Actual Welding Process Research Articles

Development of an indirect measurement method for the Contact Tube to Workpiece Distance (CTDW) in the Direct Energy Deposition – Arc (DED-ARC) process for different arc types

During the layer-by-layer build-up in the Direct Energy Deposition (DED) - Arc additive manufacturing (AM) process, the distance between the contact tube and the workpiece, effectively the welded layer, changes. Since the weld paths are predefined by the path planning software, a constant Contact Tube to Workpiece Distance (CTWD) and weld bead height is assumed. However, even small changes in geometry, such as crossovers of weld paths, result in higher weld beads than assumed. Similarly, an incorrectly assumed bead height as input to the path planning will result in a change in the CTWD. The sum of the deviations of the real weld geometries from the assumed ones in the path planning can greatly influence the CTWD. This implies that the dimensional accuracy may be significantly compromised. This research presents an approach for a general indirect measurement method using the welding current to obtain the CTWD during the actual welding process. A real-time process control method is implemented and validated using the mechanically controlled short arc and the pulsed arc process. Varying process parameters are used to validate the general applicability for a specific material. For the mechanically controlled short arc process, the model underestimates the measured CTWD by a mean error of 3.4 mm. The pulse process is overestimated by a mean error of 2.2 mm. The standard deviation for the pulse process with 1.3 mm is slightly smaller than for the short arc process with 1.7 mm.

A dual-robot cooperative arc welding path planning algorithm based on multi-objective cross-entropy optimization

In this paper a novel discrete multi-objective cross-entropy optimization (CrMOCEO) algorithm is proposed to solve the path planning problem of dual-robot cooperative arc welding. We strive to find a low-cost, fast and more efficient solution for robotic welding of large complex components. Firstly, an optimization model of dual-robot welding path planning is established by considering various variables and constraints in the actual welding process. Then, three strategies are introduced to improve the multi-objective cross-entropy optimization (MOCEO) algorithm to better solve the discrete path planning problem. Finally, in order to verify feasibility and effectiveness of the proposed algorithm, it is used to solve the 2-, 3-, 5- and 7-objective WFG2–9 problems and plan some typical welding seams of a large complex component, the MOCEO, NSGA-Ⅱ, MOPSO and MOGWO are used for comparison. The simulation demonstrates that the CrMOCEO can obtain better solutions for multiple objectives than the other four algorithms, and the path solved by the CrMOCEO is tested in the Gazebo physical model and workshop site, the results further verified the effectiveness of the CrMOCEO algorithm. Particularly, a series of experiments provide more solutions for actual production.

Changes in Welding Angle and Current Voltage

This article mainly studies the impact of changes in the angle of the weld seam groove on the welding current and voltage during welding. Different angles of the groove are selected for zigzag welding using a welding gun. The simulation results show that there is a significant change in current and voltage during the actual welding process as the angle of the groove changes. At the same time, it can also be derived in reverse based on the changes in current and voltage.

Process Simulation and Optimization of Arc Welding Robot Workstation Based on Digital Twin

For the welding cell in the manufacturing process of large excavation motor arm workpieces, a system framework, based on a digital twin welding robot cell, is proposed and constructed in order to optimize the robotic collaboration process of the welding workstation with digital twin technology. For the automated welding cell, combined with the actual robotic welding process, the physical entity was digitally modeled in 3D, and the twin welding robot operating posture process beats and other data were updated in real time, through real-time interactive data drive, to achieve real-time synchronization and faithful mapping of the virtual twin as well as 3D visualization and monitoring of the system. For the robot welding process in the arc welding operation process, a mathematical model of the kinematics of the welding robot was established, and an optimization method for the placement planning of the initial welding position of the robot base was proposed, with the goal of smooth operation of the robot arm joints, which assist in the process simulation verification of the welding process through the virtual twin scenario. The implementation and validation process of welding process optimization, based on this digital twin framework, is introduced with a moving arm robot welding example.

A Dual-Robot Cooperative Arc Welding Path Planning Algorithm based on Multi-Objective Optimization

In this paper a novel improved multi-objective genetic algorithm (R-NSGA-Ⅱ) is proposed to solve the problem of dual-robot arc welding path planning. We strive to find a low-cost, fast and more efficient solution for large complex components. Firstly, a multi-objective optimization model of path planning is established by considering various variables and constraints in the actual welding process. Then, the R-NSGA-Ⅱ introduces a recombination mechanism to replace the mutation operation of NSGA-Ⅱ; this can increase the diversity of individuals and populations, and find the global optimal solution with greater probability. Finally, in order to verify feasibility and effectiveness of the proposed algorithm, it is used to plan some typical welding seams of a large complex component, the NSGA-Ⅱ and OMOPSO are used for comparison. The simulation demonstrates that R-NSGA-Ⅱ can obtain better Pareto front than the other two algorithms. Particularly, the R-NSGA-Ⅱ reduces the waiting time by 42.39% and the no-load distance by 10.50% compared with NSGA-Ⅱ.

Physics-driven modeling of electron beam welding of Al-Cu alloys from molten pool flow, microstructure to mechanical properties

The process-structure-property relationship has always been the research focus in welding, where computational prediction is valuable. However, some important physical phenomena are often simplified when modeling the melting and solidification processes. In this work, an integrated modeling framework is adopted to comprehensively predict the welding quality, from a computational fluid dynamics (CFD) model for molten pool dynamics, to a cellular automata (CA) model for dendrite growth, and finally to analytical and finite element method (FEM) models for mechanical properties. Using Al-Cu alloy as a model material, the complex melting and solidification processes in electron beam welding is reproduced, and various strengthening mechanisms are considered to predict the mechanical response. Notably, the material property inhomogeneities due to inhomogeneous microstructure in the welds are considered when predicting the overall mechanical properties. Based on the simulation results, the second phase strengthening proportion reaches almost 50%. The maximum relative errors of predicted Vickers hardness and tensile strength are 13.62% and 13.30%, respectively. The simulation results show quantitative agreement with experimental data, demonstrating the appealing potential of this modeling framework. This study could be helpful for optimizing the actual welding process to tailor the microstructures and mechanical properties. • A physics-driven process-microstructure-property modeling framework is adopted. • Various strengthening mechanisms based on the microstructure modeling are considered to predict the mechanical response. • The material property inhomogeneities are considered when predicting the overall mechanical properties. • The simulation results show quantitative agreement with experimental data.

Thermomechanical phase change peridynamic model for welding analysis

In numerical welding modelling, it is critically important to adopt a heat source model that fits the actual welding process since the heat source model has significant influence on the calculation accuracy of the transient welding temperature field, especially near the heat source. An inappropriate source model can produce an overestimated or underestimated temperature field, leading to displacement field errors in the mechanical analysis. In this study, a new non-linear transient peridynamic model employing a variety of heat source models is developed to predict the temperature distribution and displacement variation. More importantly, as an essential physical phenomenon in heat conduction, phase transformation is considered in the peridynamic model. The importance of how the latent heat in the phase change can affect the temperature distribution and displacement field is also emphasized. The simulation results are compared with the finite element method results. Close agreements are observed which demonstrates the capability of the proposed non-linear transient peridynamic model for thermomechanical phase change analysis for welding modelling.

Modeling of microstructure evolution coupled with molten pool oscillation during electron beam welding of an Al-Cu alloy

The physical understanding of electron beam welding (EBW) and prediction of the weld microstructure are valuable but challenging. In this work, a multi-physics modeling framework is adopted to simulate the microstructure evolution during the EBW process. A molten pool model incorporating multiple driving forces and a dynamic heat source model provides the temperature field as the input for the microstructure simulation. Both the temperature and chemical concentration are considered in the grain growth process. Additionally, an efficient method is adopted to track the second phase in the solidification process, and a practical algorithm is proposed to identify the complex weld shapes. The mechanism of microstructure evolution under the effect of molten pool oscillation is elaborated. Based on the simulated results, the effects of the process parameters on the grain morphology, grain size, segregation and second phase are quantified. These predicted results are compared to experimental observations and measurements. This study could be helpful for both understanding microstructure evolution and optimizing the actual welding process to tailor the microstructure.

Numerical Analysis of Electron Beam Welding Deformation for the Vacuum Vessel Lower Port Stub of 316L Stainless Steel

The China Fusion Engineering Test Reactor vacuum vessel has strict tolerances requirements and a large number of fully penetrated joints in the manufacturing and assembly processes. As the most complicated component of vacuum vessel, port stubs have stricter tolerance requirements, to guarantee the high assembly accuracy with the vacuum vessel. Due to the small deformation of electron beam welding, this method is adopted for the welding of port stub. However, welding deformation cannot be avoided, thus it is necessary to carry out finite element analysis to analyze and control the welding deformation of the port stub. In this paper, based on thermo-elastic–plastic theory, the double ellipsoid and cone-shaped hybrid heat source can accurately outline the electron beam weld pool contour of the 316L stainless steel with 50 mm thickness, which is further verified by the welding process experiment. The above hybrid heat source is applied to analyze the welding deformation of the lower port stub, and according to the deformation simulation results, the welding fixture is designed to reduce the welding deformation. The welding deformation analysis can effectively provide theoretical data support and practical guidance for the actual electron beam welding process of port stub.

A Dual-Robot Cooperative Welding Path Planning Algorithm Based on Improved Ant Colony Optimization

In this paper a novel path planning algorithm based on improved ant colony optimization is proposed for dual-robot cooperative welding. We seek to provide a low-cost, fast and effective solution for such problems. The optimization model of dual-robot collaborative welding is established based on actual welding process constraints and shortest welding path target. Then, a dynamic transfer strategy and information update strategy are proposed to improve the ant colony algorithm (ACO+) based on this model. Finally, the proposed ACO+ algorithm is implemented to solve the dual-robot path planning problem in the welding task of a large complex component. The simulation demonstrates that the proposed method has faster convergence rate and shorter welding path compared with the unmodified ant colony algorithm. Particularly, this algorithm is suitable for path planning of dual-robot cooperative welding for symmetrical complex component.

Dissimilar metal joining of Q235 mild steel to Ti6Al4V via resistance spot welding with Ni–Cu interlayer

Dissimilar metal joining between Q235 mild steel and TC4 titanium alloy was carried out via resistance spot welding with Ni–Cu alloy as filler metal (abbreviated as resistance welding with interlayer). The results were compared with the welded joints obtained by directly conventional resistance spot welding without interlayer (abbreviated as D-RSW). The effect of Ni–Cu alloy on the macro-characteristics, interfacial structure, and microstructure, mechanical properties (including shearing force and microhardness) of the welded joints were investigated. Also, the temperature field in the actual welding process was dynamically simulated using MSC.Marc software, which validity of the numerical results was confirmed by the actual temperature collected at the same location via the infrared thermal imaging. The results showed that the maximum temperature was less than the melting point of TC4, Q235, and interlayer. The reaction layer and diffusion layer were formed between TC4 and Q235 by atomic diffusion due to the introduction of the interlayer, which replaced the welding nugget generated in the D-RSW welding process. Ti2Ni, Cu3Ti2, TiNi, TiCu, and TiFe2 intermetallic compounds (IMCs) could be generated at the welded joints by resistance welding with interlayer. Moreover, there were no other welding defects in the welded joints. The maximum ultimate shearing force was up to 12,726 N in this way, which was more than twice that obtained by D-RSW. Correspondingly, the interfacial fracture was obtained for the former instead of the brittle facture for the latter. There was a narrow range of highest-value microhardness according to the reaction layer.

Modeling and numerical study of the molten pool dynamics during scanning electron beam welding of aluminum alloys: Physical mechanism, prediction and parameter selection

Physical understanding of the scanning electron beam welding (EBW) process and prediction of weld forming quality are always a focus and a challenge in the field of material processing. In this paper, a three-dimensional molten pool model is developed to study the molten pool dynamics during EBW with beam oscillation. The model involves an innovative heat source model that considers the broadening effect of metal vapor on the electron beam radius and direct coupling between the electron beam and keyhole wall. The model is validated by comparing the areas of the weld longitudinal section and weld dimensions from experiments and simulations. In addition, the number of porosity defects in the experimental weld seam is examined to prove the rationality of the theoretical analysis. Based on the molten pool model and the theoretical analysis, a Gaussian process regression (GPR) method for rapidly predicting the weld dimensions and a new method for quantifying the molten pool stability are proposed. Eventually, we propose an innovative and rapid method for selecting welding process parameters. This study is expected to provide a deeper understanding of the scanning EBW process and to improve confidence in optimizing and controlling the actual welding process.

A modified version of MATLAB application window for predicting the weld bead profile and stress–strain plot of AA5052 CMT weldment using ER4043

The present study deals with the extended version of our previous research work. In this article, for predicting the entire weld bead geometry and engineering stress–strain curve of the cold metal transfer (CMT) weldment, a MATLAB based application window (second version) is developed with certain modifications. In the first version, for predicting the entire weld bead geometry, apart from weld bead characteristics, x and y coordinates (24 from each) of the extracted points are considered. Finally, in the first version, 53 output values (five for weld bead characteristics and 48 for x and y coordinates) are predicted using both multiple regression analysis (MRA) and adaptive neuro fuzzy inference system (ANFIS) technique to get an idea related to the complete weld bead geometry without performing the actual welding process. The obtained weld bead shapes using both the techniques are compared with the experimentally obtained bead shapes. Based on the results obtained from the first version and the knowledge acquired from literature, the complete shape of weld bead obtained using ANFIS is in good agreement with the experimentally obtained weld bead shape. This motivated us to adopt a hybrid technique known as ANFIS (combined artificial neural network and fuzzy features) alone in this paper for predicting the weld bead shape and engineering stress–strain curve of the welded joint. In the present study, an attempt is made to evaluate the accuracy of the prediction when the number of trials is reduced to half and increasing the number of data points from the macrograph to twice. Complete weld bead geometry and the engineering stress–strain curves were predicted against the input welding parameters (welding current and welding speed), fed by the user in the MATLAB application window. Finally, the entire weld bead geometries were predicted by both the first and the second version are compared and validated with the experimentally obtained weld bead shapes. The similar procedure was followed for predicting the engineering stress–strain curve to compare with experimental outcomes.

Effect of Mg Addition on the Microstructure and Properties of a Heat-Affected Zone in Submerged Arc Welding of an Al-Killed Low Carbon Steel.

To reveal the effect of Mg treatment on the microstructure evolution behavior in the actual steel welding process, the microstructure and properties of Al-deoxidized high-strength ship plate steel with Mg addition were analyzed after double-side submerged arc welding. It was found that the Al–Mg–O + MnS inclusion formed under 26 ppm Mg treatment could promote acicular ferrite (AF) nucleation in the coarse-grained heat-affected zone (CGHAZ) and inhibit the formation of widmanstätten ferrite and coarse grain boundary ferrite. In the fine-grained heat-affected zone (FGHAZ) and intercritical heat-affected zone (ICHAZ), polygonal ferrite and pearlite were dominant. Al–Mg–O+MnS cannot play a role in inducing AF, but the grain size of ferrite was refined by Mg addition. The impact toughness in HAZ of the Mg-added steel was higher than that of Mg-free steel. With the heat-input rising from 29.55 to 44.11 kJ/cm, it remained relatively stable in Mg-treated steel. From the fusion line to the base metal, the micro-hardness of the fusion zone, CGHAZ, ICHAZ and FGHAZ decreased to some extent after Mg addition, which means the cold cracking tendency in the welding weak zone could be reduced. Finally, the mechanisms of Mg-containing inclusion-induced AF were also systematically discussed.

Welding robot path planning problem based on discrete MOEA/D with hybrid environment selection

Welding robot path planning gradually has increasingly widespread attention in automatic production on account of improving the production efficiency in the actual production process. It is a combinational optimization problem to find an optimal welding path for the robot manipulator by arranging the sequence and directions of welding seams. To solve the problem with two objectives, path length and energy consumption, this paper proposed an improved discrete MOEA/D based on a hybrid environment selection (DMOEA/D-HES) with a parallel scheme to search the optimal sequence and directions simultaneously for welding seams. The discretized reproduction and adaptive neighborhood provide a larger search range in solution space to overcome difficulties in duplication and uneven distribution of solutions. Adaptive decomposition method and improved hybrid environment selection promote solutions converge to the optimal direction and further balance convergence and diversity. Eight TSPLIB problems were tested with the proposed algorithm and the other four algorithms. Besides, the algorithm is compared with four multi-objective evolutionary algorithms (MOEAs) on the multi-objective welding robot path planning on the balance beam. The test results indicate DMOEA/D-HES outperforms other algorithms on convergence with a competitive diversity, which is effective to be applied in the actual welding process.

Multi-scale simulation of solidification behavior and microstructure evolution during vacuum electron beam welding of Al-Cu alloy

A multi-scale model is established to study the complex melting and solidification behaviors during the electron beam welding of an Al-Cu alloy. The model combines a macroscopic thermal-fluid algorithm for molten pool behavior and a microscopic cellular automaton algorithm for the microstructure evolution. The solidification parameters, including the thermal gradient and cooling rate, build a bridge between the macroscopic and microscopic simulations. The model is validated by comparing the experimental fusion profile results, microstructure, morphology, grain size and element distribution that result from different welding parameters. On the macroscopic scale, with an increase in beam current, the molten pool fluctuation intensity increases, the thermal gradient increases and the cooling rate decreases. On the microscopic scale, the grain growth process includes nucleation, growth and competitive growth. After solidification, the concentration of Cu on the grain boundaries is larger than that inside the grains. With increasing beam current, the grain size tends to increase, and the segregation ratio decreases. The power-law function between the grain size and cooling rate can be summarized as d∝CR−0.55, where d is the grain size and CR is the cooling rate. Moreover, the segregation ratio first increases and then decreases slowly with decreasing solidification time. We expect this study to provide a deeper understanding of how to control weld formation and microstructure and improve confidence in optimizing the actual welding process.

Heat treatment simulation investigation on the mechanical performance of the inter-critical heated affected zone (ICHAZ) in ship plate steel weld joint

Simulated ICHAZ specimens of ship plate steel (DH36) with different heat-treated durations, which represent various heat input for the actual welding process, were comprehensively studied on the tensile deformation and the fracture mode of impact toughness. The evolution of microstructure and misorientation distribution was characterized using an optical microscope (OM), electron backscatter diffraction (EBSD), transmission electron microscope (TEM). Results indicate that as the cooling duration increased, less lath bainite (LB) formed with the growth of polygonal ferrite (PF) and MA constituents which locates at grain boundary and intragranular, corresponding to a phenomenon that high angle grain boundary (HAGB) increase with the decrease of low angle grain boundary (LAGB). Compared with specimens treated with short heat treatment durations, which t8/5 includes 15s and 30s, samples treated with 75s of t8/5 exhibited higher tensile strength and ductility, which was associated with the increase of the defects volume fraction (ρ) relative to a prior austenite grain (PAG). Instrumented impact test results confirmed that the void coalescence formed in the crack propagation process was blocked by HAGB with high heat input, presenting a high value of ρ.

Numerical simulation of the ITER BTCC prototype case enclosure welding

Abstract The 20mm thick 316LN austenitic stainless-steel plate was used as a case material to protect the inner side superconductive winding pack to resist the electromagnetic cyclic loads during the operation. The enclosure welding of the BTCC(short for bottom and top correction coils) case was consist of 18mm thick laser welding and 2mm TIG cover welding. To control the welding deformation of the large-scale prototype case, the numerical simulation was carried out to obtain the deformation distribution of the case. The result shows that the combined heat source model with double ellipsoid heat source and 3D Gauss heat source model was suitable to simulate 18mm thickness deep penetration laser welding and the warping deformation happened at both ends of the BTCC case. Although some simplification has been applied on the calculated model, the result could still consistent with the actual welding process. The established heat source and the result of the simulation process which will be benefit to predict the welding deformation of the BTCC case enclosure welding.

WeldForming: a new inline process combination to improve weld seam properties

The high heat input during fusion welding leads to transformations of the microstructure in the area subjected to welding, mostly resulting in a heterogene crystalline structure and an overall deterioration of the mechanical properties. To reduce the detrimental effect, posttreatment processes which are typically separated from the actual welding process are state of the art. The present work shows the new methodology, WeldForming, which intends to eliminate subsequent treatment processes. The new in-line process combination harnesses the synergies of a welding and a rolling process to ultimately prevent the typical zone formation of the heat affected zone. Experimental investigations combined with a detailed numerical simulation of the coupled welding and forming process indicate the functional proof of the new methodology. The validation of the numerical model is carried out with the aid of temperature profiles, cross sections, and microstructure analysis as well as flow curves determined by upsetting tests on thermomechanical simulation systems.

Rapid welding technology for polyethylene gas pipes at temperatures below standard

Rapid polyethylene pipes welding technology at temperatures below standard is proposed. This technology consists of preheating, equalization to acceptable temperature, reflow in regulated mode, and cooling under heat insulation layer or in heat-insulating chamber. Additional welding parameters, including heating and temperature equalization duration, heat-insulating layer thickness or heat-insulating chamber dimensions, are calculated from condition of ensuring heat process flow according to welding pattern at acceptable temperature. For mathematical model adequacy to actual heat welding process, it is proposed to consider polyethylene phase transformation heat in temperature range. When solving problem using end-to-end counting method, effective heat capacity coefficient is introduced, which is determined using temperature dependence of polymer material crystallinity degree. Crystallinity degree in welding process is determined by differential scanning calorimeter. Results of calculating cooling rates for polyethylene pipes electrofusion welding at various temperatures are given. Significant increase of cooling rate in heat-affected zone during welding at low temperatures, at which fine-crystalline structure is formed, which causes weld material plasticity, is shown. It is shown that when welding polyethylene pipes in low ambient temperatures, preheating, temperature equalization and cooling with thermal insulation with calculated parameters lead to thermal process in heat-affected zone according to welding patterns at acceptable temperature.