METALS LASER WELDING

Apart from the high involvement of laser technology in industrial cutting applications, Laser Beam Welding of metal parts actually meet the highest favour in industry, with a really unique variety of applications. After the consolidation of the laser welding process on low-to-medium thickness, where LBW allows relevant advantages in terms of productivity and product quality, the trend, favoured by the increase of available powers, is addressing to heavy sections components too. In addition, hybrid systems are entering the market, in most cases MIG-laser but also TIG-laser may be seen, where two different technologies are matched to exploit both potentials. CO 2 sources and YAG/fibrelaser sources (diode sources are rarely taken into account for welding applications) are used in industrial production, the choice being determined by the kind of process, the processed material, thickness and geometry, the quality requirements, the productivity target and the related investment and management costs.

 

 

 

 

 

LASER WELDING OF THE MAIN METALLIC MATERIALS

Mild steels, carbon steels, low alloyed steels
Mostly weldable by laser, limits are submitted to C content, to S and P impurity levels, to the content in Cr and in other hardening elements. In the case of thin metal sheets, weldability may be good up to very high Equivalent Carbon values, but with increasing thickness, a level of C higher than 0.3% may cause internal defects and brittle behaviour, and may require the use of preheating and filler material. Preheating may be required in Cr-Mo low alloyed grades.
Austenitic, duplex, ferritic, martensitic stainless steels
Very good weldability on austenitic steels and in general on ferritic grades which exhibit a tendency to the enlargement in grain size, martensitic grades require preheating according to the processed thickness, while duplex steels need post weld heat treatments to restore the required phase distribution.
Aluminium alloys
High thermal conductivity and reflectivity do not ease LBW of these materials, yet good results on a conspicuous number of alloys have been assessed, mainly using YAG sources or equivalent. The presence of alloying elements as Si, Mn, Mg, Cu, Zn generally favours keyhole formation, but also complicates weldability.
Titanium alloys
Very good weldability thanks to the low thermal conductivity and to the good radiation absorption. Yet, the material is sensitive to contamination by oxygen, nitrogen and hydrogen and, consequently, it needs a good surface cleaning and an accurate gas shielding during processing.
Superalloys
Laser weldability is typically good, however special cares are requested, also in view of the usually demanding applications in aeronautics.
Copper alloys
The high reflectivity of the materials requires the use of YAG sorurces, however the alloying elements may completely change this situation. Brass is typically the most difficult to be approached, but in some cases high quality reliable production has been achieved.

LASER WELDING OPERATING PHASES
Feasibility study
Workstation equipment set-up
Laser processing
Laboratory analysis
Quality testing on finished product

By now, laser welding applications are present in all industrial sectors and they are individually customised, in order to focus and exploit properly technological advantages, such as productivity rate, flexibility, distortion control or aesthetic quality.