Welding Sequence Research Articles

Efficient Industrial Solution for Robotic Task Sequencing Problem With Mutual Collision Avoidance & Cycle Time Optimization

In the automotive industry, several robots are required to simultaneously carry out welding sequences on the same vehicle. Coordinating and assigning welding points between robots is a manual and difficult phase that needs to be optimized using automatic tools. The cycle time of the cell strongly depends on different robotic factors such as the task allocation among the robots, the configuration solutions and obstacle avoidance. Moreover, a key aspect, often neglected in the state of the art, is to define a strategy to solve the robotic task sequencing with an effective robot-robot collision avoidance integration. In this paper, we present an efficient iterative algorithm that generates a high-quality solution for Multi-Robotic Task Sequencing Problem. This latter manages not only the mentioned robotic factors but also aspects related to accessibility constraints and mutual collision avoidance. In addition, a home-developed planner ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RoboTSPlanner</i> ) handling 6 axis has been validated in a real case scenario. In order to ensure the completeness of the proposed methodology, we perform an optimization in the task, configuration and coordination space in a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">synergistic</i> way. Comparing to the existing approaches, both simulation and real experiments reveal positive results in terms of cycle time and show the ability of this method to be interfaced with both industrial simulation software and ROS-I tools.

Study of Residual Stress Evolution in SUS304/Q235 Bimetallic Clad Plate Butt-Welded Joints Considering Welding Sequence

Abstract Residual stress prediction and controlling is important for structural integrity assessment of weldments. In this work, finite element (FE) and experimental methods were integrated to study the influence of welding sequence on the SUS304/Q235 bimetallic clad plate (BCP) joints during multilayer and multipass welding. The results show that the peak residual stress values on flyer plate surface are weakly affected by welding sequences but the width of high surficial longitudinal stress area of joint with base layer welded first is bigger. Meanwhile, welding sequence has a great influence on the longitudinal residual stress evolution law inside joints. When base seam layer is welded first, the highest stress concentration appears in the transition layer. However, it would be transferred into the first base seam layer due to martensite phase transformation when flyer seam layer is welded first. Residual stress controlling in the BCP joint should attract more attention from researchers.

Hybrid-laser welding-induced distortions and residual stresses analysis of large-scale stiffener panel

The weld induced-residual stresses and distortions due to hybrid laser welding of a ship deck panel are estimated. A 3-D finite element analysis is developed to estimate the post-weld-induced distortions and residual stresses using a transient indirect, decoupled, thermo-mechanical analysis. The welding simulation and analysis cover butt and fillet welding. The welding sequence is defined as a one-pass butt-weld, and after the cooling process is ended, the fillet weld of stiffeners is applied. The results of the transient thermo-mechanical analysis are validated and compared with experiments. It is concluded that the developed numerical model estimates very well the hybrid laser welding induced distortion and residual stresses. The developed model can be directly implemented in fatigue and ultimate strength structural analysis.

Automated Derivation of Optimal Production Sequences from Product Data

Customer specific, individual products nowadays lead to larger product variance and shorter time to market. This requires efficient production system planning. In addition, due to a larger system complexity, each iteration of the planning process itself gets soaringly complex. Time constraints and complexity, therefore, emphasize the necessity of supporting humans in planning modern production systems.Especially the determination of the production sequence holds immense potential and tends to get even more complex within specific production technologies. Exemplarily, this article focuses on welding sequences. Here, domain knowledge from product development and production planning needs to be holistically integrated. Furthermore, implicit, historic knowledge needs to be formalized and used in today’s planning tasks.This article introduces a methodical approach and a corresponding toolchain to derive optimal production sequences from customer product data which is validated using welding processes. For this, firstly, a reference system is build up consisting of historic product data (e.g. part list, CAD data) and corresponding production system characteristics (e.g. number and specifications of machines). The main aspect is to use similarities between the new product variant and assemblies from the reference system, to determine implications of product specifications on the process sequence. Overall, such restrictions can be displayed using Model-Based Systems Engineering. Relevant information (e.g. weld seam lengths) can be used to compute the optimal weld seam order regarding minimal cycle times, for example. This requires a parametric encoding of product and production system. In a nutshell, this approach covers the automated derivation of an optimal production sequence for new product variants, based on system information and product similarities, to tackle time constraints and complexity by suggesting initial planning drafts.

Effect of Welding Sequence and Constraint on the Residual Stress and Deformation of Thick Welded Butt Joint Made of Q345qD Steel

In this paper, the residual stress and deformation of 32 mm thick welded butt joints made of Q345qD steel using gas metal arc welding (GMAW) are studied by using the thermoelastic‐plastic finite element analysis (FEA). Element birth and death technique is used to simulate the deposition of the welding consumables, and the volume heat source in double‐ellipsoidal distribution is used. An in‐house python code is developed to enable the volume heat source movement. After the finite element model was verified against the experimental results, the effects of five welding sequences and two types of boundary constraint conditions on the residual stress and deformation of the thick welded butt joints were investigated. Results of the experimental measurement and the numerical simulation are in good agreement. The transverse residual stress and the vertical deformation can be significantly reduced by increasing the alternating times of the welding beads in two halves of the weld. The transverse residual stress and the vertical deformation can be reduced by 21.4% and 87.4%, respectively. In addition, the residual stress and deformation of the thick welded butt joints are significantly affected by the applied constraints. Increasing the constraint significantly increases the overall level of the transverse residual stress but can decrease the maximum longitudinal residual stress by 51.8% and the vertical deformation by 65.9%.

Computational analysis of welding radial deformation of typical pressure cylindrical shell with ring stiffener

We report on the evaluation of the radial deformation caused by the welding process on a typical pressure cylindrical shell with ring stiffeners. Welding experiments on butt and fillet welding were conducted beforehand, and temperature-dependent material properties were considered. The out-of-plane welding distortion and residual stress were measured using a three-coordinate measuring machine and X-ray diffraction, respectively. Effective thermal elastic plastic FE analysis based on parallel computation technology was performed to examine the mechanical behaviors. Computed results were validated by comparison with experimental measurements. Welding inherent deformations of the examined butt and fillet joints were then evaluated by integrating computed plastic strains. The elastic FE analysis, with welding inherent deformation as mechanical loading, was employed to examine the dimensional variation of the considered pressure cylindrical shell. The influence of ring stiffener on welding radial deformation was also discussed. Moreover, the application of welding sequence modification and inverse deformation was numerically examined with the proposed elastic FE analysis to reduce the welding radial deformation and enhance the fabrication accuracy. • Thermal and mechanical behaviors of welding experiments were holistically examined with advanced measurement approach. • TEP FE analysis was employed to represent welding response, and computed results have good agreement with measurement. • Ring stiffener has significant influence on dimensional accuracy by elastic FE analysis with welding inherent deformation. • Welding sequence and inverse deformation have significant effect to prevent radial deformation of pressure cylindrical shell.

Welding-induced stresses and distortion in high-strength steel T-joints: Numerical and experimental study

The main objective of this study is to develop a computational approach based on the finite element (FE) method to efficiently predict welding deformations and residual stresses of fillet welded T-joints made of high strength steel (HSS), S700, using different welding sequences and external constraints. With this aim, thermo-elastic-plastic FE models were developed in ABAQUS FE code based on Goldak's double ellipsoidal heat source model, material non-linearity and geometrical non-linearity. The results of the FE models in terms of temperature fields, angular distortion and transverse residual stress were verified against measurements. The results showed that angular distortion and transverse residual stress were significantly impacted by configuration of the external constraints, while longitudinal stress were less affected. It was found that the welding sequences had a smaller effect on the sequential and cumulative welding distortions and final residual stresses than the configuration of the external constraints. The results of this study are meaningful for understanding of the calibration and accuracy of FE computational approaches to simulate welding processes. Additionally, from a practical point of view, the results are important to understand the distortions and residual stress control measures of structural members made from HSSs.

Path planning of spot welding robot based on multi-objective grey wolf algorithm

The path planning of traditional spot welding mostly uses manual teaching method. Here, a new model of path planning is established from two aspects of welding length and welding time. Then a multi-objective grey wolf optimization algorithm with density estimation (DeMOGWO) is proposed to solve multi-object discrete problems. The algorithm improves the coding method and operation rules, and sets the density estimation mechanism in the environment update. By comparing with other five algorithms on the benchmark problem, the simulation results show that DeMOGWO is competitive which takes into account both diversity and convergence. Finally, the DeMOGWO algorithm is used to solve the model established of path planning. The Pareto solution obtained can be used to guide the welding sequence of body-in-white(BIW) workpieces.

Welding distortion prediction and mitigation in thick steel plate structures on ships

ABSTRACT In the ship fabrication process, welding distortion will affect the dimension accuracy. In this paper, an industrialisation prediction method for thick steel plate structures on ships is proposed based on a combination of thermal-elastic-plastic finite element method and inherent deformation theory to reduce the welding distortion in the design stage, and its applicability is verified through a comparison of measurements in the shipyard and numerical simulations. The thick plate models produced by multi-pass welding technology are selected to analyse the welding distortion. The results show that the numerical prediction results are in good agreement with the measurement on site. The transverse bending distortion is the main factor that affects the fabrication accuracy. To mitigate welding distortion, the influence of welding sequence and flame heating is examined. This research may provide a macro concept for understanding the distribution characteristics of welding distortion and serve as a mitigation reference for manufacturing engineers.

A Study on Minimizing Welding Deformation of Joints for the Sealing of Emission After-Treatment Structure.

As the environmental pollution issue has recently become significant, environmental regulations in Europe and the United States are being strengthened. Thus, there is a demand for the quality improvement of emission after-treatment systems to satisfy the strengthened environmental regulations. Reducing the amount of welding heat distortion by optimization of the welding order of each part could be a solution for quality improvement since the emission after-treatment system consists of many parts and each assembly is produced by welding individual ones. In this research, a method to derive a welding sequence that effectively minimizes welding deformation was proposed. A two-stage simulation was performed to obtain the optimal welding sequence. In the first stage, the welding sequence was derived by analyzing the number of welding groups in each assembly of a structure. The derived welding sequence was verified by performing a thermal elasto-plastic analysis and comparing it with the experimental results.

FEM Research on Welding Thermal Deformation of Copper Alloy Sheet and Optimization of Welding Sequence

To reduce the residual stress and deformation of the copper alloy sheet after welding, and improve the welding quality of the copper alloy sheet, the finite element method (FEM) research on welding thermal deformation and welding sequence optimization was carried out. First, a finite element model of copper alloy sheet welding was established based on ANSYS, the mechanical property parameters of the model at high temperature were determined, and the thermal–structural coupling calculation was performed on the model. Then, the change trend and magnitude of the residual stress and deformation of the model after welding were analyzed. Finally, different welding sequence schemes were designed, and numerical simulation calculations were carried out. The results of the welding sequence solution show that the change trend of the residual stress after welding of the base metal under different welding sequences is basically the same; repeated heating of the base metal at the same position causes large residual stress; the weldment vertical plate is subjected to opposing forces in the x-axis and y-axis directions at the same time. Among four welding schemes, the welding scheme that alternately welds symmetrically from the start and end positions of the weld seam to the middle position of the plate causes the least welding deformation. Compared with the other three schemes, its deformation reduces by 26.6%, 18.3%, and 19.4%, respectively.

Influence of Interlayer Temperature and Welding Sequence on the Temperature Distribution and Welding Residual Stress of the Saddle-Shaped Joint of Weldolet-Header Butt Welding.

In this paper, based on Simufact Welding finite element analysis software, a numerical simulation of the temperature and residual stress distribution of the weldolet-header multi-layer multi-pass welding process is carried out, and the simulation results are verified through experiments. The experimental results are in good agreement with the numerical simulation results, which proves the validity of the numerical simulation results. Through the results of the numerical simulation, the influence of the welding sequence and interlayer temperature on the temperature and residual stress distribution at different locations of the saddle-shaped weld was studied. The results show that the temperature and residual stress distribution on the header and weldolet are asymmetric, and the high-stress area of the saddle-shaped welded joint always appears at the saddle shoulder or saddle belly position. When the interlayer temperature is 300 °C, the peak residual stress reaches a minimum of 428.35 MPa. Adjusting the welding sequence can change the distribution trend of residual stress. There is no high-stress area on the first welding side of the two-stage welding path-2. The peak values of residual stresses for continuous welding path-1 and two-stage welding path-2 are 428.35 MPa and 434.01 MPa, respectively, which are very close to each other.

Framework for Mitigation of Welding Induced Distortion through Response Surface Method and Reinforcement Learning

Welding induced distortion causes dimensional inaccuracies in parts being produced and assembly fit-up problems during manufacturing. In this study, a framework is proposed to mitigate weld distortion at the design stage. A sequential approach is adopted to optimize the welding process. In the first phase, welding process parameters are optimized through the response surface method. The effect of these parameters on the overall distortion of the welded part is observed by a simulation of the welding process. In the second phase, the weld sequence is optimized using the optimum weld parameters. A reinforcement learning-based Q-learning technique is used to select the optimum welding path by sequential observation of weld distortion at each segment being welded. The optimum process parameters and weld path sequence have been selected for 3 mm steel plates having a lap joint configuration and a 2 mm vent panel with a butt joint configuration. It is concluded that the combination of the optimum welding parameters and welding sequence yields minimum distortion. By applying this framework, a reduction of 19% is observed in overall welding induced distortion.

Influence of welding sequence on the mechanical properties of a latticed shell formed by orthogonal and oblique members

With the development of economy and the improvement of people’s aesthetic level, large-span latticed shells are increasingly used. Such structures are commonly large in volume and huge in welding. In order to select an optimum welding sequence and avoid correcting complex welding deformation, a latticed shell formed by orthogonal and oblique members was taken as the research object in this paper. The finite element models of single and whole latticed shells were established respectively, and according to the equal deformation principle, the influence of different welding sequence on the deformation and internal force of the structure in each construction stage was quantitatively analyzed. The results show that in the welding and assembling stage of small assembling units in the single latticed shell, welding sequence has the greatest impact on the longitudinal deformation, and the change rate of the longitudinal deformation is up to 83.63%; whereas in the tension, sliding and closure stages of each piece of the latticed shell, the transverse deformation is most affected by welding sequence, and the change rate is 33.05%; in different construction stages, the axial stress of the latticed shell is less vulnerable to welding sequence. Furthermore, it is feasible to control the welding shrinkage deformation by selecting a reasonable welding sequence, and the symmetrical welding sequence from both ends to the middle should be adopted during construction.

Spot-welding path planning method for the curved surface workpiece of body-in-white based on a memetic algorithm

Aiming at the problem of complex path planning in the processing of curved surface workpieces of body-in-white, a hybrid path planning method based on a memetic algorithm is proposed. The method is divided into two parts: welding sequence planning and welding path planning between weld points. By establishing the kinematic model of a spot welding robot based on the pipper criterion and z-y-z Euler angle solution method, the motion constraints of path optimization are analyzed. Under the framework of the memetic algorithm, the improved A-star algorithm with redundant node deletion and a post-smoothing process is used to obtain the smooth collision-free optimal path set between weld points and to construct the objective function of travelling all weld points with the shortest path length and highest smoothness. The multiobjective elitist-simulated annealing genetic algorithm (MESAGA) is used to achieve the welding sequence planning of all weld points. The variable neighborhood search method improves the mutation operator; the elitist strategy is introduced to improve the probability of elitist individual crossover and mutation operation, and a simulated annealing algorithm is used to jump out of local search to obtain the global optimal solution. According to the motion constraints, the joint space path is obtained by the optimal path in Cartesian space. Simulation analysis results demonstrate that the hybrid path planning method based on the memetic algorithm can effectively optimize the path of spot welding robots and lay the foundation for control and trajectory planning during welding processes.

Comparing the local-global deformation mechanism in different friction stir welding sequences of Ti-4Al-0.005B titanium alloy T-joints

Titanium alloy T-joints were produced using two different friction stir welding (FSW) sequences, and the local-global deformation mechanisms until fracture were compared. Due to their differing FSW sequence characteristics, the optimal parameter ranges for the two T-joints are different. The stir zone (SZ) of the single-weld T-joint consists of lamellar α grains, while fine equiaxed α grains develop in the double-weld T-joint due to the selection of low heat input. Due to the different local microstructure zones in the joint, deformation inhomogeneity of the T-joint during tensile testing is observed. Independent of the welding sequence and for optimal process conditions, both T-joint configuration show nearly the same maximum tensile strength as the base material (BM), however at a relatively low fracture strain, below 20% of the BM. The local strain hardening rate in different zones of the T-joint was investigated. The strain hardening ability of SZ with fine grains is significantly higher than elsewhere, because the grain size contributes greatly to strain hardening behavior at low strain levels. The single-weld T-joint experienced a symmetric local strain distribution between advancing and retreating side. For the double-weld T-joint, there are significant differences between the first and the second weld area. The fracture morphologies of both T-joints are typical ductile, where the toughness of the single-weld joint is higher than that of the double-weld joint.

Analysis of the coefficient of linear relationship, generated by the exponential heating during the welding process for an A36 steel plate

The present study presents the relationship of temperature and deformation as well as the analysis of heat transfer and deformation produced during welding of a steel plate. The method consists of strategically welding a base metal plate (A-36) with a high-hardness filler material to obtain an overall increment in wear resistance. However, the thermal cycles generated during welding produced deformation, thus changing the flatness of the plate. Different sequences of welding were applied to obtain a relationship between the heat transfer and deformation. A filler material was applied to 100 holes (1/2” diameter and 8 mm depth) in a ½” steel plate. The temperature and deformation were measured for 3 different welding sequences. Plate 1 reached a final mean temperature of 467 °C and deformation of 0.016”, plate 2 reached 472.9 °C and -0.008”, and plate 3 reached 354.2 °C and 0.020”. The results indicate that the deformation is not function of the final temperature, instead the deformation is function of the slope of the curve temperature vs deformation. The behavior of the curve temperature vs deformation is linear for all cases studied, confirming the findings of the lowest deformation for plate 2 which exhibited the lowest slope.

Welding-induced residual stresses and distortions of butt-welded corroded and intact plates

The welding-induced residual stresses and distortions of butt-welds between non-corroded and corroded steel plates are studied experimentally and numerically, simulating a repair in an aged structure. Butt welds are made between plates with different corrosion levels and intact ones, and temperature distributions and distortions have been measured. Finite element analyses of the butt-welded corroded and non-corroded plates are performed to estimate the welding-induced distortions and residual stresses for different levels of corrosion degradation. The environmental conditions during the welding repair process are also accounted for. Experimentally evaluated mechanical properties of corroded steel plates as a function of the temperature during the welding process are employed in non-linear finite element analyses. The importance of the material properties as a function of the severity of the steel plates' corrosion degradation on the welding-induced distortions and residual stresses is also quantified. This study shows the importance of considering the ageing of steel in the repair process. The developed methodology allows critical operational decisions to be made with greater ease and confidence in analysing the welding-induced distortions and residual stresses when ageing structures are repaired to extend their service life. Furthermore, different welding sequence scenarios may be analysed to identify the most appropriate repair solution in minimising the repair cost.

Effects of residual stress on the stability of multi-welded integral stiffened panels

In order to clarify the influence of residual stress on the stability of 2024-T3 friction stir welded(FSWed) integral stiffened panels with multi-welds, the ANSYS software was used to establish the finite element models of two typical multi-FSWed stiffened panels. The residual stresses of two typical multi-welded stiffened panels (Panel A and Panel B) were calculated respectively using the thermal-mechanical coupling method. And the buckling and post-buckling responses of the stiffened plates were analyzed. It is shown that the residual stress distribution of stiffened panel was affected by the welding sequence. The maximum residual stress of Panel A mainly appears on the right side of the stringer, and that of Panel B appears on the stringer that is welded later. The residual stress has a great influence on the stability of the welded stiffened panels. When the residual stress profiles are taken into consideration, the critical buckling loads of welded Panel A and Panel B will decrease 14.2% and 12.4% respectively.

A Multi-Case-Based Assembly Management Method for the Shipbuilding Industry

Abstract This article describes a method for planning the assembly of ship hulls that focuses on a welding sequence, takes into account subassembly processes and makes use of a previously built database of structures. Different degrees of similarity between structures are taken into account. The described research led to the development of an intelligent hybrid sequencing method for structure assembly that uses fuzzy clustering, case-based reasoning and evolutionary optimization. The method is called ‘Multi-case-Based Assembly Planning (MBAP)’. The method is developed to provide satisfactory solutions with low user effort. The analyses carried out show that the calculations are highly time-efficient. The developed evolutionary algorithm converges on sub-optimal solutions. The MBAP method can be directly implemented by any shipbuilder that assembles hulls. Apart from this, fuzzy clustering integrated with case-based reasoning can be applied in practice. The integration of fuzzy clustering and case-based reasoning has been taken to a level higher than previously described in the literature.