Remote Welding Research Articles

Joining thin copper wire and copper busbar by remote laser welding for electric motor assembly: Impact of welding parameters and pre-welding surface treatment

Joining thin copper wire and copper busbar by remote laser welding for electric motor assembly: Impact of welding parameters and pre-welding surface treatment

Effect of laser power on weld microstructure of AA6082 sheets remote laser welded by circular beam wobbling

This paper aims to investigate the combined effect of circular beam wobbling and varying laser power on crack formation, weld geometry, microstructure and hardness during remote laser welding of AA6082 alloy. AA6082 sheets of 2 mm thickness were joined in overlap weld configuration using wobbling mode remote laser welding at 4 kW, 3 kW and 2.5 kW. Full penetration was achieved in the joints made at 4 kW and 3 kW, with severe crack formation. Welds at 2.5 kW showed partial penetration and no cracks; however, porosity formation was observed. While no significant change was observed in the dendritic structure and compound contents in fusion zones with full penetration, compound clusters dominated by Cu and Si elements were revealed in the seam root region at 2.5 kW (partial penetration). In full penetration welds (4 and 3 kW), the hardness decreased in the center of the fusion zone but increased from the surface to the root zone. However, for the partial penetration weld (2.5 kW), a limited change in the hardness values determined in the same direction was observed.

Reduced-order modelling for real-time physics-based variation simulation enhanced with adaptive sampling and optimized interpolation

AbstractManufacturing industries require a right-first-time paradigm to remain competitive. Variation simulation (VS) is a key tool to predict variation of the final shape of flexible assemblies, allowing to reduce defects and waste. VS models involving compliant sheet-metal parts commonly integrate physics-based simulation with statistical approaches (usually Monte Carlo simulation). Although increasingly used as a backbone of synthesis techniques for (stochastic) optimization of assembly systems, the main roadblock of VS methods is the intense computational costs due to time-intensive simulations and high-dimensional design space. Driven by the need of time reduction, this paper presents an innovative real-time physics-based VS model of assembly systems with compliant sheet-metal parts. The proposed methodology involves a non-intrusive reduced-order model (niROM), empowered by a novel adaptive sampling procedure for dataset generation, and a cross-validation-based optimized radial basis function (RBF) formulation for interpolation. Demonstrated through two case studies—(i) a remote laser welding operation to predict mechanical distortions, with two input parameters, and (ii) the assembly of an aircraft vertical stabilizer with five input parameters—the methodology achieves accurate real-time results, with up to a 43% improvement in accuracy compared to traditional sampling techniques. Findings highlight the critical influence of the sampling strategy and the number of input parameters on ROM accuracy. Better results are reached by employing adaptive sampling in combination with optimum RBF, which additionally disengages the user from the choice of the interpolation settings. This study unlocks new avenues in the field of variation simulation and dimensional/quality monitoring by narrowing the gap between any advanced CAE solver and VS models with real-time physics-based simulations.

A sequential modelling approach to determine process capability space during laser welding of high-strength Aluminium alloys

Remote laser welding (RLW) technology has become a prominent joining technology in automotive industries, offering high production throughput and cost-effectiveness. Recent advancements in RLW processes such as beam oscillation have led to an increased number of input process parameters, enabling precise control over the heat input to weld metallic materials. A critical necessity in laser welding entails selecting robust process parameters that satisfy all weld quality indicators or key performance indicators (KPIs) during two stages: production stage (often implemented as robotic welding); and repair/rework stage (implemented as cobotic/manual welding to identify process parameters for weld defects) as addressing these factors in both stages is necessary to satisfy near-zero-defect strategy for some e-mobility products.. This research presents a comprehensive methodology that encompasses the following key elements: (i) the development of physics-based simulations to establish the correlation between KPIs and process parameters; (ii) the integration of a sequential modelling approach that strikes a balance between accuracy and computation time to survey the parameter space; and (iii) development of the process capability space for the quick selection of robust process parameters.Three physical phenomena are considered in the development of numerical models, which are (i) heat transfer, (ii) fluid flow and (iii) material diffusion to investigate the effect of process parameters on the weld thermal cycle, solidification parameters and solute intermixing layer during laser welding of dissimilar high-strength aluminium alloys. The governing physical phenomena are decoupled sequentially, and KPIs are estimated based on the governing phenomena. At each step, the process capability space is defined over the parameters space based on the constraints specific to the current physical phenomena. The process capability space is determined by the constraints based on the KPIs. The process capability space provides the initial combination of process parameter space during the early design stage, which satisfies all the KPIs, thus decreasing the number of experiments. The proposed methodology provides a unique capability to (i) simulate the effect of process variation as generated by the manufacturing process, (ii) model quality requirements with multiple and coupled quality requirements, and (iii) optimise process parameters under competing quality requirements.

Investigating impact of zinc vapor jet on keyhole dynamics and liquid ejection from molten pool during remote laser welding of zinc-coated steel in zero-gap lap joint configuration

When Zn-coated steels are laser welded in a zero part-to-part gap lap joint configuration, highly pressurised Zn vapors are readily produced, generating spatters in the weld. The best practice is to set a non-zero gap to facilitate vapor degassing; however, this necessitates additional operations, escalating production costs. This paper aims to investigate the keyhole dynamics and the ejections from the molten pool due to the interaction between high-pressure Zn vapors and the liquid metal, during remote laser welding of Zn-coated DX57D+Z steel sheets at zero nominal part-to-part gap in lap joint configuration. This is achieved by complementing experimental trials with multi-physics Computational Fluid Dynamics (CFD) simulations. The findings showed that the interplay between heat-affected zone, Zn evaporation zone, size/shape of the laser beam are critical factors for controlling the effect of Zn vapors jet on keyhole stability and liquid ejections. Opportunities for laser beam shaping are discussed throughout the paper.

Controlling solidification cracks during remote laser welding of AA6005 alloy using Al2O3 alumina nanoparticles dispersed coating

Solidification cracks are among the most common defects observed in the remote laser welding (RLW) of 6xxx aluminium alloys. This study assesses a novel route to mitigating solidification cracking during RLW of the AA6005 alloy using alumina nanoparticles (Al2O3) within the fusion zone. The AA6005 sheets were electrodeposited using a CuSO4 bath containing 40 nm sized Al2O3 at different concentrations and deposition time. Characterisation of the welds was conducted using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), energy dispersive X-ray spectroscopy (EDS) and mechanical lap shear testing. The results show that the incorporation of Al2O3 nanoparticles can be effective in producing centreline crack-free welds. Furthermore, the microstructural analysis also reveals grain refinement by 65% with increasing of Al2O3 concentration from 1 to 5 g/L, this corresponds to a 10% improvement in shear strength of the welds, compared to a standard un-coated AA6005 alloy.

Understanding the interplay of Zn vapours and formation of intermetallic compounds during remote laser welding of Zn-coated steel to aluminium in a zero-gap lap joint configuration

Remote laser welding (RLW) of Zn-coated steel to aluminium is challenged by: (1) Zn vaporisation causing spatters and poor seam surface when welding in a zero-gap lap joint configuration; and (2) brittle intermetallic compounds (IMCs) at the weld interface, leading to cracks and poor weld integrity. This paper aims to study the impact of Zn coating during the RLW of Zn-coated steel to aluminium in a nominal zero part-to-part gap lap configuration. The combination of metallurgical and mechanical analysis with an in-process monitoring approach, using a high-speed camera, allowed the study of the interplay between Zn formation/out-gassing, molten pool dynamics and formation of IMCs. Findings revealed that the presence of a Zn coating results in an un-even connection area between steel and aluminium, with localised lack of fusion. A significant 72% joint efficiency compared to parent aluminium was achieved when Zn is removed, opposed to 65% when Zn is present.

Development and comparison studies of XR interfaces for path definition in remote welding scenarios

Development and comparison studies of XR interfaces for path definition in remote welding scenarios

Effect of placement configuration on the microstructure, porosity and mechanical performance of dissimilar remote laser welding of additive manufactured AlSi10Mg alloy and conventionally manufactured 1050 aluminium sheet

Additive manufacturing (AM) has gained significant attention in automotive applications, while the low weldability of AM material poses challenges when assembling AM materials with conventionally manufactured materials. This study investigated the laser welding of AM AlSi10Mg and AA1050 sheet metal in an overlap configuration, specifically focusing on the impact of placement configuration of two materials on weld properties. This aims to provide valuable insights for optimizing the localized geometry of AM components to enhance the joint performance. Results showed that positioning AM AlSi10Mg on top leads to a higher weld penetration and higher Si content within the molten pool, especially in the upper sheet. Additionally, weld zone grain structure was greatly influenced by alternating the placement configuration, where welds with AM AlSi10Mg on top exhibiting more equiaxed grains in the weld centre and refined columnar grains near the fusion boundary of upper sheet. Furthermore, significantly reduced weld porosity was determined by positioning AM AlSi10Mg at the bottom (3.2 ± 0.4 %∼7.1 ± 0.9 %) compared to placing it on top (16.9 ± 0.9 %∼20.1 ± 0.9 %) in all scenarios ranging from full penetration to partial penetration. This can be related to the fact that the hydrogen bubbles originating from AM AlSi10Mg experienced a shorter exposure in the molten pool, limiting the merging and growth of small bubbles. However, a slightly lower joint strength was determined in welds with AM AlSi10Mg at the bottom which may be due to the plastic deformation incompatibility between large columnar grains in the fusion zone and the fine grains in the as-printed material.

Experimental analysis of overlap fiber laser welding for aluminum alloys: Porosity recognition and quality inspection

In recent years, laser welding has become increasingly popular in the manufacturing industry due to its advantages, including a narrow heat affected zone, low levels of distortion, the possibility of remote processing, and high welding speeds compared to conventional electric arc welding techniques. In the automotive industry, the need for overlapped joint welding, particularly for chassis assembly, has become increasingly relevant. The internal porosity detection and control in laser welding of aluminum alloys has gained significant attention. To support laser users in optimizing the welding process, this paper presents an experimental methodology followed by a phenomenological analysis of the quality of overlapped welded joints. The study focuses on the laser welding of two different aluminum alloy configurations (1.6-mm-thick AA 6061-T6 and 2-mm-thick AA 6061-T6) using three welding strategies (ScanLab remote laser welding system, Trumpf D70 laser head, and Precitec YW52 wobbling head) to evaluate single and multiple laser variants for process parameter tuning. Additionally, the paper discusses the use of X-ray technology as an offline monitoring method for porosity recognition, and analyzes laser beam characterization and beam profile shape to calculate beam distribution. Then, statistical analysis of all methods is conducted and regression analysis is performed. These findings provide valuable insights into the integration of laser welding technology in the automotive and surface transportation industries. The analysis of results indicates that as the spot size decreases, the real spot size changes more abruptly with increasing Z position, whereas with a larger spot size, the beam size remains stable up to +/- 20–30 mm in Z position due to the large lens. Porosity is mainly caused by either a too small spot size (in the absence of wobbling; ≤0.4 mm) or low travel speed (≤4.0–4.5 m/min). On the other hand, if the spot size is too large, hot cracking can occur in autogenous laser welding.

Comprehensive benchmarking of laser welding technologies including novel beam shapes and wavelengths for e-drive copper hairpins

Laser welding is the industrially accepted method for the joining of Cu hairpin windings in the production of electric drives. High brilliance laser beams are scanned over the bare ends of the Cu wires producing a rapid connection through deep penetration remote welding. Despite being an accepted manufacturing method, laser welding of Cu hairpins still requires detailed studies concerning manufacturing productivity and quality. As the availability of novel laser sources with higher power levels, new wavelengths, and beam shaping capabilities increase, the need for benchmarking studies emerges. In this work, six different laser welding systems were compared in terms of process productivity and quality during the welding of Cu hairpins used for automotive traction. The different solutions presented power levels from 3 to 6 kW, with wavelengths from near infrared (NIR) to visible, including in source dynamic beam shaping. The weld bead formation was observed through high-speed imaging. The welds were analyzed in terms of their geometry, internal defects, and most relevantly for their mechanical strength. The results showed advantages of each of the employed system while the laser systems providing the highest irradiance profile produced the fastest weld with more elevated mechanical strength independently from the wavelength.

Tailoring the weld microstructure to prevent solidification cracking in remote laser welding of AA6005 aluminium alloys using adjustable ringmode beam

Solidification cracking is a prevalent defect in welding aluminium alloys which can be effectively mitigated by employing grain refinement strategies. This paper investigates the feasibility of tailoring the weld zone grain structure of 6xxx series aluminium alloys using an adjustable ring mode (ARM) laser beam to reduce the centreline cracking susceptibility. An in-process monitoring approach, comprising a high-speed camera and an ad-hoc Digital Image Correlation, was adopted to examine the strain development during laser welding on a self-restraint test rig. Results revealed that transverse strain in the weld centre exhibits a parabola-like relationship with the core/ring power ratio, with the minimum strain determined at the power ratio of ∼1.5, regardless of the total power employed. The microstructural analysis demonstrated that increasing the core/ring power ratio can lead to the refinement of columnar and equiaxed grains. Furthermore, the formation of secondary equiaxed grains is promoted when the power ratio increases, and this is proved to be related to the characteristic of the ARM laser by the like-for-like comparison. Overall, a fine-tuned power ratio of 1.5 is determined in the studied material and welding configuration for achieving a centreline crack free weld, benefiting from the improved microstructure and reduced thermal strain.

On Welding of High-Strength Steels Using Laser Beam Welding and Resistance Spot Weld Bonding with Emphasis on Seam Leak Tightness

The design of most electric vehicles provides for the positioning of the heavy energy storage units in the underbody of the cars. In addition to crash safety, the battery housing has to meet high requirements for gas tightness. In order to test the use of high-strength steels for this sub-assembly, this paper examines welded joints utilizing resistance spot weld bonding and laser remote welding, with special regard to the gas tightness of the welds. For this purpose, the pressure difference test and helium sniffer leak detection are presented and applied. The combination of both leak test methods has proven ideal in experimental investigations. For laser remote welding, gas-tight seams can be achieved with an inter-sheet gap of 0.1 mm, even if occasionally leaking samples cannot be prevented. Resistance spot welding suits gas-tight joining with both one- and two-component adhesives. Against the background of leak tightness, process fluctuations that lead to weld spatter and defects in the adhesive layer must be prevented with high priority.

Weld depth dynamics measured with optical coherence tomography during remote laser beam oscillation welding of battery system

This paper represents nondestructive quality monitoring technique using optical coherence tomography (OCT). It addresses online monitoring of weld depth during laser beam oscillation welding and aims at the application in joining cells in large battery assemblies. The weld depth was continuously detected with OCT while the OCT beam position was adjusted highly dynamically in accordance with the scanning optics position. By displacing the OCT measurement beam according to the current machining direction, the correlation between the position of the laser beam in an oscillating circular pattern along the circular feed direction and the periodic fluctuations of the measured weld depth was explored. It was found that the deepest part of the keyhole is located at the trailing position of the laser beam. This effect can be attributed to the large heat input due to the overlapping circular movements. The results confirm once again that instant weld depth monitoring with OCT ensures superior weld quality.

Effects of the adjustable ring-mode laser on intermetallic formation and mechanical properties of steel to aluminium laser welded lap joints

Research has confirmed a positive effect of laser beam shaping on controlling weld profiles and keyhole stabilisation, with significant reductions of porosity in weldments. However, few attempts with scattered results have studied the impact of laser beam shaping on intermetallicphase formation. This paper implements the adjustable-ring mode (ARM) laser and studies the impact of the core/ring power ratio to explore the impact on intermetallic phase formation and mechanical properties during remote laser welding of IF steel to 1050 aluminium. It was found that in conduction mode, the core/ring power ratio of 0.2 provided a larger surface area for bonding at the weld interface, and this was translated through the maximum lap-shear strength of 97.6 N/mm2 (joint efficiency 71%). Furthermore, this significantly reduced the Fe2Al5 intermetallic compound (IMC) thickness by 62% and total IMC thickness by 40% in contrast to a core-dominant beam (power ratio greater than one). In keyhole mode, cracking and lower lap-shear strengths were observed compared to the conduction mode. Notably, with a core/ring power ratio of 0.5 a significant grain refinement in the steel side of the weld was observed.

Fusing optical coherence tomography and photodiodes for diagnosis of weld features during remote laser welding of copper-to-aluminum

This study has been designed to investigate whether variations in the features of laser weldments can be isolated and diagnosed by fusing photodiodes and optical coherence tomography (OCT). Two manufacturing scenarios (variation in laser power and focal offset) have been considered during remote laser welding of 0.2 mm thick Cu foils on 2 mm thick Al 1050 plates with an adjustable ring mode laser integrated with a 1D oscillation head. The process was monitored by measuring weld penetration depth with OCT and by process emissions (plasma and back-reflection) via photodiodes. The acquisition frequency of all signals was 40 kHz. Strong correlations (r > 0.75) were shown between plasma, back-reflection, and OCT signals and measured depth and width of the weld. Weak correlations (r < 0.5) between voids, cracks, and sensor signals were observed. Although plasma is the predominant signal that carries most of the information about the process, and the OCT allows direct measurement of the penetration depth, their integration reached 87% classification accuracy of the tested welding scenarios. The main misclassification was observed between “good weld” and “over weld,” defined by the measured weld depth. Sensor fusion strategies with manufacturing implications are discussed throughout the paper.

Numerical study of beam oscillation and its effect on the solidification parameters and grain morphology in remote laser welding of high-strength aluminium alloys

This study investigated the effect of beam oscillation on the solidification behaviour during laser welding of Al-5754 to Al-6061 alloy. In this study, a finite element model has been developed to simulate temperature and fluid flow fields by implementing different combinations of volumetric heat source models. Solidification parameters such as temperature gradient (G), solidification rate (R), cooling rate (G × R) and G/R are evaluated to understand the mechanism of microstructure formation. It was found that beam oscillation improves the tensile strength by 21.4% for full penetration welding due to an increase in the percentage of formation of equiaxed grains. Modelling results revealed that the cooling rate increases with an increase in oscillation frequency. However, tensile strength followed a parabolic distribution with a peak at the oscillation frequency of 300 Hz.

Numerical simulation of transport phenomena and its effect on the weld profile and solute distribution during laser welding of dissimilar aluminium alloys with and without beam oscillation

Remote Laser Welding (RLW) of Aluminium alloys has significant importance in lightweight manufacturing to decrease the weight of the body in white. It is critical to understand the physical process of transport phenomena during welding which is highly related to the mechanical performance of the joints. To investigate the underlying physics during welding and to understand the influence of beam oscillation on heat transfer, fluid flow and material mixing a transient three-dimensional Finite Element (FE) based Multiphysics model has been developed and validated from the experiments. The effect of welding speed, oscillation amplitude and oscillation frequency on the fusion zone dimensions, flow profile, vorticity profile, cooling rate and thermal gradient during the butt welding of Al-5754 to Al-6005, with sinusoidal beam oscillation, is analysed. It was found that one additional vortex is formed during beam oscillation welding due to the churning action of the oscillating beam. With the increase in oscillation amplitude, welds become wider and the depth of penetration decreases. An increase in oscillation frequency leads to an increase in the flow rate of the molten metal suggesting that the beam oscillation introduces a churning action that leads to an increase in mixing. It was highlighted that the material mixing depends on both diffusion and convection.

Using photodiodes and supervised machine learning for automatic classification of weld defects in laser welding of thin foils copper-to-steel battery tabs

This paper has been designed to study whether photodiodes and supervised machine learning (ML) algorithms are sufficient to automatically classify weld defects caused by simultaneous variation of the part-to-part gap and laser power during remote laser welding (RLW) of thin foils, with applications in battery tabs. Photodiodes are used as the primary source of data and are collected in real-time during RLW of copper-to-steel thin foils in the lap joint. Experiments are carried out by the nLight Compact 3 kW fiber laser integrated with the Scout-200 2D scanner. The paper reviews and compares seven supervised ML algorithms (namely, k-nearest neighbors, decision tree, random forest, Naïve–Bayes, support vector machine, discriminant analysis, and discrete wavelet transform combined with the neural network) for automatic classification of weld defects. Up to 97% classification rate is obtained for scenarios with simultaneous variations of weld penetration depth and part-to-part gap. The main causes of misclassification are imputed to the interaction between welding parameters (part-to-part gap and laser power) and process instability at high part-to-part gap (high variation in the process not captured by the photodiodes). Arising opportunities for further development based on sensor fusion, integration with real-time multiphysical simulation, and semi-supervised ML are discussed throughout the paper.

Remote laser spot welding of AISI 430 sheets by fiber lasers—A phenomenal effect in refining weld microstructure with nanosecond pulses

In the present work, we have compared the results of microstructural and mechanical property characterization of AISI 430 ferritic stainless steel spot welds made remotely using a repetitive nanosecond pulsed fiber laser and a CW fiber laser. Optical/electron microscopy, microhardness test, and tensile shear tests were performed for evaluation of the welds. Welds made by the pulsed nanosecond laser were found to be superior due to the presence of the very narrow heat-affected zone along with finer grains in the fusion zone. The welds were also found to withstand more load before fracture and were more ductile. Use of short duration laser pulses with lower heat input were found to be responsible for the refinement of grains in the fusion zone and improvement of mechanical properties of nanosecond laser weld specimens.