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1
Cunningham, Ross, Cang Zhao, Niranjan Parab, Christopher Kantzos, Joseph Pauza, Kamel Fezzaa, Tao Sun, and Anthony D. Rollett. "Keyhole threshold and morphology in laser melting revealed by ultrahigh-speed x-ray imaging." Science 363, no. 6429 (February 21, 2019): 849–52. http://dx.doi.org/10.1126/science.aav4687.
Анотація:
We used ultrahigh-speed synchrotron x-ray imaging to quantify the phenomenon of vapor depressions (also known as keyholes) during laser melting of metals as practiced in additive manufacturing. Although expected from welding and inferred from postmortem cross sections of fusion zones, the direct visualization of the keyhole morphology and dynamics with high-energy x-rays shows that (i) keyholes are present across the range of power and scanning velocity used in laser powder bed fusion; (ii) there is a well-defined threshold from conduction mode to keyhole based on laser power density; and (iii) the transition follows the sequence of vaporization, depression of the liquid surface, instability, and then deep keyhole formation. These and other aspects provide a physical basis for three-dimensional printing in laser powder bed machines.
2
Al-Aloosi, Raghad Ahmed, Zainab Abdul-Kareem Farhan, and Ahmad H. Sabry. "Remote laser welding simulation for aluminium alloy manufacturing using computational fluid dynamics model." Indonesian Journal of Electrical Engineering and Computer Science 27, no. 3 (September 1, 2022): 1533. http://dx.doi.org/10.11591/ijeecs.v27.i3.pp1533-1541.
Анотація:
The process of remote laser welding is simulated in this study to identify the keyhole-induced porosity generation mechanisms and keyhole. Three processes are simulated and discussed: laser power levels, laser-beam shaping configurations, and laser keyhole process. The simulation finding reveals that pore development is caused by strong melt flow behind the keyhole. As verification, the equivalent experimental test is also carried out. According to the findings, a welding speed with a high level helps to keep the keyholes released and prevents the flow of strong melt; a big advanced leaning-angle also provides inactive molten pool flow, making it difficult for bubbles to float to the backside of the molten pool. The conclusions of this study offer crucial insight into the method of porosity of aluminum (Al) alloys laser welding, as well as advice on how to avoid keyhole-induced porosity. It is also obtained that a smaller laser beam with constant power raises the velocity, welding pool depth, and liquid metal temperature.
3
Fabbro, Remy. "Depth Dependence and Keyhole Stability at Threshold, for Different Laser Welding Regimes." Applied Sciences 10, no. 4 (February 21, 2020): 1487. http://dx.doi.org/10.3390/app10041487.
Анотація:
Depending of the laser operating parameters, several characteristic regimes of laser welding can be observed. At low welding speeds, the aspect ratio of the keyhole can be rather large with a rather vertical cylindrical shape, whereas at high welding speeds, low aspect ratios result, where only the keyhole front is mainly irradiated. For these different regimes, the dependence of the keyhole (KH) depth or the keyhole threshold, as a function of the operating parameters and material properties, is derived and their resulting scaling laws are surprisingly very similar. This approach allows us to analyze the keyhole behavior for these welding regimes, around their keyhole generation thresholds. Specific experiments confirm the occurrence and the behavior of these unstable keyholes for these conditions. Furthermore, recent experimental results can be analyzed using these approaches. Finally, this analysis allows us to define the aspect ratio range for the occurrence of this unstable behavior and to highlight the importance of laser absorptivity for this mechanism. Consequently, the use of a short wavelength laser for the reduction of these keyhole stability issues and the corresponding improvement of weld seam quality is emphasized.
4
Zhao, Cang, Niranjan D. Parab, Xuxiao Li, Kamel Fezzaa, Wenda Tan, Anthony D. Rollett, and Tao Sun. "Critical instability at moving keyhole tip generates porosity in laser melting." Science 370, no. 6520 (November 26, 2020): 1080–86. http://dx.doi.org/10.1126/science.abd1587.
Анотація:
Laser powder bed fusion is a dominant metal 3D printing technology. However, porosity defects remain a challenge for fatigue-sensitive applications. Some porosity is associated with deep and narrow vapor depressions called keyholes, which occur under high-power, low–scan speed laser melting conditions. High-speed x-ray imaging enables operando observation of the detailed formation process of pores in Ti-6Al-4V caused by a critical instability at the keyhole tip. We found that the boundary of the keyhole porosity regime in power-velocity space is sharp and smooth, varying only slightly between the bare plate and powder bed. The critical keyhole instability generates acoustic waves in the melt pool that provide additional yet vital driving force for the pores near the keyhole tip to move away from the keyhole and become trapped as defects.
5
Ur Rehman, Asif, Muhammad Arif Mahmood, Fatih Pitir, Metin Uymaz Salamci, Andrei C. Popescu, and Ion N. Mihailescu. "Keyhole Formation by Laser Drilling in Laser Powder Bed Fusion of Ti6Al4V Biomedical Alloy: Mesoscopic Computational Fluid Dynamics Simulation versus Mathematical Modelling Using Empirical Validation." Nanomaterials 11, no. 12 (December 3, 2021): 3284. http://dx.doi.org/10.3390/nano11123284.
Анотація:
In the laser powder bed fusion (LPBF) process, the operating conditions are essential in determining laser-induced keyhole regimes based on the thermal distribution. These regimes, classified into shallow and deep keyholes, control the probability and defects formation intensity in the LPBF process. To study and control the keyhole in the LPBF process, mathematical and computational fluid dynamics (CFD) models are presented. For CFD, the volume of fluid method with the discrete element modeling technique was used, while a mathematical model was developed by including the laser beam absorption by the powder bed voids and surface. The dynamic melt pool behavior is explored in detail. Quantitative comparisons are made among experimental, CFD simulation and analytical computing results leading to a good correspondence. In LPBF, the temperature around the laser irradiation zone rises rapidly compared to the surroundings in the powder layer due to the high thermal resistance and the air between the powder particles, resulting in a slow travel of laser transverse heat waves. In LPBF, the keyhole can be classified into shallow and deep keyhole mode, controlled by the energy density. Increasing the energy density, the shallow keyhole mode transforms into the deep keyhole mode. The energy density in a deep keyhole is higher due to the multiple reflections and concentrations of secondary reflected beams within the keyhole, causing the material to vaporize quickly. Due to an elevated temperature distribution in deep keyhole mode, the probability of pores forming is much higher than in a shallow keyhole as the liquid material is close to the vaporization temperature. When the temperature increases rapidly, the material density drops quickly, thus, raising the fluid volume due to the specific heat and fusion latent heat. In return, this lowers the surface tension and affects the melt pool uniformity.
6
Dong, William, Jason Lian, Chengpo Yan, Yiran Zhong, Sumanth Karnati, Qilin Guo, Lianyi Chen, and Dane Morgan. "Deep-Learning-Based Segmentation of Keyhole in In-Situ X-ray Imaging of Laser Powder Bed Fusion." Materials 17, no. 2 (January 21, 2024): 510. http://dx.doi.org/10.3390/ma17020510.
Анотація:
In laser powder bed fusion processes, keyholes are the gaseous cavities formed where laser interacts with metal, and their morphologies play an important role in defect formation and the final product quality. The in-situ X-ray imaging technique can monitor the keyhole dynamics from the side and capture keyhole shapes in the X-ray image stream. Keyhole shapes in X-ray images are then often labeled by humans for analysis, which increasingly involves attempting to correlate keyhole shapes with defects using machine learning. However, such labeling is tedious, time-consuming, error-prone, and cannot be scaled to large data sets. To use keyhole shapes more readily as the input to machine learning methods, an automatic tool to identify keyhole regions is desirable. In this paper, a deep-learning-based computer vision tool that can automatically segment keyhole shapes out of X-ray images is presented. The pipeline contains a filtering method and an implementation of the BASNet deep learning model to semantically segment the keyhole morphologies out of X-ray images. The presented tool shows promising average accuracy of 91.24% for keyhole area, and 92.81% for boundary shape, for a range of test dataset conditions in Al6061 (and one AliSi10Mg) alloys, with 300 training images/labels and 100 testing images for each trial. Prospective users may apply the presently trained tool or a retrained version following the approach used here to automatically label keyhole shapes in large image sets.
7
Jin, Xiangzhong, Yuanyong Cheng, Licheng Zeng, Yufeng Zou, and Honggui Zhang. "Multiple Reflections and Fresnel Absorption of Gaussian Laser Beam in an Actual 3D Keyhole during Deep-Penetration Laser Welding." International Journal of Optics 2012 (2012): 1–8. http://dx.doi.org/10.1155/2012/361818.
Анотація:
In deep penetration laser welding, a keyhole is formed in the material. Based on an experimentally obtained bending keyhole from low- and medium-speed laser penetration welding of glass, the keyhole profiles in both the symmetric plane are determined by polynomial fitting. Then, a 3D bending keyhole is reconstructed under the assumption of circular cross-section of the keyhole at each keyhole depth. In this paper, the behavior of focused Gaussian laser beam in the keyhole is analyzed by tracing a ray of light using Gaussian optics theory, the Fresnel absorption and multiple reflections in the keyhole are systematically studied, and the laser intensities absorbed on the keyhole walls are calculated. Finally, the formation mechanism of the keyhole is deduced.
8
Lai, Wai Jun, Supriyo Ganguly, and Wojciech Suder. "Study of the effect of inter-pass temperature on weld overlap start-stop defects and mitigation by application of laser defocusing." International Journal of Advanced Manufacturing Technology 114, no. 1-2 (March 8, 2021): 117–30. http://dx.doi.org/10.1007/s00170-021-06851-8.
Анотація:
AbstractLaser keyhole initiation and termination-related defects, such as cracking and keyhole cavities due to keyhole collapse, are a well-known issue in laser keyhole welding of thick section steels. In longitudinal welding, run-on and run-off plates are used to avoid this problem. However, such an approach is not applicable in circumferential welding where start/stop defects remain within the workpiece. These issues can hinder industry from applying laser keyhole welding for circumferential welding applications. In this paper, the effect of inter-pass temperature on laser keyhole initiation and termination at the weld overlap start-stop region was investigated. This study has identified that defects occurring within this region were due to laser termination rather than laser initiation because of keyhole instabilities regardless of the thermal cycle. The laser termination defects were mitigated by applying a laser defocusing termination regime to reduce the keyhole depth gradually and control the closure of the keyhole.
9
Hao, Zhongjia, Huiyang Chen, Xiangzhong Jin, and Zuguo Liu. "Comparative Study on the Behavior of Keyhole in Analogy Welding and Real Deep Penetration Laser Welding." Materials 15, no. 24 (December 16, 2022): 9001. http://dx.doi.org/10.3390/ma15249001.
Анотація:
In deep penetration laser welding, the behavior of the keyhole has an important influence on the welding quality. As it is difficult to directly observe the keyhole and detect the pressure inside the keyhole during metal laser welding, theoretical analysis and numerical simulation methods are commonly used methods in studying keyhole behavior. However, these methods cannot provide direct real information on keyhole behavior. In this paper, a method of analogy welding is proposed, in which high speed gas is used to blow the liquid to generate the keyhole. Relevant process experiments were conducted to explore keyhole behavior in analogy welding and real deep penetration laser welding. The pressure balance of the keyhole, both in analogy welding and real deep penetration laser welding, were analyzed. The laws obtained in analogy welding and real deep penetration laser welding are similar, which indicates that studying keyhole formation and the maintenance principle using the analogy welding method proposed in this paper may be helpful for deep understanding of the keyhole formation and maintenance mechanisms in real deep penetration laser welding.
10
Henze, Insa, and Peer Woizeschke. "Laser Keyhole Brazing." PhotonicsViews 18, S1 (February 2021): 30–31. http://dx.doi.org/10.1002/phvs.202100013.
11
Hong, Wang, Ling Yun Wang, and Ri Sheng Li. "Porosity Formation after the Irradiation Termination of Laser." Advanced Materials Research 800 (September 2013): 201–4. http://dx.doi.org/10.4028/www.scientific.net/amr.800.201.
Анотація:
Porosity is formed because of the keyhole collapse. The porosity formation is associated with the melt pool dynamics, the keyhole collapse and solidification processes. The objective of the paper is t to investigate porosity formation mechanisms and fluid flow in the melt pool using the volume of fluid method. The results indicate that the formation of porosity in continuous wave keyhole mode laser welding is associated to keyhole collapse, backfilling of liquid metal close the gas exit of the laser welding keyhole, surface tension of the gas/liquid interface play an important role in the backfilling downward to the keyhole right after laser beams left.Keywords: porosity; keyhole; collapse; welding; model
12
Peng, Jin, Jigao Liu, Xiaohong Yang, Jianya Ge, Peng Han, Xingxing Wang, Shuai Li, and Zhibin Yang. "Numerical Simulation of Droplet Filling Mode on Molten Pool and Keyhole during Double-Sided Laser Beam Welding of T-Joints." Crystals 12, no. 9 (September 6, 2022): 1268. http://dx.doi.org/10.3390/cryst12091268.
Анотація:
The effects of droplets filling the molten pools during the double-sided laser beam welding (DSLBW) of T-joints was established. The dynamic behavior of the keyhole and the molten pool under different droplet filling modes were analyzed. The results indicated that compared with the contact transition, the stability of metal flow on the keyhole wall was reduced by free transition and slight contact transition. At the later stage of the droplet entering the molten pool via free transition, slight contact transition, and contact transition, the maximum flow velocity of the keyhole wall was 5.33 m/s, 4.57 m/s, and 2.99 m/s, respectively. When the filling mode was free transition or slight contact transition, the keyhole collapsed at the later stage of the droplet entering the molten pool. However, when the filling mode was contact transition, the middle-upper part of the interconnected keyholes became thinner at the later stage of the droplet entering the molten pool. At the later stage of the droplet entering the molten pool via free transition, the flow vortex at the bottom of the keyhole disappeared and the melt at the bottom of the keyhole flowed to the rear of the molten pool, however, the vortex remained during slight contact transition and contact transition.
13
Gao, Xiang Dong, Qian Wen, and Seiji Katayama. "Elucidation of Welding Stability Based on Keyhole Configuration during High-Power Fiber Laser Welding." Advanced Materials Research 314-316 (August 2011): 941–44. http://dx.doi.org/10.4028/www.scientific.net/amr.314-316.941.
Анотація:
During deep penetration laser welding, a keyhole is formed in the molten pool due to the intense recoil pressure of evaporation. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. The configuration and characteristics of a keyhole are related to the welding stability. In a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser, an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. The configurations of a keyhole were analyzed through image processing techniques such as median filtering, wiener filtering and gray level threshold segmentation to obtain the edge of a keyhole. The width and the area of a keyhole were defined as the keyhole characteristic parameters, and the deviation between the laser beam and weld center as a parameter reflecting the welding stability. By analyzing the change of the keyhole characteristic parameters during welding process, it was found that these parameters were related to the welding stability. Welding experimental results and analysis of the keyhole characteristic parameters confirmed that the welding stability could be monitored and distinguished by a keyhole configuration during high-power fiber laser welding.
14
Mostafa, Massaud, J. Laifi, M. Ashari, and Z. A. Alrowaili. "MATLAB Image Treatment of Copper-Steel Laser Welding." Advances in Materials Science and Engineering 2020 (April 21, 2020): 1–13. http://dx.doi.org/10.1155/2020/8914841.
Анотація:
Continuous Yb:YAG laser keyhole welding of the pure copper plate to steel 316L sheet is performed for different laser parameters. The laser-generated welding keyhole and weld melted zone are observed by a high-speed camera. The image is treated by MATLAB and simple code is built to calculate the keyhole and melted zone area. This treatment is validated by the actual welding measurements, and the accuracy of the measurements is tested by the confidence interval law. The images obtained of keyhole and melt zone area in dissimilar laser welding are treated and analyzed to study the effect of changing the laser parameters.
15
Zhou, Jun, Hai-Lung Tsai, and Pei-Chung Wang. "Transport Phenomena and Keyhole Dynamics during Pulsed Laser Welding." Journal of Heat Transfer 128, no. 7 (December 7, 2005): 680–90. http://dx.doi.org/10.1115/1.2194043.
Анотація:
Numerical and experimental studies were conducted to investigate the heat transfer, fluid flow, and keyhole dynamics during a pulsed keyhole laser welding. A comprehensive mathematical model has been developed. In the model, the continuum formulation was used to handle solid phase, liquid phase, and mushy zone during melting and solidification processes. The volume-of-fluid method was employed to handle free surfaces. The enthalpy method was used for latent heat. Laser absorptions (Inverse Bremsstrahlung and Fresnel absorption) and thermal radiation by the plasma in the keyhole were all considered in the model. The results show that the recoil pressure is the main driving force for keyhole formation. Combining with the Marangoni shear force, hydrodynamic force, and hydrostatic force, it causes very complicated melt flow in the weld pool. Laser-induced plasma plays twofold roles in the process: (1) to facilitate the keyhole formation at the initial stage and (2) to block the laser energy and prevent the keyhole from deepening when the keyhole reaches a certain depth. The calculated temperature distributions, penetration depth, weld bead size, and geometry agreed well with the corresponding experimental data. The good agreement demonstrates that the model lays a solid foundation for the future study of porosity prevention in keyhole laser welding.
16
Seidgazov R. D. and Mirzade F. Kh. "Features of the keyhole evolution during deep penetration of metals by laser radiation." Technical Physics Letters 48, no. 14 (2022): 12. http://dx.doi.org/10.21883/tpl.2022.14.52104.18838.
Анотація:
The paper presents the results of fast detection of the keyhole formation in titanium under point exposure to laser radiation. The fact has been established that the keyhole evolution ends with a collapse even before the cessation of the action (switching off) of the continuous laser radiation. Keywords: deep penetration, keyhole, collapse, laser radiation.
17
Li, Quanhong, Zhongyan Mu, Manlelan Luo, Anguo Huang, and Shengyong Pang. "Laser Spot Micro-Welding of Ultra-Thin Steel Sheet." Micromachines 12, no. 3 (March 23, 2021): 342. http://dx.doi.org/10.3390/mi12030342.
Анотація:
This paper reports a mechanism understanding how to reduce the solder joint failure phenomenon in the laser spot micro-welding process of ultra-thin steel sheets. An optimization method to improve solder joint service life is proposed. In this study, the time-dependent dynamic behaviors of the keyhole and the weld pool are simulated, and the temperatures in the keyhole of two different laser pulse waveforms are compared. The results show that laser energy attenuation mode (LEAM) can only obtain shallow weld depth because of the premature decay of the laser power of waveform, resulting in the laser beam that cannot be concentrated in the keyhole. The temperature inside the keyhole of LEAM fluctuates significantly, which shows a downward trend. Due to the existence of the peak power of waveform in laser energy continuous mode (LECM), the large angle of inclination of the wall of the keyhole inside the melt pool is more conducive to the multiple reflections of the laser beam in the keyhole and increases the absorption rate of the laser energy by the base material, resulting in the “keyhole effect”. But the temperature in the keyhole gradually rises, close to the evaporation temperature. A method combining LEAM and LECM to improve the solder joint service life by optimizing the temperature in the keyhole indirectly by adjusting the peak power of the laser pulse waveform is proposed in this study. The experimental results show that the weld depth can be optimized from 0.135 mm to 0.291 mm, and the tensile strength can be optimized from 88 MPa to 288 MPa. The bonding performance between the upper and lower plates is effectively improved. It can reach the required weld depth in a short time and improve the welding efficiency of the laser spot micro-welding process. The simulation results show that the temperature inside the keyhole is well optimized below the evaporation temperature of the material, which can avoid the violent evaporation of the welding process and keep the whole welding process in a stable state. By optimizing the laser pulse waveform, the temperature inside the keyhole can reach 3300 K, and it is always in a stable state than before optimization. The stable temperature inside the keyhole can help to reduce violent oscillation and spattering of the molten pool and improve welding efficiency and joint life. The research can help provide effective process guidance for the optimization of different laser pulse waveforms in the micro-welding process.
18
Bhardwaj, Vijay, B. N. Upadhyaya, and K. S. Bindra. "Mathematical model to study the keyhole formation in pulsed Nd:YAG laser welding of SS 316L material and its experimental verification." Journal of Laser Applications 34, no. 3 (August 2022): 032010. http://dx.doi.org/10.2351/7.0000704.
Анотація:
A mathematical model to study keyhole formation and its propagation in the material is developed for laser welding performed in an open atmosphere. The present model overcomes the limitations of existing models in assuming sonic vapor jet velocity to calculate vaporization-induced recoil pressure responsible for keyhole formation. In the present model, the exact value of vapor jet velocity is calculated using gas dynamics equations. The minimum threshold value of absorbed laser beam intensity required to perform keyhole welding irrespective of laser pulse duration for laser beam radius of 0.6 mm has been found to be 0.8 × 105 W/cm2 and is in good agreement with the experimental value. In between conduction mode welding and keyhole mode welding, a transition mode exists where a keyhole mechanism develops itself and melt displacement is not considerable in this zone. Weld penetration occurs mainly through heat diffusion in this transition mode. The predicted values for keyhole penetration velocity are also in good agreement with the experimental values. At a longer pulse duration, the model over-predicts the keyhole penetration velocity as compared to the experimental value due to nonconsideration of vapor plasma absorption of the laser beam.
19
Gao, Xiang Dong, Ling Mo, and Seiji Katayama. "Seam Tracking Monitoring Based on Keyhole Features during High-Power Fiber Laser Welding." Advanced Materials Research 314-316 (August 2011): 932–36. http://dx.doi.org/10.4028/www.scientific.net/amr.314-316.932.
Анотація:
Seam tracking is an important field to obtain good welding quality. During the high-power fiber laser welding, the laser beam focus must be controlled to track the welding seam accurately. A method of detecting the offset between the laser beam focus and the welding seam based on analyzing the keyhole features was researched during high-power fiber laser butt-joint welding of Type 304 austenitic stainless steel plates at a continuous wave fiber laser power of 10 kW. The joint gap width was less than 0.1mm. An infrared sensitive high speed camera was used to capture the thermal images of a molten pool in welding process. Two parameters called the keyhole centroid and keyhole shape were defined as the eigenvalues of seam tracking offset to determine the offset between the laser beam focus and the desired welding seam. The welding experiments confirmed that the offset between the laser beam focus and the welding seam could be monitored and estimated by the keyhole centroid and keyhole shape parameters effectively.
20
Liu, Yong Hua, and Xiang Dong Gao. "Extraction of Characteristic Parameters of Keyhole during High Power Fiber Laser Welding." Applied Mechanics and Materials 201-202 (October 2012): 352–55. http://dx.doi.org/10.4028/www.scientific.net/amm.201-202.352.
Анотація:
During deep penetration laser welding, a keyhole is formed in the molten pool. The characteristics of keyhole are related to the welding quality and stability. Analyzing the characteristic parameters of a keyhole during high power fiber laser welding is one of effective measures to control the welding quality and improve the welding stability. This paper studies a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser, and an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. A combination filtering system with a filter length of 960-990nm in front of the vision sensor was used to obtain the near infrared image and eliminate other light disturbances. The width, the area, the leftmost point, the rightmost point, the upmost point and the bottommost point of a keyhole were defined as the keyhole characteristic parameters. By using the image preprocessing method, such as median filtering, Wiener filtering, threshold segmentation and Canny edge detection methods, the characteristic parameters of a keyhole were obtained. By analyzing the change of the keyhole characteristic parameters during welding process, it was found that these parameters could reflect the quality and stability of laser welding effectively.
21
Xie, Xigui, Wenhao Huang, Jianxi Zhou, and Jiangqi Long. "Study on the molten pool behavior and porosity formation mechanism in dual-beam laser welding of aluminum alloy." Journal of Laser Applications 34, no. 2 (May 2022): 022007. http://dx.doi.org/10.2351/7.0000630.
Анотація:
Based on the mechanism of dynamic coupling between molten pool and keyhole, a three-dimensional (3D) transient model for the dual-beam laser welding of aluminum alloy is established by considering the surface tension, Marangoni force, and recoil pressure. The morphology of the molten pool, porosity formation process, and the heat transfer mechanism during the process of laser welding under different parameters are analyzed. A double rotating 3D Gaussian heat source is used to represent the laser beam, and the volume of fluid method is used to track the gas-liquid free surface, and the gas-liquid interface force is transformed by the continuous surface force model. The results show that in the process of dual-beam welding, the interaction between the two keyholes enhances the fluid flow perpendicular to the spot line, and the shape of weld pool surface changes from elliptical to circular. Furthermore, welding speed and spot spacing have a significant effect on the shape of the molten pool. Furthermore, it is observed that dual-beam welding can improve the stability of the keyhole and reduce the maximum oscillation amplitude and the number of keyhole breakups. At a specific spot spacing, a unique process of separation and fusion is discovered in addition to the common stages of growth, maintenance, breakup, and shrinkage of the keyhole. The simulation results are in good agreement with the existing experimental results. Overall, this paper provides useful insights into the dynamics of the molten pool in dual-beam welding and reveals the molten pool behavior and porosity formation mechanism.
22
Fan, Xi’an, Xiangdong Gao, Yuhui Huang, and Yanxi Zhang. "Online Detection of Keyhole Status in a Laser-MIG Hybrid Welding Process." Metals 12, no. 9 (August 30, 2022): 1446. http://dx.doi.org/10.3390/met12091446.
Анотація:
During laser-metal inert gas (MIG) hybrid welding, a large amount of welding status information is generated in droplet transfer, keyhole and molten pool. In this paper, austenitic stainless steel was adopted as an experimental object, with a dual high-speed camera system used to obtain real-time images of droplet transfer, keyhole and molten pool in a laser-MIG hybrid welding process. The changing regulation of a keyhole in three different penetration states (i.e., non-penetration, partial penetration and normal penetration) was analyzed by extracting the morphological characteristics of a keyhole shape, and combining the droplet transition information and the shape of the weld pool. Experimental results show that the proposed method could effectively reflect the variation characteristics of the keyhole, and the correlation among the keyhole characteristics, the droplet transfer information, the weld pool shape and the welding status, and provide a new perspective for online detection of the laser-MIG welding quality.
23
SaediArdahaei, Saeid, and Xuan-Tan Pham. "Comparative Numerical Analysis of Keyhole Shape and Penetration Depth in Laser Spot Welding of Aluminum with Power Wave Modulation." Thermo 4, no. 2 (May 23, 2024): 222–51. http://dx.doi.org/10.3390/thermo4020013.
Анотація:
Keyhole mode laser welding is a valuable technique for welding thick materials in industrial applications. However, its susceptibility to fluctuations and instabilities poses challenges, leading to defects that compromise weld quality. Observing the keyhole during laser welding is challenging due to bright process radiation, and existing observation methods are complex and expensive. This paper alternatively presents a novel numerical modeling approach for laser spot welding of aluminum through a modified mixture theory, a modified level-set (LS) method, and a thermal enthalpy porosity technique. The effects of laser parameters on keyhole penetration depth are investigated, with a focus on laser power, spot radius, frequency, and pulse wave modulation in pulsed wave (PW) versus continuous wave (CW) laser welding. PW laser welding involves the careful modulation of power waves, specifically adjusting the pulse width, pulse number, and pulse shapes. Results indicate a greater than 80 percent increase in the keyhole penetration depth with higher laser power, pulse width, and pulse number, as well as decreased spot radius. Keyhole instabilities are also more pronounced with higher pulse width/numbers and frequencies. Notably, the rectangular pulse shape demonstrates substantially deeper penetration compared to CW welding and other pulse shapes. This study enhances understanding of weld pool dynamics and provides insights into optimizing laser welding parameters to mitigate defects and improve weld quality.
24
Chang, Baohua, Zhang Yuan, Hao Cheng, Haigang Li, Dong Du, and Jiguo Shan. "A Study on the Influences of Welding Position on the Keyhole and Molten Pool Behavior in Laser Welding of a Titanium Alloy." Metals 9, no. 10 (October 8, 2019): 1082. http://dx.doi.org/10.3390/met9101082.
Анотація:
Various welding positions need be used in laser welding of structures with complex configurations. Therefore, it is necessary to gain knowledge of how the welding positions can influence the keyhole and weld pool behavior in order to better control the laser weld quality. In the present study, a computational fluid mechanics (CFD) model was constructed to simulate the laser-welding process of the titanium alloy Ti6Al4V, with which the keyhole stability and the fluid flow characteristics in weld pool were studied for four welding positions, i.e., flat welding, horizontal welding, vertical-up welding, and vertical-down welding. Results showed that the stability of the keyhole was the best in flat welding, the worst in horizontal welding, and moderate in vertical welding positions. Increasing heat input (the ratio of laser power to welding speed) could increase the keyhole stability. When the small heat input was used, the dimensions and flow patterns of weld pools were similar for different welding positions. When the heat input was increased, the weld pool size was increased, and the fluid flow in the weld pool became turbulent. The influences of gravity became significant when a large heat input was used, especially for laser welding with vertical positions. Too high a heat input in vertical-up laser welding would lead to oscillation and separation of molten metal around the keyhole, and in turn result in burn-through holes in the laser weld. Based on the present study, moderate heat input was suggested in positional laser welding to generate a stable keyhole and, meanwhile, to guarantee good weld quality.
25
Jing, Haohao, Xin Ye, Xiaoqi Hou, Xiaoyan Qian, Peilei Zhang, Zhishui Yu, Di Wu, and Kuijun Fu. "Effect of Weld Pool Flow and Keyhole Formation on Weld Penetration in Laser-MIG Hybrid Welding within a Sensitive Laser Power Range." Applied Sciences 12, no. 9 (April 19, 2022): 4100. http://dx.doi.org/10.3390/app12094100.
Анотація:
The weld penetration variation in laser-MIG hybrid welding under sensitive laser power range was investigated by welding experiments and CFD (computational fluid dynamics) simulation. During this investigation, joints of AH36 sheets were welded with varying laser powers by the laser-MIG hybrid welding process. In addition, the CFD model was established based on experimental parameters and measurement results. Moreover, surface tension, electromagnetic force, buoyancy, recoil pressure, evaporative condensation, evaporative heat exchange, melt drop transfer, and other factors were considered. The influence of various factors on molten pool depth and keyhole depth were studied, including temperature, velocity, and flow direction of liquid metal. The results show that the weld-forming effect is better at the laser power is 7.5 kW in the range of sensitive laser power. After the keyhole is formed, its depth gradually entered the stage of linear increase, oscillation increase, and oscillation balance. Increasing the laser power can effectively shorten the time of the two growth stages and allow the keyhole to enter the balance stage earlier. During the oscillation balance state of the keyhole, the molten metal under the keyhole flowed to the molten pool root in the reverse direction of welding; it can also promote weld penetration.
26
Wang, Leilei, Yanqiu Zhao, Yue Li, and Xiaohong Zhan. "Droplet Transfer Induced Keyhole Fluctuation and Its Influence Regulation on Porosity Rate during Hybrid Laser Arc Welding of Aluminum Alloys." Metals 11, no. 10 (September 23, 2021): 1510. http://dx.doi.org/10.3390/met11101510.
Анотація:
Hybrid laser arc welding (HLAW) features advantages such as higher welding speed and gap tolerance as well as smaller welding deformation and heat-affected zone than arc welding. Porosity in hybrid laser arc weld due to keyhole fluctuation tends to be the initial source of crack propagation, which will significantly diminish the weld performance. A high-speed imaging technique was adopted to record and analyze the droplet transfer and keyhole fluctuation behavior during hybrid laser arc welding of aluminum alloys. A heat transfer and fluid flow model of HLAW was established and validated for a perspective of the evolution process of droplet transfer and keyhole fluctuation. The relationship between keyhole fluctuation and weld porosity was also revealed. During the droplet transfer stage, liquid metal on the top surface of the weld pool flows toward the keyhole originated by globular transfer, and the keyhole fluctuates and decreases significantly, which has a higher tendency to form a bubble in the weld pool. The bubble evolves into porosity once trapped in the mush-zone near the trailing edge of the weld pool. Therefore, globular transfer during HLAW is the principal origin of keyhole fluctuation and weld porosity. Welding current has a significant influence on keyhole fluctuation and weld porosity rate. Droplet transfer frequency, keyhole fluctuation, and porosity rate increase with higher welding current under the globular transfer mode. The porosity rate shows a nearly positive correlation with the standard deviation of keyhole fluctuation.
27
Will, Thomas, Tobias Jeron, Claudio Hoelbling, Lars Müller, and Michael Schmidt. "In-Process Analysis of Melt Pool Fluctuations with Scanning Optical Coherence Tomography for Laser Welding of Copper for Quality Monitoring." Micromachines 13, no. 11 (November 9, 2022): 1937. http://dx.doi.org/10.3390/mi13111937.
Анотація:
Optical coherence tomography (OCT) is an inline process monitoring technology for laser welding with various applications in the pre-, in-, and post-process. In-process monitoring with OCT focuses on the measurement of weld depth by the placement of a singular measurement beam into the keyhole. A laterally scanned measurement beam gives the opportunity to measure the keyhole and melt pool width. The processing region can be identified by separating higher signal intensities on the workpiece surface from lower signal intensities from the keyhole and the melt pool. In this work, we apply a scanned measurement beam for the identification of keyhole fluctuations. Different laser processing parameters are varied for laser welding of copper to evoke welds in the heat conduction regime, stable deep penetration welding, and unstable deep penetration welding. As keyhole instabilities can be related to the generation of spatter and other defects, we identified a feature for the classification of different weld statuses. In consequence, feedback can be given about possible defects which are originated in keyhole fluctuations (e.g., spatter).
28
Yao, Wei, and Shui Li Gong. "Porosity Formation Mechanisms and Controlling Technique for Laser Penetration Welding." Advanced Materials Research 287-290 (July 2011): 2191–94. http://dx.doi.org/10.4028/www.scientific.net/amr.287-290.2191.
Анотація:
The distribution and appearance characteristics of porosities in laser penetrated weld of aluminum alloy were observed, and the formation mechanisms of porosities were analyzed in detail, and the influences of twin spot laser energy distribution on porosities were investigated. It showed that there are two kinds of porosities, metallurgical and technologic porosities, in laser penetrated weld of aluminum alloy. The formation of metallurgical porosities is related to the separation, congregation and incorporation of hydrogen in the weld pool, while instantaneous instability of the keyhole is an essential reason for the occurrence of technologic porosities. Twin spot laser energy distribution can enlarge diameters of the opening and the root of the keyhole, improve fluctuating conditions of the wall of the keyhole, increase stability of the keyhole, and consequently decrease technologic porosities in number, but it has no obvious influence on metallurgical porosities.
29
Liang, Jian Bin, Xiang Dong Gao, De Yong You, Zhen Shi Li, and Wei Ping Ruan. "Detection of Seam Offset Based on Molten Pool Characteristics during High-Power Fiber Laser Welding." Advanced Materials Research 549 (July 2012): 1064–68. http://dx.doi.org/10.4028/www.scientific.net/amr.549.1064.
Анотація:
Laser welding includes the heat conduction welding and the deep penetration welding. Deep penetration welding can not only penetrate the material completely, but also can vaporize the material. An important phenomenon during deep penetration welding is that molten pool in the weldment will appear a keyhole. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. Small focus wandering off weld seam may result in lack of penetration or unacceptable welds, and largely reduce heating efficiency. In a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 6kW continuous wave fiber laser, an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. The configurations of molten pools were analyzed through image processing techniques such as median filtering, partial Otsu threshold segmentation and Canny edge to obtain the edge of keyholes and molten pools. The circular degree and the area of keyholes and the width and average gray of molten pools were defined as characteristic parameters to reflect the seam offset between the laser beam and the weld center. By analyzing the change of characteristic parameters during welding process, it was found that these parameters were related to the seam offset. Welding experimental results and analysis of characteristic parameters confirmed that the seam offset could be monitored and distinguished by molten pools configuration during high-power fiber laser welding.
30
Seidgazov R. D. and Mirzade F. Kh. "On the initial stage of the evolution of hydrodynamic parameters during deep penetration of metals by high-power laser radiation." Technical Physics Letters 48, no. 9 (2022): 57. http://dx.doi.org/10.21883/tpl.2022.09.55085.19283.
Анотація:
A qualitative analysis of changes in hydrodynamic parameters during keyhole formation by thermocapillary melt removal under the point action of CW laser radiation is presented. It is established that rapid surface deformation leads to adhesion of the viscous sublayer to the melting boundary and creation the shear structure of thermocapillary flow which stimulates acceleration of keyhole growth. Keywords: keyhole formation, laser radiation, thermocapillary effect, shear flow, viscous sublayer, sticking.
31
Duan, Ai Qin, and Shui Li Gong. "Characteristics of the Keyhole and Energy Absorption during YAG Laser Welding of Al-Li Alloy." Advanced Materials Research 287-290 (July 2011): 2401–6. http://dx.doi.org/10.4028/www.scientific.net/amr.287-290.2401.
Анотація:
In this paper, the keyhole of YAG laser welding 5A90 Al-Li alloy was observed and measured through the high speed camera. The characteristics of the keyhole and the effects of welding parameters were studied. The characteristics of the absorption of laser energy and the susceptivity for heat input in welding 5A90 were given. The results show that in this welding condition, the keyhole of laser welding 5A90 is nearly a taper and the highest temperature area is in the bottom. There are clear effects of heat input on the characteristics, especially the surface radius of keyhole and plasma/vapor in keyhole. Another phenomena is observed that sometime plasma/vapor could disappear in 0.3ms welding time, and this feature will be more remarkable as decrease of heat input. It shows that the absorption of energy is unsteady. It is known that when this instability reaches a certain value, an unsteady weld will be formed.
32
Diegel, Christian, Thorsten Mattulat, Klaus Schricker, Leander Schmidt, Thomas Seefeld, Jean Pierre Bergmann, and Peer Woizeschke. "Interaction between Local Shielding Gas Supply and Laser Spot Size on Spatter Formation in Laser Beam Welding of AISI 304." Applied Sciences 13, no. 18 (September 20, 2023): 10507. http://dx.doi.org/10.3390/app131810507.
Анотація:
Background. Spatter formation at melt pool swellings at the keyhole rear wall is a major issue for laser deep penetration welding at speeds beyond 8 m/min. A gas nozzle directed towards the keyhole, that supplies shielding gas locally, is advantageous in reducing spatter formation due to its simple utilization. However, the relationship between local gas flow, laser spot size, and the resulting effects on spatter formation at high welding speeds up to 16 m/min are not yet fully understood. Methods. The high-alloy steel AISI 304 (1.4301/X5CrNi18-10) was welded with laser spot sizes of 300 μm and 600 μm while using a specially designed gas nozzle directed to the keyhole. Constant welding depth was ensured by Optical Coherence Tomography (OCT). Spatter formation was evaluated by precision weighing of samples. Subsequent processing of high-speed images was used to evaluate spatter quantity, size, and velocity. The keyhole oscillation was determined by Fast Fourier Transform (FFT) analysis. Tracking the formation of melt pool swellings at the keyhole rear wall provided information on the upward melt flow velocity. Results. The local gas flow enabled a significant reduction in the number of spatters and loss of mass for both laser spot sizes and indicated an effect on surface tension by shielding the processing zone from the ambient atmosphere. The laser spot size affected the upward melt flow velocity and spatter velocity.
33
Hollatz, Sören, Marc Hummel, Lea Jaklen, Wiktor Lipnicki, Alexander Olowinsky, and Arnold Gillner. "Processing of Keyhole Depth Measurement Data during Laser Beam Micro Welding." Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 234, no. 5 (April 7, 2020): 722–31. http://dx.doi.org/10.1177/1464420720916759.
Анотація:
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.
34
Duan, Ai Qin, and Shui Li Gong. "The Influence of the Type and Pressure of Shielding Gas on the Porosity Formation for CO2 Laser Welding of TA15." Advanced Materials Research 753-755 (August 2013): 372–78. http://dx.doi.org/10.4028/www.scientific.net/amr.753-755.372.
Анотація:
Many studies have shown that during laser welding, shielding gases play a key role in many aspects. In this paper, a series of contrast experiments about CO2laser welding of TA15 TI-alloy were completed by using He and Ar as shielding for different pressure, respectively. The experiments results reveal that the porosities in the weld have strong relation with weld penetration, and the shielding gas have great influences on the weld penetration. So the porosities mainly form in the center of welds which are under critical penetration and lack of penetration, and have no direct relation with the type and pressure of shielding gas.From the contrast images of penetrating process, it is known that when He as shielding gas, the sizes of keyholes on the back welds are quite larger than the sizes when Ar. This means more vapor erupting from bottom keyhole and porosities not easy to form. At the same pressure, the opening times of keyholes when He as shielding gas are longer than the times when Ar. Long opening times of keyholes make the shielding gas within keyhole not easy to be involved into the molten pool and form the porosities.
35
Mohanty, P. S., and J. Mazumder. "Workbench for keyhole laser welding." Science and Technology of Welding and Joining 2, no. 3 (June 1997): 133–38. http://dx.doi.org/10.1179/stw.1997.2.3.133.
36
Fabbro, R., and K. Chouf. "Keyhole modeling during laser welding." Journal of Applied Physics 87, no. 9 (May 2000): 4075–83. http://dx.doi.org/10.1063/1.373033.
37
Peng, Jin, Hongqiao Xu, Xiaohong Yang, Xingxing Wang, Shuai Li, Weimin Long, and Jian Zhang. "Numerical Simulation of Molten Pool Dynamics in Laser Deep Penetration Welding of Aluminum Alloys." Crystals 12, no. 6 (June 20, 2022): 873. http://dx.doi.org/10.3390/cryst12060873.
Анотація:
In this paper, the numerical simulation of molten pool dynamics in laser deep penetration welding of aluminum alloys was established based on the FLUENT 19.0 software. The three-dimensional transient behavior of the keyhole and the flow field of molten pool at different welding speeds were analyzed, and the influence of the welding speed on the molten pool of aluminum alloys in laser welding was obtained. The results indicated that the generation of welding spatters was directly related to the fluctuation of the diameter size in the middle of the keyhole. When the diameter in the middle of the keyhole increased by a certain extent, welding spatters occurred. When welding spatters occurred, the diameter in the middle of the keyhole became smaller. In addition, the size of the spatters at the welding speed of 9 m/min was larger than that of the spatters at the welding speeds of 3 m/min and 6 m/min. The welding spatter formed in laser deep penetration welding included: spatter created by an inclined liquid column behind the keyhole; splash created by a vertical liquid column behind the keyhole; small particles splashed in front of the keyhole. With the increase of the welding speed, the tendency of the welding spatter to form in front of the keyhole and to form a vertical liquid column behind the keyhole became weaker. When the welding speed was 9 min, only an obliquely upward liquid column appeared on the molten pool surface behind the keyhole. Compared with the welding speeds of 6 m/min and 9 m/min, the maximum flow velocity fluctuation of the molten pool at the welding speed of 3 m/min was obviously higher.
38
Peng, Jin, Jigao Liu, Xiaohong Yang, Jianya Ge, Peng Han, Xingxing Wang, Shuai Li, and Yongbiao Wang. "Numerical Simulation of Preheating Temperature on Molten Pool Dynamics in Laser Deep-Penetration Welding." Coatings 12, no. 9 (September 1, 2022): 1280. http://dx.doi.org/10.3390/coatings12091280.
Анотація:
In this paper, a heat-flow coupling model of laser welding at preheating temperature was established by the FLUENT 19.0 software. The fluctuation of the keyhole wall and melt flow behavior in the molten pool under different preheating temperatures were analyzed, and the correlation between keyhole wall fluctuation and molten pool flow with spatters and bubbles was obtained. The results indicate that when the outer wall in the middle of the rear keyhole wall is convex, the inner wall is concave, which causes spatter or the bottom of the keyhole to collapse. When the metal layer in the middle of the rear keyhole wall turns into obliquely upward flow, welding spatter is generated. In contrast, the metal layer in the middle of the rear keyhole wall changes to flow into the keyhole, and the bottom of the keyhole collapses. When the preheating temperature is 300 K (ambient temperature), 400 K, and 500 K, the inner wall in the middle of the rear keyhole wall is concave. With the increase in the preheating temperature, the area of the concave gradually increases, and the size of the liquid column behind the keyhole opening gradually decreases. When the preheating temperature is 300 K, there are more spatters above the molten pool. In comparison, when the preheating temperature is 400 K or 500 K, there are less spatters, and the bottom of the keyhole collapses.
39
Salminen, A., H. Piili, and T. Purtonen. "The characteristics of high power fibre laser welding." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 224, no. 5 (March 19, 2010): 1019–29. http://dx.doi.org/10.1243/09544062jmes1762.
Анотація:
Laser welding has an ever growing role in manufacturing technology. Keyhole laser welding is the most important laser welding process in metal industry when exceeding the 1 mm weld penetration. This process uses efficiently the high energy density of a laser beam to vaporize and melt materials, thus producing a keyhole in the material via which the energy is brought to it. The requirements from customer side and the development of new materials have been giving justification for the development of new laser types suitable for material processing with ever higher power values. In contrast, the development of laser technologies has made it possible to build more powerful lasers with excellent beam properties and good electrical efficiency. New laser sources with good absorption and beam quality make the laser welding even more efficient when throughput and efficiency are considered. They show their ability to produce narrower welds with lower line energy. However, the validation of actual keyhole shape, size, and behaviour against the models is still lacking because of the difficulties in performing the measurements of the actual dimensions. It has been shown that the better the beam quality the higher the welding speed. When welding with high power, good beam quality, and wavelength close to 1000 nm, there are some obstacles to overcome, which are caused by high absorption and power density. Typically, problems, such as thermal lensing, can be avoided with proper parameter and tool selection. Typically, the size of the keyhole is according to the focal point size, and the stability of the keyhole plays a major role when considering the ability of the laser welding process to produce high quality welds.
40
Pordzik, Ronald, and Peer Woizeschke. "An Experimental Approach for the Direct Measurement of Temperatures in the Vicinity of the Keyhole Front Wall during Deep-Penetration Laser Welding." Applied Sciences 10, no. 11 (June 6, 2020): 3951. http://dx.doi.org/10.3390/app10113951.
Анотація:
The formation of defects such as pores during deep-penetration laser welding processes is governed by the melt pool dynamics and the stability of the vapor capillary, also referred to as the keyhole. In order to gain an insight into the dynamics of the keyhole, the temperature in the transition region from the liquid to the gaseous phase, i.e., near the keyhole wall, is a physical value of fundamental importance. In this paper, a novel method is presented for directly measuring temperatures in the close vicinity of the keyhole front wall during deep-penetration laser welding. The weld samples consist of pure aluminum with a boiling point of 2743 K. The measurement is performed using high-speed pyrometry with a refractory tantalum probe capable of detecting temperatures that significantly exceed the boiling point of the sample material. Temperature curves are recorded from the beginning of the welding process until the moment the probe is finally destroyed through direct laser-tantalum interaction. With an effective spatial resolution up to 0.3 µm in the welding direction, a detailed investigation into the temperature ranging from the prerunning melt pool front to the keyhole center is possible, exhibiting temperatures of up to 3300 K in the vicinity of the keyhole front wall.
41
Artinov, Antoni, Xiangmeng Meng, Marcel Bachmann, and Michael Rethmeier. "Numerical Analysis of the Partial Penetration High Power Laser Beam Welding of Thick Sheets at High Process Speeds." Metals 11, no. 8 (August 20, 2021): 1319. http://dx.doi.org/10.3390/met11081319.
Анотація:
The present work is devoted to the numerical analysis of the high-power laser beam welding of thick sheets at different welding speeds. A three-dimensional transient multi-physics numerical model is developed, allowing for the prediction of the keyhole geometry and the final penetration depth. Two ray tracing algorithms are implemented and compared, namely a standard ray tracing approach and an approach using a virtual mesh refinement for a more accurate calculation of the reflection point. Both algorithms are found to provide sufficient accuracy for the prediction of the keyhole depth during laser beam welding with process speeds of up to 1.5mmin−1. However, with the standard algorithm, the penetration depth is underestimated by the model for a process speed of 2.5mmin−1 due to a trapping effect of the laser energy in the top region. In contrast, the virtually refined ray tracing approach results in high accuracy results for process speeds of both 1.5mmin−1 and 2.5mmin−1. A detailed study on the trapping effect is provided, accompanied by a benchmark including a predefined keyhole geometry with typical characteristics for the high-power laser beam welding of thick plates at high process speed, such as deep keyhole, inclined front keyhole wall, and a hump.
42
JIANG, M., T. DEBROY, M. JIANG, Y. B. CHEN, X. CHEN, and W. TAO. "Enhanced Penetration Depth during Reduced Pressure Keyhole-Mode Laser Welding." Welding Journal 99, no. 4 (April 1, 2020): 110s—123s. http://dx.doi.org/10.29391/2020.99.011.
Анотація:
Keyhole-mode laser welding under reduced ambient pressure is known to provide improved weld penetration, narrower width, and reduced incidences of defects, but the underlying mechanism for these benefits is not known. We sought to elucidate the mechanism by an experimental and theoretical program of investigation. Potential causative factors, such as the depression of the boiling point of al-loys at reduced pressures and the changes in laser beam attenuation by metal vapors/plasma, were investigated using a well-tested heat transfer and fluid flow model of keyhole-mode laser welding for various ambient pressures. The model was tested with experimental data for the weld-ing of four alloys — Structural Steel Q690, Aluminum Alloy A5083, commercially pure titanium, and Nickel 201 — that have very different thermophysical properties. The results showed the changes in the boiling point alone were unable to explain the enhanced depth of penetration at low ambi-ent pressures. The experimental and calculated fusion zone geometries showed excellent agreement when both the boiling point depression and the beam attenuation by metal vapor were considered. The reduction of ambient pressure also affected the heat transfer pattern near the keyhole, owing to a decrease in the keyhole wall temperature and changes in the temperature gradient near the keyhole wall.
43
Zou, Jianglin, Na Ha, Rongshi Xiao, Qiang Wu, and Qunli Zhang. "Interaction between the laser beam and keyhole wall during high power fiber laser keyhole welding." Optics Express 25, no. 15 (July 13, 2017): 17650. http://dx.doi.org/10.1364/oe.25.017650.
44
Kim, Jong Do, Hyun Joon Park, and Mun Yong Lee. "Observation of Dynamic Behavior in Primer-Coated Steel Welding by CO2 Laser." Solid State Phenomena 124-126 (June 2007): 1425–28. http://dx.doi.org/10.4028/www.scientific.net/ssp.124-126.1425.
Анотація:
This study examines for keyhole behavior by observing the laser-induced plasma and investigates the relation between keyhole behavior and formation of weld defect. Laser-induced plasma has been accompanied with the vaporizing pressure of zinc ejecting from keyhole to surface of primer coated plate. This dynamic behavior of plasma was very unstable and it was closely related to the unstable motion of keyhole during laser welding. As a result of observing the composition of porosity, much of Zn element was found from inner surface of it. But Zn was not found from the dimple structure fractured at the weld metal. therefore we can prove that the major cause of porosity is the vaporization of primer in lap position. Mechanism of porosity-formation is that the primer vaporized from the lap position accelerates dynamic behavior of the key hole and the bubble separated from the key hole is trapped in the solidification boundary and remains as porosity.
45
Dowden, John. "Interaction of the keyhole and weld pool in laser keyhole welding." Journal of Laser Applications 14, no. 4 (November 2002): 204–9. http://dx.doi.org/10.2351/1.1514219.
46
Zhou, Jun, and Hai-Lung Tsai. "Porosity Formation and Prevention in Pulsed Laser Welding." Journal of Heat Transfer 129, no. 8 (September 5, 2006): 1014–24. http://dx.doi.org/10.1115/1.2724846.
Анотація:
Porosity has been frequently observed in solidified, deep penetration pulsed laser welds. Porosity is detrimental to weld quality. Our previous study shows that porosity formation in laser welding is associated with the weld pool dynamics, keyhole collapse, and solidification processes. The objective of this paper is to use mathematical models to systematically investigate the transport phenomena leading to the formation of porosity and to find possible solutions to reduce or eliminate porosity formation in laser welding. The results indicate that the formation of porosity in pulsed laser welding is caused by two competing factors: one is the solidification rate of the molten metal and the other is the backfilling speed of the molten metal during the keyhole collapse process. Porosity will be formed in the final weld if the solidification rate of the molten metal exceeds the backfilling speed of liquid metal during the keyhole collapse and solidification processes. Porosity formation was found to be strongly related with the depth-to-width aspect ratio of the keyhole. The larger the ratio, the easier porosity will be formed, and the larger the size of the voids. Based on these studies, controlling the laser pulse profile is proposed to prevent/eliminate porosity formation in laser welding. Its effectiveness and limitations are demonstrated in the current studies. The model predictions are qualitatively consistent with reported experimental results.
47
Yin, Ya Jun, Jian Xin Zhou, and Tao Chen. "Temperature Numerical Simulation of Laser Penetration Welding Based on Calculated Keyhole Profile." Advanced Materials Research 314-316 (August 2011): 1238–41. http://dx.doi.org/10.4028/www.scientific.net/amr.314-316.1238.
Анотація:
According to the calculation model of the keyhole porfile[1], the 3D point cloud data is calculated. Then, the paper establishes a physical model of the keyhole in the laser welding by using the 3D reverse technology. The adaptive mesh generation of the model is processed by the independent development software. Finally this paper establishes a mathematical model of the temperature field in the laser welding, which considers the factor of the welding velocity. A more accurate temperature field is obtained by using the laser welding solver which is a secondary development of OpenFOAM, adding the Guass surface source and the keyhole volume source, and setting the boundary condition of convection and radiation. The result provides more accurate bases for the welding stress field.
48
Ren, Zhongshu, Lin Gao, Samuel J. Clark, Kamel Fezzaa, Pavel Shevchenko, Ann Choi, Wes Everhart, Anthony D. Rollett, Lianyi Chen, and Tao Sun. "Machine learning–aided real-time detection of keyhole pore generation in laser powder bed fusion." Science 379, no. 6627 (January 6, 2023): 89–94. http://dx.doi.org/10.1126/science.add4667.
Анотація:
Porosity defects are currently a major factor that hinders the widespread adoption of laser-based metal additive manufacturing technologies. One common porosity occurs when an unstable vapor depression zone (keyhole) forms because of excess laser energy input. With simultaneous high-speed synchrotron x-ray imaging and thermal imaging, coupled with multiphysics simulations, we discovered two types of keyhole oscillation in laser powder bed fusion of Ti-6Al-4V. Amplifying this understanding with machine learning, we developed an approach for detecting the stochastic keyhole porosity generation events with submillisecond temporal resolution and near-perfect prediction rate. The highly accurate data labeling enabled by operando x-ray imaging allowed us to demonstrate a facile and practical way to adopt our approach in commercial systems.
49
Chen, Li, and Shui Li Gong. "The Research on YAG Laser Welding Porosity of Al-Li Alloy." Advanced Materials Research 287-290 (July 2011): 2175–80. http://dx.doi.org/10.4028/www.scientific.net/amr.287-290.2175.
Анотація:
The laser welding of Aluminum-Lithium alloy (Al-Li) alloy were conducted to investigate the weld porosity features in this paper. The results show that there are two kinds of weld porosity existing for laser welding Aluminum-Lithium alloy sheet. They are can be divided into metallurgical porosity and unstable keyhole porosity according to their different reason causing them. The mechanism of unstable keyhole porosity occurring was discussed according to the results of YAG laser welding processing. The methods how to reduce weld porosity for laser welding of Aluminum-Lithium alloy was also described.
50
Pang, Xiaobing, Jiahui Dai, Mingjun Zhang, and Yan Zhang. "Suppression of Bottom Porosity in Fiber Laser Butt Welding of Stainless Steel." Photonics 8, no. 9 (August 28, 2021): 359. http://dx.doi.org/10.3390/photonics8090359.
Анотація:
The application bottleneck of laser welding is being gradually highlighted due to a high prevalence of porosity. Although laser welding technology has been well applied in fields such as vehicle body manufacturing, the suppression of weld porosity in the laser welding of stainless steel containers in the pharmaceutical industry is still challenging. The suppression of bottom porosity was investigated by applying ultrasonic vibration, changing welding positions and optimizing shielding gas in this paper. The results indicate that bottom porosities can be suppressed through application of ultrasonic vibration at an appropriate power. The keyhole in ultrasound-assisted laser welding is easier to penetrate, with better stability. No obvious bulge at the keyhole rear wall is found in vertical down welding, and the keyhole is much more stable than that in flat welding, thus eliminating bottom porosity. The top and bottom shielding gases achieve the minimal total porosities, without bottom porosity.