Welding Deviation Detection Algorithm Based on Extremum of Molten Pool Image Contour

The welding deviation detection is the basis of robotic tracking welding, but the on-line real-time measurement of welding deviation is still not well solved by the existing methods. There is plenty of information in the gas metal arc welding（GMAW） molten pool images that is very important for the control of welding seam tracking. The physical meaning for the curvature extremum of molten pool contour is revealed by researching the molten pool images, that is, the deviation information points of welding wire center and the molten tip center are the maxima and the local maxima of the contour curvature, and the horizontal welding deviation is the position difference of these two extremum points. A new method of weld deviation detection is presented, including the process of preprocessing molten pool images, extracting and segmenting the contours, obtaining the contour extremum points, and calculating the welding deviation, etc. Extracting the contours is the premise, segmenting the contour lines is the foundation, and obtaining the contour extremum points is the key. The contour images can be extracted with the method of discrete dyadic wavelet transform, which is divided into two sub contours including welding wire and molten tip separately. The curvature value of each point of the two sub contour lines is calculated based on the approximate curvature formula of multi-points for plane curve, and the two points of the curvature extremum are the characteristics needed for the welding deviation calculation. The results of the tests and analyses show that the maximum error of the obtained on-line welding deviation is 2 pixels（0.16 ram）, and the algorithm is stable enough to meet the requirements of the pipeline in real-time control at a speed of less than 500 mm/min. The method can be applied to the on-line automatic welding deviation detection.

Acquisition and processing of coaxial image of molten pool and keyhole in Nd:YAG laser welding with high power

An experimental setup of acquiring the coaxial visual image of the molten pool and keyhole in high power Nd:YAG laser welding is introduced in this paper. It is one of the most difficult problems in acquiring coaxial image that the coaxial imaging signal of molten pool and keyhole must be separated from the laser beam with high power. This problem was resolved by designing a dichroitic spectroscope. The characteristics of imaging signal were analyzed and the coaxial image of molten pool and keyhole was acquired. A smoothing filter and a homomorphic filter were designed to remove the low frequency noise and to enhance the image according to the characteristics of imaging signal. At last, edges of molten pool and keyhole were detected and extracted based on image segmentation with threshold.

Edge detection of molten pool and weld line for CO_2 welding based on B-spline wavelet

Due to the disturbances of spatters, dusts and strong arc light, it is difficult to detect the molten pool edge and the weld line location in CO_2 welding processes. The median filtering and self-multiplication was employed to preprocess the image of the CO_2 welding in order to detect effectively the edge of molten pool and the location of weld line. The B-spline wavelet algorithm has been investigated, the influence of different scales and thresholds on the results of the edge detection have been compared and analyzed. The experimental results show that better performance to extract the edge of the molten pool and the location of weld line can be obtained by using the B-spline wavelet transform. The proposed edge detection approach can be further applied to the control of molten depth and the seam tracking.

Heat Transfer Characteristic of Molten Pool for Twin-Roll Strip Casting

Body-fitted coordinate transformation equation was deduced and used to generate the body-fitted grids of molten pool for twin-roll strip casting.The orthogonality of the grids on the boundary was modified by adjusting source item.The energy equation and the boundary conditions were transformed from physical space to computational space.The velocity field model proposed by Hirohiko Takuda was used to calculate the temperature field of molten steel,and the influence of technical factors was also discussed.

ON THE COMPOSITION UNIFORMITY AND SHAPE COEFFICIENT OF MOLTEN POOL BY LASER ALLOYING

The effect of the laser processing parameters on the composition uniformity and shape coefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloy steel has been studied.It was found that the composition uniformity depends on the shape coefficient of fusion zone,and the later is a function of both power density and interaction time.If the power density is fixed to a certain value,the shape coefficient is directly,propor- tional to the interaction time.A completely,uniform molten pool can be obtained,when the shape coefficient is between 1.6 and 3.0.

Molten pool and temperature field in CO_2 laser welding

Two measuring methods, high-speed camera and optical monitoring system, were used to study processes of laser welding. Molten pool, cooling time and temperature field were analyzed based on real measured images and optical signal data. The results show that the width of molten pool is almost equal to the width of weld, and length is about 7. 8 mm. The solidification time is about 0. 5 s and the temperature gradient is great, so HAZ is very small. The method and results will be of benefit to build the relationship between welding parameters and microstructure.

Wire-feed laser additive manufacturing of dissimilar metals via dual molten pool interface interlocking mechanism

Intermetallic compounds produced in laser additive manufacturing are the main factors restricting the joint performance of dissimilar metals.To solve this problem,a dual molten pool interface interlocking mechanism was proposed in this study.Based on a dual molten pool interface interlocking mechanism,the dissimilar metals,aluminum alloy and stainless steel,were produced as single-layer and multilayer samples,using the wire-feed laser additive manufacturing directed energy deposition technology.The preferred parameters for the dual molten pool interface interlocking mechanism process of the dissimilar metals,aluminum alloy and stainless steel,were obtained.The matching relationship between the interface connection of dissimilar metals and the process parameters was established.The results demonstrated excellent mechanical occlusion at the connection interface and no apparent intermetallic compound layer.Good feature size and high microhardness were observed under a laser power of 660 W,a wire feeding speed of 55 mm/s,and a platform moving speed of 10 mm/s.Molecular dynamics simulations demonstrated a faster rate of aluminum diffusion in the aluminum alloy substrate to stainless steel under the action of the initial contact force than without the initial contact force.Thus,the dual molten pool interface interlocking mechanism can effectively reduce the intermetallic compound layer when dissimilar metals are connected in the aerospace field.

Simulating molten pool features of shipbuilding steel subjected to submerged arc welding

Submerged arc welding process has been simulated to investigate the molten pool features of EH36 shipbuilding steel.One case only involved the surface tension model,and another one involved both the surface tension model and the interface tension model.The role of interface tension during welding is revealed,and the evolution of molten pool morphology is understood by comparing the surface temperature distribution,surface tension and interface tension distribution,and the streamline of the molten pool for the two cases.When the interface tension model is disregarded,a flow conducive to the outward expansion is formed in the surface area of the molten pool,resulting in a small weld depth-to-width ratio.After applying the interface tension model,the expanding outward flow is restrained,which leads to a deep penetration morphology with a large weld depth-to-width ratio due to the inward flow governed by the Marangoni forces.The simulation results involving the interface tension model have been verified with satisfactory predictability.

Effect of Remelting Current on Molten Pool Profile of Titanium Alloy Ingot During Vacuum Arc Remelting Process

The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity,which are strongly influenced by molten pool profile that is influenced by VAR process.To better understand the effect of remelting current on molten pool profile of titanium alloy ingot during VAR process,a 3D finite element model is developed by the ANSYS software.The results show that there are three remelting stages during VAR process when the remelting current is 2.0 kA.The molten pool depth increases gradually from 30 to 320 s,then the change of molten pool depth is very small during the steady state stage from 320 to 386 s,and lastly the molten pool depth becomes shallow after 386 s.The melting rate and temperature of superheat increase with the remelting current increasing,which leads to the augment of molten pool volume.In the end,the total remelting time and steady state molten pool time decrease with the melting current from 1.6 to 2.8 kA.

表面张力对激光焊接熔池及匙孔的影响

基于FLUENT19.0软件,建立了激光焊接热-流耦合模型,对比分析了不同表面张力温度系数(为负值)对熔池流场的影响.结果表明,随着表面张力温度系数的减小,熔池后方顺时针漩涡的流动趋势逐渐减弱,甚至消失,而且焊接飞溅的数量增多.纵截面熔池长度逐渐增加,纵截面熔池流体最大流动速度逐渐增大,熔池横截面的面积逐渐减小.当表面张力温度系数为-2.5×10^(-4)N/(m·K)时,熔池长度平均值为3.28 mm、熔池流体最大流动速度的平均值为2.89 m/s、熔池横截面面积的平均值为4.52 mm^(2);当表面张力温度系数为-3.5×10^(-4)N/(m·K)时,熔池长度平均值为3.73 mm、熔池流体最大流动速度的平均值为3.53 m/s、熔池横截面面积的平均值为4.03 mm^(2);当表面张力温度系数为-4.9×10^(-4)N/(m·K)时,熔池长度平均值为4.14 mm、熔池流体最大流动速度的平均值为4.09 m/s、熔池横截面面积的平均值为3.28 mm^(2).

基于摆动激光扫描的GMAW焊缝成形调控

将摆动激光与GMAW工艺复合,利用“8”字形摆动激光扫描液态熔池,对其温度场和流场进行调控,以改变熔池温度梯度,主动调控熔池流动以改善焊缝成形.在6061铝合金板材表面进行堆焊试验,重点探究了光丝间距、摆动幅度、激光功率对于焊缝成形的影响,采用高速摄像机拍摄激光扫描熔池过程.结果表明,摆动激光扫描可以有效抑制成形缺陷的发生,当摆动激光扫描熔池中部时可以获得最佳的焊缝成形效果.摆动激光扫描降低了熔池温度梯度分布,同时激光扫描产生的激光蒸发反力可以驱动熔池流动,促进了液态熔池的流动铺展,从而有效抑制了不规则焊缝成形缺陷,减少焊缝内部气孔和裂纹缺陷.调节摆动激光摆幅可以在一定范围内对焊缝宽度进行调控.

奥氏体不锈钢薄板激光焊表面张力驱动熔池形成的数值模拟分析

为探究奥氏体不锈钢薄板激光焊接过程中表面张力对熔池形状、熔池流速、熔池静压的影响,以期优化焊接工艺并提高焊接质量。基于数值模拟分析方法,建立了移动旋转高斯曲面体热源模型,通过改变Marangoni对流系数来模拟不同表面张力条件,分析其对熔池形成过程、熔池形状、流速及熔池内静压力的影响。模拟结果表明,表面张力是影响熔池形态和内部静压力的关键因素,表面张力指向熔池内部,驱动熔池向中心汇聚,从而促进熔池的形成;表面张力的大小与熔池峰值温度、熔深、深宽比呈负相关,与峰值流速、熔宽、熔池内部静压力呈正相关;铜衬底的加入显著增大了过冷度,加速了熔池的冷却,有助于避开奥氏体不锈钢的敏化温度区间。

小熔池激光沉积制造薄壁件沉积宽度的模型预测及试验研究

将激光沉积制造的热物理过程与薄壁件的几何特性相结合,基于层间沉积过程中的能量守恒关系建立了可以适配于小熔池激光沉积制造薄壁件沉积宽度的预测模型。该模型详细阐述了沉积宽度与激光功率、扫描速度与送粉速率之间的关系。利用Ti–6Al–4V(TC4)粉末沉积制备了多组样品来进行预测模型的验证,结果表明,该模型可以准确地预测不同工艺参数下薄壁件的沉积宽度,提高了试验参数匹配的准确性与效率,并为小熔池激光沉积制造工艺成形精度控制奠定了理论基础。

选区激光熔化过程熔池缺陷的形成机理研究

采用三维高保真计算流体动力学模型,研究了镍基高温合金GH4169在SLM过程中的熔池流动和缺陷形成过程,揭示了剥蚀和球化等缺陷的形成机理。结果表明,熔池的驱动力主要为马兰戈尼力和表面张力,马兰戈尼力促使熔池由内而外流动,而表面张力导致熔池由外向内流动。剥蚀现象一般出现在熔池附近,当剥蚀区域较小时,剥蚀呈周期性出现和消失。而当剥蚀区域较大时,少量的熔融液体无法填充大区域的剥蚀,导致表面质量退化。当熔池的长深比小于3.4时,在高温区(马兰戈尼力为主要驱动力)与低温区(表面张力为主要驱动力)的交界处更容易发生球化现象。研究成果有助于指导工艺优化提升选区激光熔化成形件的表面质量。

基于CCD的激光熔覆熔池平滑度在线监测系统研究

由于激光熔覆过程高温高亮,无法实时准确判断熔覆效果。使用CCD相机结合平滑度监测算法,对不同功率下的熔池形貌进行监测,验证算法性能,判断熔覆效果,同时尝试叶片修复。结果表明:激光功率过大或者扫描速度过慢,均会导致熔池边缘平滑度较差,进而认为熔覆参数不合适;为防止熔坏基材,可根据监测效果及时停机;发现激光功率与熔池边缘平滑度呈负相关。

激光熔化沉积过程缺陷识别方法

激光熔化沉积加工过程中的缺陷萌生是制约激光熔化沉积技术发展的关键性问题.实现对缺陷的精确自动识别是提高激光熔化沉积技术应用水平的重要途径.提出了熔池瞬态特征提取算法,分析了熔池瞬态特征对沉积层熔合不良缺陷的影响关系,建立了熔池瞬态特征数据集.对主流识别算法进行了模型训练测试,获取了相对最优模型ResNet 34.为解决ResNet 34训练损失拟合效果差、计算速度慢的问题,结合传统卷积网络和LSTM(long short-term memory)网络,建立了训练和测试精度高且计算速度快的LRCN 64模型,测试准确率达95.8%,实现了对熔合不良缺陷的识别,为实现沉积件在线无损检测提供了技术支撑.

变极性等离子弧焊技术发展及其在航天制造领域应用现状

变极性等离子弧(VariablePolarityPlasmaArc,VPPA)焊是一种高效的铝合金和镁合金焊接方法,其主要优势在于等离子电弧具有高能量密度,可以在焊接时穿透熔池形成小孔,大幅度降低焊接变形和残余应力,提高焊接质量。了解熔池小孔行为、电弧物理特性和控制方法对于优化和提高焊接过程的稳定性至关重要。本文综述了VPPA焊接技术发展的最新情况,对VPPA焊接过程信息的检测研究为深刻认识焊接稳定性机理提供了有力保障,尤其是利用X射线成像系统观测熔融金属流动的研究,对提升VPPA穿孔熔池物理本质的认识做出了重要贡献。此外,针对不同位置VPPA焊接的研究增加了这一焊接工艺的灵活性,由VPPA焊接衍生的多种拓展工艺拓宽了该焊接方法的适用范围。VPPA穿孔焊接技术以其焊接变形小、焊后无缺陷、单面焊接双面一次成形等优势,成为航空航天领域铝合金中厚板材焊接制造的优选工艺。

数字化等离子焊接系统在连续油管钢带对接中的设计与应用

为解决传统等离子焊接平台气囊夹紧力不足、焊枪行走机构精度差、焊接控制系统输出不稳定、无法实时观察问题,以及造成的对接焊缝错边、咬边、焊偏等质量问题,设计了一种数字化等离子焊接系统。该系统通过改进液压夹紧装置、设计焊枪控制系统、熔池监控装置、焊机自动定位装置及气体保护装置,实现了数字化焊接,提升了焊接质量,提高了生产效率。实际应用表明,采用设计的数字化等离子焊接系统,生产效率提升15%以上,斜焊缝一次通过率提高约8%。

激光熔覆熔池动态演化及缺陷工艺调控研究进展

激光熔覆是一种高能束增材修复技术,具有热影响区小、组织性能可控性强、材料选择范围广等系列优势,目前已广泛应用于能源动力等领域关键金属构件的增材制造成形与受损零部件的修复再制造中。激光熔覆是以“激光”为热源的能量沉积技术,包括高能激光束冲击、表面熔池熔化快凝及熔覆表面层形成等多种物理、化学过程,其中熔池内金属热流体动力演化行为与熔覆层缺陷及表层组织性能调控密切相关。金属熔池具有“急热骤冷”的凝固特征,其内部对流、传热和传质等行为决定了熔覆层中温度及应力分布状态,是诱导熔覆层内气孔、裂纹等组织内部缺陷形成的关键因素。从激光熔覆过程中熔池内部对流、传热与传质的动态物理特性出发,论述了激光热源的理论模型设计、动态熔池中“流场+温度场+应力场”的多物理场数值模拟等方面的相关研究。在此基础上,分析了激光熔覆层典型缺陷-裂纹和气孔的形成机理及特征,总结了“材料-工艺-熔凝行为-涂层缺陷”的内在关联机制。同时,针对单一工艺方式调控熔池内熔凝过程的局限性,概述了多种复合能量场调控技术对熔覆层内部缺陷的作用机制与调控效果。最后,总结了当前激光熔覆层缺陷动态形成过程中存在的问题,并对其发展趋势进行了展望。

X射线超快成像原位表征激光增材制造过程研究进展

在增材制造过程中,熔池经历快速熔化、冷却、凝固的过程,其物理、化学、结构和应力等处于极端非平衡状态,容易导致孔隙、裂纹等缺陷产生,影响制件力学性能。同步辐射X射线具有高空间分辨率和时间分辨率,可以实现增材制造过程中熔池动力学和缺陷演化的原位表征。本文综述了近年来激光增材制造原位实验平台的搭建,并从熔池结构演化、缺陷形成机理和成形工艺优化三个方面介绍了同步辐射X射线原位表征激光增材制造过程的研究进展。最后基于目前增材制造原位观察的局限性,从表征系统改进、原料多样化和计算修正等方面对未来研究进行了展望。