摘要:Dissimilar steel welding is extensively applied in subcritical boilers, where the performance of the welded joint directly impacts the boiler's operational safety and service life. This study focuses on the T22/TP304H dissimilar steel welded joint in boilers that have been in service for over 200 000 hours, analyzing the changes in its microstructure morphology and mechanical properties. The residual life of the joint is evaluated based on high-temperature endurance test results. Findings indicate that precipitate aggregation occurs in the TP304H base material and weld, which can easily induce the initiation of cracks in the welding area. The tensile strength of long-term operational joint samples is consistently lower than the minimum value required by ASME standards, indicating a significant decline in mechanical performance. The remaining life of the joint is 29 745 hours, but its operational reliability has significantly decreased. Thus, it is recommended to inspect and repair the joint area and intensify subsequent inspection work. This paper provides a theoretical reference for the study of T22/TP304H dissimilar steel welded joint structure and properties, and the safe operation of the equipment in the future.
关键词:T22/TP304H dissimilar steel;long-term service;mechanical properties degradation;remaining life assessment;maintenance strateg
摘要:To investigate the in-situ reaction process of AgCuSn-based active brazing materials, this experiment mechanically mixed elemental powders of Ag,Cu, Sn, and Ti in various mass fraction ratios, with an appropriate amount of binder and water to form a brazing paste, which was then heated to different temperatures and maintained. The microstructure of the brazing material was characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), and the in-situ reaction process was explored based on thermodynamic theory and diffusion theory. The results indicate that the in-situ reaction mainly occurs in three stages. In the first stage, the melting of Sn leads to the formation of binary intermetallic compounds Cu6Sn5 and Cu3Sn within the brazing material. In the second stage, at approximately 650 ℃ to 750 ℃, the brazing material begins to alloy, forming a ring-layered diffusion layer around the Ti metal powder, composed of CuTi binary intermetallic compounds. In the third stage, at around 850 ℃, the brazing material fully alloys, making full contact with the graphite substrate and forming a metallurgical bond.
关键词:AgCuSnTi quaternary brazing material;in-situ reaction;microstructure;metallurgical bond
摘要:Ultrasonic Lamb waves are one of the commonly used ultrasonic waves in the field of steel structure inspection and non-destructive testing, widely used because of their long propagation distance and the ability to carry overall structural information through point-to-point detection. Welded plate welds are prone to defects such as cracks due to changes in welding stress and other mechanical parameters, making them difficult to detect. Therefore, the propagation mechanism of Lamb waves in the structure of welded fillet welds and the interaction between damage and Lamb waves can be studied through finite element simulation. By setting up the excitation source in the piezoelectric ceramic model, the signal is emitted through the excitation source. Since the signal will be affected by some uncertain factors such as overlap and refraction during transmission, a method of setting up equidistant dual receiving points for signal reception is adopted. It is concluded that when the ultrasonic Lamb wave does not encounter damage in the welding angle, it propagates uniformly along the set route, following the Lamb wave spectrum, with stable amplitude strength and period. By setting an acceptable signal, the impact of different crack depths on detection can be compared, and a rule is derived that the amplitude is directly proportional to the crack depth. The wave packet of the ultrasonic Lamb wave is stable, and its flight time can be calculated through the amplitude. When the depth of damage changes, the amplitude of the ultrasonic Lamb wave will increase as the depth increases, and finally tend to a maximum value, which lays a solid foundation for the study of damage location methods.
摘要:This article is based on the elastic-plastic theory and introduces the stress state of ultra large welding drums under different loads. The strength verification formula of ultra large welding drums is obtained, providing theoretical guidance for the design of drum wall thickness. In addition, research was conducted on the welding process of the cylinder body and the outer flange plate assembly of the ultra large welding drum. The research showed that the cylinder welding joint obtained by alternating welding of the inner and outer grooves in a ratio of 1/4 has excellent comprehensive mechanical properties. The use of short weld seam segmented welding ensures the assembly welding strength and verticality requirements of the outer flange plate of the drum by correcting the alternating welding sequence on both sides.
关键词:welding drum;strength checking;welding deformation;welding process
摘要:In order to meet the requirements for long-time detection of resistance welding current and simplify the detection circuit, a drift compensation method based on software compensation was explored to address the integral drift problem in the signal conditioning when Rogowski coils were used. Several domestically produced operational amplifiers were used to construct integrators, and the drift rate of the integrator output signal was detected in constant current control mode. The average drift rate was superimposed during data processing to achieve software compensation. The integral drift voltage was treated as an error in current detection, and the accuracy of software compensation during the 2 second process of constant current output was analyzed using relative error. The results show that the drift compensation method based on software compensation performs data correction after signal detection, reducing the dependence on hardware compensation. The average relative error within the measured current range of 1~4 kA does not exceed 1.0%, which can meet the requirements of long-time detection of resistance welding current. This compensation method enriches the current signal processing methods based on Rogowski coils and has good engineering applicability.
摘要:The application of special thermoplastic engineering plastics promotes high-end manufacturing advancing towards light weight, high-performance, and environmental protection. To study the induction welding process between plastics and metals, better understand the influence of different parameters on the surface temperature of welded metals, and explore the most suitable parameters for plastic induction welding, the finite element analysis software ANSYS Maxwell was adopted for electromagnetic field simulation, the central composite design method was employed to design the parameters for plastic induction welding, then the temperature of the corresponding metal surface was solved through the finite element analysis software. Based on the multivariate nonlinear theory, an iterative strategy of stepwise regression was adopted in the multivariate nonlinear regression model to analyze the impact of current intensity, current frequency, welding gap and their interactions on the average temperature of the metal surface. The results indicated that the quadratic model had the best fit with a determination coefficient of R2=0.956. The current intensity was the principal effect that had the greatest impact on the average temperature of the metal surface. The interaction between the current intensity and welding gap was the main interactive effect that affected the average temperature of the metal surface. Based on the quadratic model, multiple optimal parameter combinations were predicted and then verified through the finite element analysis software. The deviation between the simulation experiment results and regression analysis results was within 7%, indicating a high accuracy and reliability of the quadratic model. The theories and methods related to this study provided a solid reference for the application of plastics in manufacturing fields such as automobiles, ships, aviation, and aerospace.
关键词:plastic induction welding;temperature field simulation;central composite design;parameter optimization;response surface method
摘要:This study addresses the issue of welding quality degradation in the spot welding process of car door inner panels, where the gap between workpieces expands and the sheet metal thickness changes after the robot servo welding gun passes through multiple welding points. Based on ANSYS finite element technology, a thermal conduction numerical simulation analysis of the robot spot welding process for high-strength dual-phase steel was conducted to investigate the impact of plate thickness variation on welding heat conduction efficiency and nugget diameter size. The experimental results indicate that when the plate thickness is between 1.9~2.0 mm, the nugget diameter reaches its maximum value, and as the plate thickness increases, the nugget diameter decreases, leading to a decline in welding quality. To resolve this issue, the dynamic detection function of the KUKA robot servo welding gun for plate thickness and the variable program jump command were utilized. When the plate thickness exceeds the tolerance value (1.8~2.5 mm), the robot welding program is interrupted and an alarm is issued in a timely manner, reducing defects such as spatter and false welding caused by the increase in plate gap, and improving nucleation quality and welding precision, thus ensuring the stability of the front and back welding points' quality in the spot welding of high-strength dual-phase steel for car door inner panels.
关键词:robot resistance spot welding;plate thickness;nugget diameter;heat conduction simulation;variable program
摘要:This study established a finite element model of the welding temperature field and stress field of single wire double-sided electro-gas welding using the finite element software ABAQUS. A combination of cylindrical heat source and surface heat source was selected for the heat source model, and the element birth-death technique was used for weld filling and loading. The high-temperature thermophysical parameters of EH40 steel measured experimentally were used to simulate the welding process. The simulation results show that the transverse residual stress of the welded plate is tensile stress in the middle area and compressive stress in the remaining areas. The longitudinal residual stress appears as a large tensile stress in the weld and its vicinity, while the tensile stress rapidly attenuates and transitions to compressive stress at locations far away from the weld. Comparison with experimental results reveals a high degree of agreement between the simulated thermal cycle curves and weld shapes and those obtained from actual tests, validating the accuracy of the established model. This model can be used to predict the temperature field, stress field, and residual stress distribution during the electro-gas welding process of single wire double-sided, providing a theoretical basis for welding process optimization and structural design.
摘要:This study conducted a systematic experimental and analytical investigation of the gas shielded welding process using domestically developed solid wire for 1000 MPa grade high-strength steel. Employing metallographic microscopy, scanning electron microscopy, microhardness testing, and room temperature tensile tests, the research delved into the effects of welding process parameters, including welding current and preheating temperature, on the microstructure, hardness distribution, and mechanical properties of the welded joints. The study found that the weld metal microstructure is primarily composed of martensite, with the content of bainite increasing as the welding current and the preheating temperature increases. The heat-affected zone (HAZ) of the welded joint exhibits distinct hardening and softening trends, divided into coarse grain areas, fine grain areas, and incompletely recrystallized areas. Hardness testing results indicate that the hardness is highest in the fine grain area of the HAZ and lowest in the critical heat-affected zone. Mechanical property analysis reveals that at the same preheating temperature, the tensile strength and impact toughness of the welded joint increase and then decrease as the welding current increases; while at the same welding current, the variation of tensile strength and impact toughness with different preheating temperatures is not significant. Notably, when the welding current is set to 260 A and the preheating temperature to 100 ℃, the welded joint exhibits the optimal comprehensive mechanical properties, with a tensile strength of up to 1 088 MPa and an impact toughness of 47.8 J at -40 °C.
摘要:SEM, XRD, room temperature tensile test, microhardness and other methods are used to analyze the microstructure and mechanical properties of Inconel 625 wire after rolling and drawing processandfinished wires at home and abroad, and clarify the advantages and shortcomings,so as to optimize the production process of the wire. The results show that the structure of Inconel625 alloy is a single austenite phase by XRD. After rolling and cold drawing,some diffraction peak intensity of wire become significantly higher than others because of deformation texture.Cross section microstructure of the different wires is equiaxed grains, deformation twins may be found in hot rolled and cold drawn wire, and a large number of annealed twins may be also observed in the soft state of drawn wire.Microhardness is 219.33 HV0.5 for solution state of rolling Inconel 625. Local grain abnormality growth may be observed if solution treatment temperature and time is inaccurate. Microhardness increased to 522.32 HV0.5 for Cold-drawn state of Inconel 625 because of work-hardening, while elongation reduced to 4.37%. The annealing treatment eliminated the internal stresses and work hardening of the cold draw alloy, so that the minimum average grain size grows to 9.5 μm from 2.66 μm.Elongation of 65.13%, and tensile strength of 418.92 MPa may be gained for soft drawn wire. All the indexes of the finished wires meet the requirements of domestic and foreign standards.
摘要:To investigate the microstructure and mechanical properties of the welded joints of G20Mn5 cast steel for determining the optimal welding repair process, enhancing the quality of cast steel parts, and reducing production costs, G20Mn5 cast steel parts were welded using the MAG welding method. Five different welding repair processes (including preheating before welding, post-weld heat preservation, and heat treatment conditions) were compared for the mechanical properties of the joints. The test results showed that none of the welded joints exhibited hardened martensitic structures or coarse Widmanstätten structures in the weld zone and the coarse grain area of the heat-affected zone; the tensile strength of all welded joints exceeded 480 MPa, the elongation after fracture was greater than 20%, the peak hardness was below 250 HV, and the impact energy of the weld zone and heat-affected zone was greater than that of the base material; the tensile and fatigue samples of each welded joint all fractured in the base material, with the fatigue crack source being the micro-shrinkage porosity defect inside the cast steel part. The tests have proven that the microstructure and mechanical properties of the welded joints of the five processes meet the requirements for use. Considering all factors, the optimal welding repair process is "no preheating before welding, post-weld covering for heat preservation and slow cooling, and no heat treatment."
摘要:Pre-weld cleaning is an essential step in the manufacturing process of titanium pressure vessels. This study applied laser cleaning technology to conduct pre-weld cleaning tests on the spatial structure of the welded joints between heat exchange tubes and tube sheets in titanium pressure vessels. It compared the effects of laser cleaning with conventional methods such as grinding or acetone cleaning on the generation of welding porosity and the impact on the heat-affected zone. The results indicate that laser cleaning has a high accessibility for spatial structures, providing excellent pre-weld cleaning effects on the beveled edges of titanium test plates. Test plates cleaned with laser technology can effectively reduce the tendency to produce welding porosity defects and suppress the occurrence of "black eye" phenomena in the heat-affected zone of the welded joints. The color difference between the post-weld appearance and the untreated area is minimal, hardly affecting the appearance of the weld. The tensile strengths of the laser-cleaned samples were 498 MPa and 515 MPa, respectively, both exceeding the minimum tensile strength requirement of 400 MPa as stipulated by the GB/T3621—2007 standard. The experimental study demonstrates that the laser cleaning process can replace traditional cleaning methods such as grinding, metal grinding head scraping, and acetone cleaning, offering an efficient and environmentally friendly new technological approach for the manufacture of titanium pressure vessels.
摘要:In this paper, the TC4 titanium alloy sheet with a specification of 500mm×50mm×1.2mm is taken as the research object. In order to solve the problem of deformation caused by residual stress after laser welding, a Synchronous water mist cooling method is used to synchronously cool the rear of the heat source during the welding process. The effectiveness of this method was verified by measuring and comparing the deformation and stress levels before and after welding.The test shows that the deformation and residual stress of the specimen obtained by synchronous water mist cooling are greatly improved compared with those obtained by natural cooling under the same welding process parameters. Compared with the test results under different water mist pressures, when the water mist pressure is 0.4MPa, the laser power is 800W, the welding speed is 1.3m/min, and the defocus amount is 0mm, the residual stress after welding can be reduced by 29% compared with Free cooling, and the maximum longitudinal deflection can be reduced by 17.6%.Moreover, by observing the microstructure of the weld, it can be seen that the size of the weld net basket structure under the synchronous water mist cooling is smaller and the distribution is more orderly, indicating that the water mist cooling has a certain refining effect on the microstructure and can improve the mechanical properties of the welded joint.
摘要:To explore the impact of surface tension on the shape, flow rate, and static pressure of the molten pool during the laser welding process of austenitic stainless steel sheets, with the aim of optimizing welding processes and enhancing welding quality. Based on numerical simulation analysis methods, a moving rotating Gaussian curved body heat source model was established. By altering the Marangoni convection coefficient to simulate different surface tension conditions, the effects on the formation process, shape, flow rate, and static pressure within the molten pool were analyzed. The simulation results indicate that surface tension is a key factor affecting the morphology and internal static pressure of the molten pool. Surface tension, pointing towards the interior of the molten pool, drives the pool to converge towards the center, thereby promoting the formation of the molten pool. The magnitude of surface tension is negatively correlated with the peak temperature, penetration depth, and aspect ratio of the molten pool, and positively correlated with the peak flow rate, penetration width, and static pressure within the molten pool. The addition of a copper substrate significantly increases the undercooling, accelerating the cooling of the molten pool and helping to avoid the sensitization temperature range of austenitic stainless steel.
关键词:austenitic stainless steel;laser welding;surface tension;molten pool flow;molten pool shape
摘要:The application of aluminum alloy MIG welding technology in the electric vehicle battery box effectively improves the welding efficiency and reduce the cost of production. In the actual production of aluminum alloy battery box, it is difficult to control the rate of one-pass welding because of the many welding positions and the great difference of the thickness of the welding joint plate, it is necessary to develop a welding process to improve the stability of thin and thick aluminum alloy plate welding. The usual MIG welding method for the electric vehicle battery box is DC pulse welding, the welding mode is DC pulse single-current welding or DC pulse double-current welding. Through analysis, the welding heat input can be effectively lower under the same current condition and the welding a value can be increased under the same heat input condition for DC+AC pulse welding weave method. When the thin plate and thick plate for aluminum alloy welding, DC pulse welding can be used in the position of thick plate and AC pulse welding in the position of thin plate. It can ensure deep penetration of thick plate and non-burn-through of thin plate. AC+DC weave welding technology has been applied in actual production, and has effectively improved the pass rate of welding seam and production efficiencyand improve the welding seam acceptance rate.
关键词:aluminum alloy of electric vehicle battery box;thin and thick plate;DC+AC MIG pulse welding
摘要:Considering the advantages of short deliver time and high precision of 3D-printing metal sheets, these special metal sheets could be used for welding and joining of body-in-white. Nevertheless, the reliability of body-in-white with these 3D-printing metal sheets has lacked quantitative and comprehensive evaluation results. By conducting spot welding experiments of combination of 3D-printing metal steel with normal low-carbon steel, and actual parts (reinforced parts in the inner assembly of rear lid), dual-pulse parametric spot welding process specification is more suitable for 3D-printing metal steel with normal steel from the point of view on experimental methods. Accordingly the welding process parameters, weld nugget tensile-shear force, microstructure, fatigue tests and durability tests for opening and closing of rear lid, reliability of real spot-welded parts are verified. These results show that the tensile strength of the spot welded joints between 3D-printing metal steel and normal steel is very close to that of the spot welded specimens of ordinary steel sheets; the 3D-printing metal steel side rapidly generates weld nugget while a brazing seam is formed between the normal steel and the nugget; the fatigue strength of the weld joints on the 3D-printing metal steel side is greater than that on the normal steel side, and is functionally intact after the durability testing of rear lid. The substitution of 3D-printing steel parts for traditional steel parts in technical verification is then validated as a conclusion. It also offers the technical possibility to gradually become a customized- personalized parts fitting vehicle in the future.
关键词:3D-printing steel;nugget microstructure;tensile-shear force analysis;fatigue experiment;durability tests
摘要:In order to improve the welding performance of Q350EWR1 high weather resistant steel, this article adopts pulse welding method. By using high-speed photography and recorders to observe the shape of the arc, as well as the waveform of welding current and arc voltage, under the condition of pulse width modulation (PWM) feedback, adjusting the timing of droplet shedding and consistency of droplet transition for different wire feed rates. Find out the optimal pulse frequency, pulse rise slope, pulse fall slope, pulse peak value, pulse base value to ensure the stability of welding arc, effectively control the splash amount, save welding materials and improve welding production efficiency. It has been applied in the GS6 welding machine developed by Panasonic, which provides a valuable reference for the welding process of Q350EWR1 high weathering steel.
关键词:Q350EWR1 high weather resistant steel;pulse width modulation;arc stability;droplet transfer;splash
摘要:In this paper, to evaluate the application effect of temper bead welding technology in the welding of cast low alloy steels and to investigate whether it can replace the traditional post-weld heat treatment process, manual shielded metal arc welding (SMAW) was employed using R307 and R407 welding rods to weld A217 WC6 and A217 WC9, respectively. The preheating temperature, current, voltage, lap rate, and layer thickness were controlled to achieve the temper bead welding process. After welding, the joints were subjected to metallographic, hardness, tensile, impact, and bending tests. The test results show that the A217 WC6 welded joint met the standard requirements in both the as-welded and heat-treated conditions. However, the A217 WC9 welded joint had an impact energy less than that of the parent material in the as-welded state, and surface cracks appeared near the fusion line in the full-wall thickness bending samples, with a hardness significantly higher than that in the heat-treated state. The analysis concludes that the temper bead welding process can effectively improve the microstructure and performance of A217 WC6 steel welded joints and can replace post-weld heat treatment. However, in the welding of A217 WC9 steel, the temper bead welding process failed to achieve the purpose of improving the microstructure and performance, and the performance of the welded joint did not meet the standard requirements, thus it cannot replace the traditional post-weld heat treatment process.
摘要:In order to analyze the microstructure characteristics, mechanical properties, and fracture features of the laser-welded joints of quenched 30Cr3 ultra-high strength steel, a disc-type laser generator and KUKA robot were used for laser self-fusion welding. The welding process parameters were set as a laser power of 4 200 W, welding speed of 1.45 m/min, defocus distance of +5 mm, and shielding gas flow rate of 25 L/min. The welded joints were analyzed and tested using optical microscopy, metallographic microscopy, microhardness tester, and tensile testing machine. The results show that under the optimized laser welding process, the weld formation is good, with no defects such as cracks and undercuts; the microstructure of the weld zone is dendritic, the heat-affected zone is composed of coarse martensite, and some phase transformation zones consist of tempered troostite + tempered martensite; microhardness testing indicates that the hardness of the weld pool is the highest, with an average value of 589 HV, and the hardness of some phase change zones is the lowest, with an average value of 482 HV; the average tensile strength of the welded joint is 1 727 MPa, reaching 96.7% of the base material, with an average elongation rate of 5.6%; the fracture location is concentrated in the heat-affected zone, and the fracture mode is ductile fracture. The experiment proves that the 30Cr3 ultra-high strength steel can obtain a welded joint with performance close to the base material through laser welding in the quenched state. Although there is some softening phenomenon in the partial phase change zone, the overall mechanical properties of the welded joint are good, providing a feasible welding process method for the manufacturing of pressure-containing parts such as solid rocket engine casings.
摘要:In view of the structural characteristics of the slender stainless steel cylinder product and the difficulties of the welding process of a large experimental device, the welding method and welding process parameters are optimized, and the splitting and processing optimization scheme of the slender stainless steel cylinder welding product are proposed. A UY-shaped welding joint with snap position is designed. Using the lathe chuck ,center frame and tail seat as the clamp fixing fixture for the slender stainless steel cylinder docking and welding, it effectively solves the difficulties of the slender stainless steel cylinder welding that are difficult to assemble, fix, difficult to change welding orientation and easy to skew. A simulation model of the slender stainless steel cylinder docking welding is established, which simulates the bending deformation law and welding shrinkage in the welding process, which provides an important theoretical basis for welding deformation control, welding pre-residual processing allowance, and welding bending correction. A real-time welding compensation technology based on distal cylindrical beating is proposed to organically fuse welding, detection and bending correction, which greatly improves the machining efficiency. Practical application shows that the real-time welding compensation technology can better control the axial bending deformation of slender stainless steel cylinder.
摘要:To explore the impact of welding toe process optimization schemes on the distribution of residual stress in pressure pipeline butt joint, with the aim of enhancing the pipeline's fatigue life and overall performance. Three different welding toe process optimization schemes were designed, and the effects of these schemes on circumferential and axial residual stress were simulated using finite element analysis, with blind hole testing employed to validate the simulation results. The simulation and experimental results indicate that the circumferential and axial residual stress trends of the three optimization schemes are essentially consistent; the concave transition at the welding toe (Scheme 2) performed best in reducing stress peak and average stress, with a peak circumferential residual stress of 539.22 MPa and a peak axial stress of 204.57 MPa; blind hole testing results show that the residual stress simulation is consistent with the experimental results, with an error controlled within 8.5%, verifying the reliability of the simulation model; the concave transition design at the welding toe can effectively reduce residual stress and improve the safety and durability of pressure pipelines.
关键词:pressure pipeline;butt joint;repair welding process design;residual stress
摘要:In order to optimize the assessment items for welding operators in the special equipment industry, reduce waste of corporate resources and economic losses, and improve the efficiency and quality of welding operations, an optimization plan is proposed to address the current issues of overlapping assessment items and unlicensed posts among welding operators. By analyzing the "Special Equipment Welding Operator Assessment Rules" (TSG Z6002—2010) and actual production needs, a systematic review of the assessment items for manual welding operators and machine welding operators has been conducted, taking into account various elements such as welding methods, categories of metal materials, joint types, specimen positions, weld metal thickness, outer diameter of pipe specimens, types of filler metals, and welding process factors. The assessment items for commonly used welding methods such as SMAW, GMAW (including FCAW), GTAW, and SAW have been specifically optimized. The results show that by selecting appropriate assessment items, a wider range of welding operation needs can be covered, while reducing the number of assessment items and lowering the assessment costs for enterprises. Enterprises should formulate the most optimized, economical, and widely applicable assessment items based on their own welding operation characteristics and actual production needs, to enhance the professional skills of welding operators and ensure the welding quality of special equipment.
关键词:special equipment;welder assessment;optimization of assessment items;production applicability;economic analysis