一种激光热传导钎焊的热源模型

根据熔池具有较小深宽比的特征,发展了一种适合于铍板激光热传导钎焊的热源模型.分别建立了由表面高斯热源和内部旋转体积热源,按不同比例构成的复合热源、指数旋转抛物线体热源和线性旋转抛物线体热源三种模型.利用这三种模型计算了同一焊接条件下起焊点前2 mm处一点的焊接热循环曲线和熔池横断面轮廓,并进行了试验验证.目前的研究中用...     

全位置管道焊接的纯滞后激光视觉跟踪技术

在机器人视觉引导中,激光线投射位置往往与焊枪头位置存在一定的偏差值,导致在焊缝形状多变的情况下实时纠偏精度较低。因此,提出一种基于Smith预估控制模型的纠偏方法。首先,以形态学中的skeleton和矩形开运算为核心算法提取出焊缝中心点。然后,根据焊缝中心点计算出纠偏量,将纠偏量按顺序存入容器中,采用Smith原理构建的数学模型对存储的数据进行处理。最后,使用处理后的数据逐点进行滞后纠偏。数据仿真和实际测试结果表明:实际纠偏精度在0. 35 mm以内,满足工程焊接对纠偏精度的要求,具有很强的实用性。     

基于点热源的GMAW热输入分布模式及应用

分析比较了三种基于点热源的熔化极气体保护焊(GMAW)热输入分布模式,并结合移动点热源作用下焊接温度场的瞬态解分别对其进行了计算,通过焊缝横截面熔合线几何形状计算值与实测值的比较,对三种热输入分布模式进行了评估.利用所建串热源模型模拟了Q195低碳钢和JG590低合金钢GMAW焊缝横截面熔合线的几何形状,进行了Q195钢和JG590钢的GMAW工艺试验,通过焊缝横截面熔合线的几何形状对所建模型进行了试验验证.采用计算和试验相结合的方法,分析评价了目前常用的t3/5计算公式,利用JG590钢焊接温度场的计算结果,结合JG590钢的焊接连续冷却组织转变图,成功地预测了焊接接头熔合区的组织及硬度.     

3D finite element modeling of the thermally induced residual stress in the hybrid laser/arc welding of lap joint

In this study, a three-dimensional (3D) finite element model is developed to investigate thermally induced stress field during hybrid laser–gas tungsten arc welding (GTAW) process. In the hybrid welding case, we focus on the GTAW process sharing common molten pool with laser beam and playing an augment role in the hybrid welding system. An experiment-based thermal analysis is performed to obtain the temperature history, which then is applied to the mechanical (stress) analysis. A modified material model is used to consider the influence of face-to-face contact between the top and bottom metal sheets in the thermo-mechanical analysis of welding lap joints. Results show that the normal stress components prevail in the weld zone during hybrid welding process, and maximum thermal stress exceeding the yield point of material exists at the heat affected zone (HAZ) near the weld pool. Increasing the welding speed causes the penetration and width of weld bead to decrease, and the thermal stress concentration at the welded joint is also reduced accordingly. After welding and cooling down, longitudinal tensile stress (SZ) and transverse compressive stress (SX) are retained in the formed weld, and the higher longitudinal compressive stress exists around the weld bead. In addition, a series of experiments are performed to validate the numerical results, and a qualitative agreement is achieved. Compared to the welded joint obtained by GTAW and laser welding alone, the residual stress concentration in the weld joint obtained by hybrid laser–GTAW is the minimal one.     

高能束焊接数值模拟可变新型热源模型的建立

基于电子束等高能束焊接熔池非旋转对称性以及深宽比较大的"钉头"焊缝特征,为更好地模拟焊缝形状,提高焊接模拟计算精度,建立了一带拐点的形状可变的双椭圆衰减体热源模型;新型热源模型形状的可转化性使其具有了可同时用于高能束焊接和一般焊接的通用性;模型建立过程中,对其前后能量的分布给出了明确的函数表达式,利用有限元分析软件对比分析了新型热源模型和其它几种热源模型的温度场的模拟结果,验证了其熔池形态的合理性及该热源的可扩展性.     

温度对焊接热模拟X80管线钢断裂韧性的影响

通过试验和3D有限元模拟相结合的方法分析了焊接热模拟X80管线钢在不同温度（-90,-60,-30和0℃）下的断裂韧度.文中选取标准三点弯曲试样在不同温度下进行断裂韧度测试,同时对测试件进行三维有限元实体建模与分析计算.结果表明,X80管线钢的断裂韧性随温度减低显著减小,并使其倾向于脆性断裂.材料在不同温度下的真实应力-应变曲线行为从光滑拉伸到断裂力学试样具有良好的可传递性,温度对材料的硬化行为没有明显影响,有限元计算的结果表明,应用该方法可以准确地计算X80钢焊接热影响区不同温度下的CTOD值.     

Analytical studies on thermal behaviour and geometry of weld pool in pulsed current gas metal arc welding

In view of the criticality of pulsed current gas metal arc welding (P-GMAW) due to simultaneous influence of the pulse parameters on thermal and metal transfer behaviour of the process an analytical model has been developed for predicting the temperature and geometry of the weld pool by appropriately considering two types of heat sources of different nature. The model considers the impact of heat in droplets of filler metal depositing in the weld pool in addition to initial arc heating. The model assumes the primary heat transfer to weld pool is the initial arc heating considered as continuous heat source (arc heat source) of double ellipsoidal nature followed by deposition of superheated filler metal considered as point heat source of interrupted nature superimposed on the first one. The dissimilar nature of the two heat sources is treated by different analytical techniques to estimate their temperature distribution in weld pool and HAZ at its vicinity. The geometry of the weld pool has been estimated by evaluation of the weld isotherms causing melting of the base metal under the influence of two heat sources acting on the weld pool. The impact of impinging droplets on weld pool has been considered to determine the depth at which the droplets transfer their heat in it. The predicted temperature and geometry of the weld pool as well as the temperature of HAZ are found well in agreement to the experimental values with a deviation of the order of ±10% in case of the weld deposition of Al–Mg alloy and commercial aluminium especially at high mean current of the order of 180 A and beyond the transition current of the filler wire. However, prediction of weld pool temperature and weld geometry is relatively different at comparatively lower mean current of 150 A below the transient current of the filler wires is not up to the mark.     

焊缝表面缺陷激光扫描三维重构测量

为检测工件焊缝表面缺陷,采用点激光位移传感测距法和数据拟合技术进行焊缝表面缺陷检测试验研究. 首先采集缺陷表面轮廓数据点,利用高斯滤波对原始数据降噪处理. 再对处理后的数据点进行Delaunay三角剖分,使散乱点连接并结合其空间坐标重构出缺陷的三维模型. 结果表明,基于点激光位移传感测距技术及焊缝表面缺陷三维重构方法可以准确判断焊缝成形情况.     

熔池图像质心算法的焊缝位置测量模型

建立了一种基于熔池图像质心的焊缝位置测量模型,通过视觉传感器获取焊接区熔池图像,选择熔池前端为处理区域,对该区域进行中值滤波与图像灰度变换,并计算该区域的熔池图像质心值及相对应的焊缝偏差.在不同的焊接条件下,获取多组熔池图像及对应的样本数据,应用最小二乘法建立熔池图像质心与焊缝偏差之间的关系,得到基于熔池图像质心的焊缝位置测量数学表达式.在此基础上,通过分析比较各数学表达式之间的关系,建立焊缝位置测量数学模型.计算机仿真及焊接工艺试验结果表明,该模型可有效地检测焊缝位置.     

Remanufacturing Shaping System Based on Pulsed Plasma Arc Welding

Based on the pulsed plasma arc welding(PPAW),a rapid remanufacturing shaping system,including a structured light scanning reverse engineering(RE)system,a robot system and a PPAW source system have been developed.The new rapid remanufacturing shaping system can rapidly and accurately repair the worn parts with different damaged degrees and thus extend their life cycle.In the present paper,the whole process of repairing worn parts is described.Firstly,the scanning model of a worn part is obtained by using RE system based on reconstructing approach.Compared with standard CAD model in the undamaged setting,the surface profile and the extent of damage area are obtained.Secondly,the weld repair path is designed by slicing the point cloud model of damage area.This path consists of multilayer parallel lines that produce parallel overlapped weld beads which cover the damaged area.By off-line programming techniques,the robot executable program as document format is transmitted to the robot controller for repairing worn parts.Finally,the weld repair experiments on worn steel plane plate and damaged column are performed to evaluate the remanufacturing system.     

基于改进GWO-GRNN的管道焊缝三维重构测量

为提高双目相机不同位姿下焊缝的三维重构测量精度,提出一种基于立体视觉图像误差补偿的管道焊缝三维重构测量方法。采用改进灰狼算法(IGWO)优化广义回归神经网络(GRNN)补偿焊缝三维重构图像点的坐标误差。采用混沌映射、非线性收敛因子和最优记忆保存思想对GWO算法进行改进,通过8个标准测试函数进行仿真验证;利用优化后的GRNN模型对图像点坐标误差进行预测和补偿,计算三维坐标重构出焊缝点云,三维测量焊缝的焊宽、余高和长度。试验结果表明：该模型在双目相机不同的位姿状态下都能较准确地实现焊缝的三维重构,焊缝的三维测量相对误差在0.9%以内。     

A theoretical and experimental analysis of variances in weld bead morphologies

Predictable and reproducible weld bead morphologies and dimensions are a major concern in welding. In bead-on-plate welding, the heat flow is controlled by the heat source parameters (power, speed, and radius) and the physical properties and dimensions of the workpiece, especially its thickness. Complex models that account for weld pool circulation have been developed to quantify welds. However, to some extent, fluctuations in weld dimensions can be explained with conduction models of moving Gaussian heat sources. In early investigations with point and line heat sources, relationships between process parameters and plate thickness were derived to differentiate between two- and three-dimensional heat flow. To date, the heat source radius (R) has not been taken into account. The dimensionless ratio (D*) of the plate thickness (D) to the heat source radius (R) is actually a variable to consider. With the introduction of additional dimensionless parameters (*)—speed (v*), power(q*)— relationships among governing variables, heat flow dimension, and weld bead dimensional fluctuations can be derived. Weld bead fluctuations are found to depend on dimensionless variables (v*, q*, D* ) and occur when the heat flow dimension is intermediate between two- and three-dimensional. Occasionally, experimental data exhibit trends that differ from predictions. This article presents a dimensionless version of a heat flow model and discusses the discrepancies between experimental and theoretical results. Formerly with ECN.     

焊缝偏差RBF神经网络预测算法

以10 kW大功率光纤激光焊接304奥氏体不锈钢板为试验对象,研究一种焊缝偏差预测算法.利用红外摄像机摄取焊接过程中的熔池红外图像,提取匙孔质心、匙孔形状参数和热堆积效应参数等反映激光束与焊缝位置偏差的特征量作为径向基函数RBF神经网络预测模型的输入量,建立焊缝偏差RBF神经网络预测模型.选择焊缝偏差特征量作为训练样本并对预测模型进行训练,建立焊缝偏差预测模型.结果表明,该模型能够对大功率光纤激光焊接过程中的激光束与焊缝位置之间的偏差进行有效预测.     

用于焊缝检测的比色图像偏心算法

提出了基于焊接比色图像偏心的概念并给出计算公式.从比色图像信号强度与焊接区域发射率、光谱辐射强度等的关系、比色值与焊接温度场及比色系统波长的关系以及比色图像偏心计算公式出发,分析了比色图像比色值分布对称性,推导并建立了焊接比色图像偏心与焊接区温度的函数值、焊缝中心与电弧中心偏差间关系模型.研究了以比色图像偏心作为检测对象的优异特性,给出了模型在某一焊接工艺参数条件下的数值解,发现模型的输出与输入有很好的线性关系.仿真试验证明以比色图像偏心可以代替焊缝中心偏差,为进一步研究比色图像偏心算法的实际应用打下理论基础.     

大功率光纤激光焊熔透状态模糊聚类识别方法

熔透是评价激光焊接质量的重要因素,但在焊接过程中难以直接检测熔透状态.以大功率光纤激光焊接304不锈钢紧密对接焊缝为试验对象,研究一种基于熔池红外热像的熔透状态识别方法.采用红外摄像机摄取焊接区域熔池动态图像,提取熔池特征量,应用模糊聚类算法分析熔池特征量与熔透状态之间的关系,使用模糊C-均值（FCM）和Gustafson-Kessel（GK）两种模糊聚类法建立熔透状态识别模型.激光焊接试验结果表明,熔池表征与熔透状态之间存在密切关联,通过GK模糊聚类算法建立的模型对熔透状态能达到78%以上的识别率,为大功率光纤激光焊接过程熔透状态的识别和控制提供试验依据.     

9%Cr钢厚壁管道局部焊后热处理温度场的数值模拟

基于热源追踪法开发了一个能够根据控温点温度自动调整热输入的有限元程序. 使用该程序模拟了9%Cr钢管道的局部焊后热处理温度场分布,并进行了试验验证. 结果表明,模拟结果与试验结果吻合良好. 热处理温度场沿管道轴向呈近似抛物线状分布,沿径向呈近似线性分布. 距焊缝中心两倍壁厚范围内,管道内外壁温差均约为17~18 ℃. 按照目前国内焊后热处理规程推荐的参数进行热处理,均温区宽度能够满足要求,可以保证整个接头的热处理效果. 根据温度场分布,还确定了与管道内壁焊缝中心温度相同的外壁等效点位置,以监测热处理过程中管道内壁温度的变化.     

LF6铝合金薄板平面内环焊缝焊接应力与变形的数值模拟

从力学角度出发,以LF6铝合金薄板平面内环焊缝的焊接为例,对其焊接残余应力和变形的特点进行了探讨。采用非线性有限元技术,对常规焊接条件下温度场和应力场进行了模拟,结合弹性稳定性理论对环焊缝焊接产生的特殊变形规律进行了研究。数值模拟结果表明,在环焊缝焊接过程中形成了与常规对接焊完全不同的焊接热循环过程,残余应力状态复杂;焊缝外侧的压应力超过了失稳变形极限,造成了铝合金薄板的失稳变形。     

大截面铸铝-铸钢摩擦焊接接头显微分析

采用连续驱动摩擦焊技术对大截面铸铝与铸钢异种金属进行了焊接试验,通过电子探针、透射电镜、X射线衍射分析及微区硬度测试,进行了铸铝与铸钢异种金属焊接接头的显微分析.结果表明,大截面铸铝与铸钢间具有良好的摩擦焊接性;主要元素以界面为起点向对偶面扩散,Fe原子扩散距离稍小于Al原子的扩散距离;次生摩擦面对碳诱导形成碳化物;在焊缝区,既存在晶体,又存在非晶;接头焊合区两侧硬度均略高于基材.     

钛合金焊接气孔形成机理的研究

本文研究了焊前清理和处理对气孔形成的影响,进行了改变焊接速度和氩弧点焊试验以观察熔池存在时间对气孔形成的影响。用扫描电镜对带气孔焊缝断面和气孔内表面进行观察,发现多数气孔内表面上有直径约1μ的微气泡和个别固体质点。分析了气孔的形成过程,根据前人的工作和我们的工作发展了气孔形成的“气孔核”观点,认为上述微气泡和固体质点起到“气孔核”作用,其中以微气泡的怍用为主。把气孔分为熔合线气孔和焊缝中部气孔,讨论了两类气孔形成过程的差别。焊前清理和热处理减少气孔是由于减少了“气孔核”的结果。上述观点完满地解释了前人难以解释的现象。     

基于RANSAC和卡尔曼滤波的窄焊缝识别北大核心

针对高效鲁棒的焊缝识别对于提高焊接质量和效率具有重要的作用,提出了一种基于线结构光的薄壁件窄焊缝快速识别方法。首先,对激光照射的焊缝图像进行去噪和增强;其次,分别利用Ransac算法和最小二乘法对焊缝和激光条纹进行直线拟合;接着,以二直线交点为中心建立ROI,连接ROI中的连通体获得修正后的交点;最后,对修正后的交点加以平移,以斜率为状态变量进行卡尔曼滤波,以修正后的交点为中心建立ROI并计算ROI中各点斜率,寻找具有最接近滤波后的斜率的点,将其反向平移后的坐标作为交点的最终值。实验证明该算法具有较高的鲁棒性和较快的处理速度,可满足窄焊缝的实时识别需求。