**2. Theoretical base of laser and hybrid welding**

For understanding the weld pool formation and behavior during hybrid laser-arc welding it is comfortable to use two process models: first, for steady-state case, and second, for dynamic behavior of melt pool. The steady-state model is described in more detail in [4]. All incomplete 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 formation of melt pool, so it is necessary to look into it more deeply.

there is the problem of providing required characteristics of welds. It is also important to minimize

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

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

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‐

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

For understanding the weld pool formation and behavior during hybrid laser-arc welding it is comfortable to use two process models: first, for steady-state case, and second, for dynamic behavior of melt pool. The steady-state model is described in more detail in [4]. All incomplete

ent defects, such as porosity, cracks, spiking, and humping in the weld seam.

welding stress and distortion, provide quality assessment, and process automation.

classes of welding materials.

testing of technological methods.

**2. Theoretical base of laser and hybrid welding**

and high accuracy.

132 Joining Technologies

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

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 equation [15] for electrons energy spectrum, like it was done for laser-induced plasma in the keyhole [14], taking into account the chemistry and gas dynamics of plasma plume.

**Figures 1**–**3** show examples of calculated distributions of temperature, mix density, and concentration in the plasma plume during laser welding of mild steel with initial temperature of 3200 K, flowing out of the keyhole with initial speed of 200 m/s into the helium shielding

Laser and Hybrid Laser-Arc Welding http://dx.doi.org/10.5772/64522 135

**Figure 3.** Density distribution on keyhole outlet, solid line – total density, dot line – iron vapor density.

The plasma plume interferometry experiments (**Figure 4**), made with the Michelson scheme,

**Figure 4.** Plasma plume interferogram with calculated boundary of the jet (red solid line) for NdYAG laser welding.

Plasma plume volumetric heating due to laser beam absorption and Joule heating of electric arc make strong effect on parameters of plasma plume. Calculation shows that volumetric

atmosphere of room temperature.

confirm the developed theory.

The analytic description of plasma plume in vapor-jet shielding gas mix with consideration of volumetric heating, heat conductivity, diffusion, viscosity, and compressibility effects for laser and hybrid welding is possible to get by means of application of boundary layer approach for plume gas dynamics and approach of physical kinetic for plasma of laser-arc discharge [5].

Enthalpy of vapor-gas mixture in plasma plume according to [5] in this case is given by the formula:

$$h = \left[ \left( \frac{\nu \mathcal{J} \{ 1 + B(\mathbf{x}) \}}{\mathbf{x}} \frac{\mathcal{X} \mathcal{J}\_{2\nu}}{1 - \mathcal{X} \mathcal{J}\_{2\nu}} - \frac{\alpha^2 P m C\_p}{2 \eta k \mathbf{x}^2} \frac{r^2}{2} \right) \frac{1 - \mathcal{X} \mathcal{J}\_{2\nu}}{\frac{\mathcal{X}}{2 \nu} \left( \frac{\nu \mathcal{J} \{ 1 + B(\mathbf{x}) \}}{\mathbf{x}} \right)^{\mathcal{J}\_{2\nu}}} \right] \tag{1}$$

where *r* and *x* are the polar coordinates, constants *α* and *β* are given by initial conditions of momentum and energy fluxes [5], *B*(*x*, *y*)= *∫* 0 *x Q*(*x* ′ , *y*)*γ hc* (*x* ′ , *<sup>y</sup>* =0) <sup>⋅</sup>*<sup>h</sup>* \* *<sup>d</sup> <sup>x</sup>* ′ , *hc* is the initial value of vapor enthalpy, *h*\* is the vapor enthalpy for evaporation temperature, *c* is the heat capacity, *Q* is given by the formula *<sup>q</sup>* <sup>=</sup> <sup>4</sup>*mec<sup>ρ</sup> πMFeMHe* <sup>2</sup> <sup>⋅</sup> *<sup>ν</sup>*<sup>∞</sup> 2 *N*<sup>∞</sup> <sup>2</sup>*αFe* <sup>⋅</sup> *<sup>J</sup> Fe* exp( <sup>−</sup> *<sup>J</sup> Fe <sup>ε</sup>* ) <sup>=</sup>*<sup>Q</sup> <sup>c</sup> <sup>h</sup>* , *q* = *μI*, *I* is the laser beam intensity, *μ* is the plasma absorption factor, *η* and *ν* are the dynamic and kinematic gas viscosity, and *χ* is the temperature diffusivity.

**Figure 2.** Iron concentration field in jet 1 cm above surface, solid line – compressible gas, dot line – non-compressible.

**Figures 1**–**3** show examples of calculated distributions of temperature, mix density, and concentration in the plasma plume during laser welding of mild steel with initial temperature of 3200 K, flowing out of the keyhole with initial speed of 200 m/s into the helium shielding atmosphere of room temperature.

equation [15] for electrons energy spectrum, like it was done for laser-induced plasma in the

The analytic description of plasma plume in vapor-jet shielding gas mix with consideration of volumetric heating, heat conductivity, diffusion, viscosity, and compressibility effects for laser and hybrid welding is possible to get by means of application of boundary layer approach for plume gas dynamics and approach of physical kinetic for plasma of laser-arc discharge [5].

Enthalpy of vapor-gas mixture in plasma plume according to [5] in this case is given by the

2 2

é ù ê ú

2 2 <sup>1</sup> <sup>1</sup> <sup>2</sup>

0

<sup>⋅</sup> *<sup>J</sup> Fe* exp( <sup>−</sup> *<sup>J</sup> Fe*

*hc* (*x* ′

enthalpy, *h*\* is the vapor enthalpy for evaporation temperature, *c* is the heat capacity, *Q* is given

the plasma absorption factor, *η* and *ν* are the dynamic and kinematic gas viscosity, and *χ* is

**Figure 2.** Iron concentration field in jet 1 cm above surface, solid line – compressible gas, dot line – non-compressible.

*x*

where *r* and *x* are the polar coordinates, constants *α* and *β* are given by initial conditions of

*Q*(*x* ′ , *y*)*γ*

*<sup>ε</sup>* ) <sup>=</sup>*<sup>Q</sup> <sup>c</sup>*


<sup>1</sup> <sup>1</sup> 2 2

h

*B x PmCp <sup>r</sup> <sup>h</sup> <sup>x</sup> kx B x*

a

c

n

n

æ ö <sup>+</sup> - ç ÷ <sup>=</sup> -

c

( ( ))

 n

> c n

*x*

 c

<sup>2</sup> <sup>2</sup>

, *<sup>y</sup>* =0) <sup>⋅</sup>*<sup>h</sup>* \* *<sup>d</sup> <sup>x</sup>* ′

2

c nb

n

1 <sup>1</sup> <sup>2</sup>

c n

, *hc* is the initial value of vapor

*<sup>h</sup>* , *q* = *μI*, *I* is the laser beam intensity, *μ* is

(1)

keyhole [14], taking into account the chemistry and gas dynamics of plasma plume.

formula:

134 Joining Technologies

( ( ))

momentum and energy fluxes [5], *B*(*x*, *y*)= *∫*

*πMFeMHe*

<sup>2</sup> <sup>⋅</sup> *<sup>ν</sup>*<sup>∞</sup> 2 *N*<sup>∞</sup> <sup>2</sup>*αFe*

nb

by the formula *<sup>q</sup>* <sup>=</sup> <sup>4</sup>*mec<sup>ρ</sup>*

the temperature diffusivity.

**Figure 3.** Density distribution on keyhole outlet, solid line – total density, dot line – iron vapor density.

The plasma plume interferometry experiments (**Figure 4**), made with the Michelson scheme, confirm the developed theory.

**Figure 4.** Plasma plume interferogram with calculated boundary of the jet (red solid line) for NdYAG laser welding.

Plasma plume volumetric heating due to laser beam absorption and Joule heating of electric arc make strong effect on parameters of plasma plume. Calculation shows that volumetric heating due to plasma absorption lead to increases of jet thickness (**Figure 5**). The same behavior is typical for velocity and concentration (**Figure 6**) distributions. In calculation, the beam parameters which are typical for welding with deep penetration by CO2 laser: beam power *W* = 6 kW, wavelength is 10.6 μm, focal radius *rf* = 0.23 mm, target material = mild steel, and shielding gas = He. The keyhole outlet radius (0.35 mm), initial jet velocity (200 m/s), and temperature (3200 K) were calculated by the simulation software LaserCAD [16].

the temperatures of electron and heavy plasma components, which characterize the plasma

Laser and Hybrid Laser-Arc Welding http://dx.doi.org/10.5772/64522 137

**Figure 7.** Temperature distribution along the plume axis, dot line – electron temperature, vapor-gas mix temperature –

Fast mixing of metal jet with surrounded gas limit the conductive kern formation by the region

nonequlibrity, changes along the plume.

solid line – with, double dot – without plasma absorption.

**Figure 8.** Temperature distribution in plasma plume.

near the workpiece surface, as shown in **Figure 9**.

**Figure 5.** Boundary of the jet, solid line – with plasma absorption, dot line – without.

**Figure 6.** Distribution of metal vapor concentration in plasma plume, (a) without plasma absorption, (b) with consider‐ ation of plasma absorption.

Influence of plasma absorption with concurrence of heat convection with jet velocity and conduction in radial direction in plasma plume can shift a temperature maximum from the workpiece surface, even in the surface focusing (**Figures 7** and **8**). Also the difference between the temperatures of electron and heavy plasma components, which characterize the plasma nonequlibrity, changes along the plume.

**Figure 7.** Temperature distribution along the plume axis, dot line – electron temperature, vapor-gas mix temperature – solid line – with, double dot – without plasma absorption.

**Figure 8.** Temperature distribution in plasma plume.

heating due to plasma absorption lead to increases of jet thickness (**Figure 5**). The same behavior is typical for velocity and concentration (**Figure 6**) distributions. In calculation, the beam parameters which are typical for welding with deep penetration by CO2 laser: beam power *W* = 6 kW, wavelength is 10.6 μm, focal radius *rf* = 0.23 mm, target material = mild steel, and shielding gas = He. The keyhole outlet radius (0.35 mm), initial jet velocity (200 m/s), and

**Figure 6.** Distribution of metal vapor concentration in plasma plume, (a) without plasma absorption, (b) with consider‐

Influence of plasma absorption with concurrence of heat convection with jet velocity and conduction in radial direction in plasma plume can shift a temperature maximum from the workpiece surface, even in the surface focusing (**Figures 7** and **8**). Also the difference between

temperature (3200 K) were calculated by the simulation software LaserCAD [16].

**Figure 5.** Boundary of the jet, solid line – with plasma absorption, dot line – without.

ation of plasma absorption.

136 Joining Technologies

Fast mixing of metal jet with surrounded gas limit the conductive kern formation by the region near the workpiece surface, as shown in **Figure 9**.

So, it is possible to mark that boundary layer gas dynamic model with consideration of discharge kinetics allow to explain an electric arc compression during hybrid welding by conductive kern formation in the near-surface region. The results of calculation also allowed to explain a shift of plume maximum temperature from the workpiece surface, which is often visible experimentally, not by the beam over focusing, but by the concurrence of heating with convection and conduction heat transfer.

at the HLAW of the low alloy high-strength steel with thickness of 16 mm with a various gap

Laser and Hybrid Laser-Arc Welding http://dx.doi.org/10.5772/64522 139

Experiments show that gap width makes an effect not only on weld formation stability but

It can be seen that the width of the top of the weld decreases with the increase of the gap width, subsequent increase in the gap width did not affect. The next increasing gap width did not have a strong influence on the weld metal width on the top plate. The width at the root of the weld and in the middle is increased by increasing the gap. As a result, the amount of filler metal is increased. Influence of slot width to the width of the weld is shown in **Figure 11**.

It is also visible (**Figure 12**) that the optimum size of the gap is 1.2 mm. It can be explained that with increasing gap the welding pool width increases too, and, therefore, the volume of the

Analysis of the influence of the gap between the workpieces showed that its optimum size varies in the range of 0–0.3 mm. If a gap of 0.6–0.9 mm undercuts were observed, a gap width

also on welding process heat efficiency, as illustrated in **Figure 10**.

**Figure 11.** Influence of the gap width on the weld metal geometry.

**Figure 12.** Influence of the gap width on the HLAW efficiency.

dropping melting metal is higher. The reason for this is gravity.

widths from 0 to 0.7 mm [21].

**Figure 9.** Radial distribution of mix density (solid) and metal density (dot) on the keyhole outlet and on the distances, correspondingly 0.3 and 2 cm.

Another specific problem for laser-arc welding in the case of laser-MAG and laser-MIG technology is a problem of filler wire melting. This problem can be described on the basis of one-dimensional approach with consideration of Stephan conditions on solid-liquid interface and the action of the electric force for drops transferring [17]. For solution of melt flow and heat transfer task in the melt pool, the approximation of potential flow of ideal liquid with viscous boundary layers on the melting front and keyhole surface has been used [4]. Because hybrid welding is often used for the welding of large and heavy parts, influence of gap between parts becomes especially important for this case.

**Figure 10.** Weld macrosections with different gap width: a – 0 mm; b – 0.3 mm; c – 0.6 mm; d – 0.9 mm; e – 1.2 mm.

For most tasks of welding sheets and pipes, gap width influence on the quality of welding is important. In this area a large amount of research was carried out [18]. The authors found a reduction of the tensile strength and the destruction of the HLAW sample in the HAZ [19]. Experiments show that the highest efficiency and deepest penetration of alloy elements of the welding wire at the HLAW also depend on gap width [20]. Good weld appearance was created at the HLAW of the low alloy high-strength steel with thickness of 16 mm with a various gap widths from 0 to 0.7 mm [21].

Experiments show that gap width makes an effect not only on weld formation stability but also on welding process heat efficiency, as illustrated in **Figure 10**.

It can be seen that the width of the top of the weld decreases with the increase of the gap width, subsequent increase in the gap width did not affect. The next increasing gap width did not have a strong influence on the weld metal width on the top plate. The width at the root of the weld and in the middle is increased by increasing the gap. As a result, the amount of filler metal is increased. Influence of slot width to the width of the weld is shown in **Figure 11**.

**Figure 11.** Influence of the gap width on the weld metal geometry.

So, it is possible to mark that boundary layer gas dynamic model with consideration of discharge kinetics allow to explain an electric arc compression during hybrid welding by conductive kern formation in the near-surface region. The results of calculation also allowed to explain a shift of plume maximum temperature from the workpiece surface, which is often visible experimentally, not by the beam over focusing, but by the concurrence of heating with

**Figure 9.** Radial distribution of mix density (solid) and metal density (dot) on the keyhole outlet and on the distances,

Another specific problem for laser-arc welding in the case of laser-MAG and laser-MIG technology is a problem of filler wire melting. This problem can be described on the basis of one-dimensional approach with consideration of Stephan conditions on solid-liquid interface and the action of the electric force for drops transferring [17]. For solution of melt flow and heat transfer task in the melt pool, the approximation of potential flow of ideal liquid with viscous boundary layers on the melting front and keyhole surface has been used [4]. Because hybrid welding is often used for the welding of large and heavy parts, influence of gap between

**Figure 10.** Weld macrosections with different gap width: a – 0 mm; b – 0.3 mm; c – 0.6 mm; d – 0.9 mm; e – 1.2 mm.

For most tasks of welding sheets and pipes, gap width influence on the quality of welding is important. In this area a large amount of research was carried out [18]. The authors found a reduction of the tensile strength and the destruction of the HLAW sample in the HAZ [19]. Experiments show that the highest efficiency and deepest penetration of alloy elements of the welding wire at the HLAW also depend on gap width [20]. Good weld appearance was created

convection and conduction heat transfer.

parts becomes especially important for this case.

correspondingly 0.3 and 2 cm.

138 Joining Technologies

It is also visible (**Figure 12**) that the optimum size of the gap is 1.2 mm. It can be explained that with increasing gap the welding pool width increases too, and, therefore, the volume of the dropping melting metal is higher. The reason for this is gravity.

**Figure 12.** Influence of the gap width on the HLAW efficiency.

Analysis of the influence of the gap between the workpieces showed that its optimum size varies in the range of 0–0.3 mm. If a gap of 0.6–0.9 mm undercuts were observed, a gap width of 1.2 m lack of filler material was also observed. The volume of the welding wire in the root and half depth of the weld increased simultaneously with increasing gap width. Also, increasing the gap width from 0 to 1.2 mm decreased HLAW efficiency from 30.6 to 22.7%. The results of the experiments described above allow to create a mathematical model for the prediction of the welded joint geometry at HLAW with gap. The integration of the model with the CAE system, LaserCAD [22], allows to predict the welded joint geometry at the HLAW with different gap widths.

<sup>d</sup> , dt *i i i i*

*q q*

 ¶

 ¶

¶

¶

of occurrence of porosity and spiking, as shown in **Figure 14**.

speed – 12 mm/s, focal radius – 0.2 mm, focal distance – 30 cm, arc power – 2.5 kW.

**Figure 15.** Simulation of porosity appearance due to cavity collapse (left) and results of experiment.

mined by the welding regimes.

Analysis of the obtained results shows that dense occupation of the confined areas on the phase portraits by the phase trajectories explain the turbulent character of the cavity oscillations. It explains the calculation results independence for initial conditions. Sizes attractor is deter‐

The simulation results showed that hybrid welding of different generalized coordinates have different spectra of oscillations. The low frequencies below 100 Hz are equal to the radius of the cavity and the depth of the oscillation. Increasing the depth of penetration leads to a shear

of waves of different length), consecutively, *Qi*

where *qi*

function [27].

*L L Q R*

assumes *H* (depth of penetration, *s*<sup>0</sup> (keyhole cross-section area), s1,…sn (amplitudes

The mathematical formalism of solution of this system allows to carry out the dynamic analysis

**Figure 14.** Simulation of the melt pool dynamics at HLAW, material – mild steel, laser beam power – 4.5 kW, welding


is the generalized forces, and *Ri* is the dissipative

Laser and Hybrid Laser-Arc Welding http://dx.doi.org/10.5772/64522 141

Schematically the interaction of different physical processes that are important for processing HLAW is shown in **Figure 13**. Different tasks are connected through boundary conditions; when solution of one task determines boundary condition for another, as through direct influence of equation coefficients.

**Figure 13.** Structure of physical model of HLAW process.

Mathematical formulation of this physical model have been put on the basis of a number of steady-state process models, such as [23, 24], or [25], which allow to simulate a shape and size of melt pool as well as temperature distribution in weld bath and HAZ during hybrid HLAW welding.

For successful technology development it is also necessary to have a physical adequate description of melt pool dynamic behavior, which is responsible of formation of such welding defects as humping, porosity, spiking, and undercuts. This description has been designed on the basis of dynamic model of laser welding process [26]. The model is based on the formalism of Lagrange mechanics, which allow consider phenomena—wave motion of the cavity surface, change of the shape and sizes of the weld pool in time, and influence of the cavity motion as the whole on oscillations of its depth and radius.

The system of Lagrange equations for description of melt pool dynamic behavior can be represented as [27]:

$$\frac{\text{d}}{\text{d}t} \frac{\partial L}{\partial \dot{q}\_i} - \frac{\partial L}{\partial q\_i} = \underline{Q}\_i + R\_i \tag{2}$$

where *qi* assumes *H* (depth of penetration, *s*<sup>0</sup> (keyhole cross-section area), s1,…sn (amplitudes of waves of different length), consecutively, *Qi* is the generalized forces, and *Ri* is the dissipative function [27].

of 1.2 m lack of filler material was also observed. The volume of the welding wire in the root and half depth of the weld increased simultaneously with increasing gap width. Also, increasing the gap width from 0 to 1.2 mm decreased HLAW efficiency from 30.6 to 22.7%. The results of the experiments described above allow to create a mathematical model for the prediction of the welded joint geometry at HLAW with gap. The integration of the model with the CAE system, LaserCAD [22], allows to predict the welded joint geometry at the HLAW

Schematically the interaction of different physical processes that are important for processing HLAW is shown in **Figure 13**. Different tasks are connected through boundary conditions; when solution of one task determines boundary condition for another, as through direct

Mathematical formulation of this physical model have been put on the basis of a number of steady-state process models, such as [23, 24], or [25], which allow to simulate a shape and size of melt pool as well as temperature distribution in weld bath and HAZ during hybrid HLAW

For successful technology development it is also necessary to have a physical adequate description of melt pool dynamic behavior, which is responsible of formation of such welding defects as humping, porosity, spiking, and undercuts. This description has been designed on the basis of dynamic model of laser welding process [26]. The model is based on the formalism of Lagrange mechanics, which allow consider phenomena—wave motion of the cavity surface, change of the shape and sizes of the weld pool in time, and influence of the cavity motion as

The system of Lagrange equations for description of melt pool dynamic behavior can be

with different gap widths.

140 Joining Technologies

influence of equation coefficients.

**Figure 13.** Structure of physical model of HLAW process.

the whole on oscillations of its depth and radius.

welding.

represented as [27]:

The mathematical formalism of solution of this system allows to carry out the dynamic analysis of occurrence of porosity and spiking, as shown in **Figure 14**.

**Figure 14.** Simulation of the melt pool dynamics at HLAW, material – mild steel, laser beam power – 4.5 kW, welding speed – 12 mm/s, focal radius – 0.2 mm, focal distance – 30 cm, arc power – 2.5 kW.

**Figure 15.** Simulation of porosity appearance due to cavity collapse (left) and results of experiment.

Analysis of the obtained results shows that dense occupation of the confined areas on the phase portraits by the phase trajectories explain the turbulent character of the cavity oscillations. It explains the calculation results independence for initial conditions. Sizes attractor is deter‐ mined by the welding regimes.

The simulation results showed that hybrid welding of different generalized coordinates have different spectra of oscillations. The low frequencies below 100 Hz are equal to the radius of the cavity and the depth of the oscillation. Increasing the depth of penetration leads to a shear rate range toward lower frequencies. Long (*S*1) and short (*S*2) waves have the highest frequency range to 10 kHz. These spectra also depend on the cavity depth. The increase of feeding velocity also decreases the low-frequency oscillations. The same approach can be used for analysis of porosity and spiking appearance (**Figure 15**).

This hybrid laser-arc complex contains: IPG fiber laser LS-15, arc power source with current of up to 1500 A, and numerical control filler wire feeding equipment, special working tools, CNC module of preparation, and distribution of used gases, monitoring system of the welded joint, tracking system with scanner laser sensor, process monitoring system, and control

Laser and Hybrid Laser-Arc Welding http://dx.doi.org/10.5772/64522 143

This module is used in complex welding of metallic workpieces with a possible gap of up to 2 mm, MAG torch is installed in front of the laser. This complex mainly includes positions

Stabilization of the hybrid module position and control is described in more detail in [2]. Precision of keeping the focus point position of the laser head relative to welded blanks in the

The control system of hybrid laser-arc complex is developed as a hardware-software complex. Present system controls the components of the complex. The system includes a control

It provides reading profile blanks geometry control, tracking the welding process at speeds of up to 6 m/min, the welding head positioning, control of the laser source, the control operation of the arc, and gas control system. The system also has a built-in protection against harmful

Development of the control and monitoring systems for process of laser-arc welding is still a relevant task. Using of such systems is essential for the adoption of these technologies into the

To solve this problem, it is necessary to carry out researches of the weld pool dynamics and also define basic mechanisms of defects formation specified for welding with deep penetration. For developing this system, secondary emission signals coming from laser-arc action zone

The monitoring system, designed for HLAW, is based on registration of optical emission in different spectral ranges, depending on the range [5]. Sensors are installed in two directions and are equipped with a video camera. It simplifies the guidance process and allows tracing the spatial variation of the active zone. Synchronous registration, processing, and recording

Series of experiments on welding of model samples was carried out for verifying the moni‐ toring system. Test results confirm the possibility of weld formation monitoring using the multisensor monitoring system (**Figure 17**). The presented results confirm the ability to

However, to use the monitoring system in real production it requires further research aimed at understanding the characteristics of particular process [28], identifying typical process

vertical direction is ±0.2 mm, and in the cross-section direction is ±0.5 mm.

conditions and operational control using the monitoring system.

were also analyzed and sensors for their registration were included.

of signals are realized by using developed software.

monitor porosity level in weld using the developed system.

defects, and adaptation monitoring system for this technological process.

subsystem forming welds subsystem monitoring and automatic control system.

system.

industry.

already mentioned above.
