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Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/64522

#### **Abstract**

Laser and hybrid laser-arc welding are used at present in modern industry, having many advantages over traditional welding technology. Sectors such as the automo‐ tive industry, shipbuilding, aviation and space industry, chemical machinery, defense industry, and so on cannot be imagined without these technologies. Possibility of dramatic increase of weld joint properties, robustness, and high level of process automation makes the technology of laser and hybrid material processing a prospec‐ tive part of the industry. At the same time, physical complexity of these processes, their cross-science nature, and necessity in high-level skilled stuff require many efforts for wide and successful industrial implementation. Present manuscript, devoted to discussion of physical peculiarity of laser and hybrid laser-arc welding of metals, approaches to physical-based design of technological equipment, as well as examples of industrial applications of laser and hybrid welding concerning the possibility to control welded metal structure and properties, is one of the steps on this way.

**Keywords:** laser, welding, laser material processing, hybrid welding, laser-induced plasma, technological equipment, process control, process monitoring, kinetics of phase transformations

#### **1. Introduction**

There is a tendency of modern industry to decrease construction weight that is connected to the necessity of increasing fuel efficiency. For this purpose, new high-strength, two- and threephase steels are applied, as well as new Al- and Ti-based alloys, and their properties are defined by parameters of inclusions ensembles. New technologies for automotive bodywork use tailored blanks when the welded blanks are exposed by stamping. Weight reduction blanks with the same mechanical characteristics are possible by using new high-strength steels. Nevertheless,

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there is the problem of providing required characteristics of welds. It is also important to minimize welding stress and distortion, provide quality assessment, and process automation.

models consider main peculiarities of interconnected physical processes. Problem with laser beam absorption and reflection inside the keyhole, heat transfer in solid face, and task about vapor flow in keyhole are solved by the same way as it was done in the model of laser welding [4]. The arc and plasma models, which use boundary layer approximation for mass, momen‐ tum, current, and energy equations [5], are very specific for laser-arc welding. Media com‐ pressibility, volumetric heating by laser beam and arc current, mixing of metal vapor, shielding and arc gas, and temperature influence on kinetic coefficients have to be considered as well as workpiece surface influence on arc and shielding gas flow. The hybrid electric discharge, which defines values of ionization rate, and spatial distributions of conductivity and thermal diffusivity, is also very specific. Physical nature of listed processes is also important for the

Laser and Hybrid Laser-Arc Welding http://dx.doi.org/10.5772/64522 133

**Figure 1.** Jet radial temperature distribution 1 cm above surface, solid line – compressible gas, dot line – oncompressi‐

The laser-induced plasma plume above the workpiece surface have an influence on welding process due to laser radiation absorption and refraction [6], and also can be used as an information source for online process monitoring [7] and control. As it is well known plasma plume structure and parameters are strongly dependent on radiation wavelength [8] and shielding gas nature and rate [9]. From the gas dynamics point of view, plasma plume is a subsonic submerged jet [10] of metal vapor in shielding gas with volumetric heating due to laser radiation absorption in the plasma. The numerical schemes [11] or well-known analytical solution for noncompressive submerged jet [12] are usually applied for calculation of the parameters of vapor-jet plasma. The volumetric heating, strongly influencing on jet flow, depend on plasma absorption coefficient. The theoretical descriptions of laser-induced plasma are usually supposed as thermodynamic equilibrium. The temperature of equilibrium plasma is defined ionization degree and others plasma parameters [13]. However, because absorption of radiation energy by plasma electrons and energy transfer from electrons to heavy compo‐ nent require an energy gap between light and heavy plasma components, supposition of thermodynamic equilibrium is not correct [14]. So the description of laser-induced plasma and also of plasma combined laser-arc discharge is to be based on solution of a Raiser kinetic

formation of melt pool, so it is necessary to look into it more deeply.

ble.

For these problems to be solved, intensive development and wide industrial implementation of laser and hybrid laser-arc welding (HLAW) becomes necessary in near future. Having a lot of evident advantages, beam welding due to complicity of technological processes needs to be successfully used with a deep understanding of process peculiarities, new CAE-based approaches of technology design, design of technological equipment on the basis of high brightness fiber lasers, technical vision, and process monitoring, as well as creation of new classes of welding materials.

Use of laser radiation and electric arc together for welding of metals and alloys so that both sources of heating influence on a material within just one heating zone was born 30–35 years ago [1]. Until recently, CO2 lasers with radiation in far-infrared region were used. Metal interaction with the laser radiation of 10.6 and 1.06 μm is principally different. Lasers with such wavelength radiation are of poor quality and low accuracy. Only in recent years contin‐ uous fiber power lasers with good quality has been developed. They possess high beam quality and high accuracy.

Hybrid laser-arc welding is one of the most promising technologies for joining thick and heavy parts for production of gas and oil pipes, shipbuilding industry, building constructions, and bridge sections. The main benefit of hybrid laser-arc welding is the possibility to weld by one path materials with thickness of up to 20 mm and more, including new type of steels and modern alloys. Hybrid welding can also provide high-quality weld seam whose properties are comparable with laser weld seam properties, but the use of this technology in the case of real production is restricted by high complicity of the process [2] and appearance of differ‐ ent defects, such as porosity, cracks, spiking, and humping in the weld seam.

The analysis of results of the carried investigations of hybrid laser-arc welding process enables to determine the series of problems, in which decision is needed to develop reliable welding technology of thick metals and alloys. It is necessary to exclude: an undesirable direction of crystals growth; dramatic increase of the seam width in the top part of its cross-section; existence of hardening structures in deep penetration zone; presence of set of gas pores; and inadequate values of impact strength of the axial zone, notably at negative test temperatures. The overview of modern trends and problem for solution is presented in [3]. The only way to develop a reliable technology of hybrid laser-arc welding is the use of computer engineeringbased approach to determine and optimize technological parameters as well as for finding and testing of technological methods.
