Laser Welding Process Research Articles

Online Detection of Laser Welding Penetration Depth Based on Multi-Sensor Features.

The accurate online detection of laser welding penetration depth has been a critical problem to which the industry has paid the most attention. Aiming at the laser welding process of TC4 titanium alloy, a multi-sensor monitoring system that obtained the keyhole/molten pool images and laser-induced plasma spectrum was built. The influences of laser power on the keyhole/molten pool morphologies and plasma thermo-mechanical characteristics were investigated. The results showed that there were significant correlations among the variations of the keyhole-molten pool, plasma spectrum, and penetration depth. The image features and spectral features were extracted by image processing and dimension-reduction methods, respectively. Moreover, several penetration depth prediction models based on single-sensor features and multi-sensor features were established. The mean square error of the neural network model built by multi-sensor features was 0.0162, which was smaller than that of the model built by single-sensor features. The established high-precision model provided a theoretical basis for real-time feedback control of the penetration depth in the laser welding process.

In-situ monitoring of Al/Cu dissimilar laser welding process using optical emission spectroscopy (OES)

Aluminum (Al) and copper (Cu) dissimilar laser welding is an in-demand process in the manufacture of secondary battery systems for electric vehicles. However, the absence of a robust in-situ monitoring technique for this process reduces its efficiency and increases the potential risk to the battery system. Laser-induced plasma (LIP) has been extensively studied in various laser processes because it provides crucial information regarding the interaction between the laser beam and material. In this study, the measurement of LIP was conducted using optical emission spectroscopy (OES) during the Al and Cu dissimilar welding process to gain a comprehensive understanding of the process. Moreover, the feasibility of OES as a monitoring tool for dissimilar laser welding of Al and Cu was evaluated. Plasma parameters such as emission line intensity, electron temperature, and number density were effectively used to diagnose the welding state (non-welding, threshold welding, or Cu-penetrated welding). In addition, a strong correlation between the weld geometry and intensity of the Cu emission line was found. This study demonstrates the considerable potential of OES-based in-situ monitoring system applicable for high-demand dissimilar laser welding processes.

Optimization and GRA prediction of Al–Cu pulsed laser welding process based on RSM

In this paper, the process parameters of pulsed laser welding of Al–Cu are studied using response surface methodology (RSM) and grey relation analysis (GRA) to propose optimal directions for lap-shear strength of the joints. A single-factor experiment was conducted to find the suitable process parameter windows. The RSM models were established and analyzed with laser power, welding speed, pulse width, and frequency as inputs and joint lap shear, interfacial weld width, and weld-penetration-depth as outputs. With the use of GRA of interfacial weld width and weld penetration depth with the lap-shear force of joints, the improved direction for the lap-shear force of joints can be proposed.

Laser Beam Welding Parametric Optimization for AZ31B and 6061-T6 Alloys: Residual Stress and Temperature Analysis Using a CCD, GA and ANN

Laser beam welding (LBW) is a technology that efficiently joins materials using a concentrated laser beam, providing advantages such as a small heat-affected zone (HAZ), high precision, adaptability to various materials, and seamless integration into automated processes. Precision in LBW is limited by challenges in selecting appropriate process parameters, performing expensive and risky physical experiments, and dealing with materials with high thermal conductivity and low melting temperatures, such as AZ31B and AA6061. This study aims to predict laser welding process parameters, encompassing beam power (4000W-6000W), spot size (0.4mm-0.8mm), welding speed (30mm/s-50mm/s), and segment number (5-15) utilizing the Response Surface Methodology (RSM), Genetic Algorithm (GA) and backpropagation neural networks. Beam power significantly affects peak temperature, leading to deeper laser penetration and a higher maximum temperature, while the segment number plays a crucial role in residual stress by potentially causing uneven cooling and distinct thermal gradients. The ANN results confirm the model's accuracy and the GA-predicted process parameters include a laser power of 4000W, welding speed of 50mm/s, spot size of 0.6mm, segment number of 15, peak temperature range of 888.9°C to 1020.5°C, and a preferred equivalent stress of 1396.62 MPa.

Numerical simulations and mathematical models in laser welding: a review based on physics and heat source models

The dominant phenomenon in laser welding processes is heat transfer by conduction, making it crucial to gain insights into energy distribution within the heat-affected region, including the melt pool. Thermal analysis enables the description of thermo-mechanical, metallurgical aspects, and also addresses studies related to fluid flow and energy transfer. As research in welding processes has advanced, these models have evolved. This is why it is now efficient to use computational modeling techniques as it allows us to analyze the behavior of laser welding during the process. This underlines the importance of this work which has carried out an exhaustive theoretical literature review with the objective of classifying and describing the numerical simulations of laser welding based on the physics involved. In that sense, the mathematical models and strategies used in laser welding are explored in a general way. Therefore, two types of laser welding by conduction and deep penetration are defined from this point and they are categorized according to the phenomena involved in Model Heat Conduction and Model Integral Multiphysics. This comprehensive review article serves as a valuable resource for higher education students by providing a structured and detailed exploration of laser welding and its mathematical modeling. By classifying and describing numerical simulations based on the physics involved, it offers a framework for students to understand the complexities of this field. Additionally, this innovative approach to organizing and presenting research contributes to educational innovation by facilitating a more efficient and effective learning experience, helping students acquire the knowledge and research skills necessary for advancements in the laser welding domain.

Laser welding of fiber array units.

We report the results of fabricating fiber array unit (FAU) connectors using a near IR laser welding process, locking fibers in proper position on planar glass substrates and forming strong glass-to-glass bonds, followed by final assembly using lower coefficient of thermal expansion (CTE) epoxies. A thin metal film deposited on the glass substrate provides the absorption required to attain interfacial temperatures suitable for glass-to-glass bonding. This method allows the elimination of dedicated expensive V-groove plates while still maintaining very good fiber placement accuracy. The use of epoxy is minimized to simply securing macro packaging components and protecting fibers from environmental pressure, temperature, and humidity variation. The thermal expansion properties of the epoxy used were essential for the long-term FAU reliability.

Quantitative evaluation of keyhole stability during laser welding using optical coherence tomography

Online monitoring of keyhole during laser welding is of great importance to evaluate the stability of the live process and the final quality of the weld. Indirect methods based on visual imaging and thermal radiation are lack of strong correlations with keyhole behavior, resulting in a low accuracy. Optical coherence tomography (OCT) shoots beam coaxially with the processing beam into the bottom of the keyhole, enabling direct monitoring of keyhole behavior. However, current OCT keyhole monitoring systems suffer from the harsh noise and are limited to only evaluating the keyhole depth through statistical analysis. In this paper, an enhanced OCT system was built with a capacity of capturing keyhole open/collapse behavior, opening a way of quantitatively evaluating the keyhole behavior. First, the signal was denoised and filled given the nature of fluid dynamics in time domain. Then an algorithm was developed to automatically detect the keyhole open/collapse behavior, based on which the weld status (heat conduction mode and keyhole mode) is determined, and the metrics of interests are characterized quantitatively. The proposed method provides a solid method to quantitatively evaluate the keyhole stability, which is well suited for developing new laser welding process and monitoring laser involved high volume manufacturing.

Simultaneous reduction in laser welding energy consumption and strength improvement of aluminum alloy joint by addition of trace carbon nanotubes

The widespread use of laser welded aluminum alloys in industrial production offers potential benefits to sustainable development and socio-economic progress. It simultaneously enhances the weld strength while reduces the energy consumption. Despite the promise of these alloys, research on reducing their energy consumption during laser welding is lacking. In this study, a dual effect of enhancing joint strength in 2A12 aluminum alloy and reducing energy consumption is achieved by the addition of trace carbon nanotubes (CNTs). The “welding efficiency" is defined and an energy consumption model for laser welding of aluminum alloys is developed. Next, the laser welding process with the addition of trace CNTs (LC) and the single laser welding process (LW) were compared and analyzed. The results indicate that adding trace CNTs can reduce energy consumption by more than 33 % and increase joint strength by 101 MPa. Furthermore, it is found that the LC process offers significant energy-saving advantages over other laser welding of aluminum alloy processes described in previous studies. These improvements is attributed to the increased laser absorption by the aluminum alloy induced by trace CNTs, as well as their residual presence in the joint, which acts as a strengthening medium. This work provides new insights and presents a novel approach for achieving low-carbon, high-quality welding of aluminum alloys.

In Situ Synchrotron Investigations of Beam Diameter Influence on Vapor Capillary Formation during Laser Beam Welding of Copper Alloy with a Blue Laser Beam Source

Laser beam welding as a reliable tool for high-precision joining of batteries or microelectronics is more and more the choice for achieving reproducible results in production processes. In addition to a high automation capability, the precise control of the energy deposition into the material plays an important role, especially when highly reflective materials, such as copper or aluminum, must be welded together. Alongside the use of highly brilliant fiber lasers in the near-infrared range with a focal diameter of a few tens of micrometers, diode lasers in the wavelength range of 445 nm are increasingly being used. Here, beam diameters of a few hundred micrometers can be achieved. With a wavelength of 445 nm, the absorptivity in copper can be increased by more than a factor of 10 compared to a near-infrared laser beam sources in solid state at room temperature. This paper presents the in situ X-ray observation of laser welding processes on CuSn6 with a laser beam source with a wavelength of 445 nm using synchrotron radiation at DESY Petra III Beamline P07 EH4 in Hamburg, Germany. For the experiments, the laser radiation was focused via two separate optics to focal diameters of 362 µm and 609 µm. To characterize the dynamics of the vapor capillaries depending on the different focal diameters dF, the parameters were varied with respect to laser power PL and feed rate v. For the investigations, a synchrotron beam of 2 × 2 mm2 in size with a photon energy of 89 keV was used, and the material samples were analyzed by means of phase-contrast videography to show the boundaries between solid, liquid, and gaseous material phases. The results of this paper show the welding depths achieved and how the geometry of the vapor capillary behaves by changing the focal diameter, laser power and feed rate.

A Study on Mechanical/Metallurgical Characteristic of Welded Joints According to Heat Input and Gap in Al/Cu Laser Welding

The electrical connectivity and tensile strength between battery components are crucial factors for enhancing battery performance in electric vehicles. In this study, the welding characteristics of aluminum-copper welded joints manufactured using the multi-core laser welding process were studied according to the output power of core/ring laser. Moreover, the tensile strength change behavior according to various welding processes, such as single/two-line welding, and welding gap distance were measured. The results revealed that increasing the output power of the ring beam led to an increase in the tensile strength. However, excessive laser power would increase convection between aluminum and copper during welding and cause defects owing to the difference in the solidification temperature between the two materials. In addition, the mechanical properties were improved by increasing the distance between the two lines of straight laser welding. As the spacing increased, the fraction of the equiaxed microstructure increased, and grain growth was suppressed to improve mechanical properties.

Effects of laser welding on the martensitic transformation of a shape-memory Ti-Ni alloy

The objective of this study is to investigate the martensitic transformation behavior of a Ti-Ni alloy subjected to a laser welding process. Materials characterization techniques were used to analyze the influences of this welding procedure on the phase transformation behavior. This study can provide valuable insights for the improvement of Ti-Ni alloy welding processes used for technological applications, such as in the aerospace industry. In this study, samples were prepared under three conditions: thermal treatment at 400°C, thermal treatment at 500°C, and as-received. The characterization techniques used were: Optical Microscopy (OM), Differential Scanning Calorimetry (DSC), Electron Dispersion Spectroscopy (EDS), X-Ray Diffraction (XRD), and Vickers Microhardness (HV). The results allow for analysis of thermoelastic martensitic transformation and variations in the compositions of the alloy elements. The research, in general, aims to repurpose welding waste in Ti-Ni alloys for the production of mini sensors. The enthalpy was higher for the alloy treated at 500°C and welded. The research findings led to the observation of martensitic phase transformation in the laser-welded Ti-Ni alloy, which suggests that it can be used as a sensor/actuator.

Heat source models for numerical simulation of laser welding processes – a short review

In recent decades, numerical modeling and computer simulation have become an integral part of the design, analysis and optimization of fusion welding processes, including laser welding. In general, laser welding processes involve the interaction of multiple physical phenomena, such as thermal, fluid, metallurgical, chemical, mechanical, and diffusion effects, which makes the development of a simulation model difficult and complex. In addition to the geometric characteristics of the parts to be welded, their material properties must be specified in a wide temperature range, as well as the conditions for heat removal to the environment or shielding gas. One of the most complex tasks in the preparation of a simulation model of the laser welding processes consists in the selection of an appropriate heat source model to accurately determine the heat input to the weld. Very important is also the process of experimental verification and validation of the developed simulation models. In this paper, a short examination of significant mathematical heat source models for numerical simulation of laser welding is provided. Numerical analysis of laser welding of sheets made of S650MC steel is accomplished using conical 3D heat source model with the support of the ANSYS code. The effect of geometrical characteristics of the conical volumetric heat source model on the computed width, length, and depth of the weld pool is discussed, along with evaluation of maximum weld pool temperature.

Multi-objective optimization of laser welding process parameters of steel/Al based on BO-RF and MOJS

Multi-objective optimization of laser welding process parameters of steel/Al based on BO-RF and MOJS

Reflection behaviour of SH0 from small defects in thin sheets, with application to EMAT inspection of titanium

ABSTRACT Defects can arise within the weld during the laser welding process of thin titanium sheets, and it is critical that these defects are detected. Shear horizontal (SH) waves offer good potential for defect detection, but require an understanding of how the ultrasonic waves interact with defects, in order to develop an optimised inspection setup, increasing the probability of defect detection. The geometry of a defect strongly affects the reflected signal magnitude, with finite element simulations showing that defect width and length determine the maximum SH0 wave reflection. Experiments confirm this behaviour. The defect width is shown to affect the reflection behaviour due to wave interference. Phase differences between the front face reflection and back face reflection cause a shift in the peak position. In addition, the experimental work presented in this paper also shows the potential for electromagnetic acoustic transducers to be used for the inspection of titanium components.

Al4C3 formation and joint tensile properties of dual-beam laser butt welding SiCp/6005A composite with filler wires

SiC-reinforced aluminum metal matrix composite (SiC/Al MMC) is one of the most promising structural materials that provide excellent specific modulus and weight reduction for industrial applications. When fusion welding of SiC-reinforced Al MMC, however, mechanical properties of SiC/Al MMC were significantly deteriorated due to the formation of brittle Al4C3. In this paper, a dual-beam laser welding process was developed to laser weld SiCp/6005A Al composite with ER4043 and ER5356 filler wires. The morphology, microstructure, tensile properties, and fracture behaviors of the welded joints were investigated. Compared to ER5356 filler wire, the weld quality was improved by ER4043, including better surface quality, fewer weld defects, higher tensile strength and better ductility. By introducing the silicon element of ER4043 filler wire into the molten pool, the size and amount of brittle Al4C3 compounds and the porosities were reduced and the reaction between liquid Al and reinforced SiC particles was suppressed to some extent. Furthermore, the dual laser beam energy ratio was optimized to 90%:10% (90/10), the tensile strength of the joints produced with ER4043 was significantly improved to 209 MPa, reaching 70% of the ultimate strength of the base metal.

Machine vision-based automatic focusing method for robot laser welding system

Background Defocus distance is a critical parameter in laser welding, especially when encountering changes in the contour of the welding surface. This paper proposed an automated focusing method to address the challenging issue of accurately adjusting the defocus distance. Methods The proposed method involves several steps. Firstly, a clarity evaluation function based on the Kirsch operator is employed to calculate real-time image clarity of the welding surface captured by the machine vision system. Next, an improved Canny edge detection algorithm is applied to identify the edge contours of the welding surface, from which their central points are extracted. Finally, automatic focusing is achieved by employing a variable step-size hill-climbing algorithm to search for the focal plane. Results To verify the applicability of the automatic focusing method proposed for welding the solder ring, a robot laser welding system was designed and constructed. Experimental results show that the positioning error of the robot after automatic focusing is within ±0.4 mm. The average time required for a single automatic focusing process is 16.27 s. These results demonstrated the successful accomplishment of automatic adjustment and control of the focal length. Conclusions The machine vision-based automatic focusing method proposed in this paper enhances the consistency of the robot’s position after automatic focusing in robot laser welding systems. It elevates the level of automation in the welding process and provides an efficient solution for accurately adjusting the welding focal distance during the laser welding process.

Combined experimental and theoretical approach to improve measurement accuracy of temperature-dependent reflectance of copper for near-infrared lasers

AbstractThe low process stability of laser welding of copper with near-infrared lasers requires precise input data for process control and meaningful simulations. But meanwhile, available datasets of temperature-dependent reflectance or absorptance for near-infrared lasers on copper do not show good agreement between the different sources and often do not include the fusion process, which is of crucial importance for realistic laser welding simulations. Additionally, most of the datasets are only calculated. Therefore, in a previous study, temperature-dependent reflectance measurements were performed on electro tough-pitch copper using a near-infrared laser. The measurements revealed a reflectance drift, which was induced by the setup behavior during heating, and the time-dependence of chemical reactions like the redox-reaction as possible error sources. In this study, experiments on laser melting as the fundamental process of laser welding were performed, together with corresponding simulations using the measured reflectance values for oxide-reduced and for untreated copper from the previous study. Then, the simulations were compared with the experiments to estimate the accuracy of the reflectance measurements. To provide context, the same simulations were also conducted using reflectance datasets from other authors. In a second step, the reflectance data were corrected with respect to the reflectance drift and the effects of redox reactions were adapted to the conditions of the laser melting experiments. Using the resulting reflectance curves, an improved agreement of simulation results and the experiments was achieved over a range of different test cases, without the necessity of correction factors in the simulation model.

Investigating laser intensity profile and light scattering effects in the transmission laser welding process of 3D printed parts

Transmission Laser Welding (TLW) is a promising technique for joining thermoplastic and composite components, especially those produced through additive manufacturing or 3D printing processes. However, achieving optimal welding quality and efficiency in TLW of 3D printed parts is challenging due to the presence of highly heterogeneous and anisotropic materials, which introduce light scattering and absorption issues. Light scattering is caused by the refraction phenomenon. These phenomena significantly impact the laser intensity profile within the materials and at the welding interface, thereby affecting the energy required for successful welding and the mechanical strength of the final assembly. In this paper, we present an in-depth investigation into the laser intensity profile and the effects of laser-matter interaction on the welding of 3D-printed parts. Our approach combines experimental measurements using a heat flux sensor and an analytical inverse model to measure the laser intensity distribution within the materials at the welding interface. The results obtained from the experimental measurements and numerical identification are compared and analyzed, providing insights into the laser intensity profile in TLW of 3D printed parts.

Improving the weld seam quality in laser welding processes by means of Bayesian optimization

The determination of appropriate process parameters is crucial for the development of laser welding processes. This usually requires extensive and time-consuming experimentation combined with expert knowledge. To reduce the number of experiments required to determine appropriate process parameters, Bayesian optimization was used in this work. Bead on plate laser welding of AA5754 samples was performed while optimizing the laser power, the welding speed, the focus position and the power distribution in the core-ring fiber laser system with the objective of achieving welds with a specific weld depth and low number of defects at high welding speeds. The welds were evaluated using X-ray imaging and height measurements. A cost function was developed to quantify the overall weld quality based on the weld properties. It is demonstrated that the Bayesian optimizer can determine appropriate process parameters for the given objective, based on a cost function, within a comparatively small number of 29 experiments.

Experimental analysis of the effect of ultrasonic vibration on porosity suppression in narrow gap laser welding

Abstract The welding process has a wide range of applications in aerospace, military manufacturing, machinery, and other fields, and with the continuous improvement of welding technology requirements, the inhibition of porosity in the welding process is also increasing. This study, through the narrow gap laser welding characteristics and porosity formation mechanism of the depth of analysis, for the existing narrow gap laser welding method exists in the side wall of the weld fusion is poor porosity, poor uniformity of organizational properties and other issues, proposed ultrasonic-based welding method to achieve effective inhibition of porosity. The experimental analysis of ultrasonic vibration on the formation of porosity is carried out based on narrow-gap laser welding. The peak sound pressure of narrow gap welding increases when the ultrasonic current amplitude changes from 24A to 32A. Under different ultrasonic vibration conditions, the number of welds without applied ultrasound was as high as 95, while the number of porosities gradually decreased to 48 with the increase of applied ultrasound amplitude from 12% to 37%. Furthermore, as the ultrasonic amplitude increased, the residual height decreased by 0.45 ml. In addition, at fixed ultrasonic amplitude, with the increase of laser power, the porosity increased from 0.89% to 2.21%, and the average diameter of the porosity increased from 0.29 mm to 0.43 mm. The porosity for the porosity diameter of less than 200 μm was reduced to 0.020%. The percentage of stomata with a diameter greater than or equal to 200μm increased to 2.098%. This study analyzes the inhibition effect of ultrasonic vibration on porosity to a certain extent. Moreover, the inhibition effect of ultrasonic vibration in narrow gap laser welding is significant and the smaller the laser power under the same amplitude, the better the inhibition effect, which provides a valuable reference for the research of the narrow gap laser welding process.