Welding Position Research Articles

The Initiation Characteristics of Corrosion Fatigue Crack in 18Ni (250) Steel

Maraging steel is the material of deep sea pressure equipment. The characteristics of corrosion fatigue crack initiation in 18Ni (250) were investigated by performing a tensile fatigue test under different loading conditions. The mechanism of corrosion fatigue crack initiation was analyzed considering the influence of welding. The results showed that the crack initiation life decreases with increasing load and increases with the stress ratio. In a corrosive seawater environment, crack initiation is affected by both mechanical damage and electrochemical corrosion. The proportion of the crack initiation life of the total sample life is approximately 71.45–99.55%, where the larger this proportion is, the smaller the fatigue zone is. Crack initiation and microcrack propagation in maraging steel correspond to the microfracture mechanism of dimple fractures. The microfracture mechanism is strongly affected by the presence of a weld but weakly affected by the weld position. The results of this study provide a theoretical basis for predicting the corrosion fatigue life of deep-sea submersible pressure hulls.

Effect of Position of Robotic Gas Metal Arc Welding on Bead Quality and Multi-objective Optimization Through Gray Relational Analysis

Effect of Position of Robotic Gas Metal Arc Welding on Bead Quality and Multi-objective Optimization Through Gray Relational Analysis

The prediction of deformation in the process of erecting ship blocks based on inherent strain approach

Ship structures are referred to as plated and/or welded structures. Plates are sequentially welded using a high-temperature heat source to assemble the overall ship. The heat source used in the sequential welding inevitably generates imperfections in the ship structure, e.g., welding-induced deformation. Predicting welding-induced deformation is a critical task in design and control management at a shipyard, and much research has focused on the inherent strain method among possible efficient numerical methods. However, determining the inherent strain requires the synchronisation of all strain terms as a function of time and welding uncertainty because the welding position depends on the human worker. The present study thus derives time-dependent terms for inherent strain of the overall welding process and includes the welding position and cooling method in the function of the heat transfer coefficient. The inherent strain is derived through the detailed analysis of the overall welding process in terms of the application and utilisation, and it is simulated and reviewed for the erection of the hull block of a container ship and an LNG carrier. The inherent strain is expected to be used as a simple form of strain in the further study of various large welded structures and materials and in research on welding parameters.

Improving the Accuracy of Predicting the Shaft Part Thermal Deformation of an LNG Fuel Powered Container Ship Based on the Inherent Strain

A ship’s hull, made of steel, is welded together from individual plates. Welding can cause deformation, a common defect. Predicting this deformation is crucial for shipyard design and management. Numerical analysis using finite elements is widely used for this prediction, with extensive research on the inherent strain-based analysis method. However, determining inherent strain requires synchronizing all strain items over time and considering uncertainties like the welder’s posture and skill. This study derives an integrated inherent strain over the welding process, considering the welding position and cooling method. The derived strain has been implemented and reviewed through numerical analysis of the LNG-powered container ship’s hull assembly process. This integrated inherent strain can serve as a basis for further research on welded structures, materials, welding parameters, and inherent strain-based analysis methods.

Effect of double-pass friction stir welding and base materials position on the microstructural and mechanical behaviors of the dissimilar aluminum welded joints of AA6061 and AA2017

Friction stir welding (FSW) is a method of joining solid materials, where the parent metal’s melting temperature is below the point of amalgamation. FSW is a successful method for combining various ferrous and non-ferrous matrix materials. Many researchers’ studies suggested that FSW is suitable for both soft and high melting-point materials by changing the conditional attributes. A defect-free dissimilar weld joint of the alloys AA2017 and AA6061 was fabricated for the current investigation, and the effect of multi-pass friction stir welding (MPFSW) on the development of mechanical and different microstructural behaviors has been investigated. Welding conditions were a constant 1600 rpm weld tool rotational speed, a transverse speed is 32 mm min−1, and a tilt angle of 0°. As a consequence of the pinning effect, the results showed that increasing the number of welding passes in FSW from single to double improved the particle dispersion, which in turn improved the tensile strength, and micro-hardness of the FSWed joint. The primary objectives of this study investigate the strength that was improved because of the rise in the number of passes as well as the effective bonding of the materials’ weld interface, which gives tailor-welded blanks (TWBs) a considerably stronger joint. The findings revealed that the TWB joints’ metallurgical and mechanical properties are extremely varied from single-pass to double-pass, and the position of the base materials can significantly affect the joint properties that are produced.

Effect of tools rotational speed on the mechanical properties of one-step double-acting friction stir welded aluminum alloy AA 6061 hollow panel

The utilization of Aluminum hollow panels enhances structural strength while simultaneously ensuring a lightweight and efficient use of materials. During their application, these panels necessitate a welding process that is susceptible to porosity due to the disparity in hydrogen gas solubility between liquid and solid aluminum. Solid-state welding techniques, such as Friction Stir Welding (FSW), have proven to be effective and appropriate solutions for overcoming this issue. However, due to the thickness of the hollow panels, FSW process is unfeasible as it requires welding on both sides, resulting in prolonged production times. Consequently, the development of a one-step double-acting FSW technique becomes necessary, involving the simultaneous utilization of two tools. The usage of two tools introduces two sources of friction-stir forces, heat, and axial forces, demanding an assessment of the novel response from the specimens. This research aims to analyze the effect of a specific parameter, namely the tool rotation speed, within the one-step double-acting FSW process on the physical and mechanical properties of the AA6061 hollow panels. The One-Step Double-Acting FSW process involved conducting variations in the tool rotation speed on both sides of the welds. Specifically, for the 4G weld position (underside of the workpiece with an overhead weld position), speeds of 1200, 1500, and 1800 rpm were employed. Meanwhile, a consistent rotation speed of 1500 rpm was maintained for the 1G weld position (overside of the material with a flat weld position). The transverse speed and tilt angle are set at 30 mm/min and 2°, respectively. Elevating the tool rotation speed results in increased hardness, load capacity, and bending strength of the weld joints. The specimen subjected to the highest rotational speed (1800 rpm) exhibits the most exceptional mechanical properties, including a hardness of 73.46 HVN, load capacity of 18.47 kN, and bending strength of 60.56 MPa.

Welding of S1100 Ultra high‐Strength Steel Plates with Matching Metal‐Cored Filler Wire: Microstructure, Residual Stresses, and Mechanical Properties

This study investigates the relationship between the microstructure and the mechanical properties and the residual stresses of thermomechanically rolled, butt‐welded S1100MC ultra high‐strength steel plates. Matching metal‐cored filler wires are used for metal active gas welding of the plates in horizontal and vertical‐up positions. The effect of the heat input on the microstructures of both the weld metal (WM) and the heat‐affected zone (HAZ) is studied in detail. The microstructure of the WM consists of different types of ferrite, but the microstructure of the HAZ predominantly consists of fresh martensite at the top and bottom areas. Structure and size of the prior austenite grain boundaries are dependent on the welding positions and affect the impact toughness of the welds. HAZ of the weld produced in vertical‐up position is under intensive tensile residual stresses next to the fusion line. Even with matching filler wires, the strength of the welds is insufficient, and fracture of the weld metal occurs because the extended cooling time leads to the formation of acicular ferrite instead of martensite.

Effect of Water Cooling on the Microhardness of Friction Stir Welded High-Density Polyethylene Sheets: Experimental Study

The objective of the current work is to analyze the influence of water cooling of high density polyethylene (HDPE) sheet welding by friction stir process (FSW) on mechanical strength, based on microhardness tests. In the present work, the process using the conventional tool (C-FSW) is presented with the new procedure developed for FSW for HDPE, called water conventional friction stir welding (W-FSW). Test results for water-cooled and non-cooled welded samples were compared. HDPE sheets were initially welded by FSW process, and intensive water cooling was performed to weld after the tool exceeded the initial welding position by 30mm. The tool rotation speed of 1100 rpm and welding speed of 26 mm/min was used. The results were compared and evaluated with the hardness tests. A decrease in the hardness was observed when the sheets were treated by quenching, especially in the weld cores. It was found that the average hardness was much lower than that of untreated welded plates. Additionally, there is a region outside the core that has more or less the same stiffness value. The use of intensive quenching and conventional tooling has proven to be of great importance in improving surface finish, reducing defects, and increasing the mechanical strength of welds. The resulting recrystallization modified the hardness and thus increased the efficiency of the joint. These findings indicate the welding quality of the studied polyethylene.

Effects of Sheared Edge and Overlap Length on Reduction in Tensile Fatigue Limit before and after Hydrogen Embrittlement of Resistance Spot-Welded Ultra-High-Strength Steel Sheets

The effects of a sheared edge and overlap length on the reduction in the tensile fatigue limit before and after hydrogen embrittlement of resistance spot-welded ultra-high-strength steel sheets were investigated. Ultra-high-strength steel sheets with sheared and laser-cut edges were subjected to resistance spot welding followed by hydrogen embrittlement via cathodic hydrogen charging and subjected to static tensile shear and fatigue tests. The distance between the resistance spot weld and the sheared and laser-cut edges was changed by changing the overlap length, and the influence of the weld position was investigated. In the tensile shear test, the maximum load decreased with decreasing overlap length and the maximum load decreased with hydrogen embrittlement, but the effect of hydrogen embrittlement was smaller than that in the fatigue test. In the fatigue test, the fatigue mode changed from the width direction to the sheared edge direction with the increase in the repeated load. Even if the overlap length was reduced, the fracture changed to the sheared edge direction. In the specimens with sheared edges, the effect of fatigue limit reduction due to hydrogen embrittlement was greater than in the specimens with laser surfaces. In particular, the effect was greatest when the fatigue mode was changed via hydrogen embrittlement.

Research on molten pool flow characteristic in all-position LP-LMH welding

ABSTRACTThe flow characteristics of keyhole and molten pool impact the real-time process stability and seam formation severely in all-position low-power laser MAG hybrid (LP-LMH) welding. To probe into the molten pool’s real-time dynamics at various spatial welding positions, the high-speed camera images of metal transfer and molten pool were sensed. Meanwhile, a novel spatial flow model of molten pool was developed, and the functions of spatial position and gravity on the molten pool flow were investigated. The results proved that as the spatial position increases, the location of where droplet striking molten pool changes accordingly, further disturbing the keyhole’s stability. Meanwhile, the spatial position seriously affects the molten pool’s flow. The driving forces of molten pool flow at various spatial welding positions are basically the same, and gravity affects the overall movement of molten pool, thereby affecting the vortexes and heat transmission inside the molten pool, as reflected in weld penetration.

Cause analysis of premature fracture in the welding position of special lifting tool for aero-engines

A specialized lifting tool for aero-engine in a workshop broke down after two months of use, resulting in damage to the workpiece and significant economic losses. The incident also posed a serious production hazard in the workshop. In this study, a series of characterization methods including macroscopic trace observation, fracture analysis, physical and chemical testing, microstructure observation, and hardness testing were conducted to analyze the cause of the lifting tool fracture. Based on simulation methods, the reliability of the lifting tool design was evaluated. The results show that the lifting tool design itself is reliable, and the main reason for the fracture is poor welding quality of the welded structure. It is suspected that there are welding cold cracks in the heat affected zone, which propagate during the use of the lifting tool and eventually lead to fracture. The root cause is that the quality of the base material of the weld did not meet the design requirements, resulting in a higher carbon equivalent in the base material, lower weldability, and increased sensitivity to welding cracks, which was also the reason for the fracture occurring in the welding heat-affected zone. The unqualified material composition affects the process parameters of the pre-welding preheating and the post-welding heat treatment, resulting in the formation of high hardness (724.0HV1) and brittle martensite structure in the welding heat-affected zone.

Peningkatan Kompetensi Pengelasan Shielded Metal Arc Welding Bagi Masyarakat Desa Makarti Jaya Kabupaten Morowali

Mekarti Jaya Village is located in the PT Industrial Area. IMIP, the need for industrial workers in the PT area IMIP continues to increase as the investment value in the area increases. To prepare the people and youth of Mekarti Jaya village to be able to take advantage of job opportunities in industries located in the PT area. IMIP needs to carry out training to increase competency, especially in the field of Shielded Metal Arc Welding (SMAW) welding position 2F. The selection of SMAW welding training materials was based on survey results, in which the need for welding specialist workers was the greatest need for industries in the PT area. IMIP. Training activities are carried out for approximately 1 month, starting with the preparation, implementation, and training results stages. The activities were carried out on February 27–29, 2022. Training activities were carried out at the Morowali Metal Industry Polytechnic Machinery Maintenance Engineering study workshop. The training was attended by ± 16 young people and residents of the village of Mekarti Jaya. The results of the training carried out were an increase in understanding and knowledge before and after the training activities were carried out; this was shown by the results of the constant shape of the ridges, welding position 2F, and the results of the post-test.

Analysis of the effect of welding sequence and speed on the distortion of ASTM A36 joints by MIG method

The welding process with the Metal Inert Gas (MIG) method often produces distortions that are detrimental to product quality, one of the factors that affect the characteristics of the welding results is heat input. The heat input provided in the welding process is influenced by arc current, arc voltage, and welding speed, besides that the welding sequence can also affect the distortion of thin plates due to welding on materials such as ASTM A36 plates. The welding process uses welding wire/electrode type AWS ER 70S-6 with a diameter of 1.0 mm, the welding parameters applied are: voltage of 22 Volts, current of 150 Amperes, DC + Current type (DCEP), the shielding gas used is 100% Argon with a flow rate of 15 liters per minute, horizontal welding position (1G), the amount of heat input is differentiated by changing the welding speed and the welding sequence used is the stepping stone method. The results of the study using ANOVA indicate that welding distortion increases with an increase in input heat, the repetition of welding sequences leads to greater distortion due to thermal stress, and the welding sequence and input heat have an influence of 80.4% in reducing distortion.

Effects of electric welding on hearing loss and respiratory damage

Objective: To investigate the occupational health status of electric welding workers and explore the effects of electric welding on hearing loss and respiratory damage. Methods: From August to December 2021, the cluster sampling method was used to select workers from an automobile manufacturer in Guangzhou City as research subjects: 636 welding workers in the welding workshop as the welding group, 757 assembly workers in the engine workshop and the final assembly workshop exposed to pure noise as the assembly group. Occupational disease hazard factors were detected for welding positions and assembly positions, and occupational health examination was carried out for research subjects. The occupational health status, the trends of hearing loss and respiratory abnormalities with working age were compared and analyzed between the two groups. Binary logistic regression was used to analyze the association between hearing loss and respiratory abnormalities in welding workers. Results: The excess rates of welding fumes, manganese and its compounds in the welding position were both 9.68% (3/31). Its noise exposure intensity [ (85.36±2.68) dB (A) ] and excess rate [48.39% (15/31) ] were not significantly different from those in the assembly position [ (84.86±3.28) dB (A) and 43.24% (16/37) ] (P>0.05). The results of the occupational health examination showed that the detection rates of hearing loss, digital radiography (DR) chest X-ray abnormality, alanine aminotransferase abnormality, deazelaic aminotransferase abnormality and white blood cell count abnormality of workers in the welding group were higher than those in the assembly group (P<0.05). The detection rates of hearing loss, DR chest X-ray abnormality, pulmonary ventilation abnormality in the welding group and the detection rate of hearing loss in the assembly group increased with the working age of the workers (P<0.05). The hearing loss detection rate and DR chest X-ray abnormality detection rate of the workers with ≥9 years working age in the welding group were both higher than those in the assembly group workers with same working age (P<0.05). The binary logistic regression analysis showed that abnormal pulmonary ventilation and abnormal DR chest X-ray were the risk factors for hearing loss in welding workers (OR=10.83, 95%CI: 7.31-16.06; OR=16.59, 95%CI: 5.72-48.10; P<0.05) . Conclusion: Hearing loss and respiratory damage are prominent problems among welding workers, and the detection rates of abnormality increase with the working age of the workers. Hearing loss in welding workers is associated with abnormal pulmonary ventilation and abnormal DR chest X-ray.

Influence of thermal flow and predicting phase transformation on various welding positions

Influence of thermal flow and predicting phase transformation on various welding positions

Mechanisms of Gravitational Influence on Weld Pool Behavior and Weld Bead Performance in Variable Polarity Plasma Arc Welding across Different Welding Position.

This article comprehensively explores the cross-scale effects of gravity on macroscopic flow formation and weld bead formation in variable polarity plasma arc welding. Gravity-induced changes in welding direction were achieved through welding at different spatial positions. The properties of the weld bead were investigated at various spatial locations. Additionally, an elemental tracing technique was employed to study the internal flow behavior of molten metal. In the flat welding position, there is an observable trend of increasing grain size in the welded bead, accompanied by a significant expansion of the coarse grain zone. Consequently, the properties of the weld bead in the flat position are inferior to those achieved in the vertical welding position. This phenomenon can be attributed to the accumulation of molten metal at the exit side of the keyhole, resulting in temperature accumulation. Research indicates that the internal flow within the weld pool plays a critical role in causing this phenomenon. The study's findings reveal the presence of two distinct vortex flow patterns within the weld pool: one aligned with the welding direction and the other directed towards the interior of the weld pool. Particularly noteworthy is the substantial expansion of the flow channel area in the flat welding position, which significantly amplifies the impact of internal flow. This enhanced flow intensity inevitably leads to the increased buildup of molten metal at the keyhole exit side. These studies lay the groundwork for achieving high-quality and controllable spatial-position welding.

Cross-scale process quality control of variable polarity plasma arc welding based on predefined temperature field

This study investigates the underlying causes of Variable Polarity Plasma Arc Welding (VPPAW) spatial positional instability and its adverse impact on weld seam quality. Microstructural analysis reveals that the primary cause of poor transverse mechanical properties is the asymmetric distribution of grains. Through the study of heat and mass transfer in the molten pool, it was found that the asymmetric flow of molten metal under the influence of gravity is the main factor leading to uneven temperature distribution and asymmetric grain distribution in the weld pool. A novel approach based on a predefined temperature field is proposed to regulate the weld pool's stability and welding quality. The implementation of the predefined temperature field effectively improves VPPAW weld pool flow, leading to enhanced temperature distribution and grain size and distribution. These findings provide a theoretical foundation and valuable engineering recommendations for achieving high-quality spatial position welding in VPPAW.

A Study on Changes of Bead Shape and Metal Transfer Mode Affected by Molten Pool Behavior for Welding Position in GMAW Process

In gas metal arc welding, the molten pool is affected by gravity and this affects welding phenomena. This study investigated the changes in bead shape and metal transfer mode caused by the molten-pool behavior. We conducted gas metal arc welding with various welding positions. Images from high-speed camera and signals from current and voltage sensors were used to determine the differences with welding positions. Bead shapes were quantified through transverse cross-sectional bead images and image processing. Molten-pool images from the camera were analyzed through the molten-pool length and distance from the wire position. These were used to explain the differences between transverse and longitudinal cross-sectional bead images with welding positions. Changes in metal transfer based on current and voltage signals were investigated. To determine the exact change in metal transfer, the number of short-circuit transfers and spray transfers within the same time was captured by the welding position camera.

The impact of fatigue on shipyard welding workers’ occupational health and safety and performance

Welding processes are critical for shipbuilding operations in shipyards. Welders’ performance is critical for the quality and speed of the welding; on the other hand, welding requires awkward and repetitive body postures for long durations, which has a negative impact on the Occupational Health and Safety (OHS) of the welding workers. This study, therefore, investigates the long-term impact of welding workload on the body for different age groups and experience levels, as well as the long-term impact on chronic fatigue and inter-shift recovery. In order to determine the impact, this study conducted a comprehensive data collection campaign in the shipyard through observation and questionnaires. Results indicate that the eyes, knee, neck and waist are the most discomforted body parts for investigated welding positions. The age of welders was an important parameter of the most affected body part.Moreover, the short-term fatigue impact on welding performance was also investigated to identify the impact on productivity. The Discrete event simulation (Rockwell ARENA) demonstrated that efficiency loss from short-term daily fatigue is around 22,9% compared to the rested condition. The main contribution of this study was investigating fatigue impact on OHS and productivity for selected shipbuilding tasks. The findings of this study can be utilised for shipyard production capacity and resource planning and OHS improvements. The results can also be used further as a coefficient of performance in the production simulation analysis when studying shipyard efficiency. This is a valuable contribution to the literature on shipyard productivity.

A Wideband Antenna Calibration Network Using Multi-Layer Coupling Technology

In this paper, the design methodology of an antenna calibration network using multi-layer stripline-slotline coupling is proposed. A multi-layer coupler and a two-stage Wilkinson power divider are designed to ensure the basically stable amplitude-phase characteristics of coupling and achieve the wide frequency band. To minimize phase imbalance, the lengths of channels should be kept equal to the maximum extent possible. In addition, the transmission line conversion structure is applied at each port for integration with the antenna array. Aiming at the problems of signal crosstalk and mutual coupling, the isolated via holes are installed near the lines and metal spacers are placed over the ports. By using the semi-closed structure, part of substrates is dug out to expose the resistor welding position. A semi-closed calibration network in series-parallel-fed is fabricated to verify the design methodology. In 8-16 GHz, the amplitude-phase characteristics are considerable, in which the coupling is 37-44 dB and phase deviation is below 8∘. The isolation between ports T1-T16 is greater than 33 dB and voltage standing wave ratio (VSWR) of them is lower than 1.8.