Laser Beam Welding Process Research Articles

A multi-fidelity information fusion metamodeling assisted laser beam welding process parameter optimization approach

Selecting reasonable laser beam welding (LBW) process parameters is very helpful for obtaining a good welding bead profile and hence a high quality of the welding joint. Existing process parameter optimization approaches for LBW either based on cost-expensive physical experiments or low-fidelity (LF) computer simulations. This paper proposes a multi-fidelity (MF) metamodel based LBW process parameter optimization approach, in which different levels fidelity information, both from LF computer simulations and high-fidelity (HF) physical experiments can be integrated and fully exploited. In the proposed approach, a three-dimensional thermal finite element model is developed as the LF model, which is fitted with a LF metamodel firstly. Then, by taking the LF metamodel as a base model and scaling it using the HF physical experiments, a MF metamodel is constructed to approximate the relationships between the LBW process parameters and the bead profile. Two metrics are adopted to compare the prediction accuracy of the MF metamodel with the single-fidelity metamodels solely constructed with physical experiments or computer simulations. Results illustrate that the MF metamodel outperforms the single-fidelity metamodels both in global and local accuracy. Finally, the fast elitist non-dominated sorting genetic algorithm (NSGA-II) is used to facilitate LBW process parameter space exploration and multi-objective Pareto optima search. LBW verification experiments verify the effectiveness and reliability of the obtained optimal process parameters.

Comparative study on experimental and numerical investigations of laser beam and electron beam welded joints for Ti6Al4V alloy

This paper reports a numerical and experimental investigation of laser beam welding (LBW) and electron beam welding (EBW) for the Ti6Al4V titanium alloy. The microstructure of LBW and EBW welded joints is compared. A defect-free, fine-grain, and high-quality joint is produced using the EBW process, while undercut and some pores are observed in the LBW welded joint. The simulated temperature distribution and the cross section of the experimental specimen are compared to evaluate the model validity. The calibrated model is applied to determine the thermal cycles on three selected nodes for both LBW and EBW processes. It is observed that the energy density of the electron beam is higher than that of the laser beam, which causes the weld-seam width of the EBW to be larger than that of the LBW weld seam. Narrow weld-seam, fine grain, and no defect make the EBW a more suitable method to join Ti6Al4V titanium sheets compared with the LBW process.

Influence of Porosity on the High Cycle Fatigue Behaviour of Laser Beam Welded Ti-6Al-4V Butt Joints

Surface defects and internal discontinuities are inevitable results of the laser beam welding (LBW) process regardless of the material used. Comprehensive understanding of the fatigue degradation caused by these defects is of major concern for the introduction of LBW into manufacturing or repair processes. The present paper focuses on the effect of inherent welding-induced material flaws on the high cycle fatigue behaviour of the laser welded Ti-6Al-4V butt joints. If the surface quality of the welded joint is sufficiently high, the transition of the crack origin from the surface to the subsurface occurs. The mechanisms of internal fatigue crack formation and growth at the early stages were studied. A typical fish-eye pattern of fracture surface was observed in close proximity to the crack origin. The model based on fracture mechanics for durability prediction in the presence of randomly distributed porosity was developed. The link between theory, modelling and experiment was successfully demonstrated.

Autogenous double-sided T-joint welding on aluminum alloys using low power fiber laser

In this study, a successive double sided laser beam welding process was used to join dissimilar aluminum alloys, AA2024-O and AA7075-T6 using a low power Yb-fiber laser in a T-joint configuration without additions of filler materials. The influence of welding speeds and focal distances were evaluated. First, the welding speeds were varied from 12 mm/s to 21 mm/s at a constant laser power of 270W. Optical microscopic observations have shown that the minimum gap line of 0.8mm was obtained at a laser welding speed of 12mm/s, while the maximum gap line of 1.8mm was obtained at a laser welding speed of 21mm/s. The focal distance with offsets of -1, 0 and +1 at welding speed 18mm/s were evaluated, showing variations in the gap line. Vickers microhardness evaluation across the welding region showed the hardness values at the fusion and heat affected zones were lower than those of the base metals when welding speed varied. Meanwhile, the Vickers microhardness increases when focal distance is defocused +1. The pull test showed the force needed to fracture the welded specimens increased from 101N to 427N as the welding speed decreased from 21mm/s to 12mm/s. For constant welding speed and laser power, the fracture force increased from 100N to 400N as the focal distance changes from -1 to +1. It was observed that a lower welding speed and positive offset value of focal distance will result in deeper penetration, leading to better weld quality between alloys AA2xxx and AA7xxx.

Review on experimental study of Nd:YAG laser beam welding, with a focus on aluminium metal matrix composites

The demand for high performance materials particularly in aviation and automobile industries gradually increases, CO2 and Nd: YAG lasers are becoming most popular in processing these advanced materials. In this context, one of the most important process is joining by welding. It has been a constant endeavour by researchers to explore various methods and techniques to enhance the process efficiency of autogenous Nd: YAG laser welding of various materials i.e. without any filler materials. In this work, we present a comprehensive review of major research findings for the last decades or so, obtained by researchers about the effect of process parameters on autogenous laser beam welding (LBW) process performance. Main objective of such experimental research was to improve laser weld quality such as tensile strength, weld micro structure, heat affected zone (HAZ), weld penetration etc. In this paper, discussions are also made about different parameter optimisation techniques, design of experiments (DOE), modelling and simulation techniques, adopted by different researchers to achieve optimum weld quality. This review tries to bring out a foresight for direction of further research needed in this field.

Effect of Nd:YAG laser beam welding on weld morphology and mechanical properties of Ti–6Al–4V butt joints and T-joints

A Nd:YAG single-sided laser beam welding process study for Ti–6Al–4V butt joints and T-joints was performed to investigate joining techniques with regard to the process-weld morphology relationship. An alloy compatible filler wire was used to avoid underfills and undercuts. The quality of the butt joints and T-joints was characterized in terms of weld morphology, microstructure and mechanical properties. Joints with regular shapes, without visible cracks, pores, and geometrical defects were achieved. Tensile tests revealed high joint integrity in terms of strength and ductility for both the butt joint and T-joint geometries. Both the butt joints and T-joints showed base material levels of strength. The mechanical performance of T-joints was also investigated using pull-out tests. The performance of the T-joints in such tests was sensitive to the shape and morphology of the welds. Fracture always occurred in the weld without any plastic deformation in the base material outside the weld.

Evaluation of Residual Stresses and Mechanical Properties of IF Steel Welded Joints by Laser and Plasma Processes

Interstitial free (IF) steel has an extensive application in the automotive industry where the Laser Beam Welding (LBW) process is widely used due to its high productivity. Similarly, the other used process, Plasma Arc Welding (PAW), is characterized by a greater energy concentration and current density and therefore lower distortion, higher welding speeds and higher penetration may be obtained. However, while the traditional welding processes have been extensively studied with regard to the generation of residual stresses, there are few studies about residual stresses analysis and characterization of LBW and PAW joints. Therefore, the aim of the present work is to analyse the residual stresses resulting from LBW and PAW processes by X-ray diffraction technique with sin2ψ method in IF steel butt joints. For both joints, macro and microstructure were characterized and mechanical properties were determined. Tensile residual stresses in the heat-affected zone (HAZ) and in the fusion zone (FZ) were verified for both welding processes.

Laser beam welded structures for a regional aircraft: weight, cost and carbon footprint savings

Laser beam welded structures offer great opportunities for the lightweight design of fuselage structures in order to reduce structural weight for increased fuel efficiency. Our main objective is to validate and demonstrate that laser beam welding (LBW) technology provides the best opportunities in terms of weight reduction, production time and energy consumption for manufacturing aircraft components. To this end, a comparison in terms of energy, process time, cost and carbon footprint is assessed against the ‘conventional’ manufacturing process of riveting, to prove that LBW is actually an environmental friendly process. Manufacturing of a four-stringer stiffened flat subscale component was the case of the present work that was called in the Clean Sky Eco-Design Airframe (EDA) project as the B1 demonstrator (742mm×384mm). The LBW process has been broken down into several sub-processes and activities according to the Activity Based Costing (ABC) methodology and the weight reduction, production time and energy consumption results were compared against the respective of the riveting process. It was proved that for the specific subscale LBW component, it consumes half the energy and can be processed in less than half the time needed (in serial processing of the component) with riveting. Manufacturing of the component with the LBW process (door to door approach) is more environmentally friendly, since it produces 53% less CO2e emissions than the respective riveted process. This is a clear advantage to this manufacturing process in order to assure a sustainable life cycle of the final product.

Welding with High-power Lasers: Trends and Developments

High-power laser beam welding became new stimuli within the last 10 years due to the availability of a new generation of high brightness multi kilowatt solid state lasers. In the welding research new approaches have been developed to establish reliable and praxis oriented welding processes meeting the demands of modern industrial applications during this time. The paper focuses on some of the current scientific and technological aspects in this research field like hybrid laser arc welding, simulation techniques, utilization of electromagnetic fields or reduced pressure environment for laser beam welding processes, which contributed to the further development of this technology or will play a crucial role in its further industrial implementation.

Finite Element Modeling for the Structural Analysis of Al-Cu Laser Beam Welding

Laser beam welding of aluminum and copper (Al-Cu) materials is a cost efficient joining technology to produce e.g. connector elements for battery modules. Distortion low connections can be achieved, which have electrical favorable properties. Numerical simulation of the laser beam welding process of Al-Cu dissimilar materials can provide further insight into principal process mechanisms and mechanical response of the joint parts. In this paper a methodology is introduced to investigate the structural behavior of Al-Cu joints in overlap joint with respect to welding distortions and residual stresses. First the material model of the homogeneous base materials are validated. Next, a generic material model approach is used to simulate the structural behavior of heterogeneous Al-Cu connections.

Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields

Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solid–liquid phase transition was taken into account and the solidification was modelled by the Carman–Kozeny equation for porous medium morphology.The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics.

The Effects of Drilling Parameters on Pore Size in Keyhole Mode Welding

The pore sizes affected by different drilling parameters during high power density laser and electron beam welding processes are theoretically determined in this study. The drilling parameters include incident energy absorbed by the mixture in the keyhole, radius, and Mach number at the base, drilling speed, and location of the shock wave or surrounding pressure. The factors affecting the pore sizes are still lacking, even though porosity often occurs and limits the widespread industrial application of keyhole mode welding. In order to determine the pore shape, this study introduces the equations of state at the times when the keyhole is about to be enclosed and when the temperature drops to melting temperature. The gas pressure, temperature, and volume required at the time when the keyhole is about to be closed are determined by calculating the compressible flow of the vapor–liquid dispersion in a vertical keyhole with varying cross sections, paying particular attention to the transition between annular and slug flows. It is found that the final pore size decreases as absorbed energy, radius, and Mach number at the base increase, and decreases axial location of the shock wave or higher surrounding pressure for the keyhole containing a supersonic mixture. For a subsonic mixture in the keyhole, the final pore size decreases as released energy, radius, and Mach number at the base increase. This work provides an exploratory and systematical investigation of the pore size during keyhole mode welding.

Numerical Prediction Of Deformations In Laser Welded Sheets Made Of X5CrNi18-10 Steel

AbstractThe work concerns the numerical modelling of coupled thermal and mechanical phenomena occurring in the laser beam welding process. Commercial Abaqus FEA engineering software is adopted to numerical computations in order to perform a comprehensive analysis of thermo-mechanical phenomena. Created in Fortran programming language additional numerical subroutines are implemented into Abaqus solver, used to describe the power intensity distribution of the movable laser beam heat source. Temperature dependent thermomechanical properties of X5CrNi18-10 steel are adopted in the numerical analysis of stress and strain states. Mathematical and numerical models are verified on the basis of a comparison between selected results of computer simulations and experimental studies on butt-welded joints.Numerical simulations are presented for steel sheet with a thickness of 2 mm. Temperature distributions, the shape and size of melted zone as well as residual stress and deformations are presented for analyzed elements. Numerically determined deflections are compared with the measured deflection of welded joint.

Studies on Microstructure and Mechanical Properties of GTAW, Laser and Friction Stir Welded ZM21 Magnesium Alloy

Present work pertains to welding of ZM21 magnesium alloy using three different welding techniques namely Gas Tungsten Arc Welding, Laser Beam Welding and Friction Stir Welding. After careful trial and error method, the process parameters were identified to produce defect free, full penetration welds successfully. The microstructure and mechanical properties of ZM21 magnesium alloy using GTAW, LBW and FSW processes were analyzed by optical microscopy, tensile testing and Vickers micro hardness measurements. The results show that the tensile properties of Friction stir welds and Laser beam welds are much better than those of gas tungsten arc welds. The formation of very fine grains in the friction stir welded region and absence of HAZ in LBW are found to be main reasons for better tensile properties. It has been concluded that the ZM21 magnesium alloy exhibits good weldability in all the three welding processes and laser beam welding process offers higher joint efficiency when compared with GTAW and FSW.

Sensors and their classification in the fusion weldingtechnology

In this paper the most commonly used sensing systems in modern welding industry, which nowadays includes robotic systems, are listed and analyzed. According to mechanisms of action and measured parameters, several classifications of sensor systems have been presented. MIG/MAG, resistance and laser beam welding processes are the most commonly robotized ones in the industry and therefore special attention has been given to them. Several characteristic, limitations and advantages of sensor systems are presented and mechanisms of action are briefly described.

The Effects of Entrainment on Pore Shape in Keyhole Mode Welding

This study theoretically investigates the effects of the entrainment accompanying mass, momentum, and energy transport on pore size during high power density laser and electron beam welding processes. The physics of macroporosity formation is not well understood, even though macroporosity often occurs and limits the widespread industrial application of keyhole mode welding. This work is an extension of a previous work dealing with collapses of keyholes induced by high intensity beam drilling. In order to determine the pore shape, this study, however, introduces the equations of state at the times when the keyhole is about to be enclosed and when the temperature drops to melting temperature. The gas pressure required at the time when keyhole collapses is determined by calculating the compressible flow of the two-phase, vapor–liquid dispersion in a vertical keyhole with varying cross sections, paying particular attention to the transition between annular and slug flows. It is found that the pore size increases as entrainment fluxes decrease in the lower and upper regions of the keyhole containing a supersonic mixture. The pore size also increases with decreasing total energy of entrainment and an increasing axial velocity component ratio between entrainment and mixture through the core region. With a subsonic mixture in the keyhole, the final pore size increases with entrainment fluxes in the lower and upper regions. This work provides an exploratory and systematical investigation of pore size induced by entrainment accompanied by mass, momentum, and energy transport during keyhole mode welding.

A comparison of microstructure and mechanical properties of welded thin Ti6Al4V with three different types of laser

Many items of medical, aeronautical, electronic and military equipment are exposed to corrosive conditions, and it is a common practice to protect these in laser beam welded titanium-alloy micro-packages, which require very small and precise weld zones. A range of laser types has been applied to this task, including Nd:YAG, diode and (more recently) fibre lasers. Compared with other laser beam welding (LBW) processes, fibre lasers are widely recognised to result in lower overall heat input, a narrower weld zone, less distortion and high process efficiency. This paper contrasts the mechanical and metallurgical properties of laser welded titanium alloy (Ti6Al4V) in the form of thin (0·7 mm) sheet, typical of that used in micro-packages. Welds were produced with three different laser types, namely, Nd:YAG, diode and fibre lasers. Despite the widely accepted advantages of fibre laser processing, weld quality following processing with a Nd:YAG laser was found to be higher than that of welds produced with either the fibre laser or diode laser; welds processed with the fibre laser exhibited serious porosity defects because of excessive laser-workpiece traverse speeds, nor large spot diameter and poor beam quality characteristic of diode lasers.

Development of laser beam welding transverse-varestraint test for assessment of solidification cracking susceptibility in laser welds

In order to quantitatively evaluate the solidification cracking susceptibility in laser welds of type 310S stainless steel, a transverse-Varestraint testing system using a laser beam welding apparatus was newly constructed. The timing-synchronization between the laser oscillator, welding robot and hydraulic pressure devices was established by employing high-speed camera observations together with electrical signal control among the three components. Moreover, the yoke-drop time measured by the camera was used to prevent underestimation of the crack length. The laser beam melt-run welding used a variable welding speed from 10.0 to 40.0 mm/s, while the gas tungsten arc welding varied the welding speed from 1.67 to 5.00 mm/s. As the welding speed increased from 1.67 to 40.0mm/s, the solidification brittle temperature range of type 310S stainless steel welds was reduced from 146 to 120 K. It follows that employing the laser beam welding process mitigates the solidification cracking susceptibility for type 310S stainless steel welds.

Microstructural Characteristics and Mechanical Properties of Ti6Al4V Alloy Fiber Laser Welds

In this paper an experimental analysis on laser beam welding process of Ti6Al4V titanium alloy was performed. Butt joints with a thickness of 2mm were produced and assessed. A high brightness fiber laser was adopted to carry out the analysis. No filler wire and shaped grooves were used. An experimental plan was implemented keeping constant the laser power and varying the welding speed. A proper device was adopted to prevent oxidation phenomena that involve Ti at high temperatures reached during the thermal process. The geometric characteristics of the welding beads were studied through metallographic inspection of the cross sections. Vickers micro-hardness tests were conducted at the mid thickness of the cross sections of the joints and its variation in function of the distance from the welding line was achieved. Two tensile strength tests for each welding condition were performed in order to evaluate the mechanical properties of the welds. Results revealed a contained extent of the FZ and HAZ in the cross sections. The reduction of mechanical properties of the welds in comparison with those typical of the parent metal was about 20%, which is a good result in comparison with other previous research works.

One-sided laser beam welding of autogenous T-joints for 6013-T4 aluminium alloy

Autogenous T-joints for aluminium skin-stringer component performed by one-sided laser beam welding process was conducted using a high power Yb-fiber laser. The influence of the shielding gas, seam angle, beam focal position, and beam positioning relative to weld centerline were investigated regarding to weld microstructural features. The joint mechanical behavior was evaluated concerning to the sheet rolling directions. It was observed that a precise control of the process parameters enabled to obtain weld beads with acceptable dimensional and geometric characteristics and minimizing weld defects. Helium shielding gas produced higher aspect ratio welds than those with pure argon. Although, pores were observed in the fusion zone, they represented only about 5% of the weld bead area. The optimal beam positioning should remain up to 0.2mm relative to junction line, for seam angles between 10° and 15°. The weld mechanical behavior depended on the sheet rolling direction. Joint efficiency up to 85% were obtained after hoop tensile tests when the weld bead longitudinal-section was perpendicular to skin rolling direction and parallel to the stringer rolling direction.