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LASER WELDING
At present, industry is strongly focusing on laser welding,
also thanks to the presence on the market of high power laser sources
that assure high quality performances with good reliability and
repeatability, and this at high accuracy standards and mass-productivity
levels. Therefore, laser welding is a strong alternative to the
traditional joining systems, not only in the case of very high production
rates or when severe quality and repeatability requirements are
specified, but even when it is necessary to respect a strict tolerance
on the product and sensitive aesthetic criteria. Applicable solutions
cover a wide range of system configurations, from medium-sized plants,
user friendly and easy to be installed and integrated on existing
production lines, with a total or partial level of automation, up
to complex plants for large-size 3D parts where, as per the correct
positioning beam-workpiece, an outstanding role is played by the
steady improvement of sensory systems, more and more integrated
with on-line process monitoring systems.
The laser welding process is characterised by a high specific power,
enabling a remarkable depth of penetration with very high aspect
ratio (ratio between weld penetration and width). This is possible
thanks to the onset of a capillary channel, the so-called keyhole,
held in equilibrium by high temperature plasma: through the keyhole,
energy is delivered in depth inside the workpiece. The distinctive
characteristic of laser welding is to be a low heat input autogenous
technique, suitable to any geometry and configuration of component
which are sensitive to heating and distortion. In some cases, it
is possible to use a filler material, generally in the form of wire
feeding, in order to improve joint weldability and performance,
and in most cases gap bridgeability, almost negligible in autogenous
welding. With increasing welding thickness, double pass welding
with opposite runs, while rarely multipass wire feeding is used.
LASER WELDING ADVANTAGES
Autogenous welding with an accurate control of weld penetration
and bead width
Limited thermal input and high aspect ratio (depth/width), with
consequent reduction in distortion compared to traditional methods
and remarkable saving in post-processing operations
Reduced heat-affected zone and limited segregation of compounds
of alloying elements, with related good metallurgical quality and
creation of high performance thin structures
Single pass weld, mostly at a very high feed rate
Possibility of welding in any position and in spots with difficult
access, by special configurations of the welding head
Absence of physical contact and limited distortions, resulting in
reduced need of fixing equipment
High production rate
High flexibility allowing a single source to be used on a vast range
of different processes (welding, cutting, surface treatment)
INDICATIVE VALUES FOR STEEL WELDING PERFORMANCE
10-12 mm for full penetration welds and up to 15 mm for partial
penetration joints using a 12 kW CO2 laser source (technological
limits around 20-25 mm for the higher available power level)
4 mm for full penetration welds and up to 5 mm for partial penetration
joints using a 3 kW Nd:YAG laser source (technological limits around
6 mm for YAG lasers, while may be similar to CO2 limits for ytterbium
fibrelaser sources at the 10-20 kW power level)
FIELDS OF APPLICATION
Automotive
Railway coaches
Aerospace
Energy
Shipbuilding industry
Household appliances
Electromechanical
Informatic
Heating systems
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SAMPLES OF JOINTS CONFIGURATION USED IN LASER WELDING
