Nd:YAG激光深熔焊接过程中小孔的形态特征

通过图像处理得到了Nd:YAG激光深熔焊接过程中小孔内外边缘宽长比、内外边缘中心到激光光斑中心以及内外边缘中心之间的距离,并将其作为小孔的形态特征参数,研究了小孔形态随焊接工艺参数变化的规律.研究结果表明,激光功率的增大使小孔径向形状趋向圆形并使其在深度方向上的倾斜程度减小;在低速焊时,小孔形态基本不变,而在中高速焊接时,随着焊接速度的增大,小孔径向形状沿焊接方向拉长,小孔的倾斜程度也不断增大;在一定离焦量范围内,离焦量的变化对小孔在径向和深度方向上的形态影响较小.     

Nd∶YAG激光深熔焊接过程中小孔的形态特征

通过图像处理得到了Nd∶YAG激光深熔焊接过程中小孔内外边缘宽长比、内外边缘中心到激光光斑中心以及内外边缘中心之间的距离,并将其作为小孔的形态特征参数,研究了小孔形态随焊接工艺参数变化的规律。研究结果表明,激光功率的增大使小孔径向形状趋向圆形并使其在深度方向上的倾斜程度减小;在低速焊时,小孔形态基本不变,而在中高速焊接时,随着焊接速度的增大,小孔径向形状沿焊接方向拉长,小孔的倾斜程度也不断增大;在一定离焦量范围内,离焦量的变化对小孔在径向和深度方向上的形态影响较小。     

激光深熔焊接小孔的反射吸收

采用高速摄影的方法清晰、完整地观测了激光深熔焊接GG17玻璃时的小孔，并根据观测到的小孔的形状和尺寸，计算比较了小孔孔壁的反射吸收以及由于热传导和对流所引起的热损失，分析了小孔形成时平衡表面张力的主要作用力，建立了基于小孔孔壁前沿能量平衡的自适应模型，为系统研究激光深熔焊接时的小孔效应提供了一种新的方法和手段。     

铍的Nd:YAG激光焊接阈值功率影响因素

利用Nd:YAG激光焊接了铍环,研究了不同激光入射角度和铍环直径变化对阈值功率变化的影响,得到了铍在激光焊接过程中阈值功率密度变化规律.结果表明,铍环直径大小对阈值功率密度有显著影响,随着铍环直径的增加,铍环的曲率减小,由背反射引起的调Q脉冲增强,导致出现深熔焊的阈值功率密度降低.对同一直径的铍环,激光入射角度从0°调整到3°后,由于消除了背反射激光在谐振腔内形成调Q脉冲,激光焊接时出现深熔焊的临界功率密度增加.深熔焊形成的焊缝深宽比值较大,为1.0～1.5,而热传导焊形成的焊缝深宽比值较小,只有0.2左右.     

工艺参数对Nd:YAG激光熔覆层几何尺寸和性能的影响

研究了电压、脉宽和激光重复频率对Nd：YAG激光熔覆层几何尺寸和性能的影响，解释了造成这些影响的原因。结果表明，在其它工艺参数一定的情况下，电压越高，或脉宽越大，或频率越大，将使熔覆层高越小，熔深越大，熔覆层宽越大；随着脉宽、激光重复频率或电压的增加，熔覆层气孔率越小；当脉宽、激光重复频率或电压在一定范围内增加时，熔覆层均不会开裂。     

铍的Nd∶YAG激光焊接阈值功率影响因素

利用Nd∶YAG激光焊接了铍环,研究了不同激光入射角度和铍环直径变化对阈值功率变化的影响,得到了铍在激光焊接过程中阈值功率密度变化规律。结果表明,铍环直径大小对阈值功率密度有显著影响,随着铍环直径的增加,铍环的曲率减小,由背反射引起的调Q脉冲增强,导致出现深熔焊的阈值功率密度降低。对同一直径的铍环,激光入射角度从0°调整到3°后,由于消除了背反射激光在谐振腔内形成调Q脉冲,激光焊接时出现深熔焊的临界功率密度增加。深熔焊形成的焊缝深宽比值较大,为1.0~1.5,而热传导焊形成的焊缝深宽比值较小,只有0.2左右。     

超薄板材上Nd:YAG脉冲激光送粉熔覆研究

研究了为满足特定图案要求在超薄板材 ( 0 1～ 0 15mm)上进行Nd :YAG脉冲激光送粉精细熔覆过程中激光熔覆特性、侧向和同轴喷嘴送粉熔覆、基体的真空吸附夹紧和强迫制冷、熔覆层几何形貌、元素分布和微观组织特性等因素。得到了熔覆层高宽比为 0 88和 0 5、质量良好的熔覆图案     

激光焊接体能量及其对激光深熔焊缝熔深的影响

定义焊接体能量用来综合评价激光焊接过程中激光功率、焊接速度、离焦量及焦点尺寸等焊接工艺参数对激光深熔焊接过程的影响,并分析了焊接体能量对激光深熔焊缝熔深的影响.焊接体能量与激光功率成正比、与焊接速度成反比、与离焦量成四阶指数关系,与焦点尺寸成平方关系.结果表明,在激光深熔焊接过程中,焊接体能量决定焊缝熔深;随着焊接体能量的增大,焊缝熔深近似呈线性增大.     

超薄板材上Nd：YAG脉冲激光送粉熔覆研究

研究了为满足特定图案要求在超薄板材（０．１～０．１５ｍｍ）上进行Ｎｄ：ＹＡＧ脉冲激光送粉精细熔覆过程中激光熔覆特性、侧向和同轴喷嘴送粉熔覆、基体的真空吸附夹紧和强迫制冷、熔覆层几何形貌、元素分布和微观组织特性等因素。得到了熔覆层高度比为０．８８和０．５、质量良好的熔覆图案。     

保护气流量对不锈钢激光-MAG复合焊接头组织和性能的影响

对8 mm厚SUS301L-MT不锈钢进行激光-MAG复合焊接,研究不同保护气流量对焊缝成形、显微组织和力学性能的影响。试验结果表明:当其他焊接参数一定时,在该试验条件下保护气流量对焊缝成形影响较小,焊缝区域组织相似,主要为柱状奥氏体树枝晶+少量的δ铁素体。接头显微硬度和冲击韧性随保护气流量的变化不明显。接头的抗拉强度随保护气流量的增加而提高,当保护气流量为40 L/min时,接头抗拉强度最高为765 MPa,达到母材抗拉强度的86.5%。分析拉伸断口发现,不同保护气流量断口微观形貌相似,断口中分布着大量韧窝,表现为韧性断裂。     

Critical power of keyhole formation in CW Nd：YAG laser deep penetration welding

The energy model was founded to calculate the critical power of keyhole formation by using the limit principle in CW （ continuous wave ） Nd： YAG laser deep penetration welding process. The model was validated by experiments. The results show that ＇.there are two errors between the calculated critical power of keyhole formation and that of experiments ： one is that the calculated results is less than those of experiments, which is caused by not considering the energy loss by heat conduction in the model of keyhole formation. The other is that there is 0. 9 mm error between the axis of the calculated curve of critical power with location of laser focus and that of experimental curve, which is induced by the excursion of laser focus in laser deep penetration welding. At last, the two errors were revised according to the analyses of the errors.     

激光焊接同轴气体保护嘴结构设计

针对激光焊接过程中需要同轴吹气保护的需要,设计了保护气嘴与工件的距离自由可调的结构。采用该焊接头对复杂图形进行焊接试验,分析气嘴与工件的距离对焊接过程的影响,结果表明,这种同轴吹气结构设计合理,调试方便。     

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.     

Dynamic keyhole profile during high-power deep-penetration laser welding

Based on a butt-joint configuration assembled from transparent glass and stainless steel, the dynamic keyhole profile was observed during 10-kW fiber laser welding. The “gauffers” and vapor flow on the front keyhole wall moved downwards to the bottom of the keyhole. The downward-flowing vapor met the upward-flowing vapor at the bottom of the keyhole, which resulted in a whirlpool of vapor. The suspended droplets were drove to move in a random fashion by the whirlpool. The fluctuating vapor flow and pressure were the key factors causing the fluctuating keyhole wall and resulting in a vapor-generated wave (VGW) on the rear keyhole wall. The dynamic VGW was a very important factor affecting the dynamic welding process. When the VGW broke at the keyhole outlet, it was accompanied by swellings, spatter, columns, a decrease of the diameter of keyhole inlet, and a change in the direction of plume.     

激光深熔焊接抛物面小孔模型

激光深熔焊接由于其无与伦比的优良特性成为高功率激光工业应用的主要方面.在假设小孔为旋转抛物面结构的基础上,通过分析小孔内的压力平衡、蒸发压力、表面张力、能量平衡、小孔壁的温度以及小孔底部的能量平衡问题,采用数值迭代方法求解出小孔的深度和宽度.将焊接中的理论分析由假设小孔形状为圆柱面只能适合低速焊接推广到中高速焊接.计算了在不同焊接速度下小孔的深度、宽度以及与焊接试验的焊缝深度,与焊接试验中得到的结果进行了比较,理论计算结果也比较吻合实际焊接情况.     

基于同轴视觉传感的激光穿透焊接焊缝尺寸检测

利用CMOS同轴视觉传感系统,通过分析匙孔和熔池区域光辐射的特征,对Nd:YAG激光深熔焊接的焊缝形态进行了检测.结果表明,在匙孔穿透型激光深熔焊接中,匙孔在工件背面穿透将导致光辐射衰减区域的出现,衰减区域的尺寸和光辐射衰减的程度均随着焊接速度的增加而减小,且相对于匙孔的前沿,其位置向熔池的后方移动.通过分析匙孔区域的光辐射衰减程度和匙孔前壁角度的变化,将光辐射分布的特征与焊缝的尺寸结合起来,建立了两者之间的对应关系,从而实现了焊缝尺寸的检测.     

激光深熔焊中匙孔形成过程的动态模拟

为了准确的模拟出激光深熔焊接中匙孔变化的动态过程,根据匙孔内激光的能量吸收机制,采用射线跟踪法产生热源,建立了激光深熔焊接过程中气、液、固三相统一的数学模型,并采用了VOF方法追踪自由液面,模型中考虑了表面张力、热浮力和反冲压力的作用,通过数值计算得到了匙孔变化的动态过程与相应的温度分布.结果表明,匙孔形成的主要驱动力是反冲压力,在加热初期,激光主要用来加热金属基体,随着激光辐照时间的增加,熔池表面温度急剧升高,金属进而汽化,产生匙孔.针对304不锈钢的工艺试验表明计算结果与实际相符合.     

YAG laser welding with surface activating flux

YAG laser welding with surface activating flux has been investigated, and the influencing factors and mechanism are discussed. The results show that both surface activating flux and surface active element S have fantastic effects on the YAG laser weld shape, that is to obviously increase the weld penetration and D/W ratio in various welding conditions. The mechanism is thought to be the change of weld pool surface tension temperature coeffwient, thus, the change of fluid flow pattern in weld pool due to the flux.     

CO2激光-MAG电弧复合焊接保护气体的影响规律

保护气体是决定CO2激光-MAG(metal active gas)电弧复合焊接工艺稳定性、焊接熔深和接头质量的关键因素,但是相关的试验研究报道有限.对此,采用He-Ar和CO2-Ar混合气体在Q235钢板上进行了CO2激光-MAG电弧复合焊接工艺研究.结果表明,保护气体种类与配比对工艺和焊缝特征有明显的影响.He-Ar焊缝能够得到更大的焊接熔深和焊缝硬度.CO2-Ar中的CO2在高温下分解形成氧进入熔池后改变了表面张力系数,进而改变了熔池流动方向,导致在CO2≥30%后形成平整的焊缝余高,焊缝电弧区和激光区的过渡更加平滑.当CO2含量＞30%后,复合焊接工艺稳定性变差,焊缝硬度急剧降低.