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Dynamic keyhole behavior and keyhole instability in high power fiber laser welding of stainless steel
摘要： A three-dimensional numerical model, considering the real-time multiple reflections of a laser beam, adiabatic bubble model and shear stress, was developed to study the dynamic keyhole behavior and keyhole instability in fiber laser welding of stainless steel. The inner dynamic keyhole behavior and weld defect formation were directly observed in a high resolution assisted by transparent glass. The numerical and experimental results showed that the keyhole width reached the quasi-steady state earlier than the keyhole depth did during fiber laser welding of stainless steel. Due to the large recoil pressure at rear keyhole wall caused by the irradiation of laser energy reflected by the bulge at the front keyhole wall, the rear keyhole wall was severely deformed at keyhole bottom and keyhole middle. The rear keyhole wall was collapsed due to the high surface tension pressure and hydrostatic pressure. The whole keyhole collapse was attributable to the capillary instability of the keyhole associated with large depth/width ratio and the strong flow of the bulges at the keyhole wall. When the laser power was increased, the keyhole depth/width ratio was increased, so the keyhole was more capillary instable. The average inclined angle of the front keyhole wall was decreased.
关键词： Bubble formation,Dynamic keyhole behavior,Keyhole instability,Fiber laser welding
更新于2025-11-28 14:24:20
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Observation of the keyhole behavior, spatter, and keyhole-induced bubble formation in laser welding of a steel/glass sandwich
摘要： Laser welding of a steel/glass sandwich is carried out to clearly observe the keyhole behavior, spatter, and keyhole-induced bubble formation. The formation mechanisms of the spatter and keyhole-induced bubble are analyzed, and the relationship between the spatter and keyhole-induced bubble formation is also discussed. There are five necessary steps for the spatter formation around the keyhole: the formation of the bulges at the keyhole wall, the decrease of the keyhole entrance size caused by the upward flow of the bulges, the formation of the melt column around the keyhole, the increasing of the melt column size, and the spatter formation around the keyhole. The decrease of the keyhole entrance size contributes to the increase of the vapor shear stress, and thus accelerates the spatter formation. The large deformation of the top rear keyhole wall decreases the vertical component of the vapor shear stress, so few spatters are formed at the rear keyhole wall. Two types of the keyhole-induced bubble are formed by the whole keyhole collapse between the front keyhole wall and rear keyhole wall, and the rear keyhole wall collapse. The influence of the keyhole-induced bubble formation on the spatter formation is not obvious.
关键词： Spatter,Keyhole behavior,Keyhole-induced bubble,Laser welding
更新于2025-11-28 14:24:20
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Numerical and experimental study on keyhole and melt flow dynamics during laser welding of aluminium alloys under subatmospheric pressures
摘要： Porosity defects was highly related to the keyhole and melt flow dynamic during laser welding process. In this paper, a novel 3D numerical model was developed to describe the keyhole dynamic and melt flow behaviors during laser welding of 5A06 aluminium alloy under subatmospheric pressures. The effect of ambient pressure on laser welding process was taken into consideration by optimizing the boiling point of aluminium alloy and recoil pressure of evaporated metallic vapor jets based on vapor–liquid equilibria calculation and Wilson equation. A moving hybrid heat source model was employed to describe the laser energy distribution under subatmospheric pressures. Numerical results indicated that a wider and deeper keyhole with less humps was produced under subatmospheric pressure comparing with that of atmospheric pressure. The vortices in the rear keyhole wall became unapparent or even disappeared with the decrease of ambient pressures. The melt flow velocity on the keyhole wall was larger under a lower pressure. A smaller difference between boiling point and melting point was produced and this led to the formation of a thinner keyhole wall and improved the stability of molten pool. Larger recoil pressure produced under subatmospheric pressure was responsible for the weakened vortices and enhanced melt flow velocity. Bigger keyhole opening size, larger melt flow velocity, thinner keyhole and the weakened vortices all resulted into the reduction of porosity defects during laser welding of aluminium alloys. Based on the simulation results, the plasma distribution, weld formation and porosity defects had been demonstrated. The compared results showed that the simulation results exhibited good agreements with the experimental ones.
关键词： Porosity defects,Keyhole stability,Numerical simulation,Subatmospheric pressure,Melt flow dynamic,Laser welding
更新于2025-11-28 14:24:20
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Mechanism study on the effects of power modulation on energy coupling efficiency in infrared laser welding of highly-reflective materials
摘要： High-reflectivity of materials, such as magnesium, copper and aluminum, results in low thermal efficiency of their infrared laser welding processes. AZ31 magnesium alloy was selected to study the effects of power modulation on energy coupling efficiency in laser welding of highly-reflective materials. A model for the relationship between energy coupling efficiency and modulation parameters was obtained. The energy coupling efficiency in optimized modulated-power laser welding was about 1.58 times that in constant-power welding. The mechanism was explored by analyzing keyhole evolution and the resulted pressure distribution along keyhole wall during welding. The keyhole evolutions in laser continuous welding of common material (Q345 steel, reflectivity of 65%) and highly-reflective material (AZ31, reflectivity of 85%) were observed through high-speed imaging by utilizing a half sandwich method. The results indicated that the secret of improving energy coupling efficiency of laser welding process of highly-reflective materials through power modulation was the formation of a deep keyhole and its long life. When instantaneous power decreased from the peak, there was still enough recoil pressure at the bottom of keyhole to resist surface tension and hydrostatic pressure of liquid metal, which was the fundamental reason for the long time existence of keyhole with a large depth.
关键词： laser welding,magnesium alloy,recoil pressure,keyhole,highly-reflective materials,power modulation
更新于2025-11-28 14:24:20
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Hybrid laser-metal inert gas keyhole welding of thick steel/Al butt joints
摘要： Dissimilar joining of steel/Al joints has become more and more signi?cant in industrial applications with particular weight saving interest. However, directly welding of steel/Al joints even in thin thickness is very di?cult. In the present study, the hybrid laser-metal inert gas (MIG) source focused on the steel side in keyhole mode was introduced to weld steel/Al butt joints of 6 mm in thickness. E?ects of the laser o?sets on the weld shape, interface microstructures, and ultimate tensile strength (UTS) of the steel/Al joints were investigated. Sound steel/Al butt joints were obtained by using this hybrid laser-MIG keyhole welding process. By increasing the laser o?sets from 0.6 and 0.8 mm, the welds exhibited a better shape with a smooth appearance attributable to the reduced heat input. The positions through the thickness of the steel/Al joints played an important role in the morphology and thickness of the intermetallic compound (IMC) layers at the Al/weld interface. The IMC layers had a thick irregular morphology at the upper part and the lower part, while the layers at the middle part exhibited a relatively thin and uniform morphology. With some certain welding conditions, the Al/weld interface at the lower part of the steel/Al joints transformed to a welding-brazing mode from a fusion one. The island-shape structures were formed at the Al/weld interface, and the IMC layers were composed of Fe2Al5 layer and needlelike Fe4Al13 phases. The maximum UTS of 87.0 MPa was obtained at a laser o?set of 0.6 mm. Although the failure occurred in the IMC layers revealed a brittle fracture, the fracture morphology and locations were a mixed failure, which had a certain resistance to the crack propagation of the IMC layers.
关键词： laser-metal inert gas welding,ultimate tensile strength,keyhole welding,intermetallic compound,steel/Al joints
更新于2025-11-28 14:24:20
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Keyhole cutting of carbon fiber reinforced polymer using a long-duration nanosecond pulse laser
摘要： The machining performance of a high-energy nanosecond pulse laser with a near-infrared wavelength is investigated for carbon fiber-reinforced polymer (CFRP) with two different fiber arrangements. This research work demonstrates for the first time that a keyhole mode cutting can be achieved for CFRP materials using a high-energy nanosecond pulse laser of a Long Pulse mode (120 ns). Specifically, it is shown that the short-duration Q-Switch mode (8 ns) results in ineffective material removal for CFRP, despite much higher peak laser power intensity than the Long Pulse mode. In Long Pulse mode, multi-pass straight line and contour cutting experiments are further performed to investigate the effect of laser processing parameters and resultant machined surface integrity. Plasma absorption effects using both pulse modes are discussed. The results show that a 2.2 mm thick cross-ply CFRP panel can be cut through using as few as 6 laser passes, and a high-quality machined surface can be produced with a limited heat-affected zone and minimal fiber pull-out using Argon assist gas. The successful outcomes from this work provide the key to enable efficient CFRP laser machining using high-energy nanosecond pulse lasers, and offer insight into the unique energy absorption mechanisms for CFRP laser machining.
关键词： Laser cutting,Keyhole,Long pulse,Nanosecond pulse laser,Carbon fiber reinforced polymer
更新于2025-11-21 11:08:12
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Microstructures and Mechanical Properties of Dissimilar Al/Steel Butt Joints Produced by Autogenous Laser Keyhole Welding
摘要： Dissimilar Al/steel butt joints of 6.0 mm thick plates have been achieved using fiber laser keyhole welding autogenously. The cross sections, interface microstructures, hardness and tensile properties of Al/steel butt joints obtained under different travel speeds and laser beam offsets were investigated. The phase morphology and thickness of the intermetallic compound (IMC) layers at the interface were analyzed by scanning electronic microscopes (SEM) using the energy-dispersive spectrometry (EDS) and electron back-scattered diffraction (EBSD) techniques. The results show that travel speeds and laser beam offsets are of considerable importance for the weld shape, morphology and thickness of IMC layers, and ultimate tensile strength (UTS) of Al/steel butt joints. This proves that the IMC layers consist of Fe2Al5 phases and Fe4Al13 phases by EBSD phase mapping. Increasing laser beam offsets from 0.3 mm to 0.7 mm significantly decreases the quantity of Fe4Al13 phases and the thickness of Fe2Al5 layers at the interface. During tensile processing, the Fe2Al5 layer with the weakest bonding strength is the most brittle region at the interface. However, an intergranular fracture that occurred at Fe2Al5 layers leads to a relatively high UTS of Al/steel butt joints.
关键词： laser keyhole welding,IMC layers,Al/steel joints,tensile properties,EBSD phase mapping
更新于2025-09-23 15:21:21
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Dynamic Laser Absorptance Measured in a Geometrically Characterized Stainless-Steel Powder Layer
摘要： The relationship between real powder distributions and optical coupling is a critical building block for developing a deeper physical understanding of laser-additive manufacturing and for creating more reliable and accurate models for predictable manufacturing. Laser-light absorption by a metal powder is distinctly different from that of a solid material, as it is impacted by additional parameters, such as particle size, shape distribution, and packing. Here, we use x-ray computed tomography to experimentally determine these parameters in a thinly spread austenitic stainless-steel powder on a metal substrate, and we combine these results with optical absorptance measurements during a 1 ms stationary laser-light exposure to simulate the additive-manufacturing process. Within the thinly spread powder layer, the particle volume fraction changes continuously from near zero at the powder surface to a peak value of 0.72 at a depth of 235 μm, with the most rapid increase taking place in the first 100 μm. The relationship between this particle volume fraction gradient and optical absorptance is investigated using an analytical model, which shows that depth-averaged absorptance measurements can measure the predicted average value, but will fail to capture local effects that result from a changing powder density. The time-averaged absorptance remains at levels between 0.67 and 0.80 across a two orders of magnitude range in laser power, which is significantly higher than that observed in solid stainless-steel experiments. The dynamic behavior of the absorptance, however, reveals physical phenomena, including oxidation, melting, and vapor cavity (keyhole) formation, as well as quantifying the effect of these on the absorbed energy.
关键词： keyhole formation,laser-additive manufacturing,stainless-steel powder,x-ray computed tomography,optical coupling,optical absorptance,particle volume fraction
更新于2025-09-23 15:21:01
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Correlations between thermal history and keyhole porosity in laser powder bed fusion
摘要： Additive manufacturing has the potential to revolutionize the production of metallic components as it yields near net shape parts with complex geometries and minimizes waste. At the present day, additively manufactured components face qualification and certification challenges due to the difficulty in controlling defects. This has driven a significant research effort aimed at better understanding and improving processing controls – yielding a plethora of in-situ measurements aimed at correlating defects with material quality metrics of interest. In this work, we develop machine-learning methods to learn correlations between thermal history and subsurface porosity for a variety of print conditions in laser powder bed fusion. Un-normalized surface temperatures (in the form of black-body radiances) are obtained using high-speed infrared imaging and porosity formation is observed in the sample cross-section through synchrotron x-ray imaging. To demonstrate the predictive power of these features, we present four statistical machine-learning models that correlate temperature histories to subsurface porosity formation in laser fused Ti-6Al-4V powder.
关键词： in-situ measurement,keyhole porosity,machine learning,laser powder bed fusion,x-ray imaging
更新于2025-09-23 15:21:01
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Processing of Keyhole Depth Measurement Data during Laser Beam Micro Welding
摘要： Analysing the quality of weld seams is still a challenging task. An optical inspection of the surface is giving limited information about the shape and depth of the weld seam. An application for laser beam welding with high demands regarding the weld depth consistency is the electrical contacting of battery cells. The batteries themselves have a limited terminal or case thickness that must not be penetrated during the welding process to avoid leakage or damage to the cell. That leads to a minimum weld depth to ensure the electrical functionality, and a maximum weld depth indicated by the case thickness. In such applications, a destructive analysis is not suitable which leads to the demand for a non-destructive measurement during the process. Using a coaxial, interferometric measurement setup, the keyhole depth during the deep penetration welding is measureable. For a keyhole with a depth of a couple of millimetres, such a system is commercially available. In micro scale, however, these systems are facing several challenges such as scanning systems, small spot diameters of a few tens of micrometres and narrow keyholes. This study contains an investigation of an interferometric measurement of the keyhole depth and the suitability for laser micro welding. Therefore, the data processing of the achieved measurements is investigated, and the results are compared with the depth measurement of metallographic analysed samples. Stainless steel is used to investigate the behaviour and the stability of developed data processing strategy and the resulting depth values.
关键词： Laser welding,battery,copper,spatial power modulation,aluminium,keyhole depth measurement
更新于2025-09-23 15:21:01