Weld Depth Research Articles

Online modeling and prediction of weld bead geometry in robotic gas metal arc based additive manufacturing using grey prediction model

In the directed energy deposition process, online monitoring of weld bead geometry can give real-time information to researchers and manufacturers to understand and control the metal deposition layer by layer. In the current work, an optimization Grey model OGM(1,N)-based online monitoring system was built to monitor the height and depth of metal deposition in each layer. The OGM(1,N) needs fewer training samples with poor information. The training data was updated to improve accuracy in prediction by removing old data and introducing more recent data. The inputs to the OGM(1,N) include the welding time, current, absolute difference in current at regular time intervals (5 s) and arc force. An optimum set of input parameters was identified by calculating the root mean square error (RMSE) for various parameter combinations for the most accurate weld bead height and depth prediction. The interaction of time, current, and arc force significantly affected the height and depth of weld beads. The predicted height and depth of weld beads using the time, current, and arc force showed RMSEs of 2.52 and 0.23, respectively, compared to experimental results. This methodology can assist manufacturers and researchers in understanding and achieving an appropriate balance between process parameters and weld bead height with no training time.

Porosity inhibition of aluminum alloy by power-modulated laser welding and mechanism analysis

Porosity is a significant issue when conducting laser welding (LW) of aluminum (Al) alloys. Laser oscillating welding appears a good choice for suppressing porosity, but it is accompanied by energy losses. To address the above issues, this paper proposes an innovative power-modulated LW system that simultaneously achieved porosity suppression, power modulation, and energy loss reduction. To demonstrate the effectiveness of the system, comparative experiments were performed using three welding modes: conventional LW, constant power (CP) laser oscillating welding, and gradient power (GP) laser oscillating welding. The results of the experiments indicated that the GP mode was more effective at reducing porosity and the weld depth was greater than that of the CP mode. Numerical simulations were conducted to describe this process. The results showed that changes in the molten pool (MP) flow behavior of the GP mode determined the welding effect. The physical mechanism by which the GP mode suppressed porosity and reduced energy losses was revealed.

Optimization of laser spiral welding using Response surface methodology and genetic algorithms

In the laser spiral welding (LSW) process, the welding parameters have a significant impact on the weld quality. In this paper, experiments were conducted and experimental data were collected on galvanized steel sheets using the LSW process, and mathematical models were developed using response surface methodology (RSM) and genetic algorithm (GA) to verify the specific effects of each process parameter on the weld and to perform process optimization. Laser power, welding speed, gap and focal length were selected as the influencing factors, and melt depth, melt width and concave as the output results. In the RSM model we found that the laser power was positively correlated with the weld depth and width, while the welding speed was inversely correlated with the weld depth and width, the gap was positively correlated with the amount of concave, and the focal length had no significant effect on the weld. In the GA model we use a large amount of experimental data for BP neural network training and iterative optimization using a genetic algorithm. Validation experiments were conducted on two models, and the results indicated that the two models had higher accuracy in predicting the welding depth and width compared to predicting the concave. The GA model had an 8% increase in tensile strength and a 25% increase in plasticity of the weld joint obtained from the optimal process compared to the RSM model. The GA model has higher accuracy in optimizing the LSW process.

EVALUATION OF FILLET WELDS PROPERTIES PERFORMED BY COLD METAL TRANSFER ROBOTIC METAL ACTIVE GAS WELDING TECHNOLOGY

The article is the result of research evaluating the quality of fillet welds used in the production of rear seat backrests for passenger cars and manufactured robotically by Cold Metal Transfer (CMT) robotic Metal Active Gas (MAG) welding. When robotizing the process, parameters such as the speed of the process itself, accuracy and quality of the welded joints are important. Dual-phase ferritic-martensitic steel HCX 590X was used for the experiment and four weld nodes were evaluated. The quality of welded joints was evaluated by visual and capillary methods. Based on the metallographic analysis, the weld depth of the weld root was evaluated. The measured values were subsequently processed by statistical method ANalysis Of Variance (ANOVA). The research confirmed that the final quality of the welds depends on the depth of the weld root weld into the Base Material (BM). This parameter has the greatest effect on the welds made and results in the entire product being taken out of service.

An Efficient Method for Laser Welding Depth Determination Using Optical Coherence Tomography.

Online monitoring of laser welding depth is increasingly important, with the growing demand for the precise welding depth in the field of power battery manufacturing for new energy vehicles. The indirect methods of welding depth measurement based on optical radiation, visual image and acoustic signals in the process zone have low accuracy in the continuous monitoring. Optical coherence tomography (OCT) provides a direct welding depth measurement during laser welding and shows high achievable accuracy in continuous monitoring. Statistical evaluation approach accurately extracts the welding depth from OCT data but suffers from complexity in noise removal. In this paper, an efficient method coupled DBSCAN (Density-Based Spatial Clustering of Application with Noise) and percentile filter for laser welding depth determination was proposed. The noise of the OCT data were viewed as outliers and detected by DBSCAN. After eliminating the noise, the percentile filter was used to extract the welding depth. By comparing the welding depth determined by this approach and the actual weld depth of longitudinal cross section, an average error of less than 5% was obtained. The precise laser welding depth can be efficiently achieved by the method.

The influence of bypass current on arc energy density and metal transfer behaviour in bypass current compressed gas metal arc welding

A new welding method, bypass current compressed gas metal arc welding (BCC-GMAW), was developed to enhance the arc energy density and welding stability of GMAW. When the bypass current was applied, the arc energy density was increased with the constraining effect of the circumferential bypass electrode, which was studied by current density and arc pressure, resulting in an increase of 46% in weld depth and a decrease of 38% in weld width. As the coupled arc increased the melting speed of wire and forces of droplet downward transfer, the droplet transfer frequency increased by 185%, and the metal transfer mode was changed from short-circuit transfer to stable small globule transfer, obtaining a smooth and uniform weld appearance.

Integrated modeling of cracking during deep penetration laser welding of nickel alloys

During deep penetration laser welding of nickel alloys, interactions between composition and processing conditions can lead to the formation of defects. Inconel 740H, for example, has demonstrated a susceptibility to horizontal fusion zone cracking at locations between 70% and 80% of the weld depth during laser welding at powers above 5 kW. Coupling three-dimensional heat transfer, fluid flow, and stress modeling tools allowed that both the strain rate and stress normal to the solidification direction to be calculated. In the Inconel 740H welds, cracks formed at locations where the strain rate and stress simultaneously reached critical levels. No cracking was observed in the Inconel 690 welds, since the strain rate and stress did not simultaneously reach these critical levels.

Toward accurate prediction of partial-penetration laser weld performance informed by three-dimensional characterization – Part II: μCT based finite element simulations

The mechanical behavior of partial-penetration laser welds exhibits significant variability in engineering quantities such as strength and apparent ductility. Understanding the root cause of this variability is important when using such welds in engineering designs. In Part II of this work, we develop finite element simulations with geometry derived from micro-computed tomography (μCT) scans of partial-penetration 304L stainless steel laser welds that were analyzed in Part I. We use these models to study the effects of the welds’ small-scale geometry, including porosity and weld depth variability, on the structural performance metrics of weld ductility and strength under quasi-static tensile loading. We show that this small-scale geometry is the primary cause of the observed variability for these mechanical response quantities. Additionally, we explore the sensitivity of model results to the conversion of the μCT data to discretized model geometry using different segmentation algorithms, and to the effect of small-scale geometry simplifications for pore shape and weld root texture. The modeling approach outlined and results of this work may be applicable to other material systems with small-scale geometric features and defects, such as additively manufactured materials.

Welding investigations on mechanical property and microstructure of TIG and A-TIG Weld of Hastelloy C-276

Hastelloy C-276 is a nickel-based alloy with high strength and corrosion resistance at cryogenic to high temperatures. The issue of Hastelloy C-276 shallow penetration by Tungsten Inert Gas (TIG) welding was addressed in the current investigation by applying A-TIG welding with variable oxide flux. In the current investigation, constant welding conditions were used to perform TIG and A-TIG welding using SiO2, TiO2, and a 50% mixture of SiO2 + TiO2 flux. The weld bead width and depth of penetration of the weld bead profile were measured, and the mechanical and metallurgical properties of the weld metal was investigated. SiO2 flux attained the highest D/W ratio and depth of penetration during A-TIG welding when compared to other fluxes used. A-TIG welding using SiO2 flux improved the depth of penetration and the D/W ratio by 118% and 263%, respectively, in comparison with conventional TIG welding. Additionally, the A-TIG welded sample with SiO2 flux had an ultimate tensile strength of 738.295 MPa and a percentage of elongation of 52.75%.

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.

Assessment of the Structural Integrity of a Laser Weld Joint of Inconel 718 and ASS 304L

For high-temperature industries operating at nearly 750 °C (advanced ultra-super critical boilers), dissimilar welding between Inconel alloys and austenitic stainless steel (ASS) are commonly adopted. The high-temperature resistive properties of Inconel and ASS alloys are highly qualified for high-temperature applications. In this experimental study, dissimilar autogenous laser beam welding (LBW) between Inconel 718 and ASS 304L is investigated. This paper explains the detailed study on the microstructural and mechanical behavior of the LBW dissimilar joint. The microstructural study indicates the presence of laves phases in the weld zone. Additionally, the weld zone shows heterogeneous microstructural formation, owing to the non-uniform welding heat in the different areas of the weld zone. The optical images show the presence of mixed dendrites, i.e., equiaxed, cellular, and columnar morphology, in the weld zone and in the fusion zones of either side. The energy-dispersive spectroscopy (EDS) results show the presence of segregated elements (Nb, Mo, Cr, and Ti) at the weld center. These segregated elements are the reason for the occurrence of the laves phases in the weld zone. The presence of Nb and Mo may form the laves phase (Fe, Ni, Cr)2 (Nb, Mo, Ti) along with Fe, Ni and Cr. The presence of an unmixed zone is observed in the HAZ of the Inconel 718, whereas the HAZ of the ASS 304L shows the presence of an unmixed zone (UZ) and a partially mixed zone (PMZ), as observed on the optical and SEM images. To obtain the mechanical properties of the laser weld, the tensile test, microhardness test, and impact test were measured at room temperature. The tensile specimens show a brittle failure at the ASS 304L side, which was initiated from the weld top, with average tensile stress of 658.225 MPa. The reason for the ASS 304L fracture is because of the presence of UZ and PMZ, and the lower hardness value of the ASS side. The UZ and PMZ lead to the fracture of the tensile specimen along the ASS 304L side’s HAZ. The measurement of microhardness carried out along the transverse length indicates an average microhardness of 214.4 HV, and the value is 202.9 HV along the weld depth. The mixed morphology of the microstructure promotes the variation in hardness in both directions. The hardness along the length shows a high hardness value in the weld zone and uniformly decreases along the base materials. The Charpy impact test of the weld zone shows the brittle fracture of the impact specimens. From the microstructural and mechanical results, the LBW dissimilar weld between Inconel 718 and ASS 304L is qualified for safe use in high-temperature end applications, such as AUSC power plants.

Keyhole-in-keyhole formation by adding a coaxially superimposed single-mode laser beam in disk laser deep penetration welding

Laser deep penetration welding is characterized by the formation of a vapor capillary (keyhole) and a high overall absorption (coupling rate) of the laser radiation in comparison to heat conduction welding. Due to multiple reflexions within the highly dynamic keyhole, the absorption mechanisms are very complex. The questions, how a laser beam interacts with the existing keyhole, and, if shadowing effects occur, are a matter of concern for several researchers. In this study, the hypothesis that the beam of a laser source can be transmitted to a significant extent through an existing keyhole and acts predominantly at the keyhole bottom was investigated. Experiments were carried out on mild steel and technical pure aluminum, using a specially designed optical system, which allows to coaxially combine two laser beams and to adjust their settings like the energy and the focal plane individually. A combination of a disk laser with a focal diameter of 390 µm and a single-mode fiber laser with a focal diameter of 30 µm was used. Weld depths and seam shapes were analyzed in cross and longitudinal sections. Based on the results, it is shown that the much smaller focal diameter of the single-mode laser beam acted at the bottom of the keyhole and caused a kind of “keyhole-in-keyhole formation” in the form of a local maximum in weld depth whose expression depended on the focal plane of the single-mode laser beam.

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.

Laser welding of different pure copper materials under consideration of shielding gas influence and impact on quality relevant surface topographical features

The high demand for electronic products increases the need for high-quality welds of copper. Laser welding can be applied but may result in undesired weld characteristics such as humping or spatter. Process control is needed to identify defective welds in the production line. Surface topographical features can be used to identify different weld characteristics by optical coherence tomography (OCT). The resulting surface topography of a weld can be influenced by process parameters like its material properties or the application of process gas. In this work, we investigate the influence of different pure copper materials and process gas on weld seam surface features for the classification of quality-relevant weld characteristics. First, the resulting changes in weld depth and metallographic cross sections are qualitatively and quantitively characterized for different pure copper materials under the consideration of weld categories such as melt ejection, deep penetration welding, humping, and heat conduction welding with and without the application of shielding gas. Afterward, a qualitative and quantitative analysis of weld surface features is performed for the beforementioned categories under consideration of the copper material and shielding gas. As a result, an influence on the achievable weld depth could be identified for pure copper with residual phosphor content. No significant changes in surface topographical features could be identified for different material properties of copper. The influence of shielding gas and pure copper material is found to be negligible on surface topographical characteristics for process control.

Development of Nano – flux powder from bio-waste for welding application

Oxyacetylene welding is a fast-growing means of joining metals that were developed to address the drawbacks of other welding techniques. The use of chemical compounds known as fluxes in the welding process does this, resulting in improved weld characteristics and increased weld depth. Chemical synthesis was used to create a new nanoparticle flux powder from Egg shell powder for this research. The powder was studied micro-structurally and spectroscopically using SEM, TEM, FTIR, and EDS techniques, and it was discovered to be a compound made up of 57.31 % calcium, 12.31 % sodium, and 6.86 % carbon. The flux was tested on, 8 mm mild steel rods, 3 pcs each of 10 x 10 mm and 50 x 50 mm galvanized steel plates, utilizing oxyacetylene welding techniques. 50 x 50 mm mild steel plates and galvanized steel plates Control samples were made utilizing the oxyacetylene welding techniques with and without the use of a flux (Easy-Flo powder). The mild steel welds generated with the created flux were found to be harder, with hardness values of 98.45 and 115.78 BHN for oxyacetylene welding procedures, respectively. Welds produced without flux powder were able to withstand higher loads than the welds produced using the other methods of welds produced with the developed flux.

Bio-Waste as an Enhancement Additive for Nano-Flux Powder in Welding- An Overview

Oxyacetylene welding is quite a novel technique of connecting metals with each other that was developed to address the drawbacks of other welding techniques. The use of chemical compounds known as fluxes in the welding process does this, resulting in improved weld characteristics and increased weld depth. Recently, the use of agro-wastes as alternate fluxes has received keen interest from researchers. This is partly because agro-wastes recycling facilitates cleaner environments and could be cheaper. In this study, a critical review was carried out on some particular types and properties of welding. The review also considers the assessments carried out on welded joints and the use of agro-waste.

Electron beam weld penetration depth prediction improved by beam characterisation

Predicting the penetration depth during electron beam welding (EBW) is important, but the accuracy of current predictive models is highly varied, depending on the type and number of data used. This paper develops and compares several penetration depth prediction models for EBW and uniquely compares the influence of the number and type of data used, as well as the measurement and modelling methods. Although accelerating voltage, beam current and welding speed data are essential modelling inputs, additional data for beam focal position and beam shape, measured using a novel 4-slit beam probing method, greatly improve the accuracy of predictions for models based on an empirical equation, a second-order regression and an artificial neural network (ANN). Optimised models predict weld depths that deviate, on average, by less than 5% from measured depths, are valid for very broad linear electron beam power density ranges (86–324 J/mm) and are close to the estimated 4% inherent variability in the process and its measurement. Within this linear electron beam power density range, the ANN yields accurate and reliable depth predictions, demanding as few as 36 welding trials, decreasing the number required for models that do not consider beam focal position and shape, for the same targeted accuracy, by more than 60%. Adding large volumes of virtual data generated by less reliable analytical or regression models did not improve the predictive capability for the ANN developed in this study.

Algorithms for Weld Depth Measurement in Laser Welding of Copper with Scanning Optical Coherence Tomography.

In-process monitoring of weld penetration depth is possible with optical coherence tomography (OCT). The weld depth can be identified with OCT by statistical signal processing of the raw OCT signal and keyhole mapping. This approach is only applicable to stable welding processes and requires a time-consuming keyhole mapping to identify the optimal placement of a singular OCT measuring beam. In this work, we use an OCT measurement line for the identification of the weld depth. This approach shows the advantage that the calibration effort can be reduced as the measurement line requires only calibration in one dimension. As current literature focuses on weld depth measurement with a singular measurement point in the keyhole, no optimal algorithm exists for weld depth measurement with an OCT measurement line. We developed seven different weld depth processing pipelines and tested these algorithms under different weld conditions, such as stable deep penetration welding, unstable deep penetration welding, and heat conduction welding. We analyzed the accuracy of the weld depth processing algorithms by comparing the measured weld depth with metallographic weld depths. The intensity accumulation approach is identified as the most accurate algorithm for successful weld depth measurement with a scanning OCT measurement line.

Study on LBW/SPF/DB technology of TA15 four-storey lightweight high strength cylinder

This paper investigates the application of Laser beam prewelding/superplastic forming/diffusion bonding (LBW/SPF/DB) process in cylindrical parts. The forming die design and the processing process have been researched. A numerical simulation was carried out to determine the parameters of the superplastic forming/diffusion bonding process. The causes of defects are analysed and effective optimization methods are presented. In this paper, the main research contents are as follows, (1) Considering the characteristics of the structure and process of the workpiece, a design idea using a flapping tool and wedge fastening is presented. The process scheme for forming the core barrel step is described. (2) A laser welding power of 1300W and a welding rate of 1000mm/min were determined as the welding parameters for the SPF/DB process. The weld depth and weld width were considered suitable for parameters for laser welding. (3) The results of high temperature material performance indicate that 900 °C and a strain rate of 0.1s-1 strain rate were selected to simulate the forming process. (4) Verify the workpiece in accordance with the simulation parameters and evaluate defects, such as grooves on the surface of the workpiece and triangular areas between vertical bars. All the cylinders’ indexes can meet the requirements, and the process quality is stable and controllable.

Effect of Oxide Flux Particle Size on Weld Bead Morphology of Hastelloy C-22

Activated tungsten inert gas welding (ATIG) welding is a new approach to Tungsten Inert Gas (TIG) welding that has the potential to improve weld penetration. This paper investigates the effect of micro and nanoparticle size oxide flux during TIG welding of Hastelloy C-22. The effect of SiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> oxide fluxes in terms of particle size and thermal stability on surface appearance, bead geometry, and microhardness of the fusion zone of hastelloy C-22 is investigated. The surface appearance of ATIG weld has a better appearance using nanoparticle size oxide flux when compared with the same micro size oxide flux. A slag layer produced by nano flux decomposition during TIG welding is very less compared to micro oxide fluxes. Nanoparticle SiO<sub>2</sub> flux has the potential to improve weld penetration and depth to width (D/W) ratio in the generated weldment when compared to microparticle SiO<sub>2</sub> flux during TIG welding Process. When nanoparticle Al<sub>2</sub>O<sub>3</sub> is used in TIG welding, weld penetration or the D/W ratio do not increase significantly. Due to the high voltage produced at the same arc length, TIG welding with nanoparticle SiO<sub>2</sub> flux produces a high heat input. Furthermore, higher arc temperatures produce by nanoparticle fluxes at the arc column, resulting in increased penetration depth.