schweissen atmosphaere

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).

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.

  1. High vacuum area
    about 10-4 mbar by a turbo-molecular pump or oil-diffusion pump
  2. Beam generator
    optimized to suppress arcings
  3. Pressure stage 2 ca. 10-2 mbar
  4. Pressure stage 1 approx. 1 mbar
  5. 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

Steigerwald Strahltechnik GmbH
Emmy-Noether-Str. 2
82216 Maisach · Germany
Phone: +49 8141 3535-0
Fax: +49 8141 3535-215
E-Mail: info@sst-ebeam.com
Member of Global Beam Technologies AG

PTR Strahltechnik