Laser Welding Process Research Articles

Cell teardown and characterization of an automotive prismatic LFP battery

A key challenge in lithium-ion battery research is the need for more transparency regarding the cell design and production processes of battery as well as vehicle manufacturers. This study comprehensively benchmarks a prismatic hardcase LFP cell that was dismounted from a state-of-the-art Tesla Model 3 (Standard Range). The process steps and manufacturing peculiarities were traced by disassembling the cell and analyzing the characteristics on the material level. A butterfly-design with two jelly rolls was found for the cell design in order to minimize the void volume (6.4%). Cross-sections and microscopy analyses from the cell cap revealed the application of multiple laser-welding processes that are needed to provide a high stability and tightness. The coatings of the approximately 22m long electrodes showed a high homogeneity with thickness fluctuations less than 2µm. Scanning electron microscopy images revealed a pure graphite anode and a bimodal particle distribution within the lithium iron phosphate cathode, whereby the edges of the cathode were covered in a 27µm thick aluminum oxide (Al2O3) insulation layer. Electrochemical analyses were performed showing the improved performance of the inherent electrolyte over a common LP572 electrolyte. A gravimetric energy density of 163Wh/kg and a volumetric energy density of 366Wh/l was determined based on a nominal cell capacity of 161.5Ah. Overall, the purpose of this work is to demonstrate which design decisions and manufacturing challenges are addressed in industrial cell production, so that the focus of academic research can align with the state-of-the-art.

Effects of laser power on the microstructural evolution and mechanical performance in laser dissimilar welding of TC4 to SiCp/6092Al composite

In this study, an overlap configuration for Ti6Al4V alloy (TC4) and SiC particle reinforced aluminum matrix composites (AMC) was achieved by laser welding process. The influence of laser power on the microstructural evolution, intermetallic compounds formation and mechanical properties of TC4/AMC joints were investigated. The presence of reinforced phase SiC complicated the metallurgical reaction in the molten pool, resulting in the formation of intermetallic compounds, such as Al4C3, TiC, TiAl, and TiAl3. The influence of laser power was more pronounced on the penetration depth compared to its impact on the weld width. The thickness of TiAl intermetallic compounds at the TC4/AMC interface increased as the laser power was raised. Abundant dislocations existed surrounding the TiAl3 phase because of the different thermal-mechanical properties between Al matrix and TiAl3 phase. The tensile shear force of TC4/AMC joints can be considerably improved by reducing the thickness of the TiAl3 phase. The maximum tensile shear force of 1675.6 N for the TC4/AMC joint was obtained at a laser power of 1500 W when the thickness of the TiAl3 layer reached the lowest value of 7.1 μm. The research results have the potential to improve laser welding techniques for TC4/AMC hybrid structures and provide valuable guidance for the design of TC4/AMC welded joints in the future.

Effect of Laser Welding Parameters with Different Fillers on Solidification Cracking and Mechanical Properties of AA7075

AA7075 is considered a ‘non-weldable’ alloy using fusion welding methods. In this study, laser welding is applied in pulse mode to weld 2 mm thick AA7075 aluminum alloy plates using different fillers. The aim is to identify the influence of welding parameters and fillers on solidification cracking susceptibility during laser welding using the circular patch test (CPT). X-ray radiography was used to detect and measure cracks in the CPT samples. Furthermore, the effects of the laser welding process and chemical composition of fillers on the accumulated crack length (CCL), microstructure, and mechanical properties were investigated. Moreover, the mechanical behavior and local deformation of the fusion zone (FZ) were investigated using micro-flat tensile tests with digital image correlation. The mechanical properties of the FZ were correlated with the CCL as well as with the microstructure of the FZ, which was investigated experimentally. The results show that the chemical composition of fillers and welding speed affect the CCL of solidification cracks. Changes in the microstructure were observed within the fusion zone, and the structure became uniform and finer with the formation of Mg2Si and magnesium-rich, copper, and zinc (η-phase) particles.

Experimental evaluation of poly methyl methacrylate-acrylonitrile butadiene styrene transmission welding using mold-integrated simultaneous laser welding technology

Automotive lamps have not only functional roles but also highly esthetic purposes in the design of a car. As such, they use complex three-dimensional shapes to implement various designs. The main manufacturing challenge comes from the plastic bonding process of the complex components, which currently is done by thermal bonding, ultrasonic bonding, and laser welding. Laser welding processes with a narrow joint area are preferred since they require minimal joint area and produce no burr. In this study, an optimization study for simultaneous bonding of lamps is carried out using multiple light sources generated by connecting specially manufactured bundle optical fibers with a diode laser source. The diode laser beams with a wavelength of 915 nm and a power of 80 W, each, were simultaneously delivered through a 30-optical fibers bundle. The fibers were integrated within the mold that holds the lamp achieving transmission welding through the overlapped upper transparent polymer PMMA (IF850) and the lower nontransparent polymer ABS (HL121H). The process parameters investigated were the laser power, duration time, waveguide gap, and clamping pressure. We present optimized process parameters that achieved no pores and relatively uniform melting. In the shear test, the average load was approximately 1300 N, and the base sheet fractures along the welding joints were observed.

Influence of fusion welding processes on microstructure and mechanical properties of dissimilar metal (AISI 304 SS-Copper) weldment

Dissimilar metal welding of AISI 304 stainless steel (304 SS) and commercially pure copper (CP copper) has been taken up to understand the influence of the different fusion welding processes on microstructure and mechanical properties of the weldment. The fusion welding processes specifically involve continuous wave CO2 laser, pulsed wave Nd: YAG laser and pulsed wave tungsten inert gas (P-TIG) welding. The primary objective of the present work is to develop a successful weld between two dissimilar metals without using any filler material by different fusion welding processes. An overall comparison of the results obtained from different sets of analyses is represented. The optical image of the top surface of the weld revealed that the no spatter formation during CO2 laser and P-TIG welding process, whereas minimal spatter for Nd: YAG laser. In comparison to laser processes, the weld face formed by P-TIG welding was much wider. However, 100 % penetration was achieved with all three types of welding. The average widths of heat affected zone (HAZ) found to be 10 µm and 23 µm for CO2 and Nd:YAG laser respectively. The way the microstructure changes at the fusion zone was the same in all cases. For example, copper channels form, dendrites grow epitaxially, etc. SEM pictures indicate the Cu tubular channels observed more often for P-TIG welding. The microhardness distribution in the weld zone was found to be larger than that of copper and close to that of 304 SS. The acceptable ultimate tensile stress (UTS) for dissimilar metal welding of SS-Cu couples was found 275 MPa, 278 MPa and 195 MPa for CO2 laser, P-TIG and Nd:YAG laser respectively.

Aluminum alloy oxidation prediction during laser welding process based on random forest regression analysis of spectral signals

Aluminum alloys are one of the most important materials in modern industries; however, they are susceptible to oxidation during the welding process. In an automated welding process, the online monitoring and prediction of weld bead oxidation degree are particularly important. This study proposes a novel method to real-timely predict the oxidation degree of the aluminum alloy during the laser welding process based on the laser plasma spectral signals. First, the characteristics of laser plasma spectral signals are analyzed under various oxidation degree conditions. And then, a random forest regression model is built to extract the principal characteristic wavelengths of spectral signals and predict the oxidation degree of weld bead based on these spectral signals. Finally, through experiments, the prediction validity of the proposed method is verified.

Numerical analysis of the effect of energy distribution on weld width during oscillating laser welding of aluminum alloy

The weld morphology of aluminum alloy oscillating laser welding has an important influence on the quality of welded joints. To understand the formation process of the weld morphology, the three-dimensional numerical simulation model and energy distribution model for circular shaped oscillating laser welding of 6061 aluminum alloy are developed in this paper to analyze the characteristics of weld morphology and the effect of the energy distribution on the weld width. The cross section of the weld and the energy distribution on the processing surface are obtained under the conditions of different oscillation frequencies. It is found that the left width of the weld is larger than the right width of the weld and the energy density on the left side of the weld is more concentrated than that on the right side of the weld. With the oscillation frequency increases, the weld width and peak of energy density decrease. Furthermore, the formation mechanism of the difference in weld width is revealed based on the energy distribution law of the oscillating laser welding process, which is of great significance for improving the quality of aluminum alloy oscillating laser welding.

Understanding the formation of “false friends” (hidden lack of fusion defects) in laser beam welding by means of high-speed synchrotron X-ray imaging

This paper provides a fundamental understanding of “false friend” formation, i.e., hidden defects associated with lack of fusion, using an experimental setup that allowed an insight into the processing zone based on high-speed synchrotron X-ray imaging. The setup enabled the welding of a lap joint of AISI 304 high-alloy steel sheets (X5CrNi18-10/1.4301), with the ability to adjust different gap heights between top and bottom sheet (up to 0.20 mm) and to acquire high-speed X-ray images at 100 kHz simultaneously with the welding process. On this basis, a time-resolved description of the “false friend” formation can be provided by visualizing the interaction between keyhole and melt pool during laser welding and solidification processes within the gap area. The bridgeability of the gap was limited due to the gap height and insufficient melt supply leading to the solidification of the bridge. The distance between the solidified bridge and the keyhole increased with time, while the keyhole and melt pool dynamics initiated the formation of new melt bridges whose stability was defined by melt flow conditions, surface tension, and gap heights. The alternating formation and solidification of melt bridges resulted in entrapped areas of lacking fusion within the weld, i.e., “false friends.” Finally, based on the results of this study, a model concept is presented that concludes the main mechanisms of “false friend” formation.

Study on the Step by Step Process and Performance of Laser Welding for the Spent Fuel Pool Floor

Abstract In order to realize the steel liner underwater repairing of the spent fuel pool of the third generation nuclear power plant, the laser welding process tests were carried out step by step in three environments: air, shallow water, and simulating-repairing of the spent fuel pool floor(high-pressure condition). Through the process optimization, the high-quality forming of the underwater laser welding of duplex stainless steel was realized, and the underwater local dry laser welding process suitable for the spent fuel pool floor of nuclear power plant was developed. The results of nondestructive testing (including visual testing, liquid penetrant testing, ultrasonic testing, and radiographic testing) of welding test pieces under three environments were qualified, and the test results of properties (including tensile, impact, bending, intergranular corrosion, and ferrite content) meet the standard requirements. The underwater weld performance is similar to that in the air environment, and the weld quality meets the requirements of the spent fuel pool construction standard, laying a technical foundation for the application of the spent fuel pool underwater repairing.

In search of the perfect process

AbstractBattery cases in modern electric vehicles must meet very demanding functional requirements. WMG – an independent research and development Institute at the University of Warwick – tested laser welding processes for optimizing aluminum battery cases on behalf of major automotive manufacturers. In extensive laboratory tests, WMG studied which production technology could produce the best results.

One camera-based laser keyhole welding monitoring system using deep learning

The laser-beam absorptance changes dynamically during laser keyhole welding due to unstable keyhole movements, and monitoring the absorptance can provide a deep understanding of the process. Recently, Kim et al. [1,2] developed a deep-learning-based method to monitor the absorptance by detecting the top and bottom keyhole apertures and estimating the absorptance from the reconstructed keyhole shape based on the detected apertures. However, this method was limited in that it required simultaneously observing the top and bottom keyhole apertures using two cameras. In this study, we proposed a novel deep-learning-based method to monitor the laser-beam absorptance in a keyhole using only one camera during laser keyhole welding of Al 5052-H32 alloy. In this method, both the top and bottom keyhole apertures were simultaneously detected from the images coaxially obtained from the top side. Although part of the bottom apertures may be sometimes obscured when viewed from above, this study demonstrated that the predicted absorptance was accurate enough and sufficient for monitoring laser welding processes of aluminum alloys. Using the developed method, changes in welding mode and generation of welding defects were successfully detected.

Using the numerical simulation and artificial neural network (ANN) to evaluate temperature distribution in pulsed laser welding of different alloys

The temperature field during laser welding process plays an important role on determining the quality and quantity of the weld bead size, microstructure characterizations and mechanical properties of the welding interface in the thermal engineering applications. In this study, using the numerical simulation, the influence of pulse duration and frequency on the temperature distribution and velocity field in distinctive laser welding of stainless steel 420 (S.S 420)/stainless steel 304 (S.S 304), and Bohler 303 (B 303)/stainless steel 304 (S.S 304) was examined. The results of numerical modeling illustrated that shear stress of Marangoni and buoyancy force are the most curtail aspects in the formation of the flow of liquid metal. A novel artificial intelligence method is proposed to optimally predict the melting ratio, and maximum temperature of the materials. To this end, a combination of ANN and Particle Swarm Optimization (PSO) algorithms are employed. The PSO algorithm is used to optimize the architecture and training algorithm of the ANN, while the ANN is employed for the regression problem. Based on the results, a three-layer feed-forward architecture with sigmoid transfer functions having 17 and 8 neurons in the hidden layers combined with the scaled conjugate gradient backpropagation training scheme is recognized by the PSO as the optimal configuration. Application of optimal ANN to the regression problem results in an acceptable level of error for the training, validation, and test datasets. Finally, the optimized ANN can be utilized to anticipate the melting ratio and thereby the resultant temperature.

The influence of welding speed on nanosecond laser welding of AZ31B magnesium alloy and 304 stainless steel

Nanosecond pulse laser welding was performed on AZ31B magnesium alloy and 304 stainless steel to investigate the impact of welding speed on the joining process. The temperature field of the magnesium/steel laser welding process was simulated using COMSOL software. The findings revealed that a welding speed of 10 mm/s resulted in significant spattering and larger porosity defects in the joint due to excessive heat input. However, when the welding speed was increased to 30 mm/s, these defects disappeared, and the porosity decreased to a minimum, leading to an increased bonding area at the interface. As the speed increased, the heat input decreased, making it more challenging for the porosity to escape from the molten pool and resulting in the formation of larger pores. The shear force test results indicated that the highest shear force was 298.7 N at a welding speed of 30 mm/s. The reduction in porosity and greater penetration depth of the magnesium alloy contributed to the desired mechanical performance. Additionally, the fracture modes were classified as button pullout failure (BPF), base material tearing failure (BTF), and interface failure (IF). The outermost weld seam served as the initial fracture path for both BPF and BTF modes, with BTF ultimately fracturing in the steel base material during tearing. Oxide inclusions, porosity, and the angle of distortion contributed to the fracture path of IF.

Topology and Size Optimized Design and Laser Welding of the U-Frame for Free-Space Laser Communication Telescopes

The success of laser communications heavily relies on the stiffness, dynamic properties, static performance, and manufacturability of the U-frame. The U-frame is a fundamental element in satellite-to-ground laser communication telescopes. However, there is currently a lack of research on the optimal design of U-frames, leading to a significant gap between ideal construction and practical manufacturability. To address these concerns, this study proposes a comprehensive approach that combines multi-objective topology optimization and multi-start size optimization techniques. This approach considers the multidisciplinary constraints imposed by mechanical, control, and optical systems. The objective is to achieve both the conceptual and detailed design of a novel U-frame, while also ensuring thorough consideration of the structure’s manufacturability during the optimization process. The prototype of the optimized U-frame was successfully fabricated using laser welding processes. The tensile test conducted on the prototype supported the idea that laser welding can enhance the micro-grain size of the joint, leading to improved overall mechanical properties. In particular, the joint strength achieved through laser welding was found to be 1.5 times greater than that achieved through TIG (Tungsten Inert Gas) welding. Additionally, the results obtained from the free vibration experiment closely aligned with the simulation, confirming the feasibility of manufacturing the optimized structure. The optimized structure demonstrated an improvement of 7.13% in dynamic performance and 29.61% in static performance compared to the first-generation structure. Additionally, there was a reduction of 29.89% in mass without affecting the remaining performance aspects. The successful fabrication of the prototype validates the feasibility of the proposed welding process and highlights the superiority of the new U-frame.

Microstructure evolution, interface and mechanical properties of SiCp/2A14 joint during laser keyhole welding

Welding problems have restricted the applications of lightweight SiCp/Al composites in aerospace. In this work, the controllability of the keyhole mode, nucleation mechanism, and mechanical properties of the laser-welding process are studied in detail. The extrusion effect formed by the open keyhole pushes SiC particles to the bottom of the molten pool. To observe the nucleation and growth mechanism of the Al4C3 of keyhole laser-welded SiC/2A14Al composites, the dissolution–precipitation behavior of the SiC particles and growth behavior of the Al4C3 tip were observed. Owing to its high chemical properties, Al4C3 mainly begins nucleating from the open edges of the SiC particles and its formation is mainly distributed along the direction of Al grains. Al4C3 was the main crack source and propagation path while the small-sized SiC particles hindered the crack propagation. This work innovatively regulates the keyhole mode to achieve ‘small damage breakdown’ laser welding, greatly reducing the volume fraction of Al4C3. It also provides new insight into fusion welding of SiC particle-reinforced Al matrix composites.

Laser welding of GH3539 alloy for molten salt reactor: Processing optimization, microstructure and mechanical properties

GH3539 is a most promising material for next-generation molten salt reactors (MSR) due to its excellent performance in harsh high temperature molten salt environments. To promote the application of laser welding of GH3539 alloy in the molten salt reactor, the effect of various laser welding parameters on the weld geometry was investigated, as well as the microstructure and mechanical properties of GH3539 laser welded joints. The results indicate that GH3539 alloy has good laser weldability. The weld geometry of the laser welded alloy joint is significantly affected by the laser welding parameters. After processing optimization, the optimized laser welding process parameters were obtained. The microstructure close to the fusion line is a columnar crystal growing perpendicular to the direction of the fusion line. The core of the central portion of the welded joint consists of equiaxed crystals. No apparent “softened” heat-affected zone (HAZ) was discovered in the laser-welded joints. The hardness of the weld metal (WM) is approximately 130% of the hardness of the base metal (BM). Hardness values in different areas of the WM display unique distributions due to the influence of microstructure and intergranular carbides. A small amount of tiny solidification cracking, liquidation cracking is found in welded joints. Compared to specimens at room temperature (RT), both the tensile strength and elongation dropped significantly under the circumstances of elevated temperature. All fractures are located in the BM with a brittle fracture pattern.

Multi-response optimization for laser transmission welding of PMMA to ABS using Taguchi-based TOPSIS method

Recently, the usage of laser transmission welding (LTW) technology in the automotive industry has been rising for joining thermoplastic parts regarding its superior properties in comparison to other welding technologies. However, specifying the process parameters is a crucial step to obtain satisfactory welding quality for the vehicle parts. In this context, this paper addresses the LTW process of Polimetil metakrilat (PMMA) to Akrilonitril bütadien stiren (ABS) materials for the production of taillights in an automotive company and proposes a new multi-response Taguchi-Based TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) method to optimize machining parameters in the laser welding process. In the proposed solution methodology, the main effects of the parameters on different outputs are identified by using the [Formula: see text] orthogonal array of the Taguchi method. Regarding the best parameter set for each output, the best parameter set for multi-response is identified by using the TOPSIS method, in which alternatives are evaluated through the interrelated quality measures. To optimize welding process in taillight production, PMMA and ABS samples with the dimensions of [Formula: see text] in width, [Formula: see text] in length, and [Formula: see text] in thickness are used in the experiments. The samples are welded by using LPKF Twinweld 3D 6000® laser welding machine. For the welding process, laser power, welding speed, and pressure force are taken into account as the input parameters to optimize three responses: weld strength, breaking strain, and weld width. To identify the best process parameter values, the Taguchi Method is initially employed to calculate the main effects of LTW parameters for each output. Then, the TOPSIS method is carried out to evaluate a number of alternative parameter sets generated through the Taguchi results. As a consequence of the TOPSIS ranking scores, the best parameter set that jointly optimizes three outputs of the LTW process is identified for the taillight production as [Formula: see text] power, [Formula: see text] speed, and [Formula: see text] pressure force. Based on the conducted experiments, this parameter setting achieves the highest weld strength, breaking strain level, and above-average weld width. The results of the experiments show that the proposed methodology is capable of optimizing LTW parameters for a multi-response with fewer experiments in the joining of plastic vehicle parts.

Finite element analysis of butt joint of 316Ln steel thin plate welded by laser welding process

This study focuses on the FEM-based thermal analysis of laser welding for 1.5 mm thick austenitic stainless steel 316Ln, which is commonly used in high-temperature applications such as oil & gas industries and thermal power plants. The objective is to investigate the thermal behavior of the welding process and validate the FEM-based calculations with measured thermal cycles. The thermal cycles at a distance of 10 mm from the welding zone were measured using K-type thermocouples. To analyze the thermal behavior, a Finite Element Method (FEM) approach was employed using the SYSWELD software. The FEM-based calculated thermal distribution was then compared and validated against the measured thermal cycles. In order to accurately model the laser heat source distribution, two different heat source models were selected: a conical model and a combined double ellipsoidal plus conical model. The findings of this study provide valuable insights into the thermal characteristics of laser welding for austenitic stainless steel 316Ln. The validated FEM-based thermal analysis helps in understanding the temperature distribution and thermal effects during the welding process. Such knowledge is crucial for optimizing the welding parameters and ensuring the integrity and quality of the welded joints in high-temperature applications.

An Inhomogeneous Model for Laser Welding of Industrial Interest

An innovative non-homogeneous dynamic model is presented for the recovery of temperature during the industrial laser welding process of Al-Si 5% alloy plates. It considers that, metallurgically, during welding, the alloy melts with the presence of solid/liquid phases until total melt is achieved, and afterwards it resolidifies with the reverse process. Further, a polynomial substitute thermal capacity of the alloy is chosen based on experimental evidence so that the volumetric solid-state fraction is identifiable. Moreover, to the usual radiative/convective boundary conditions, the contribution due to the positioning of the plates on the workbench is considered (endowing the model with Cauchy–Stefan–Boltzmann boundary conditions). Having verified the well-posedness of the problem, a Galerkin-FEM approach is implemented to recover the temperature maps, obtained by modeling the laser heat sources with formulations depending on the laser sliding speed. The results achieved show good adherence to the experimental evidence, opening up interesting future scenarios for technology transfer.

Simulation of temperature field and residual stress in high-power laser self-melting welding process of CLF-1 steel medium-thick plate

To mitigate the adverse effects of residual stress and deformation during high-power laser welding, this study established a finite element model based on thermodynamic conditions for high-power laser welding of CLF-1 steel for nuclear fusion applications. The temperature field and residual stress of the weld were simulated by using the composite heat source model together with Gaussian model and conical model. The results showed that the temperature field simulation was in good agreement with the real temperature field. The simulation results of the weld metal (WM) and the heat affected zone (HAZ) in the cross sections were basically consistent with those of the real cross sections. Moreover, the margin of error between the simulation results and the real data was ≤ 1.3% (the largest error ≤0.04 mm). The Von Mises equivalent stress in WM was distributed irregularly, and its largest value was ≤ 220 MPa; the equivalent stress declined with an increase in distance from the center of WM. The transverse stress distribution in the center of WM was in accordance with the vertical stress distribution, which was essentially the same as the experimental data of the vertical stress. The simulation results of deformation in the Z direction of the weld showed that the maximum deformation was about -0.2 mm at the center of the weld corresponding to the length of 300 mm. In summary, the thermal source model, combined with laser welding process parameters, can provide high-precision prediction of stress variations and deformation control during the actual welding manufacturing process of the test blanket module (TBM) structure.