Weld Geometry Research Articles

An improved simulation of temperature field in PMHW of Ti-6Al-4V alloy

This article describes a coaxial plasma–MIG hybrid welding (PMHW) method to improve the welding quality of titanium alloy plates. Aiming at the temperature field analysis of a Ti-6Al-4V alloy plate in the PMHW process, an improved hybrid heat source model capable of accurately characterising the heat input of a hybrid arc on workpieces and the arc deflection phenomenon, is proposed. Experiments were conducted on 4-mm Ti-6Al-4V plates in PMHW surfacing, and a corresponding simulation analysis was performed. To calculate the weld geometry, a weld pool shape was used in accordance with the experimental results. The results showed that, as plasma current increased from 60 to 80 A, the weld reinforcement and offset decreased, and the size of the weld pool increased. Plasma arc power had a greater effect on the length than on the width of the molten pool. Hybrid arcs had a stronger penetrating ability; hence, achieving deep penetration welding and high welding efficiency in the PMHW of the Ti-6Al-4V alloy was easier. Microstructure analysis showed that the Ti-6Al-4V alloy base metal zone was organised by α- and β-phase transformations; β grains in the weld zone were internally formed by a mixture of Weischer tissue and net basket tissue; and the size of β grains in the heat-affected zone decreased with the increase in the distance from the weld.

Numerical design calculation of structural steel welds

This paper focuses on designing fillet welds made from high-strength steel (HSS). It presents a numerical design calculation (NDC) method for assessing weld strength using the regular inclined shell element model (RISEM) in the finite element method (FEM). NDC uses FEM to design joints according to standardised procedures. The inclined shell element in RISEM represents the geometry and stiffness of welds, controlling its stresses in the plane. The paper recommends using a common inclined shell element with rigid links to accurately represent the geometry and rigidity of fillet welds. A new strength criterion is proposed based on stresses on the inclined shell element, using maximum equivalent stress as an indicator. Validation of the method is confirmed by comparing RISEM and test results using finite element (FE) simulation. Additionally, the weld resistance computed from the equation in prEN 1993-1-8:2020 is also in good agreement.

Transmission laser welding of thermoplastics: Influence of welding parameters and rib dimensions on the strength of welded joints

Laser transmission welding of injection moulded thermoplastics is commonly used in industrial applications such as electronic packaging, textiles, biomedical devices, windows, signs, food and medical packaging, visual displays and automotive components due to very precise control of the process parameters, including the amount of energy delivered and its location, which results in high joint quality. In this article, the influence of laser transmission contour welding parameters and geometry of welding rib on joint force is investigated. Velocity with which the laser beam moves on the sample, temperature applied, clamp force, laser beam size and number of laser passes were studied for various dimensions of the rib with rectangular and triangular cross section. Samples of different thermoplastic materials, PMMA and PC/ABS, were produced and then joined by transmission laser welding and after that were subjected to tensile tests, in order to measure strength of the joint between the plastic parts. Initially, optimal welding conditions were found for each studied rib and their influence on the force of the joint was analysed. Afterwards, a comparison between the best results obtained for each rib was performed, in order to define the dimensions of the rib that result in the highest joint force. It was observed that samples with triangular ribs achieved higher joint strength. For both studied geometries of rib cross section, an increase of the width of the ribs improves the joint strength, while an increase of the height worsens it.

Adaptive Predictive Control of Backside Weld Width in Pulsed Gas Metal Arc Welding Using Electrical Characteristic Signals as Feedback

The control of backside weld width in pulsed gas metal arc welding (GMAW-P) is achieved with two electrical characteristic signals as feedback in the present work. The GMAW-P process is adjusted by changing the parameters of the base current period to provide the needed heat input, while the backside weld width is characterized during the amplitude-fixed peak current period. The two characteristic signals, i.e., the relative change in arc voltage and the average arc voltage during the peak current period, exhibit negative linear relationships with backside weld width and are employed as sensing signals. With these two characteristic signals as outputs, the backside weld width control system in GMAW-P is modeled and analyzed. The adaptive predictive controller is thus designed and validated in real-time control. This work provides an easily implemented way for weld geometry control in GMAW-P and thus has a practical meaning.

Optimization of resistance spot welding with surface roughness dissimilar mild steel with stainless steel

Resistance spot welding plays a critical role in the manufacture dissimilar material industry. However, there are differences in mechanical properties between mild steel and satinless steel so as to reduce the quality of welded joints. In order for differences in mechanical properties to be corrected, surface roughness was treated. The aim of this study was to optimize the welding parameters of DRSW with surface roughness by analysis using the Taguchi and Anova Methods. In this study discusses about investigates the Resistance spot welding parameters on weld geometry, mechanical properties, and SEM EDS on dissimilar materials of mild steel and stainless steel. The material thickness of the mild steel and stainless steel are 1 mm, respectively. The process parameters of the resistance spot welding joint used, example; surface roughness, current, welding time, and electrode force. Quality welding joint test results include weld geometry, mechanical properties, and SEM EDS. Weld geometry testing to determine the weld nugget profile. The mechanical properties test was shear tensile test, while the SEM EDS included macrostruture and microstructure observations. The results showed the highest nugget diameter 6.65 mm highest shear tensile strength 7.66 kN. The most influential parameter is current by 75.08 %, then surface roughness by 12.35 %. The highest tensile strength has fewer defects. Surface roughness treatment before welding is very good to make welding quality joints between mild steel and quality stainless steel increase. Surface roughness treatment was very good to be included when making welding procedures for welding engineers for welding processes resistance spot welding dissimilar mild steel with stainless steel.

Automated data evaluation in phased-array ultrasonic testing based on A-scan and feature training

In this study, a training dataset and neural network were newly configured to develop a diagnostic artificial intelligence (AI) for phased-array ultrasonic testing (PAUT), and three experiments were conducted to verify its performance. The main problem of this study is to properly classify the suspicious normal signal and defect signal, which is difficult because the welding boundary and geometry signal must be considered together. First, in order to collect high-quality data necessary for training neural network, 40 welding specimens were manufactured and a total of 120 defects were included in the specimens. Then, the neural network was trained using data from 120 defects inspection. Through the first experiment, it was determined that three convolutional layers are sufficient to learn the A-scan signals. In the second experiment, a comparison experiment was performed by adding four features to the training dataset, and it was confirmed that the classification accuracy was significantly improved. Finally, in the third experiment, the trained network was utilized to perform data evaluation for each inspection result file. As a result, the evaluation results by diagnostic AI were mostly consistent with the reference expert's results, while the other expert were unable to properly identify the defect types. In conclusion, the proposed method in this study remarkably improved the classification accuracy of the signals and led to successful data evaluation, which is expected to help the PAUT experts make more accurate data evaluation.

Mechanical properties of MAG butt welded dissimilar structural steel joints with varying strength from grade S355 up to S960

AbstractMixed connections made of normal-strength and high-strength structural steels allow for optimized material usage and production effort in applications where, as a result of different mechanical effects on materials of the same type, it would otherwise be necessary to adjust the plate thickness. Reduced material consumption and smaller weld geometries can thus generate ecological and economic advantages. When welding high-strength structural steels, however, significant softening can occur in the heat-affected zone, which can influence the load-carrying behavior of the overall joint. Since there are currently no appropriate standards for butt welds made of steels with different strengths up to S960, a separate design concept is required. In this paper, the weldability and load-carrying capacity of multilayer MAG welded butt joints designed as mixed connections of a normal-strength structural steel S355 and a high-strength structural steel in the range S690 to S960 are investigated. Extensive experimental investigations are carried out, in which other influencing variables such as the filler metal used, the heat input, the plate thickness, and the weld geometry are varied in order to identify their effects on the load-carrying capacity of the welded joints. Among other things, the results form the basis for an empirically based design model for mixed connections.

An Improved Method for Deriving the Heat Source Model for FCAW of 9% Nickel Steel for Cryogenic Tanks.

The International Maritime Organization (IMO) is tightening regulations on air pollutants. Consequently, more LNG-powered ships are being used to adhere to the sulfur oxide regulations. Among the tank materials for storing LNG, 9% nickel steel is widely used for cryogenic tanks and containers due to its high cryogenic impact toughness and high yield strength. Hence, numerous studies have sought to predict 9% nickel steel welding distortion. Previously, a methodology to derive the optimal parameters constituting the Goldak welding heat source for arc welding was developed. This was achieved by integrating heat transfer finite element analysis and optimization algorithms. However, this process is time-consuming, and the resulting shape of the weld differs by ~15% from its actual size. Therefore, this study proposes a simplified model to reduce the analysis time required for the arc welding process. Moreover, a new objective function and temperature constraints are presented to derive a more sophisticated heat source model for arc welding. As a result, the analysis time was reduced by ~70% compared to that previously reported, and the error rates of the weld geometry and HAZ size were within 10% and 15% of the actual weld, respectively. The findings of this study provide a strategy to rapidly predict welding distortion in the field, which can inform the revision of welding guidelines and overall welded structure designs.

Influence of Siliconized Zn-Graphene Oxide Complex Nanoparticles on the Microstructure and Mechanical Properties of AA5083: Focus on Gas Metal Arc Welding

Aluminum alloy 5083 has low density, mechanical properties, high corrosion resistance, and high welding capability. Due to high thermal conductivity, specific heat, and latent heat, as well as the relatively high coefficient of thermal expansion of aluminum, achieving a connection with good mechanical properties is always very important. This study aimed to investigate nanoparticles’ surprising and unexpected effects in forming various microstructures, which directly improve the mechanical properties of the welding process as a new and surprising idea. The effects of siliconized Zn-graphene oxide complex nanoparticles on weld geometry, mechanical properties, and microstructure of AA5083 were investigated. The gas metal arc welding process welded the samples, and different amounts of nanoparticles were investigated. The results reveal that utilizing nanoparticles can be affected by the weld geometry and the properties of weld metal. 0.25 g of nanoparticles had low face reinforcement, and the bead width and penetration depth dramatically increased. The presence of nanoparticles inside the molten zone and its effect on grain size improved mechanical properties, according to the Hall–Petch relationship. The ultimate tensile strength and yield strength of the S0.25 sample increased by 58.24 and 28.28%, respectively, compared to the welded sample without the presence of nanoparticles. Also, the ductility of this sample during the failure test showed that elongation increased by 36.75%.

Investigations on the material behaviour of weld seams for the use in finite element analyses

AbstractThe design of complex structural steel connections by finite element analysis is common practice nowadays. However, for welded joints there are no normative regulations for the static finite‐element‐analysis. To analyse the specific material behaviour in the weld area and derive a geometry and material model for the finite element analysis, tensile tests on specimens with different weld geometries are made at the Technical University of Darmstadt. During the tests an optical measuring method, called Digital Image Correlation, is used. It records the deformations on the surface of the specimen and assigns the recorded analogue test load to the images. By this way, the load‐deformation‐behaviour in all areas of the weld can be determined. In addition to the tensile tests, microsection examinations are carried out. The applied colour etching makes the microstructure of the weld zones visible so they can be geometrically superimposed with the strain images of the tensile tests. In welded connections the stress state is very complex. Therefore, numerical investigation must be performed to derive the final stress‐strain‐curves of the weld area. These curves can then be implemented as a material model for the finite element analysis of welded connections.

Structural behaviour of Cold‐Formed Steel back‐to‐back welded sections subjected to longitudinal shear

AbstractThe current study focuses on understanding the behaviour of flare v‐groove welds on back‐to‐back connected Cold‐Formed Steel welded sections (G300) subjected to longitudinal shear. A novel welding technique called Cold Metal Transfer (CMT) welding was used for fabrication with copper‐coated steel welding wire as a filler metal (ER70S‐6). This mode of welding has the advantage of controlled material deposition compared to the spray or globular mode of welding. Lap shear tests were carried out on unlipped channels including thickness of the weld, and length of the weld. The weld geometry was observed under an optical microscope after polishing and chemical etching of the weld cross‐section, as American Iron and Steel Institute (AISI) design standard provides no specification on thickness of flare v‐groove welds for CMT welding process. In general, the lap shear specimens failed in plate tearing failure mode and brittle fracture of weld at the weld contours. Additionally, the appropriateness of AISI's shear design strength equations for flare v‐groove welds was verified and preliminary design guidelines are provided addressing the lacunae in AISI design standard.

Towards In-line Control of Continuous Resistance Welding for Joining Structural Thermoplastic Composites

The continuous resistance welding (CRW) process consists of an end-effector which moves along the length of a weld seam, heating a conductive implant while compacting the joint locally throughout the melt and solidification stages of the thermoplastic material. The performance of the joint has been shown to be highly dependent on the process temperature at the weld interface; however, this cannot be measured directly during the process in a non-invasive manner. Other parameters such as boundary conditions, substructure properties, or part geometry may vary along the length of the weld. As such, a physics-based simulation is developed founded upon an “MSTEP” framework which defines how the materials (M), shape (S), tooling (T), and equipment (E) interact to determine the process (P). Detailed finite element (FE) models are developed for thermal analysis based on the weld geometry, boundary conditions, and previously developed and validated melt/crystallization models for the thermoplastic matrix. Experimental CRW tests are presented to validate simulations and calibrate suitable control variables.

Influence of the geometry of butt welds and longitudinal attachments on their fatigue resistance

AbstractMany constructions, such as wind turbines, bridges and crane runways, are cyclic loaded so that fatigue failure may occur. Therefore, in the course of the revision of Eurocode 3, two research projects funded by AiF‐DASt re‐investigate the classification of constructional details of EN 1993‐1‐9. This paper focuses on the geometrical influence on the fatigue resistance of butt welds and longitudinal attachments. First, the influence of the plate thickness on butt welds was investigated. Both a meta‐study based on test results of various research projects and our own test series on butt welds up to 80 mm thickness led to interesting conclusions.Furthermore, the influence of the length and radius of longitudinal attachments on the fatigue resistance was investigated. By experiments and numerical analysis, clarification has been sought whether the transition radius larger than 150 mm or the ground weld toe is decisive for the improvement of the fatigue resistance. Since previous meta‐studies could not provide a clear result on the influence of the longitudinal attachment length, this was also investigated.A database established in the projects allows to integrate and assess the specified details of butt welds and longitudinal attachments in the context of the overall approach in EN 1993‐1‐9.

Solidification Crack Free Welding Strategy via Ultra High Precision Laser Scanning at a Single Grain of Directionally Solidified and Single Crystal Superalloys

In this study, possibility of solidification crack-free welding of directionally solidified CM247LC and single crystal CMSX-4 superalloys was metallurgically investigated using single-mode fiber laser scanning. The key metallurgical factors of solidification cracking have been identified as the formation of highly misoriented solidification grain boundaries (low level of epitaxial growth behavior) at the fusion zone that affects the repulsive force between two adjacent dendrites and dendrite coalescence undercooling at the terminal stage of weld solidification. In particular, under extremely low heat input and ultra-high-speed laser beam scan conditions (welding speed: 1,000 mm/s, heat input: 2 J/mm, and energy density: 65 J/mm<sup>2</sup>), an effective fusion zone could be achieved within a single directionally solidified grain of CM247LC alloy owing to the characteristics of single-mode fiber laser. The fusion zone successfully showed a 99.9% of epitaxial growth achievement ratio (that is, low fraction of highly misoriented solidification grain boundaries at the fusion zone) without solidification cracking. Based on these results on CM247LC alloy, solidification crack-free welds could be successfully achieved using quadruple-pass and square-type weld geometries.

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.

Using Fundamental Parameters and Artificial Neural Network for Controlling the Laser Welding of Metals

The present work aims to design an artificial neural network (ANN) for controlling the geometry of the fusion zone in different welding conditions. AA5754 aluminium plates with 6 mm thickness were welded in butt configuration by using an Yb-doped fiber laser in continuous wave regime. Laser power, travel speed, beam diameter and shielding gas were considered as process-related factors, while the weld geometry was evaluated in terms of penetration depth and bead width. The accuracy of the model was endorsed by using untrained test data. Results showed a good agreement between the ANN output and the experimental values.

Mathematical modelling to predict bead geometry in MIG welded aluminium 6101 plates

MIG (Metal Inert Gas) welding is a popular metal joining process due to its ability to weld a wide variety of metals. The mechanical properties of a weld are governed by the weld geometry parameters, namely the height of reinforcement, the width of the bead and penetration depth. The input welding parameters like wire feed rate, voltage, welding speed etc. in turn decide the above bead geometry parameters. The present research work aims at developing mathematical models connecting these input parameters to the bead geometry parameters for MIG welded aluminium 6101 plates. The mathematical models were generated by the central composite rotatable design technique. The developed models’ adequacy was verified by ANOVA (Analysis of variance) and RSM (Response Surface Methodology) was used to analyze the results graphically.

Weld Geometry Prediction Based on Binocular Vision and Deep Learning

To improve the level of welding automation in the industry, there are increasing requirements for highly intelligent and accurate inspections of the welding process in real time. This paper proposed a new method for predicting weld dimensions based on binocular imaging information and a deep learning system. The binocular imaging information was acquired by binocular vision equipment and an image processing algorithm. A convolutional neural network structure was developed by adding a fully connected block and loss function judgment. A new calculating procedure was proposed to extract and link the information of the processed weld pool image and the weld parameters effectively. With the help of 7394 training samples, the results of 1849 testing samples showed that the overall accuracy of the proposed model was higher than 93% for the prediction of weld dimensions, which could meet the requirements in practical applications.

The Use of the Linear Energy Calculation Model in High-Frequency Induction (HFI) Tube Welding Technology to Obtain Optimal Microstructure and Weld Geometry

The article presents a calculation model of the linear energy of welding P235GH steel tubes with high-frequency currents in order to obtain an optimal microstructure and geometry of the weld of high internal purity. The model was developed based on real data for the standard linear energy used in the steelworks Huta Łabędy and presented as the power factor P/V and P/(V·t), where P is the power [kW], V the production speed [m/min] and t the wall thickness. The model can be used for two ranges of pipe diameters: 114.3–168.3 mm and 219.1–323.9 mm. The data from the model were implemented into the High Frequency Induction (HFI) control panel of Huta Łabędy in order to produce test tubes which were subsequently tested with ultrasounds to verify the quality of the internal weld. In addition, samples were taken for metallographic analysis, which was supposed to check whether the applied linear energy calculation model allows the obtainment of the optimal weld geometry and the optimal angle of the metal flow line allowing for swelling and the extrusion of melted impurities from the inside of the joint by the squeeze rolls. The metallographic analysis also determined the nature of the occurrence of ferrite inside of the center diffusion bond and the zonal microstructure of the joint, the control of which is based on the correlation of the parameters of the mechanical process of forming the tube with the linear energy of welding. Carrying out the technological and technical process based on the applied HFI linear energy calculation model allowed us to obtain a weld of high purity and metallurgical consistency. This model can be used in the future on an industrial scale for the production of pipes using the HFI method.

Assessment of corrosion fatigue in welded joints using 3D surface scans, digital image correlation, hardness measurements, and residual stress analysis

Corrosion can significantly reduce fatigue resistance of steel constructions including offshore support structures. This can be attributed to either localized stress concentration caused by pitting corrosion or to embrittlement of the material during the corrosion process. In addition to the stress concentrations that can arise from pitting corrosion, offshore steel structures are characterized by a significant number of notches at weld seams, which may also cause stress concentrations. Therefore, it is of great importance to study the interaction between the pre-existing notches from welds and the notches from corrosion. Thus, reference material specimens as well as butt- and fillet-welded specimens from a mild steel S355 were investigated in this study. Before being stored in a salt spray chamber, the specimens were clean blasted as usually carried out for offshore support structures. After one month of exposure, the specimens were tested against fatigue and monitored by digital image correlation (DIC). The specimens were scanned with high-resolution 3D-scanners before and after corrosion exposure. In addition, material hardness and residual stresses were investigated to quantify the influence of corrosion on the material side and the influence from the welding process. It is shown that corrosion strongly influences the weld geometry. Both, individual pits and uniform corrosion are observed at the weld toe, which is relevant for fatigue. It was also shown that the fatigue strength of welded specimens depends not only on the geometry and its degradation by corrosion, but to a greater extent on the residual stresses present after corrosion. The residual compressive stresses applied by clean blasting were partly relieved by corrosion. The fatigue tests have shown increased fatigue strength after clean blasting and subsequent reduction due to corrosion. The fatigue strength of fillet welded specimen, for example, were increased from 74 N/mm2 in its as-welded condition to 158 N/mm2 through clean blasting. However, due to corrosion, fatigue strength decreases to 98 N/mm2.