Weld Formation Research Articles

Prediction of MAG Welding Formation Based on Fuzzy Interpolation Reasoning

Welding is an important production and processing method in industrial production. Due to the uncertainty of its process and the complexity of its mechanism, it is challenging to construct an accurate welding process parameter model to describe it. Fuzzy interpolation reasoning is a valuable tool in the realm of intelligent systems. It helps to reduce the complexity of fuzzy models and can be used for reasoning in fuzzy systems with sparse rule bases. This paper provides an interpolation reasoning method that combines fuzzy set distance and similarity. The proposed method is applied to welding forming predictions, and welding penetration is predicted by the given welding current and speed. The results show that the algorithm has high calculation accuracy.

Supporting Imaging of Austenitic Welds with Finite Element Welding Simulation—Which Parameters Matter?

The basic principle of ultrasound is to relate the time of flight of a received echo to the location of a reflector, assuming a known and constant velocity of sound. This assumption breaks down in austenitic welds, in which a microstructure with large oriented austenitic grains induces local velocity differences resulting in deviations of the ultrasonic beam. The inspection problem is further complicated by scattering at grain boundaries, which introduces structural noise and attenuation. Embedding material information into imaging algorithms usually improves image quality and aids interpretation. Imaging algorithms can take the weld structure into account if it is known. The usual way to obtain such information is by metallurgical analysis of slices of a representative mock-up fabricated using the same materials and welding procedures as in the actual component. A non-destructive alternative to predict the weld structure is based on the record of the welding procedure, using either phenomenological models or the finite element method. The latter requires detailed modelling of the welding process to capture the weld pool and the microstructure formation. Several parameters are at play, and uncertainties intrinsically affect the process owing to the limited information available. This paper reports a case study aiming to determine the most critical parameters and levels of complexity of the weld formation models from the perspective of ultrasonic imaging. By combining state-of-the-art welding simulation with time-domain finite element prediction of ultrasound in complex welds, we assess the impact of the modelling choices on the offset and spatial spreading of defect signatures. The novelty of this work is in linking welding simulation with ultrasonic imaging and quantifying the effect of the common assumptions in solidification modelling from the non-destructive examination perspective. Both aspects have not been explored in the literature to date since solidification modelling has not been used to support ultrasonic inspection extensively. The results suggest that capturing electrode tilt, welding power, and weld path correctly is less significant. Bead shape was identified as having the greatest influence on delay laws used to compute ultrasonic images. Most importantly, we show that neglecting mechanical deformation in FE, allowing for simpler thermal simulation supplemented with a phenomenological grain growth loop, does not reduce the quality of the images considerably. Our results offer a pragmatic balance between the complexity of the model and the quality of ultrasonic images and suggest a perspective on how weld formation modelling may serve inspections and guide pragmatic implementation.

Development of approaches to real-time optical diagnostics for laser weld formation process using laser emission spectroscopy

Welding of metals is subject to various random processes that degrade the quality of the weld, ranging from the presence of inhomogeneities in the metal to spontaneously occurring pulsating processes. Pre-weld destructive testing cannot eliminate the presence of inhomogeneities and is ineffective for spontaneous deviations in the welding process. Therefore, the development of new approaches for real-time diagnosis of the laser welding process is particularly relevant today, especially with the widespread implementation of fiber lasers. The objective of this study was to develop approaches for optical diagnostics of the process of forming heterogeneous material based on laser emission spectroscopy. An experimental setup was created to develop approaches for optical diagnostics of the process of forming heterogeneous material, which is a critical task for additive technologies and laser welding. It was demonstrated that for industrially relevant aluminum alloys 1420, 1580, AMG (Russia), it is possible to record the spectra of the gas-plasma plume that occurs when laser radiation interacts with the metal surface. These spectra depend on the radiation exposure conditions and reflect the processes of atom and molecule evaporation from the molten pool. Further research will allow establishing the nature of this connection and developing optimal modes for technological processes, enabling real-time control of these processes.

Improving weld forming quality and process adaptability by using a copper liner in laser-MAG hybrid overhead welding

During overhead welding, gravity inevitably drives the molten pool downward, resulting in poor adaptability and concave defect. To address this issue, this paper proposed a novel laser-MAG hybrid overhead welding technique utilising a copper liner (COL). Compared to single-arc welding, laser-MAG hybrid welding can reduce the volume of the molten pool, while the laser increases its support force. The COL can accelerate the molten pool's solidification rate. Additionally, the adhesion force between the molten pool and the COL can partially counterbalance gravity. As a result, good weld formation still was achieved even when the misalignment was 0–1 mm and the butt gap was 0–2 mm. Moreover, the back reinforcement height and width were not less than 0.71 and 3.66 mm, respectively.

Heat source modeling, penetration analysis and parametric optimization of super spray MAG welding

Main drives, cutterheads and other critical components of tunnel shield machines require welding with thick plates that leave roots over 5 mm. Full penetration welds cannot be achieved by conventional Pulsed MAG welding methods. This article introduces Super Spray MAG Welding technology and investigates its penetrating regularities and mechanisms through high-speed camera images, finite element simulation, and microstructural analysis. An optimal welding procedure was generated using a combination of Genetic Algorithm and Back Propagation Neural Network. The data show that Super Spray MAG arc exhibits greater concentration and stability than traditional MAG arc, marking its strong qualities in emitting high-energy beams. The morphological solidification pattern of the molten pool closely matches the FEM simulation results of the composite Gaussian surface heat source model and peak linear attenuation Gaussian cylinder heat source. The welding current mainly affects the penetration of the weld, followed by the extension of the wire, and lastly the welding speed. Increasing the welding current can transition droplet transfer from globular to spray, as well as alter microstructure development and mechanical characteristics. Suggested parameters for penetrating the 5 mm root were put forward. The BPNN-GA model established can effectively predict weld formation, and points out the optimal welding parameters.

Dynamic recrystallization in friction stir welded AA2014 aluminium alloy joints to replace riveted joints

Abstract The demand for lightweight materials (aluminium and magnesium alloy) in structural applications is increasing due to strength ratio, corrosion resistance, formability, and recyclability. Fusion welding of aluminium and its alloy is difficult due to the formation of hot cracking, alloy segregation, porosity, etc. Henceforth, fusion welding is not an ideal process for joining aluminium and its alloy. Steel rivets are being used to join similar and dissimilar alloys in different joint configurations. Since the use of steel rivets, aircraft weight has increased drastically. Although, dissimilar metal corrosion has been encountered. These two are the main problems in structural fabrication industries. The solid-state welding friction stir welding process eliminates the issues mentioned earlier. This process can weld materials well below the melting point. Moreover, the formation of weld in the weld line could be achieved by severe plastic deformation and recrystallized grains. This metallurgical joint may replace the rivets.

Thermal Effect of Bobbin Tool Friction Stir Welding on the Mechanical Behavior of High Density Polyethylene Sheets: Experimental Study

Bobbin friction stir welding (BT-FSW) is a variant of the conventional friction stir welding (C-FSW). This method has been applied of welding high density polyethylene (HDPE) plates; where a rotating symmetrical tool causes a fully penetrated bond, it can weld the upper and lower surface of the work-piece in the same pass. BT-FSW process involves complex heat generation and HDPE flow, which directly affects on the weld area and on mechanical properties of welded joint. Heat generation and material flow during BT-FSW are significantly affected by the tool design features, process parameters and mechanical behavior of work piece materials. Studying the temperature of polyethylene sheets welded by BT-FSW can help in analyzing the mechanism of weld formation and also can provide theoretical guidance for the tool design, process parameter selection and even new process development. In the unique work described in this paper, the 11.4 mm-thick HDPE plates were welded successfully by bobbin-tool friction stir welding. Measurements of the material temperatures were performed by thermocouples which are placed near and at the weld seam. The weld quality was determined in terms of no defects in the stir zone and the tensile strength of the joint. It was found that considerable melting occurred between the rotating shoulders and on the trailing side of the rotating pin. Movement of the molten material by the rotating tool created a very black band in the stir zone. Thermocouples measurements indicated that the temperatures were higher on the advancing side (AS) compared to those on the retreating side (RS). Tensile tests and hardness measurements were performed on welded and seamless sheet samples. The results were analyzed to compare the mechanical properties. To demonstrate the variation in micromechanical properties between welded and seamless sheet samples, micro hardness (HV) testing was used to explain the difference. The HV of the HDPE plates weld by BT-FSW, were relatively symmetrical with respect to the parting line. The maximum hardness levels were reached in the weld bead at around 66 HV in the welded nugget; there was a rise in the level of hardness, in particular at retreating side (RS) and at advancing side (AS) where the value reached 68.60 HV.

A novel approach to optimize weld formation and regulate interfacial microstructure in TC4/304SS dissimilar arc welding by active hybrid shielding gas

CO2 shielding gas was innovatively employed for TC4/304SS dissimilar metal arc welding, overcoming the limitation of active gas application for Ti welding. The effect of CO2 addition on welding process was investigated. Our results show that the CO2+Ar hybrid shielding gas eliminated the problem of insufficient bonding at the backside of the steel plate, and was helpful to obtain a full weld joint. Moreover, the microstructure of the weld joint was modified due to the intense mass transfer inside the molten pool. The typical Ti/Cu interface was divided into two layers. No Ti–Fe compounds were found within the Ti/Cu interface for pure Ar shielding gas. However, the interface morphology was found to change due to induced CO2. Some TiFe2+Ti5Si3 dendrites were formed in layer Ⅱ. And the TEM results showed that the addition of CO2 did not contribute to the generation of a new phase, but the island-shaped Ti2Cu3 was transformed to a lath shape. In the weld seam center, Ti–Fe–Si ternary compounds was formed instead of Ti–Fe or Ti–Cu compounds. The hardness of the entire joint increased with increasing CO2 content. An average strength of 480 MPa was obtained for 3% CO2 content, which is an increase of 57.9% compared to that for pure Ar shielding condition. The fracture surface morphology showed small cleavage flatforms with some shallow dimples. Better weld formation and the optimization of the interface microstructure both contributed significantly to the improvement of the tensile strength of the Ti/steel joint.

Development of Approaches to Optical Diagnostics of Laser Weld Formation Process in Real Time Based on Laser Emission Spectroscopy

Development of Approaches to Optical Diagnostics of Laser Weld Formation Process in Real Time Based on Laser Emission Spectroscopy

Effects of Oscillation Width on Arc Characteristics and Droplet Transfer in Vertical Oscillation Arc Narrow-Gap P-GMAW of X80 Steel

In fields, such as oil and gas pipelines and nuclear power, narrow-gap welding has often been used for the connection of thick and medium-thick plates. During the welding process, a lack of fusion was prone to occur due to groove size limitations, seriously affecting the service safety of large structures. The vertical oscillation arc pulsed gas metal arc welding (P-GMAW) method was adopted for narrow-gap welding in this study. The influence of the oscillation width on arc morphology, droplet transfer behavior and weld formation during narrow-gap welding was studied. Oscillation widths from 0 to 4 mm were used to weld narrow-gap grooves with a bottom width of 6 mm. The results show that, in non-oscillation arc welding, the arc always presented a bell cover shape, and the droplet transfer was in the form of one droplet per pulse, while the sidewall penetration of the weld was relatively small, making it prone to a lack of fusion. With an increase in the oscillation width, the arc gradually shifted to the sidewall. The droplet transfer mode was a mixed transfer of large and small droplets, and the sidewall penetration continued to increase, which was conducive to the fusion of the sidewall. However, when the oscillation width was wider than 3 mm, it led to the phenomenon of the arc climbing to the sidewall, and the weld was prone to porosity, undercutting and other welding defects. The oscillation width has a major impact on the stability of the welding process in vertical oscillation arc narrow-gap welding.

STUDY OF DROPLET TRANSFER CHARACTERISTICS AND WELD FORMATION WITH ER430LNb FERRITIC STAINLESS STEEL DURING GAS METAL ARC WELDING

An ER430LNb ferritic stainless steel wire was used for a gas metal arc welding (GMAW) test. The characteristics of droplet transfer and its corresponding voltage and current waveforms were investigated using a high-speed camera and synchronous acquisition of electrical signals. The weld formation, droplet transfer patterns and corresponding microstructures under different welding parameters were observed, and the effect of the current level on the droplet transfer frequency was discussed. As the results show, there were three typical metal transfer patterns during the GMAW using the ER430LNb ferritic stainless steel wire, namely short circuit transfer, mix transfer and spray transfer. With an increase in the welding current, the weld formation is changing constantly, and the droplet transfer frequency increases exponentially. With the change in the transfer pattern, the columnar ferrite structure of the weld is continuously coarsening. In addition, hardness measurements were taken on joints welded at different welding currents for comparison.

Amendments of weld formation in human skin laser soldering.

A computational modeling is employed for quantitative assessment of weld formation and area of tissue temperature necrosis during the human skin laser soldering. The evaluation is carried out depending on the components composition of using solders, including bovine serum albumin (BSA), indocyanine green (ICG), and carbon nanotubes (CNT), as well as the angle of incidence of laser light and its pulse duration. The influence of CNT on the change of thermodynamic characteristics of albumin denaturation and the rate of formation of the laser weld is investigated. The obtained results suggest to limit the duration of laser light pulse by temperature relaxation time to minimize transfer of thermal energy to reduce the heating of human skin tissues. The developed model has a great potential for further optimization of laser soldering of biological tissues technology with greater efficiency in minimizing the weld area. This article is protected by copyright. All rights reserved.

Development of a Virtual Reality-Based System for Simulating Welding Processes

Arc welding processes, such as shielded metal arc welding (SMAW), metal inert gas (MIG), and tungsten inert gas (TIG), play an important role in industrial applications. To improve the efficiency of the exploitation of traditional welding systems, new technologies have been used. Virtual reality technology is one of them. The virtual reality (VR)-based welding system enables to increase the frequency of practice to help learners obtain welding experience to avoid errors that occur during actual welding processes. This paper presents a VR-based system for simulating three welding processes: SMAW, MIG, and TIG. The developed system includes hardware components and VR software installed on a computer. The change in the physical devices, such as moving the welding torch and the distance from the welding torch to the plates to generate the weld bead, will update in real time and appear on the virtual environment. The functionality of the developed system for simulating the welding processes, such as in the real welding environment, was tested successfully. For implementing the system, welding speed and the distance from the welding torch to the plates are important process parameters, which determine the weld size or the weld formation. In this research, the ranges of the welding speed are 70 ÷ 120 mm/min; 240 ÷ 460 mm/min; and 250 ÷ 450 mm/min for the SMAW, TIG, and MIG processes, respectively. These values were tested experimentally. The distance from the welding torch to the plates to display the weld joint is 1.5 ÷ 5 mm. Outside of this range, no weld joint is formed. The welding widths are 4.4 ÷ 12.9 mm, 7.1 ÷ 12.4 mm, and 7.4 ÷ 11.3 mm for the SMAW, TIG, and MIG processes, respectively.

Investigation of ultrasonic welding of CF/PA66 using stainless steel mesh energy directors

This paper employs stainless steel mesh as energy director (ED) to join carbon fiber reinforced PA66 composite (CF/PA66). The effect of mesh size on the lap-shear failure load, cross-sectional microstructure, and fracture morphology is investigated. The results show that the mesh size has important impact on the weld formation and joint mechanical property. A small wire spacing leads to more pore defects in a joint; a large wire diameter increases the lack of fusion defects, and a large mesh area reduces the energy concentration effect. Mesh energy directors with large wire spacing, small wire diameter, and small area contribute to high joint strength. Under the appropriate welding energy and mesh size, the failure loads of joints are above 10000 N, and the failure model of these joints is workpiece fracture.

Технологические особенности ультразвуковой сварки разнородных пластмасс

The paper considers technological features of heterogeneous plastics ultrasonic welding, which specificity is manifested in the volumetric interaction nature. Results of studying the mechanism of a welded joint formation showed that micro-volumes mixing, polymer molecules mutual diffusion in the contacting surfaces and emergence of the new chemical bonds with the block copolymers formation were the simultaneous processes. Their common feature was that all these processes proceeded in the temperature range corresponding to the polymer viscous-flow state. It was experimentally confirmed that one of the criteria for weldability of the heterogeneous plastics was their compatibility in terms of acoustic properties being estimated by the melt density and viscosity. Technological methods were proposed making it possible to compensate for differences in the welded materials acoustic properties, and thereby obtain the high-quality welded joints. Four stages of the welded joints formation mechanism were determined during ultrasonic welding of the heterogeneous plastics. It was established that physical and mechanical properties of the heterogeneous plastics were playing a decisive role in the mechanism of heat generation during the ultrasonic welding. An ultrasonic welding unit for welding the heterogeneous plastics in vacuum was developed.

Influence of Heat Input on Microstructure and Mechanical Properties of Laser Welding GH4169 Bolt Assembly—Numerical and Experimental Analysis

By conducting the numerical and experimental analysis, the influence of heat input on the microstructures and mechanical properties of laser welding GH4169 bolt assembly is systematically investigated. The weld formation, temperature field, and residual stress distribution during laser welding by using the finite element modeling are consistent with experimental results. The numerical simulation results show that the increase of heat input imparts lower residual stresses and higher temperature gradient. During the process of laser welding, the steepest temperature gradient and the peak residual stress arise in the fusion zone (FZ). In addition, the dissolution of γ″ and γ′ toward the fusion line increases in heat affected zone (HAZ), but only Laves phase is observed in FZ. With increasing heat input from 24 to 48 J mm−1, the ultimate tensile strength of welded joints decreases. Both the lowest microhardness values and tensile failure of GH4169 alloy laser welded joint are in FZ. Herein, it is that the relationship among the heat input, microstructures, and mechanical properties of GH4196 bolt assembly in laser welding is systematically established, which will be of guiding significance for the selection of welding parameters in aerospace.

The response of force characteristic to weld-forming process in friction stir welding assisted by machine learning

In this study, the response of welding force characteristic to weld-forming process in friction stir welding (FSW) was systematically investigated. Assisted by machine learning technique, we found that both the force value and some detailed characteristics of force waveform are very important in reflecting the characteristics of weld formation. The mapping relations between force characteristics and weld/defect characteristics were comprehensively summarized for the first time. The results show that the distortion of the force waveform signifies the formation of defect, and the distortion degree and deflection direction of the force waveform show high relevancy to the size and location of defect. Meanwhile, the force waveform is decomposed into three standard sinusoidal waves with different frequencies, and the three sinusoidal waves correspond to the formation of the periodic weld microstructures in nugget zone. The causes of force fluctuations, with associated material deformation and flow behaviors during the FSW process, were also clarified to explain the above correspondences. The main reason is that force characteristics are closely related to the tool motion, probe geometric profile and welding parameter, which are key in heat generation and control the material flow in FSW. Therefore, it is concluded that the welding force characteristic is powerful in revealing some key information of the complicated weld-forming process, which can help us to make a deep understanding of FSW and develop intelligent FSW technologies.

The Analysis of Energy Distribution Characteristics of Molten Pool in Welding of Aluminum Alloy with Oscillating Laser

The energy distribution in molten pool is highly related to the quality of the weld formation in aluminum alloy welding. The forming defects in the weld are often improved by adjusting the molten pool dynamic behaviors affected by energy distribution. Therefore, the energy distribution characteristics in the molten pool during the welding of aluminum alloy with oscillating laser in the “∞” shaped path are explored in this paper. The pore defects are found to be greatly reduced in welds from the oscillating laser welding of aluminum alloy compared to those from non-oscillating laser welding. The corresponding distribution characteristics of energy in the molten pool of welding with oscillating laser are obtained and analyzed. The dynamic behaviors and forming process of welds under welding conditions of different distribution characteristics of energy in the molten pool are discussed. The obtained results are in good agreement with the experimental results. Therefore, the proposed method can provide the desired energy distribution for stable dynamic behaviors of molten pool to improve welding quality.

A novel seal-flow multi-vortex friction stir lap welding of metal to polymer matrix composites

The friction stir lap welding (FSLW) of metal to polymer is a challenging work due to the unavoidable polymer overflowing. Facing this problem, a novel seal-flow multi-vortex friction stir lap welding (SM-FSLW) technology based on the subversively-designed multi-step pin was put forward. Choosing 7075 aluminum alloy and short glass fiber-reinforced polyether ether ketone (PEEK) as research subjects, the welding temperature, material flow, formation and tensile shear strength of dissimilar materials lap joint under the SM-FSLW were studied and compared with those under traditional FSLW based on the conical pin. The multi-step pin rather than the conical pin effectively hindered the polymer overflowing due to the formation of vortexes by the step, thereby attaining a joint with a smooth surface. Compared with traditional FSLW, the SM-FSLW obtained the higher welding temperature, the more violent material flow and the larger area with high flow velocity, thereby producing the macro-mechanical and micro-mechanical interlockings and then heightening the joint loading capacity. The tensile shear strength of lap joint under SM-FSLW was 27.8% higher than that under traditional FSLW. The SM-FSLW technology using the multi-step pin provides an effective way on obtaining a heterogeneous lap joint of metal to polymer with the excellent formation and high strength.

Influence of heat source arrangement on coupling characteristics of low-power pulsed laser-MAG hybrid welding

Low-power pulsed laser-MAG hybrid welding was carried out by different heat source arrangement methods (lead mode, distance between laser spot and welding wire tip (DLA)). The coupling effect and welding characteristics of hybrid heat sources under different modes were studied by using high-speed image (HSI) and real-time electrical signals. HSI observation and electronic signals showed that the lead mode and DLA significantly affected the coupling state of the heat source and welding characteristics (weld morphology, process stability, and droplet transfer). The influence of lead mode on weld forming was more significant than that of DLA. In laser-lead mode, when DLA = 1 ~ 2 mm, the laser and arc generated a perfect coupling effect, resulting in a good weld formation, less spatter, and greater penetration. In arc-lead mode, the weld formation was poor and the undercut defect was common, while the penetration was greater than that in laser-lead mode. In terms of welding process stability, the arc-lead mode was better than the laser-lead mode. When DLA = 1 ~ 2 mm, stable droplet transfer could be realized under both modes.