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As additive manufacturing (AM) technology grows both more advanced and more available, the challenges and limitations are also made more evident. Most existing solutions for AM build structures layer by layer using strictly vertical material deposition. As each layer must vertically adhere to the previous layer, support structures must be added if there are to be any kinds of overhangs. For methods requiring the build to be performed within a chamber, the size of the structure is also very limited. The research presented in this paper explores possible solutions to these challenges, focusing on wire-arc additive manufacturing in order to effectively build structures that can not easily be constructed using in-box, layer-based methods for AM. By non-vertical material deposition using an industrial robot manipulator, metal structures with overhangs are built onto a fixed, horizontal surface without any support structures. Cross sections of two different structures are examined by optical microscopy and hardness measurements to reveal potential differences between the areas with and without intersections or overhang. [Display omitted] • Continuous building using WAAM can effectively construct thin-walled structures. • Construction of unsupported overhang on fixed, horizontal surface is investigated. • Tested set-based control method can build thin-walled structures, but not overhangs. • Vertical but skewed material deposition when using WAAM can create small overhangs. • Overhangs can be constructed using non-vertical orientation of welding gun. [ABSTRACT FROM AUTHOR]

Hybrid laser arc welding simultaneously utilizes the arc welding and the laser welding, in a common interaction zone. The synergic effects of laser beam and eclectic arc in the same weld pool results in an increase of welding speed and penetration depth along with the enhancement of gap bridging capability and process stability. This paper presents the current status of this hybrid technique in terms of research, developments and applications. Effort is made to present a comprehensive technical know-how about this process through a systematic review of research articles, industrial catalogues, technical notes, etc. In the introductory part of the review, an overview of the hybrid laser arc welding is presented, including operation principle, process requirements, historical developments, benefits and drawbacks of the process. This is followed by a detailed discussion on control parameters those govern the performance of hybrid laser arc welding process. Thereafter, a report of improvements of performance and weld qualities achieved by using hybrid welding process is presented based on review of several research papers. The succeeding sections furnish the examples of industrial applications and the concluding remarks. [ABSTRACT FROM AUTHOR]

This paper focusses on effect of flat wire electrode on gas metal arc welding (FW-GMAW) inline during the process to improve quality of weld bead. Since the flat wire electrode perimeter has enlarged, the turbulence of the molten droplet characteristics is altered due to the effect of electromagnetic force. To bring out, butt joint welding are proven with use of the flat wire electrode. The experimental results indicated that, the flat wire electrode and their orientations are significantly factors to improve the weld bead dimensions, due to the increased in steady state temperature and heat density. The end result also evident that the depth-to-width (D/W) ratio was improved on an average by 7.7% than regular wire electrode used in GMAW. To validate, a comprehensive numerical model was developed, the result confirmed that the initial arc and steady state temperature are high for FW-GMAW. In addition, improvements in metallurgical and mechanical properties are discussed in this paper. [Display omitted] • Development of experimental setup for continuous formation of flat wire electrode inline during GMAW process. • Numerical analysis for electrical influences on flat wire electrode. • Determination of flat wire electrode dimensions. • Experimental investigations on bead characteristics (weld bead geometry) of GMAW with flat wire electrode with considering the effect of weld input process parameters on bead characteristics. • Analyze the transient thermal analysis of weld bead and investigated the mechanical and metallurgical characterization of weld bead. [ABSTRACT FROM AUTHOR]

Abstract: A novel system which allows arc-welding defect detection and classification is presented in this paper. The spectroscopic analysis of the plasma spectra produced during the welding process is a well-known technique to monitor the quality of the resulting weld seams. The analysis of specific emission lines and the subsequent estimation of the electronic temperature profile offers a direct correlation between this parameter and the corresponding weld seams. However, the automatic identification and classification of weld defects has proven to be difficult, and it is usually performed by means of statistical studies of the electronic temperature profile. In this paper, a new approach that allows automatic weld defect detection and classification based in the combined use of principal component analysis (PCA) and an artificial neural network (ANN) is proposed. The plasma spectra captured from the welding process is processed with PCA, which reduces the processing complexity, by performing a data compression in the spectral dimension. The designed ANN, after the selection of a proper data training set, allows automatic detection of weld defects. The proposed technique has been successfully checked. Arc-weld tests on stainless steel are reported, showing a good correlation between the ANN outputs and the classical interpretation of the electronic temperature profile. [Copyright &y& Elsevier]

This paper focuses on the kinematic control of a redundant robotic system taking into account particularities of the arc welding technology. The considered system consists of a 6-axis industrial robot (welding tool manipulator) and a 2-axis welding positioner (workpiece manipulator) that is intended to optimise a weld joint orientation during the technological process. The particular contribution of the paper lies in the area of the positioner inverse kinematics, which is a key issue of such system off-line programming and control. It has been proposed a novel formulation and a closed-form solution of the inverse kinematic problem that deals with the explicit definition of the weld joint orientation relative to the gravity. Similar results have also been obtained for the known problem statement that is based on a unit vector transformation. For both the cases, a detailed investigation of the singularities and uniqueness-existence topics have been carried out. The presented results are implemented in a commercial software package and verified for real-life applications in the automotive industry. [Copyright &y& Elsevier]

The systematic analysis of robotic arc welding processes requires unified structured data, which is currently not available due to the diversity of data sources. This paper proposes an integrated data structure for the specific domain of robotic gas metal arc welding. The presented data structure contains a description of the welding system, the design of the welded parts, welding instructions, and time series of measured process data. Collected data enriched with semantic context is stored and analyzed using this data structure. The usefulness is exemplified but not limited by a use-case suggesting welding process parameters to the worker. [ABSTRACT FROM AUTHOR]

The double-ellipsoidal heat power density model proposed by Goldak, has been widely used as the basis for modelling heat transfer in arc welding operations for more than thirty years. This approach has proved to be extremely effective for a wide range of arc welding operations. However, the application of a double-ellipsoidal heat power density distribution is less appropriate for keyhole-laser or electron-beam welding operations, or in situations where arc welding takes place within deep narrow grooves. In this paper the double-ellipsoidal distribution is extended to a double-ellipsoidal-conical heat power density model in order to accurately describe transient temperature fields for a wider range of geometries and welding processes. The new extended model was validated through comparing predicted welding thermal cycles with those measured for a single pass electron beam weld, as well as those measured in a multi-pass narrow groove gas-tungsten-arc weld. In both cases, excellent agreement was obtained between predicted and measured thermal transients. [ABSTRACT FROM AUTHOR]

Arc welding is a common joining method, which is usually characterized by high energy consumption and low energy efficiency. With the recent focus on energy management and carbon emissions, energy saving has become a priority for manufacturing industry. In the past, energy saving technologies for welding had primarily aim for heat source improvement, with less emphasis on parameter optimization. It is obvious that parameter optimization methods for energy reduction can be applied to existing equipment where large investments are not required. Therefore, a multi-objective optimization method based on Fitness Sharing Genetic Algorithm (FSGA) is proposed for energy reduction and thermal efficiency improvement of arc welding process in this paper. Two objectives including energy consumption and thermal efficiency are considered in the optimization model with two independent variables, namely welding current and welding velocity. Additionally, the limits of the variables and welding quality are also considered. A case study of rail track joints using Shielded Metal Arc Welding (SMAW) is conducted for the verification of the proposed optimization method. Finally, the optimization method and results are analyzed with the actual data and Genetic Algorithm (GA) respectively. Comparison with actual data shows that the proposed approach has a more significant effect on energy saving and thermal efficiency improvement. The optimization analysis shows that FSGA has a better population diversity and global search capability compared with GA. [ABSTRACT FROM AUTHOR]

The electrical energy needed in welding processes is a major factor of energy consumption in manufacturing processes that use welds to fabricate structures. In the arc welding process an intense electrical arc is used as the heat source to melt locally metallic materials to join them once they solidify. Although the arc is focused at the joint, a large portion of energy is dissipated as heat through the base metals to the surroundings. In this paper it is shown that selecting the welding parameters appropriately, viz., the power supplied to the arc and the translation speed of the arc, can reduce the energy consumed per unit length of weld. The range of parameters examined was selected such that the vaporization of the molten metal was negligible. It is shown that increasing the arc power in conjunction with increasing the travel speed of the arc leads to reduced energy consumption per unit length of weld; this reduction in energy consumption is for equivalent welds, i.e., welds with identical geometric features. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, a numerical model of spot pulsed current GTA welding for partially and fully penetrated weld pools is presented. Heat transfer and fluid flow in the weld pool driven by the combination of electromagnetic force, buoyancy force, surface tension gradient and latent heat are included in our model. A new formulation of the electromagnetic problem is introduced to take into account eddy current in the weld pool. The shape of the free deformable surface under the action of pulsed arc force is also handled after the magneto-hydrodynamic calculation. The numerical model was applied to 304 stainless steel welding. We compare the influence of various pulsed welding parameters such as pulse frequency and current ratio on the weld quality. Experimental study is conducted to compare our numerical prediction with welding macrographies. It shows a good agreement of the model. [Copyright &y& Elsevier]

Abstract: This paper proposes a support vector machine-based fuzzy rules acquisition system (SVM-FRAS) for modeling of the gas tungsten arc welding (GTAW) process. The character of SVM in extracting support vector provides a mechanism to extract fuzzy IF–THEN rules from the training data set. We construct the fuzzy inference system using fuzzy basis function. The gradient technique is used to tune the fuzzy rules and the inference system. Theoretical analysis and comparative tests are performed comparing with other fuzzy systems. Modeling is one of the key techniques in the automatic control of the arc welding process, and is still a very difficult problem. Comprehensibility is one of the required characteristics in modeling for the complex GTAW process. We use the proposed SVM-FRAS to obtain the rule-based model of the aluminum alloy pulse GTAW process. Experimental results show the SVM-FRAS model possesses good generalization capability as well as high comprehensibility. [Copyright &y& Elsevier]

Abstract: The knowledge of thermodynamics and transport properties of gas mixtures at high temperature is important for many industrial applications. Spark ignition, re-entry problems of space-vehicles, gas dischargers, arc welding, and circuit breakers can be mentioned as examples. This paper focuses on metal/inert-gas mixtures in the temperature range from 300 to 30,000K, which are important for arc welding processes. As metals we consider iron, copper, aluminium, and calcium and as inert gases nitrogen, argon, and helium. The results are validated by comparison with transport properties from literature. Furthermore, this study also significantly extends and improves the transport model developed earlier [S. Selle, U. Riedel, Ann. NY Acad. Sci. 891 (1999) 72–80; J. Prager, G. Baldea, U. Riedel, J. Warnatz, Equilibrium Composition and Electrical Conductivity of High-Temperature Air, 21st ICDERS (2007); J. Prager, U. Riedel, J. Warnatz, Proc. Combust. Inst. 31 (2007) 1129–1137]. The transport properties are calculated using Chapman–Enskog theory. The model is universally applicable and needs little input data. A multicomponent mixture formulation or simple mixing rules can be used. [Copyright &y& Elsevier]

Abstract: This paper is reviewing the metal transfer according to the progress made in the welding sources and techniques development. It critically analysis the actual classification of the metal transfer in GMA welding, describing the relevant phenomenon and proposing improvements, to make the understanding and the work easier in the field of arc welding. Basic concepts are overviewed and defined or re-defined: fundamental transfer modes, natural vs. controlled transfer mode, variants vs. variances, mixed vs. combined modes, drop spray transfer. The new classification is simpler, without loosing the logic of numbering, both from fundamental point of view (the physics of the transfer) and the technological one (the increasing of the values of the welding parameters). It is extremely important for all the specialists involved in study, design or industrial applications of the arc welding technologies to have know–how about the metal transfer and its implications on the process and weld parameters. [Copyright &y& Elsevier]

Abstract: This paper proposes a fuzzy modeling method based on support vector machine (SVM) for the arc welding process. SVM provides a mechanism to extract support vectors for generating fuzzy IF-THEN rules from training data. In the proposed SVM-based fuzzy system (SVM-FS), SVM is used to extract IF-THEN rules; the fuzzy basis function inference system is adopted as the fuzzy inference system. So the approach possesses good comprehensibility as well as satisfactory generalization capability. Modeling is one of the key techniques in the automatic control of the arc welding process, and is still a very difficult problem. We give the main steps of modeling for the process using SVM-FS, including selecting input/output variables, acquiring raw data, extracting fuzzy rules and fuzzy inference. Experimental results show that the proposed approach outperforms the rough set method. [Copyright &y& Elsevier]

In this paper, mathematical models for calculation and prediction of melting rate in arc welding with a triple-wire electrode are described. The quantities affecting the melting rate of the filler material were determined by experimental work. Mathematical models with which it is possible to calculate and predict, with a strong probability, the melting rate in triple-wire arc welding in different shielding media were elaborated by statistical methods. [Copyright &y& Elsevier]

k-Type thermocouple (NiCr–NiAl) joints are currently manufactured by argon arc welding. One of the weaknesses of this joining method is that the weld bead diameters are about three times of the thermocouple wires. This slows the response time of these thermocouples. Furthermore, porosity exists in the joints affecting the conductivity and repeatability for temperature measurement. In this paper, the feasibility and the characteristics of welding 0.2 and 0.5 mm diameter k-type thermocouples using a 120 W diode laser and a 400 W Nd:YAG laser are reported. The energy density requirement and the effects of shroud gas are described and analysed quantitatively. The performances of the laser welded thermocouples are evaluated against the commercial ones. Reductions of 35 and 15% in response time have been achieved compared to the commercial and the Nd:YAG laser welded 0.2 mm diameter thermocouples, respectively, whereas for the 0.5 mm diameter thermocouples, the HPDL welded ones performed 5% better and the Nd:YAG welded ones performed 9% better. The tensile strength of the diode laser welded thermocouples was found to be around 1620 N mm−2 at 0.2 mm diameter and 480 N mm−2 at 0.5 mm diameter. This is well above the industrial standard of 400 N mm−2. The work shows that diode laser welding can generate beadless and porosity-free butt joints in the thermocouples superior to the ones produced by argon arc welding. [Copyright &y& Elsevier]

The arc welding process involve complex physical and chemical phenomena, which makes mathematical modeling difficult. Its modeling uses the heat source concept to model the energy input, that requires geometric parameters to be calibrated. However, to obtain an adequate accuracy, some heat sources have many parameters to be defined, which demands great computational time, even using optimization methodologies. In this paper, an optimization methodology, including a new technique called Reduced Geometry, is proposed to find the optimal parameters of heat sources, by using an inverse problem approach and Genetic Algorithms. The methodology is validated to the GTAW process of butt and lap joints of AISI 1020 carbon steel and AISI 304 stainless steel, which allows to test symmetric and asymmetric welds. The thermal numerical simulations are performed using the Finite Element Method, where three types of moving heat sources are considered: a Gaussian, a Conical and a Double Ellipsoid heat sources. The fusion zone shapes and thermal cycles, obtained from experiments are compared with numerical ones. Analyses of the computational time, as well as accuracy in relation to experiments are carried out. In general, thermal results obtained by numerical simulations are in good agreement with the experiments, for all cases, and the proposed methodology strongly decreases the computational time, when compared with a standard approach, with negligible loss in accuracy. Unlabelled Image • A new optimization methodology is proposed. • A new technique, called Reduced Geometry, is developed. • A software for optimization of heat sources is created. • The computational efficiency is higher than that of standard approaches. [ABSTRACT FROM AUTHOR]

• Vast knowledge on welding can be used in additive manufacturing. • Criteria to optimize parameters in additive manufacturing is proposed. • Proposed criteria provides an upper bound limit for key process parameters. • A dimensionless parameter is proposed to compute the energy density. • The dimensionless parameter allows to compare works from different research groups. Additive manufacturing technologies based on melting and solidification have considerable similarities with fusion-based welding technologies, either by electric arc or high-power beams. However, several concepts are being introduced in additive manufacturing which have been extensively used in multipass arc welding with filler material. Therefore, clarification of fundamental definitions is important to establish a common background between welding and additive manufacturing research communities. This paper aims to review these concepts, highlighting the distinctive characteristics of fusion welding that can be embraced by additive manufacturing, namely the nature of rapid thermal cycles associated to small size and localized heat sources, the non-equilibrium nature of rapid solidification and its effects on: internal defects formation, phase transformations, residual stresses and distortions. Concerning process optimization, distinct criteria are proposed based on geometric, energetic and thermal considerations, allowing to determine an upper bound limit for the optimum hatch distance during additive manufacturing. Finally, a unified equation to compute the energy density is proposed. This equation enables to compare works performed with distinct equipment and experimental conditions, covering the major process parameters: power, travel speed, heat source dimension, hatch distance, deposited layer thickness and material grain size. [ABSTRACT FROM AUTHOR]