Welding at atmosphere

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).

Aluminium cockpit carrier

Process principle

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
Workpiece
at atmosphere pressure, about 10 - 25 mm distance to beam nozzle

nvgenerator

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

Technique

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

Example of a NVEBW machine
nvebw maschine

Welding at atmosphere