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Influence of oscillation frequency and focal diameter on weld pool geometry and temperature field in laser beam welding of high strength steels
摘要： As weld pool geometry and thermomechanical strains are known to affect formation of solidification cracks, the influence of a superimposed beam oscillation on these characteristics is investigated for this paper. In this context the effects of the oscillation frequency and focal diameter on the weld pool and temperature field are determined by means of infrared thermography. As a result an increase of the weld pool size for larger focal diameters and a more even shape of the seam edges for higher frequencies can be identified.
关键词： infrared thermography,beam oscillation,laser beam welding,solidification conditions,temperature field,weld pool geometry,high strength steels
更新于2025-09-12 10:27:22
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Influence of the degree of dilution with laser beam vacuum-welded Cu-Al mixed joints on the electrical properties
摘要： A great potential for light-weight construction lies in the substitution of copper by aluminum. The state of the art, so far, has put the focus only on the identification of the crack-sensitive intermetallic phase. External influential factors, such as temperature, current-feed and time bring about the change of the joining zone structure by diffusion and electro-migration. Moreover, a temporal change of the technological properties (increase of the electric resistance, reduction of strength) of the dissimilar material joint will occur. Findings about this behavior for laser beam under vacuum welds will allow to draw conclusions about the expected life-time.
关键词： Laser beam welding,Dissimilar material joint,Single-moder fiber laser,Copper,Aluminum
更新于2025-09-12 10:27:22
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Surface modification methods for fatigue properties improvement of laser-beam-welded Ti-6Al-4V butt joints
摘要： Surface and internal defects formed upon laser beam welding (LBW) have been recognized as a serious problem because they cause stress concentration leading to premature failure of a welded component. This paper seeks to remedy these weld imperfections by applying various post-weld treatments and analyzing their effect on the high cycle fatigue (HCF) performance of welded joints. High efficiency of laser-based post-processing techniques after welding such as laser surface remelting (LSR) and laser shock peening (LSP) was demonstrated and compared with conventional approaches. The study reveals that welding porosity determines the internal crack initiation of the surface-treated weldments. Influence of process parameters on porosity level and the HCF properties is presented in detail. Based on an extensive experimental study, practical guidelines needed to mitigate the notch effect from defects and to maximize the fatigue performance of the laser-welded Ti-6Al-4V butt joints are given.
关键词： laser shock peening,Laser beam welding,high cycle fatigue,porosity,defects
更新于2025-09-12 10:27:22
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Aluminum pretreatment by a laser ablation process: influence of processing parameters on the joint strength of laser welded aluminum – polyamide assemblies
摘要： Laser welding of metal – polymer assemblies is an innovative bonding process. It was already demonstrated that laser surface pretreatments of aluminum (Al), prior to laser welding with a polymer, impacts joints strength. This work adopts a design of experiments (DoE) approach to investigate the influence of several Al laser ablation parameters on joint strength of laser welded Al – polyamide (PA6.6) assemblies. Significant parameters were highlighted, process window was outlined, and optimal parameters were identified. After assembly failure, the joint area was evaluated using optical microscopy. Depending on the laser ablation parameters, the joint area can be enhanced resulting in a significant increase in the corresponding bearable shear load.
关键词： Metal-polymer assemblies,Laser ablation,Laser beam welding,Hybrid joining
更新于2025-09-12 10:27:22
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Effects of Postweld Heat Treatment on Microstructure and Properties of Laser-Welded Ti-24Al-15Nb Alloy Joint
摘要： The microstructure evolution and mechanical properties of laser-welded joints of Ti-24Al-15Nb alloy under different postweld heat treatment (PWHT) conditions were systematically investigated. The results show that the microstructure is very sensitive to PWHT temperatures. The weld zone consists of B2 and O phases after PWHT. With the PWHT temperatures increasing from 850 to 1000 °C, the amount of O phase decreases gradually, while the grains of O precipitates become coarser. After PWHT, there are some thin acicular O precipitates in heat-affected zone (HAZ), and the decomposition of a2-phase caused by niobium diffusion can be observed in the HAZ. The PWHT can significantly increase the microhardness of joints, resulting from O phase precipitation hardening effect. The tensile strength and elongation of joints can be remarkably improved after PWHT, which was closely related to the strengthening effect of O precipitates and slip transmission between O and B2 phases. In addition, the results indicate that the best mechanical properties can be achieved only when the number and size of O phase and B2 phase are the best match.
关键词： Ti-24Al-15Nb alloy,microstructure,postweld heat treatment,mechanical properties,laser beam welding
更新于2025-09-12 10:27:22
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Weld pool shape observation in high power laser beam welding
摘要： The geometry of the melt pool in laser beam welding plays a major role to understand the dynamics of the melt and its solidification behavior. In this study, a butt configuration of 15 mm thick structural steel and transparent quartz glass was used to observe the weld pool geometry by means of high-speed camera and an infrared camera recording. The observations show that the dimensions of the weld pool vary depending on the depth. The areas close to the weld pool surface take a teardrop-shape. A bulge-region and its temporal evolution were observed approximately in the middle of the depth of the weld pool. Additionally, a 3D transient thermal-fluid numerical simulation was performed to obtain the weld pool shape and to understand the formation mechanism of the observed bulging effect. The model takes into account the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature. The numerical results showed good accordance and were furthermore used to improve the understanding of the experimentally observed bulging effect.
关键词： high power laser beam welding,transient weld pool shape,bulging,numerical process simulation
更新于2025-09-12 10:27:22
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Modulation of the local grain structure in laser beam welds to inhibit the propagation of centerline hot cracks
摘要： The morphology and the size of the grains of a weld result from the solidification rate and the temperature gradient during solidification. The heat input and the velocity of the welding process directly affect these quantities. The laser power, the welding velocity and the beam diameter were periodically modulated to achieve a periodical change of the solidification conditions during welding. It leads to a continuous change of the type of grain structure over the welded length. The metallographic analysis of welds in close edge position shows the periodical interruption of centerline cracks at local changes of the grain structure.
关键词： Laser Beam Welding,Grain Structure,Aluminum Alloys,Hot cracks
更新于2025-09-12 10:27:22
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Vision based beam offset detection in laser stake welding of T-joints using a neural network
摘要： This paper presents an experimental study where a vision camera integrates coaxially into a laser beam welding tool to monitor beam deviations (beam offset) in laser stake welding of T-joints. The aim is to obtain an early detection of deviations from the joint centreline in this type of welding where the joint is not visible from the top side. A polynomial surface fitting method is applied to extract features that can describe the behaviour of the melt pool. A nonlinear autoregressive with exogenous inputs neural network model is trained to relate eight image features to the laser beam offset. The performance of the presented model is evaluated off-line by different welding samples. The results show that the proposed method can be used to guide post weld inspection and has the potential for on-line adaptive control.
关键词： T-joint,process monitoring,laser beam welding,neural network,vision camera
更新于2025-09-12 10:27:22
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Beam offset detection in laser stake welding of tee joints based on photodetector sensing
摘要： This paper presents an experimental study where a photodetector is used in a laser beam welding tool to monitor beam deviations (beam offsets) in stake welding of tee joints. The aim is to obtain an early detection of deviations from the joint centerline in this type of welding where the joint is not visible from the top side. The photodetector used is a GaP diode sensitive in the spectral range 150-550 nm corresponding to the spectral emissions form the plasma plume during keyhole welding. The photodetector signal has been evaluated by change point detection methods with respect to their detection performance. Both an off-line and an on-line method have been evaluated. The off-line method can be used to guide post weld inspection and the on-line method has the potential to enable on-line adaptive position control and/or the possibility to stop the process for repair. The results shows that the proposed method can be used as a go/no go system and to guide post weld inspection.
关键词： process monitoring,tee joint,photodetector,laser beam welding
更新于2025-09-12 10:27:22
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Effect of Laser Beam Welding on the Cyclic Material Behavior of the Press-hardened Martensitic Chromium Steel X46Cr13
摘要： For the application of high-strength materials in welded joints, a point of principle is how the strength of the sheet metal is affected by cyclic loading and by welding. For the investigation of the cyclic material behavior of the press-hardened martensitic chromium steel X46Cr13, strain-controlled fatigue tests were performed and evaluated. The aim of compensating the limitations in the weldability of this press-hardened material is achieved by a reduced heat input of the laser beam welding and a defined heat treatment. The effect of laser beam welding on the fatigue properties is shown by the cyclic behavior of butt joints. The cyclic material behavior is the basis of strain-based fatigue assessment approaches. Both cyclic stress-strain curves and strain-life curves are used for the fatigue life estimation. No clear difference between the press-hardened base material and butt joints has been found in the cyclic stress-strain curves. Transient effects are found by comparison of hysteresis loops of the initial loading, at the cyclically stabilized state and at crack initiation. Cyclic hardening is concluded from the initial loading and the cyclically stabilized state. By comparison of strain-life curves, a difference in the number of cycles to crack initiation between the base material and butt joints is found. Cycles to crack initiation of butt joints tested under strain control result in over 50 % of the base material’s fatigue strength at 1·106 cycles to failure.
关键词： high manganese TWIP steels,high-strength steel,MnCr steels,butt joint,laser beam welding,Martensitic stainless steel,integral fatigue life estimation method,press-hardening,cyclic material behavior
更新于2025-09-12 10:27:22