The present invention works with the regarding gas mixtures formed solely from helium arid nitrogen in a laser welding process, operating at a maximum power of 12 kW, for welding austenitic, martensitic or ferritic metal pipe.
It has recently been proposed to weld tubes, longitudinally or helically, using a laser beam.
In fact, laser beam welding can be a very high-performance joining process as it makes it possible to obtain, at high speeds, very great penetration depths compared with other more conventional processes, for plasma welding, MIG (Metal Inert Gas) welding or TIG (Tungsten Inert Gas) welding.
This is explained by the high power densities involved when focusing the light beam by much more more mirrors or lenses in the joint plane of the workpieces become welded, as an example power densities that may exceed 106 W/cm2.
These high power densities cause considerable vaporization at the surface of the workpieces which, expanding for the outside, induces progressive cratering of the weld pool and just results in the formation of a narrow and deep vapour capillary called a keyhole from the thickness among the plates, is definitely to say in the joint airliner.
This capillary allows the energy of the laser beam to be directly deposited depthwise as plate, than the more conventional welding processes in which the energy deposition is localized at first glance.
his capillary is formed from metallic vapour/metal vapour plasma mixture, the particular feature of which is it absorbs the laser beam and therefore traps origin . within the actual capillary.
One within the problems with laser welding is the organization of a shielding gas plasma.
This is really because the metal vapour plasma, by seeding the shielding gas with free electrons, may bring about the appearance of a shielding gas plasma which is prejudicial towards welding operation.
The incident laser beam may therefore be greatly disturbed by the shielding gas plasma.
The interaction of the shielding gas plasma associated with laser beam may take various forms but commonly results in effect whereby the incident laser beam is absorbed and/or diffracted and this could lead in order to some substantial lowering of the effective laser power density at the surface for this target, giving you a cut of the penetration depth, or even in a loss of profits of coupling between the beam and also the material so because of this a momentary interruption all of the welding act.
Now, when welding a pipe, its paramount because there to be total or almost total penetration of the weld so that you can avoid any subsequent fracture of the pipe thus welded, during forming operations such as bending or flaring, or during its subsequent use, when the pipe is subjected to several stresses, pertaining to example thermal and/or mechanical stresses, or else when it must be used to convey corrosive substances.
However, the issue is that arises with type of of Ar/He mixture will be the it just isn't longer worthwhile for higher laser power densities, since the threshold which the shielding gas plasma is created is then exceeded, thereby preventing a full-penetration weld to be obtained when welding a stainless steel pipe.