis contouring ability making it easy to follow complicated weld paths as well as slope the weld power to penetrate through varying thicknesses. EB welding can make for a viable approach to produce larger composite cast parts when the sizes of individual castings are limited.
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Is it possible to weld 4 plates, 60mm thickness each, together to form a rectangular box using Electron Beam Welding?”
Yes, it is possible to electron beam weld 4 plates together to form a rectangular box. EB welded corner joints are typically achieved using one of the three configurations seen below. Electron beam welding is used in this application for reasons such as: low distortion, providing a hermetic seal, low heat input, welding adjacent to electronic components or rubber seals or simply for minimizing raw material requirements.
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We need to join copper-molybdenum to copper bars of the same diameter. We currently braze but have trouble obtaining 100% fill rates. We have looked at EB welders and they look promising. However, we expect that they would be cost prohibitive. We would like to know your opinion on whether or not we should pursue this process.”
Yes, we do think electron beam welding would be worth looking at for your copper-molybdenum application. Copper + copper alloys lend themselves to EB Welding compared to other welding processes in that electron beam key hole welds can maintain a high depth to width ratio because there are little losses due to conduction, which can be a major problem when welding copper.
If you have enough volume of these parts, the purchase of an Electron Beam Welding system would make sense for your company. However, another feasible solution for smaller scale production levels is to sub-contract out the EB Welding to an experienced job shop such as our own.
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What is an Electron Beam?”
In an electron beam welder, electrons are “boiled off” as
current passes through a filament which is in a vacuum
enclosure. An electrostatic field, generated by a negatively
charged filament and bias cup and a positively charged
anode, accelerates the electrons to about 50% to 80% of the
speed of light and shapes them into a beam. Due to the
physical nature of the electrons – charged particles with an
extremely low mass – their direction of travel can be easily
influenced by electromagnetic fields. Electron beam
welders use this characteristic to electromagnetically focus
and very precisely deflect the beam at speeds up to 10 kHz.
Recent machine developments make it possible even to go
up to 200 kHz. With today’s CNC controls, the beam focus
as well as the beam deflection are part of the weld schedule
and can be variably programmed along with other process
parameters.
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How does the process work?”
When fast moving electrons hit a metal surface they are decelerated which transforms the kinetic energy of each individual electron in the beam into thermal energy in the component. This transformation is stable in the high 90% range for all metals regardless of whether the electrons hit the surface at a perpendicular or a shallow angle. As a practical matter, this physical behavior makes the process very robust and reliable!
When electrons in a focused beam hit a metal surface, the high energy density instantly vaporizes the material, generating a so-called key hole. A characteristic of this phenomenon is that it allows the unique capability for deep, narrow welds with very small heat affected zones (HAZ) and minimized thermal distortions of welded assemblies. Depth-to-width ratios of up to 40:1 have been achieved in production for many years.
Special circumstances may require conduction mode welding (as opposed to key-hole welding) that typically produces wide and shallow welds. Conduction type welds can be used e.g. for cosmetic paths to smoothen the top bead of key hole welds in a subsequent operation. How is this done? By lowering the beam power and either defocusing the beam and/or widening the beam by
using a deflection pattern.
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