Laser Welding It is a union process based on localized fusion in the joint, through bombardment from a high-intensity, concentrated, monochromatic and coherent light beam. The area to be welded is protected by using an inert gas, usually argon or a mixture of inert gases

- When the light beam reaches the surface of the metal the metal absorbs its energy converting it into heat that penetrates into the interior of the metal by conduction - Owing to a high concentration of heat the metal is taken to its melting point and a series of events culminates in the formation of a keyhole or spots that will be filled with the melted metal

Advantages 1-Less distortion compared to conventional welding methods 2-It can be executed directly in the working model 3-Less time consuming 4-Allows welding in regions near the resins and porcelain 5- Allows welding with the structures in close contact or with minimal space for welding using filler metal

Disadvantages 1- The residual stress introduced into welding joints by thermal stress of heating and cooling cycles of the welding process 2- The presence of porosities in the region of the union 3- Insufficient penetration of the laser beam causes a big bubble or internal failure 4-Biohazard 5- High cost equipment that is due to the inclusion of argon gas, which is necessary to maintain the inert atmosphere during the welding procedure and thus minimize interaction with air elements. These bubbles and crashes act as initiators of fractures and points of stress concentration, and can lead to the failure of welded structures in a short period of time the depth of penetration of the weld is the main factor that affects the values of resistance for laser-welded frameworks

Welding of ceramics Very issued process due to: 1- Small thermal conductivity 2- High thermal expansion (Crystal lattice) Because of the relatively small thermal conductivity compared with the high thermal expansion, stresses in the material can occur leading to its destruction inevitably The cause can be found in the structure of crystal lattice. A comparison to metals may show it: in metals the crystal lattice only consists of positive metal ions, the gabs between them being filled with flexible, negatively charged electron gas. It is characterised by a high density of misalignments . In case of an extern mechanical force this structure enables a migration of the misalignments. Ceramics are characterised by a lattice consisting of alternating positive and negative ions with high binding forces. This constellation effects in case of an external force that the ions are driven towards fields of same charge. They react with high repulsion. This leads to high stresses, especially in the cooling phase. The amount of the resulting stresses depends on the temperature gradient, on the physical properties of the material, and also on the procedure requirements. The knowledge of this basic behaviour is a precondition for the development of a laser welding technology of ceramics that represents a combination of the difficult behaviour of ceramics and the advantages of laser material processing.

Dual beam laser welding A new welding process employing two independent laser beams is used to produce crack-free welds These cracks disappear when a second laser beam is placed at a precise position behind the first one with suitable intensity J.-M. Drezet, M.S.-F Lima, J.-D. Wagnière, M. Rappaz, W. Kurz, Crack-free aluminium alloy welds using a twin laser process, in Proceedings of the Inter. Institute of Welding Conference, edited by P. Mayr, G. Posch, H. Cerjak, pp. 87-94, 2008

Two laser beams 1-One Co2 laser beam of 10.6 μm wave length is deflected by two scanner mirrors 2- Some minutes later the welding Nd:YAG laser beam of a wavelength of 1.06 μm can join the parts crack free

Advantages of double beams welding laser 1- Less time consuming than coventional laser welding (only few minutes) 2- Can be performed in the atmosphere (no protective gas) 3- Result in less internal stress and cracks 4- By using selective preheating it is possible to fix the material by metals H. Exner, Anne-Maria Nagel, “Laser welding of functional and constructional ceramics for Microelectronics”, Proc. SPIE, Laser Applications in Microelectronics and Optoelectronic Manufacturing IV, vol. 3618, pp. 262-268, July15, 1999