At present, non vacuum EB welding is mainly used in Germany for welding aluminium, e.g. for cockpit carriers made of aluminium.
The NVEBW method is advantageous for the increased use of high strength fine metal plates in industry. First of all it is possible to achieve high welding speeds, and secondly it allows lightweight designs to be conceived using a combination of various types of materials, e.g. joining aluminium and steel.
As the energy input can be precisely controlled, durable weld-solder joints can be made (in this case the steel stays hard and the aluminium is fused to it).
Also at this process the electron beam is generated in a high-vacuum system (se above). But for the NVEBW method the formed beam is "guided out" then to the free atmosphere passing some fine nozzles which separate the different pressure stages.Due to the collisions of the electrons with the atmosphere's particles the beam widens gradually at increasing working distance (nozzle - workpiece). However, within the recommended distance the energy density of the beam is still strong enough to produce a key-hole welding process.
With respect to the application this method distinguishes to the in-vacuum process by avoiding any vacuum chamber for workpiece handling. So the user can save the evacuation time and effort, and even large components can be welded economically.
Only to protect from the danger of X-rays (generated in each electron beam process) the working area of a NVEBW machine has to be shielded by adopted lead walls.
The shown sketch illustrates the beam generation system.
- High vacuum area
about 10-4 mbar by a turbo-molecular pump or oil-diffusion pump
- Beam generator
optimized to suppress arcings
- Pressure stage 2 ca. 10-2 mbar
- Pressure stage 1 approx. 1 mbar
at atmosphere pressure, about 10 - 25 mm distance to beam nozzle
Advantages of the method
|Electrical wall-plug efficiency||> 50% (incl. all auxiliaries)|
|Energy absorption on the workpiece||nearly independent on kind of material, surface state, angle of incidence, moving direction|
|Weldable sheet thicknesses||0.5 to 10 mm, in special cases even more|
|Edge preparation for butt welds||regular cut|
|Able to bridge gaps||up to 20% of the sheet thickness, 0.5 mm maximum (without filler),
no weld sink when thicknesses are combined
application of filler wire possibly
|Edge-mismatch capability||up to half sheet thickness|
|Welding speed||generally very high, depending on material and thickness/depth;
for example on Al alloy: 14 m/min at 3 mm depth;
60 m/min at 1 mm depth
|Seam width||Minimum 1 mm, up to 4 mm at larger thicknesses|
|Energy input per length||comparable small, narrow HAZ|
|Minimum heat input||less hardness, minimum part's distortion|
|Beam to part tolerances||sideways up to 20% of the sheet thickness|
|Maximum deviation in working distance||up to 10% of set value|
|Available beam power||maximum 30 kW|
|Beam control||by CNC, in common with the weld path|
|High voltage||175 kV, switch mode, nearly interruption free|
|Welding parameters||programmable, controlled, supervised|
|Operation||by a convenient and clear touch panel|
|X-ray protection||< 1 µSv/h by adopted (tailored) lead shielding|
|Beam guidance||using Helium effluence|
Consumption / Maintenance
|Electrical Energy||3 x 400 V, 50/60 Hz, PEN
15 kW (for basic consumption) plus welding power
|Wear parts||cathodes and nozzles, exchange needs
depend on working conditions
(e.g. 60 hours at 60% on-time),
exchange takes 30 min
|Further consumption||Compressed air, Helium (4.6), pump oils, sealings|