Multi-layer Welding Research Articles

Controlling Dilution in Multilayer Welding for Additive Manufacturing

Controlling Dilution in Multilayer Welding for Additive Manufacturing

Robot welding process planning and process parameter prediction of medium-thick plate based on three-line laser

In order to realize the intelligence and flexibility of V- groove robot welding of medium-thick plates, a multi-layer welding process control strategy for welding with a weaving robot is proposed based on three-wire structural light vision. For the optical localization of the welding start point, a “rough first, accurate later” guidance approach is proposed. A technique utilizing Gaussian-weighted plane fitting is employed to model the groove and extract information about the weld shape. The welding torch’s orientation planning is based on the angular bisector of the groove, and the GA-BP neural network is utilized to forecast welding parameters for various welding techniques. It is shown that the strategy in this paper can guide the robot to complete the welding job. The error between the guide start point and the actual welding start point does not exceed 2 mm, and the predicted welding parameter results align with the welding technology standards.

Hardness Prediction of the Heat-Affected Zone in Multilayer Welded SUS316 Stainless Steel Based on Dislocation Density Change Behavior

The effects of strain hardening and recovery/recrystallization on the hardness of the heat-affected zone (HAZ) in multilayer welded austenitic stainless steel SUS316 were investigated in this study. The results revealed that strain hardening due to welding strain and softening due to recovery/recrystallization were the dominant factors affecting the hardness change in the HAZ during multilayer welding process. Furthermore, the relationship between the strain and dislocation density and that between the recovery/recrystallization and dislocation density were quantitatively investigated using positron annihilation lifetime spectroscopy. Based on these results, a new hardness prediction method based on the change in dislocation density in the HAZ during multilayer welding was proposed. The hardness values in the HAZ after the multilayer welding were predicted based on the simulated strain and thermal history, and the calculated hardness values agreed well with the measured results. This indicates that the newly proposed hardness prediction method based on the dislocation density change behavior in the HAZ during multilayer welding is valuable and effective for selecting the appropriate welding conditions before actual welding.

Virtual simulation of weld morphology for V-groove multi-layer welding

In order to study the virtual simulation of weld morphology for V-groove multi-layer welding, the prediction of characteristic parameters for weld morphology was realized by constructing the neural network models between the characteristic parameters and process parameters of different layers. At the same time, the virtual models of different layers were established according to the characteristic parameters of weld morphology and the structure parameters of V-groove. Combined with the prediction model and the virtual model, the process parameters were associated with the weld morphology, and the virtual simulation of weld morphology was realized. In the process of establishing the virtual model, first of all, the virtual model of root weld is established. Then, the virtual model of filling layer is established based on the root layer, and the virtual model of weaving layer is established based on the filling layer. Finally, validation experiments were carried out to verify the accuracy of the model. Verification results show that the prediction model can effectively predict the characteristic parameters of each layer, and the average relative errors of melting depth and width were less than 8%. The virtual simulation morphology has a high consistency with the actual morphology, and the average relative error of cross section area was less than 10%.

Effect of interlayer temperature and cold wire addition in Wire Arc Additive Manufacturing on carbon steel

Wire Arc Additive Manufacturing (WAMM) consists in the manufacture of metallic preforms from the deposition of multilayer weld beads on a substrate, that is, from a three-dimensional model, the object is divided into layers defining the trajectories in which the addition of metal will be made, with the use of a robotic manipulator. The objective of this work is to study the influence of the addition of cold wire and the effect of interlayer temperature in the WAAM process, comparing it with the deposition made with a single wire, observing mechanical properties such as tensile strength, hardness, in addition to the cooling time for different interlayer temperatures and the geometry of the manufactured parts. A GMAW (Gas Metal Arc Welding) system was used coupled to a robotic manipulator, with multiple wires of 1.6 mm in diameter for the energized wire and 1.0 mm for the cold wire, both classified as ER70S-6. In order to manufacture the specimens for the tensile test, 20 layers were superimposed in a straight line, forming a wall, varying the interlayer temperature between each layer, using 100°C, 150°C and directly, with no waiting interval between layers. In general, a shorter cooling time was observed for the walls manufactured with the addition of cold wire when compared to depositions with a single wire. In addition, it was noted that the cold wire also influences the height and thickness of the pieces. In the mechanical tests, the cold wire did not significantly influence the hardness values. The highest values were found in the 100°C samples. For the tensile tests, it was observed that, in general, the addition of cold wire tended to increase the maximum tensile strength of the samples.

A critical understanding on the microstructure and creep failure of Super304H/T92 dissimilar multilayer welds

A critical understanding on the microstructure and creep failure of Super304H/T92 dissimilar multilayer welds

Acoustic Emission Method as a Means of Quality Control in Multilayer Welding of Thick-Walled Welded Joints

Abstract The article reviews the capacities of the acoustic emission method usage to assess the technical condition and integrity of thick-walled welded structures, the quality control of welded joints in multilayer welding. As a result of the analysis of AE control data, the authors propose a set of informative parameters of the AE method, which form a criterion space for separating the reflected signals from defects and signals from interference.

High contrast corrosion mapping of dissimilar metal weld joints using alternating current scanning electrochemical microscopy: A case study with Zr-4–Ti–304L SS weld

Intermittent contact alternating current scanning electrochemical microscopy (IC-AC–SECM) has been used in the present study to image the local electrochemical activity of Zr-4–Ti–304L SS dissimilar weld joint without a redox mediator at an open circuit potential. The perturbation frequency and bias potential applied to the Pt ultramicroelectrode (UME) are found to affect the contrast of IC-AC-SECM imaging. The optimum parameters for high contrast imaging with high sensitivity were determined by performing potentiodynamic polarization and approach curves of Pt UME. The potentiodynamic polarization behaviour of Pt UME carried out in tap water revealed that the Pt UME biased with potential at −0.5 V was ideal for obtaining better sensitivity due to the maximum reduction of dissolved oxygen in the electrolyte. The effect of applied perturbation frequencies on Pt UME examined by the approach curves using the AC-SECM technique showed a transition from negative to positive feedback over 304L SS at about 10 kHz whereas for Zr-4 and Ti the transition was observed at 50 kHz but with only a minor difference in their feedback. Better contrast in mapping local current and impedance magnitude across the weld joint has been achieved by applying an optimum dc bias (–0.5 V) to the Pt tip and perturbation frequency (10 kHz). The IC-AC-SECM results have been compared with the conventional potentiodynamic polarization and electrochemical impedance spectroscopy results of Zr-4, Ti, 304L SS and the weldment in tap water, where the weld sample undergoes preferential corrosion of 304L SS region due to the galvanic coupling. The present work provides new insight into the optimal IC-AC-SECM parameters for best lateral imaging to map electrochemical activity with good contrast across a multilayer weld joint in tap water.

The Different Welding Layers and Heat Source Energy on Residual Stresses in Swing Arc Narrow Gap MAG Welding.

In this paper, in order to reduce the time cost of prediction experiments in industry, a new narrow gap oscillation calculation method is developed in ABAQUS thermomechanical coupling analysis to study the distribution trend of residual weld stresses in comparison with conventional multi-layer welding processes. The blind hole detection technique and thermocouple measurement method verify the reliability of the prediction experiment. The results show that the experimental and simulation results have a high degree of agreement. In the prediction experiments, the calculation time of the high-energy single-layer welding experiments is 1/4 of the traditional multi-layer welding. Two welding processes of longitudinal residual stress and transverse residual stress distribution trends are the same. The high-energy single-layer welding experiment stress distribution range and transverse residual stress peak are smaller, but the longitudinal residual stress peak is slightly higher, which can be effectively reduced by increasing the preheating temperature of the welded parts. This implies that in the specific case of increasing the initial temperature of the workpiece, the use of high-energy single-layer welding instead of multi-layer welding to study the residual stress distribution trend not only optimizes the weld quality but also reduces the time cost to a large extent.

ANALISIS PENGARUH ARUS PADA PENGELASAN BERTINGKAT (MULTILAYER WELDING) TERHADAP STRUKTUR MIKRO, KEKERASAN DAN KUAT TARIK SAMBUNGAN MATERIAL ASTM A106

This aims of this study to determine the effect of multilayer welding on ASTM A106 type carbon steel pipe material on the characteristics of the microstructure, hardness and maximum tensile strength of the material. ASTM A106 type carbon steel pipe is used as a raw material for welding using the Shielded Metal Arc Welding (SMAW) method. Welding on material joints is carried out in three layers (multilayer welding), namely the root pass, hot pass, and capping layers. There are two variations of welding specimens carried out in this study, namely in specimen 1 the currents used were 60, 70 and 80 A while in specimen 2 the currents used were 70, 80 and 90 A. To determine the effect of current variations on each specimen carried out three include Vickers Testing, microstructure testing and tensile testing. The results show that the base metal area is dominated by the ferrite phase, which indicates that the area has low hardness while the weld shows more perlite phase than ferrite besides the grain size is smaller and denser; this indicates that the hardness level will increase when compared to base metal. The results of the hardness test for all variations of the specimen concluded that the highest hardness value was in the weld. From the tensile test, it can be concluded that specimen 2 has a greater tensile strength of 2.5% when compared to specimen 1.

SELECTION OF A WELDING ELECTRODE TO PREVENT CONTACT CORROSION OF A STEEL 1.0402 WELD JOINT

Welded structures operate, as a rule, under conditions of simultaneous exposure to aggressive media and workloads. Thus, when protecting the metal of welded joints from corrosion fatigue, a number of specific problems arise due to the heterogeneity of their structure, the presence of multilayer welds, physical and geometric stress concentrators, and the staged nature of the change in the fine structure of the metal during fatigue loading. The result is an accelerated destruction of the metal in the junction zones of various structural forms, which are unequally adapted to the action of fatigue stresses. This fully applies to such critical structures of the oil and gas industry as pipelines, tanks, gas holders, etc. The purpose of the research was to establish the features of corrosion of welded joints made by various brands of electrodes by analyzing the change in the value of the electrode potential of the metal, which reflects the level of free energy of the surface layers in dynamics. Laboratory samples of carbon steel 1.0402 were subjected to manual arc welding (OZL-6, LB-52, MP-3 electrodes) and semi-automatic welding (EMK 6D polished wire and E71T1 rutile flux-cored welding wire with rapidly crystallizing slag). Further, their microstructural analysis was carried out and the hardness of various sections of welded joints was determined. It has been established that samples welded by semi-automatic welding are less susceptible to corrosion damage, since the distribution of electrode potentials in the zones of the welded joint indicates their lower structural inhomogeneity. In this case, general uniform corrosion takes place. In addition, the use of EMK 6D and E71T1 welding wires ensures better mechanical properties of welded joints.

Detection of reinforcement of multi-bead and multi-layer weld in additive manufacturing based on on-line visual information of weld pool

In the multi-bead and multi-layer arc additive manufacturing process, the information of cladding reinforcement reflects the welding quality to a certain extent, so it is of great significance to monitor the reinforcement of cladding layers in real time. In this paper, a point cloud density search method is used to segment the point cloud of a single weld bead in the multi bead weld seam, and then the reinforcement of each cladding bead of multi-bead and multi-layer weld is extracted separately when the bottom plate is deformed due to high temperature, and a residual-based prediction model is constructed for quantitative forecasting of the transient reinforcement before solidification of block cladding layer in real time. The following work is completed to prove the accuracy and effectiveness of the proposed model, two different strategies are used to predict the reinforcement of multi-bead and multi-layer welds. Through the experiment, we can see the mean forecast error of the reinforcement of multi-bead and multi-layer welds is less than 0.3 mm, while the time for the model to dealing with the molten pool image is 18 ms, and the optimal strategy can make the average error better than 0.15 mm, which proves that the model constructed in this paper has great generalization performance and realizes the real-time and high-precision prediction of cladding reinforcement in the case of small deformation. The study of this paper supplies a necessary basis for the online monitoring and control of morphological defects in the process of weld processing.

Analysis of residual stresses in electron beam welding with filler wire of Ti62A alloy

Residual stress significantly affects the performance of the welded joints and the tensile residual stress easily leads to the joint fracture and failure. A three dimensional nonlinear transient thermo-mechanically coupled finite element model of Ti62A alloy electron beam welding (EBW) with filler wire was established. The influence of the welding parameters, such as welding power, groove angles and number of welding layers on the temperature and residual stress evolutions was predicted and verified against existing literature data. The calculated results indicate that the high tensile stress of heat affected zone is very likely to induce the failure of the welded joints. When the welding power is 2600 W, the longitudinal residual stress along the welding direction is more symmetrical on both sides, and the force and deformation of the weldment will be more uniform. As the groove angle decreases, the transverse residual compressive stress on the joint surface becomes larger, which results in the low risk for cracking tendency of the joint. Increasing the number of welding layers reduces the weld reinforcement and the residual stress. In addition, the decline magnitude of residual stress decreases with the increase in the number of welding layers. Both the smaller groove angle and the multi-layer welding can effectively reduce the residual stress of weldments and improve the joint performance. The findings of this study will provide a good theoretical basis for optimizing welding process.

Computer analysis of plastic strain accumulation in multilayer arc welding and surfacing

Level of plastic deformations is calculated in multilayer acr welding and surfacing. The equations of compatibility of displacements caused by heating of the metal during successive application of rollers are solved. It is revealed that in the case of successive surfacing of beads and a change in the distribution of limiting temperatures, a complex pattern of the stress state of the metal arises in the zone of surfacing. This indicates the need to take into account this phenomenon in multilayer welding and surfacing in engineering practice.

Multi-Layer Welding Path Correction of Medium-Thick Plate Based on Vision System

Multi-Layer Welding Path Correction of Medium-Thick Plate Based on Vision System

Hydrogen effect on mechanical properties and cracking of creep-resistant 9% Cr P92 steel and P91 weld metal

Martensitic 9% Cr steels like P91 and P92 can show an increased susceptibility to delayed hydrogen-assisted cracking. The focus of this study was the microstructure and heat treatment effect on the mechanical properties of P92 base material and P91 multi-layer weld metal in both as-welded and post weld heat treated (PWHT) condition. Tensile tests with hydrogen-free reference samples and electrochemically hydrogen charged samples were carried out; the mechanical properties were assessed and supported by detailed fractographic analysis. Finally, a hydrogen and microstructure-dependent fracture criterion is established. All investigated microstructures showed a hydrogen-influenced degradation of the mechanical properties compared to the hydrogen-free reference samples. The as-welded martensitic P91 weld metal had the highest degree of degradation in the presence of hydrogen. The P91 PWHT weld metal and the P92 base material had comparable properties. From that point of view, a significantly increased risk for hydrogen-assisted cold cracking during welding fabrication of P91 weld joints must be considered before any heat treatment is conducted.

Control of Welding Residual Stress in Large Storage Tank by Finite Element Method

T-joint welding is a key manufacturing process of large storage tanks. However, complex residual stresses are generated and have a great effect on the structural integrity of storage tanks. The high residual stress caused by welding and the discontinuous structure may result in tank cracking and failure. In this work, the residual stress distributions on the inner surface, outer surface, and thickness direction of the T-joint were investigated by using the finite element method and indentation test method. The effect of local PWHT with different heating temperatures, heating rates, and heating widths on the residual stress distribution was also discussed. Results show that the residual stress of the T-shaped joint is high due to the serious structure discontinuity, multi-layer welding, and high strength. Among all the stresses, the circumferential residual stress is the highest and most concentrated in the outer weld connected with the annular plate. The residual stress gradually decreases with the increase in the heat treatment temperature. When the heating rate is less than 106 °C/h, the residual stress gradually decreases with the decrease in the heating rate. The large thermal deformation caused by heat treatment can be simultaneously avoided by heating the inside and outside of the T-joint. The residual stress decreases with the decrease in the width of the heating zone. The residual stress can be regulated by using a smaller width in the heating zone. An optimized heat treatment scheme with a heating temperature of 700 °C, heating rate of 56 °C/h, and heating width of 200 mm was proposed, which has a good ability to control residual stresses and improve the quality of the T-joint. It also has a good application in engineering.

A Study on the Ultrasonic Regulation of the Welding Performance and Residual Stress of 316L Stainless Steel Pipes.

Due to its extreme service conditions, low-temperature pressure piping often needs post-welding stress measurement and control. Aiming at the phenomenon of local stress concentration in welded 316L pipes, this study used ultrasound to regulate the stress in the welded area at different times during and after the multi-layer welding of the pipeline butt joint for different time lengths. Mechanical properties such as tensile strength and hardness were tested for each comparison group, and the microcrystalline phases of the weld and its surrounding microstructure were analyzed. The transverse and longitudinal surface residual stresses of each comparison group were measured. The influence of high-energy ultrasound on the surface temperature field during and after welding was analyzed. The experimental results show that ultrasonic wave regulation can speed up heat exchange and radiation in the weld zone (WZ), refine the grains in the WZ, heat-affected zone (HAZ) and fusion zone (FZ) to some extent and reduce and homogenize residual stress to a certain degree. In the 120 mm area of the weld center, the residual stress measured after the mid-welding regulation was smaller than that of any other comparison group. This regulation result was the best, followed by that of hot regulation and finally that of offline regulation. The tensile strengths obtained by the mid-welding regulation and post-welding hot regulation of this group were the best, increasing by 17.2% and 24.3%, respectively, compared with the untreated groups.

Research on Filling Strategy of Pipeline Multi-Layer Welding for Compound Narrow Gap Groove.

With the increase in transmission pressure and pipe diameter of long-distance oil and gas pipelines, automatic welding of the pipeline has become the mainstream welding method. The multi-layer and multi-pass welding path planning of large-diameter pipelines with typical narrow gap grooves are studied, and a welding strategy for pipeline external welding robot is proposed. By analyzing the shape of the weld bead section of the narrow gap groove and comparing the advantages and disadvantages of the equal-height method and the equal-area method, the mathematical model of the filling layer is established. Through the test and analysis in the workshop, the predicted lifting value meets the actual welding requirements. The microstructure of the weld was analyzed by SEM. The main structure of the weld was fine acicular ferrite, which could improve the mechanical properties of the welded joint. After multi-layer filling, the filling layer is flush with the edge of the groove. The establishment of this model lays a foundation for the formulation of welding process parameters for large-diameter pipes and the off-line programming of welding procedures.

Microstructure and Mechanical Properties of Laser Narrow-Gap Multi-Pass Weld 20 mm-Thick Ti-6Al-4V Alloy with Different Filling Layers

In the narrow-gap multi-layer welding of thick Ti-6Al-4V titanium alloy sheets, reducing the number of filling layers can effectively improve the welding efficiency and reduce the possibility of interlayer defects. In order to explore the changes in the microstructure and properties of the weld after reducing the number of filling layers, Ti-6Al-4V titanium alloy sheets with a thickness of 20 mm were successfully welded using the oscillating laser beam mode by laser narrow-gap multi-pass wire filler welding in eight, six, four, and three layers, and all of the formations were good. To reduce the number of filling layers and increase the welding line energy from 0.4 kJ/mm to 1.2 kJ/mm, the melting depth and width of the single layer were changed from 4.3 mm to 10.6 mm, and 5.7 mm to 10.3 mm. The average grain size of the needle-shaped martensite increased from 1.83 μm to 2.38 μm, while the tensile strength of the filled weld area decreased from 1301.8 MPa to 1169.8 MPa, which was higher than that of the base metal of 902.1 MPa. Since there are more columnar crystals in the center of the weld at low heat input, the impact energy was 20.53 J (60.6% of the base metal) at room temperature and 15.76 J (65.9% of the base metal) at −50 ∘C. Considering the weld formation, microstructure and mechanical property, welding four layers of fillers obtained with moderate line energy (0.8 kJ/mm) was more suitable.