Laser Welding Process Research Articles

Unveiling mechanisms and onset threshold of humping in high-speed laser welding

The fabrication of fuel cells relies on a rapid laser welding process. However, challenges arise with the occurrence of humping when the welding speed surpasses a critical threshold, which poses difficulties in achieving a smooth surface finish and a consistent weld strength. This study aims to elucidate the humping mechanisms by analyzing the morphology of molten pool and the characteristics of melt flow at varying welding speeds via in situ synchrotron high-speed X-ray imaging and computational fluid dynamics simulations. Our findings indicate that the short keyhole rear wall, the high backward melt velocity, and the prolonged tail of molten pool are the primary factors contributing to the onset of humping. Furthermore, a dimensionless humping index (πh\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\pi }_{h}$$\\end{document}) was introduced, which successfully captured the onset threshold of humping across different literatures. This index not only provides a quantitative description of the humping formation tendency but also serves as a valuable tool for optimizing the laser welding process.

Repair of Injection Moulds by Welding for Pre-Hardened 1.2714 Hh Steel

The welding of injection molds by laser deposition is a very common procedure in recent years in the maintenance departments of plastic injection factories. This is due to the advantages it has compared to traditional welding methods, namely the speed of the laser welding process, a lower deposition of the metal composition in the repaired area (small volume of deposited material), as well as the accuracy of the deposition on the surface the piece. But, in addition to these advantages, there are also a number of disadvantages compared to classic welding. As the main disadvantage in the case of laser welding of injection molds, the maximum weldable thickness is limited. This paper presents an analysis of weld quality and mechanical fracture of laser deposition according to deposition types and welding techniques of 1.2714 HH pre-hardened steel. The material 1.2714 HH is a basic material used in recent years in the production of molds due to its hardness, namely 40-45 HRC units. In laser welding, different welding strings are possible, each influencing the laser deposition preparation process, the possibility of performing the deposition in the respective area, as well as obtaining a desired mechanical stability. Starting from these considerations, a number of factors will be analyzed using 1.2714HH steel samples: welding strings, welding strings depth, filler material and welding parameters. V – notches were made and filled for welded samples with laser welding deposits. V – notches were made and filled for welded samples with laser welding deposits.

Enhancement of joint quality for laser welded dissimilar material cell-to-busbar joints using meta model-based multi-objective optimization

In the battery pack assembly, it is essential to ensure that the cell-to-busbar joints can be produced with high quality and with minimal impact on the individual battery cells. This study examines the influence of process parameters on the joint quality for nickel-plated copper and steel plates, laser welded in an overlap configuration. Artificial neural network-based meta models, trained on numerical results from computational fluid dynamics simulations of the laser welding process, are used to predict and evaluate the joint quality. A set of optimized process parameters is identified, in order to simultaneously maximize the interface width for the joints, and minimize the formation of undercuts and in-process temperatures. In an meta model-based multi-objective optimization approach, the non-dominated sorting genetic algorithm II (NSGA-II) is used to efficiently search for trade-off solutions and the meta models are used for objective approximation. As a result, the objective evaluation time is decreased from around 9 h, when evaluated directly from numerical simulations, to only tenths of a second. From the Pareto-optimal front of trade-off solutions, three optimal solutions are selected for validation. The selected solutions are validated through laser welding experiments and numerical simulations, resulting in joints with large interface widths and low in-process temperatures without a full penetration.

Investigation on metal vapor characteristics and keyhole/melt pool dynamics in high-power laser welding with side gas flow

High-power laser welding processes involve intense interactions between the laser beam and the base material, resulting in severe welding defects such as humping, spattering, and undercutting. Utilizing side gas flow may provide an effective approach for minimizing these defects. However, the effects of side gas flow on the dynamic behavior and weld formation necessitate further investigation. In this study, an innovative analysis of metal vapor characteristics and keyhole/melt pool dynamics in high-power laser welding with side gas flow is presented, combining experimental and simulation results. A three-dimensional transient fluid flow model was developed, uniquely integrating an adaptive heat source, evaporation-condensation processes, and metal vapor energy attenuation to provide a novel perspective on the effects of side gas flow in high-power laser welding. The results display that side gas flow could suppress plasma, increase thermal input to the melt pool, and intensify the flow of liquid metal toward the pool bottom during high power laser welding, thereby enhancing weld seam penetration. The numerical results indicate that variations in flow rate significantly impact metal vapor morphology, with higher flow rates reducing both the average area and height of the metal vapor and effectively suppressing the size of metal vapor/plasma. When the side gas flow rate is 20 l/min, with the gas flow impact point located at the keyhole opening and the nozzle height set to 3 mm, the side gas flow significantly enhances the depth-to-width ratio of the weld seam in 316L stainless steel laser welding. This work can provide guidance for suppression of weld defects in high-power laser welding of medium-thick steel components, which has important theoretical significance and application value.

Mechanical and Microstructural Characterization of Class 800 Complex Phase Steel before and after the Laser Welding Process

Complex phase steels, known for their high levels of conformability, energy absorption, and deformation capacity, are among the more advanced high-strength steels. The objective of this study was to compare the mechanical properties of CPW 800-class complex phase steels, with and without laser welding. The analysis involved determining tensile strength, yield strength, elongation, and area reduction through tensile tests, in scenarios both with and without laser welding. Additionally, the number of cycles was assessed via fatigue tests, and absorbed energy was measured using impact tests. The non-parametric Kruskal–Wallis test, at a 5% significance level, revealed that tensile strength, yield strength, area reduction, and absorbed energy were statistically similar regardless of laser welding. However, elongation and the number of cycles showed significant differences. The fractured surface from axial fatigue tests exhibited ductile characteristics, with the additional presence of dimples or alveoli.

Industrial picosecond pulse laser welding of stainless-steel to quartz for optical applications

We report on the development of a robust picosecond laser welding process for the industrially relevant material combination of quartz and stainless steel. The process requires high numerical aperture focusing of a 6 ps 1030 nm laser through the transparent quartz onto the interface between the two materials. It is found that increased mechanical pressure applied during welding increases reliability and weld performance and with the correct choice of welding parameters parts will survive ISO standard thermal cycling and vibration testing demonstrating the suitability of the process for industrial application.

Study on the Effect of Focusing Parameters of Ultrashort Pulses on the Process of Laser Welding of Transparent Materials with Metals

Study on the Effect of Focusing Parameters of Ultrashort Pulses on the Process of Laser Welding of Transparent Materials with Metals

Enhancing of low-temperature deformation compatibility of pure titanium welded tube by laser welding and cold-worked in welded zone

This study is aimed to improve the low-temperature deformation behaviour of titanium heat exchange tubes by optimizing welding method and weld treatment processes. The various welding processes and cold-worked in welded zone process are adopted, and the effects of macro-morphology, microstructure and mechanical properties on low-temperature deformation behaviour are studied. The results show that the width of the laser welded joint and welded zone is 3.8 mm and 2.9 mm respectively, which is 40% and 63% of TIG welded joint. Especially, the width of heat affected zone and the grain size of laser welded joint are obviously reduced due to its concentrated energy density. The cold-worked process in welded zone can relieve the macroscopical and microstructural discontinuity between base metal, heat affected zone and welded zone. The inner weld reinforcement is eliminated to improve smooth transition and the columnar α grains in welded zone are remarkable fragmented with plenty of twins. The hardness of the welded zone after cold-worked is significantly higher than that of the base metal, resulting in base metal being the main deformation area of the welded tube at low temperature, which is beneficial to improve the deformation performance of the whole welded tube. By adapting the cold-worked and laser welding process with smooth transition and narrower weld width, the pure titanium welded tube can meet the requirement of three times low-temperature deformations.

Multi-scale three-dimensional simulation of the solidification microstructure evolution in laser welding of aluminum alloys under dynamic spatial thermal cycling

Laser welding process involves three-dimensional (3D) highly dynamic spatial thermal cycling that results in intricate microstructure evolution in different zones. Understanding of the 3D topological evolution of microstructure under spatial thermal cycling is crucial for effective control in solidification processes. In this paper, a 3D multiphase-field model combined with accelerated methods and multi-scale coupling algorithms was developed for high-precision prediction of the dynamic microstructure evolution in laser welding. The heat flow distribution during laser welding varied significantly, with the cooling rates of 1.7–1.9 × 104 K/s at the middle region and 7.5–9.0 × 104 K/s at the bottom region. Considering the effects of 3D heat flow, a large angle may appear between the grains' primary growth direction and the cross-sectional plane, thereby the ultimate morphology through 2D analysis may lead to distortion from reality. The simulation of 3D microstructure evolution during distinct regions results showed that the grains at the bottom region exhibited larger characteristic dimensions (Length/Height >2.5, Length/Width >2.0) and columnar shape, while the middle region tended to form equiaxed structures. The grain size statistics revealed that the grains in the middle region exhibited larger scale due to their smaller GR (G: temperature gradient, R: growth rate) values. The simulation results were in good agreement with the electro-back-scattered diffraction testing results and the theoretical analysis.

Welding Characteristics of Medium Titanium Plates with Autogenous Laser Welding and Narrow-Gap Laser Filling Welding Modes.

Titanium and titanium alloys with a medium thickness of 5 to 12 mm are widely used for ocean platforms, military equipment and in other fields because of their light weight, appropriate strength and corrosion resistance. In this study, autogenous laser welding and narrow-gap laser welding processes were researched and compared, and the welding characteristics, weld microstructure and joint strength were analyzed. The results showed that autogenous laser welding had higher efficiency, narrower weld width and higher microstructure uniformity. Autogenous laser welding can achieve the single pass weld penetration at laser keyhole mode. The weld width of narrow-gap laser welded joint was 12.5 mm, which was nearly three times than that of autogenous laser welding. The grain size of autogenous laser welding was obviously smaller and more uniform in depth than that of narrow-gap laser welding. In the weld zone, the coarse columnar α grains grew from the fusion line, while in the heat-affected zone, equiaxed α grains with needle and sawtooth α morphologies were presented. The microhardness of the heat-affected zone was higher than in the weld zone and the base metal due to the denser needle microstructure. The tensile samples all fractured at the base metal, indicating the welded joint strength efficiency was greater than 1.

Penetration State Recognition during Laser Welding Process Control Based on Two-Stage Temporal Convolutional Networks.

Vision-based laser penetration control has become an important research area in the field of welding quality control. Due to the complexity and large number of parameters in the monitoring model, control of the welding process based on deep learning and the reliance on long-term information for penetration identification are challenges. In this study, a penetration recognition method based on a two-stage temporal convolutional network is proposed to realize the online process control of laser welding. In this paper, a coaxial vision welding monitoring system is built. A lightweight segmentation model, based on channel pruning, is proposed to extract the key features of the molten pool and the keyhole from the clear molten pool keyhole image. Using these molten pool and keyhole features, a temporal convolutional network based on attention mechanism is established. The recognition method can effectively predict the laser welding penetration state, which depends on long-term information. In addition, the penetration identification experiment and closed-loop control experiment of unequal thickness plates are designed. The proposed method in this study has an accuracy of 98.96% and an average inference speed of 20.4 ms. The experimental results demonstrate that the proposed method exhibits significant performance in recognizing the penetration state from long sequences of welding image signals, adjusting welding power, and stabilizing welding quality.

Study on Laser Transmission Welding Technology of TC4 Titanium Alloy and High-Borosilicate Glass.

As the demand for high-performance dissimilar material joining continues to increase in fields such as aerospace, biomedical engineering, and electronics, the welding technology of dissimilar materials has become a focus of research. However, due to the differences in material properties, particularly in the welding between metals and non-metals, numerous challenges arise. The formation and quality of the weld seam are strongly influenced by laser process parameters. In this study, successful welding of high-borosilicate glass to a TC4 titanium alloy, which was treated with high-temperature oxidation, was achieved using a millisecond pulsed laser. A series of process parameter comparison experiments were designed, and the laser welding behavior of the titanium alloy and glass under different process parameters was investigated using scanning electron microscopy (SEM) and a universal testing machine as the primary analysis and testing equipment. The results revealed that changes in process parameters significantly affect the energy input and accumulation during the welding process. The maximum joint strength of 60.67 N was obtained at a laser power of 180 W, a welding speed of 3 mm/s, a defocus distance of 0 mm, and a frequency of 10 Hz. Under the action of the laser, the two materials mixed and penetrated into the molten pool, thus achieving a connection. A phase, Ti5Si3, was detected at the fracture site, indicating that both mechanical bonding and chemical bonding reactions occurred between the high-borosilicate glass and the TC4 titanium alloy during the laser welding process.

The Impact of Welding Parameters on the Welding Strength of High Borosilicate Glass and Aluminum Alloy

This study adopts a new surface pretreatment method, Laser Surface Remelting (LSR). This experiment aims to establish a set of laser welding process parameters suitable for aluminum alloy and glass under this specific pretreatment. This experiment explores the impact of laser welding parameters on the welding strength between high borosilicate glass and aluminum alloy. The study specifically investigates the effects of four process parameters: defocus amount, laser power, frequency, and pulse width on the welding outcome. The results indicate that the welding quality between the aluminum alloy and glass reaches its optimum when the defocus amount is zero (i.e., when the laser converges at the interface between the glass and the metal) and the laser welding parameters are set to a power of 250 W, a welding speed of 1 mm/s, a welding frequency of 10 Hz, and a pulse width of 2.5 ms. The experiment also analyzes the fracture morphology under different parameters, summarizing the locations and causes of fractures, and establishing the relationship between the fracture location and the welding strength.

Effect of laser welding parameters on the microstructure and tensile properties of low-alloy high-strength steel

Abstract The studying employed orthogonal experimental approach to optimize the laser welding process parameters for HC420LA low-alloy high-strength steel. Through metallographic analysis, microhardness testing, and tensile testing, the study assessed and contrasted the properties of laser-welded and arc-welded joints. The findings revealed that the most optimal laser welding conditions were 1.8 kW laser power, 2.5 m min−1 welding speed, and a focus distance of 1.5 mm, resulting in a well-formed ‘X’ shaped weld bead. Comparative analysis demonstrated that the laser-welded joint exhibited a finer microstructure, primarily composed of bainite and ferrite, whereas the arc-welded joint consisted of ferrite and martensite. Notably, the laser-welded joint exhibited superior mechanical properties, including increased microhardness and tensile strength, underscoring the distinct advantage of laser welding technology in high-strength steel welding, particularly in enhancing the weld joint’s quality and performance.

Detection of Hot Cracking for 6000 Series Aluminum Alloys using a Multi-Sensor Based Deep Learning Model

This study developed a monitoring technology using a multi-sensor based deep learning model to diagnose hot cracking in aluminum alloy laser welding. Hot cracking that occurs during the laser welding process of aluminum alloys is difficult to diagnose accurately with a single sensor signal, necessitating multi-sensor based process monitoring technology. To monitor these hot cracks, laser-induced plasma, acoustic, and elastic wave signals were simultaneously measured using a spectrometer, non-contact acoustic sensor, and contact acoustic sensor during the overlap laser welding process of 6000 series aluminum alloys. The welded specimens were classified into normal and cracked specimens through bead analysis, and features related to hot cracking were extracted from each sensor signal to utilize the measured multi-sensor signals for monitoring. The extracted features from each signal were used as inputs for a Deep Neural Network (DNN) model capable of learning complex nonlinear relationships, and the hyperparameters of the DNN model were optimized using a genetic algorithm. The DNN model trained with multi-sensor data diagnosed hot cracking with an accuracy of 93.75%.

Machine learning-based in-process monitoring for laser deep penetration welding: A survey

In-process monitoring (IPM) of laser deep penetration welding (LDPW) has witnessed a rapid growth in approaches that embrace machine learning algorithms, utilizing raw sensor input to generate various weld quality evaluations, instead of concentrating on thermomechanical modeling that is hypotheses-driven and hence biased by it. Benefitting from the capability to unravel hidden interactions in the complex laser welding process, numerous data-driven IPM methods have been proposed to address different problems in this area. In this survey, we present a comprehensive analysis of both classical and recent studies, covering the unique physical mechanisms, sensing techniques, methodologies, strengths, and limitations of machine learning-based IPM-LDPW systems. We delve into several critical tasks, including mechanical performance prediction, weld penetration estimation, and weld defects detection. Meanwhile, we explore the latest developments in deep learning and how to incorporate these techniques into IPM systems for LDPW. To inspire future research, we outline unresolved challenges and explore potential opportunities and new perspectives for addressing these challenges.

Gap bridging in laser welding of EN AW 5083 with different joint configurations via beam oscillation and filler wire

The extended use of laser welding in the industry requires a less sensitive process in terms of geometrical tolerances of the joint edges. As the industrial availability of laser systems increases, the demand to use laser welding technology possibly with parts coming from less precise production steps is increasing. Gap formation is often caused by the edge quality of the parts coming from previous manufacturing steps such as sheet forming. Al alloy sheets deformed to box-shaped 3D forms often require welded joints on the edges in lap, but, and corner joint configurations. These joints are hard to carry out by laser welding due to the large gap formation caused by the tolerances of the deformation processes involved. Laser welding of Al alloys is already challenging in the absence of gap formation, while these joint configurations have been not feasible with a stationary beam due to incomplete fusion and defect formation. Laser welding with beam oscillation and wire feeding can improve the weldability of these joints. The oscillating motion of the high-intensity beam can achieve a deep weld together with a wider seam. Combined with wire feeding, the process can close gaps in the butt, lap, and corner joint configurations. On the other hand, the added oscillation and wire-related parameters require extending the experimental space, which requires a methodological study to identify feasible conditions. Accordingly, this work proposes a methodological approach to identify and set laser welding process parameters with beam oscillation and wire feeding for an EN AW 5083. Process parameters were initially studied using a simple analytical model that depicts the beam trajectory. Bead-on-plate tests were conducted to assess beam size, power, and weld speed ranges. Lap, butt, and corner joint conditions with a 0.5-mm gap were welded with high quality by manipulating the laser power, oscillation amplitude, and wire feed rate. The results show that welding speeds could be maintained as high as 55 mm/s with complete filling of gaps of up to 0.5 mm, eliminating the surface undercuts and achieving weld widths in the order of 2.5 mm. Moreover the results show the possibility control the depth of the welds from 3 mm to full-penetration conditions.

Finite element simulation and experimental validation of thermal damage to isolated porcine skin tissue by femtosecond laser welding.

The welding effect of the laser on skin tissue is reduced by thermal damage to skin tissue, and greater thermal damage to skin tissue caused by the laser is prevented by predicting thermal damage. In this paper, a finite element model is established for the temperature field of skin tissue scanned by a femtosecond laser to obtain the influence of laser process parameters and scanning path on the thermal damage parameters of skin tissue and the thermal damage area, and verified experimentally. The results show that the established finite element model is accurate and can accurately reflect the temperature distribution during the process of femtosecond laser welding of porcine skin tissues; used to predict the thermal damage parameters of the skin tissues and the thermal damage area; and provide guidance for the study of the femtosecond laser welding of the skin tissues process to obtain the optimal process parameters.

The change of the absorptance at the transition from partial- to full-penetration laser welding

Full-penetration laser welding processes are necessarily associated with significant changes of the geometrical properties of the keyhole at the beginning of the process when the keyhole expands all the way through the workpiece and finally pierces the bottom of the sheet. The impact that this transition has on the absorptance was investigated by means of X-ray imaging to determine the geometry of the keyhole and subsequent raytracing to calculate the distribution of the absorbed irradiance. The results show a significant drop of the overall absorptance when the bottom of the capillary opens through the rear side of the workpiece which in practice is noticed by an unstable behavior of the keyhole. Since the drop of the absorptance is less pronounced for smaller diameters of the keyhole, one may recommend the application of laser beams with small diameters at least during the initial phase until the keyhole is fully developed and reliably reaches through the bottom surface of the welded sheet.

Monitoring of the Weld Pool, Keyhole Morphology and Material Penetration State in Near-Infrared and Blue Composite Laser Welding of Magnesium Alloy

The laser welding of magnesium alloys presents challenges attributed to their low laser-absorbing efficiency, resulting in instabilities during the welding process and substandard welding quality. Furthermore, the complexity of signals during laser welding processes makes it difficult to accurately monitor the molten state of magnesium alloys. In this study, magnesium alloys were welded using near-infrared and blue lasers. By varying the power of the near-infrared laser, the energy absorption pattern of magnesium alloys toward the composite laser was investigated. The U-Net model was employed for the segmentation of welding images to accurately extract the features of the melt pool and keyhole. Subsequently, the penetrating states were predicted using the convolutional neural network (CNN), and the novel approach employing Local Binary Pattern (LBP) features + a backpropagation (BP) neural network was applied for comparison. The extracted images achieved MPA and MIoU values of 89.54% and 81.81%, and the prediction accuracy of the model can reach up to 100%. The applicability of the two monitoring approaches in different scenarios was discussed, providing guidance for the quality of magnesium welding.