CO2焊接熔池直接视觉图像传感研究

应用被动式视觉传感方法进行CO2焊焊接熔池的形状检测。为了消除弧光干扰并获得清晰的熔池图像,设计了由窄带滤光片、中性密度滤光片和普通焊接滤光片构成的复合滤光系统。基于CO2焊焊接弧光的光谱分布特征,首先确定了窄带滤光窗口机心波长为632．8nm。然后,通过实验确定了中性密度滤光片和普通焊接滤光片的规格,以及它们与窄带滤光片的最佳组合方式。图像检测实验结果表明,该复合滤光系统有效地消除了弧光干扰,获得了高质量的熔池图像。同时,对CO2焊焊接熔池的图像特征进行了初步分析,为进一步进行熔池图像处理和焊缝成型控制的研究奠定了基础。     

Macrostructural and microstructural features of 1 000 MPa grade TRIP steel joint by CO2 laser welding

Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity (TRIP) steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.     

Application of switch back welding to V groove MAG welding

The formation of stable back beads in a root pass weld during one side multi-layer welding is important to achieve high quality welded metal joints in MAG welding. The authors employed the switch back welding method for V groove joints without backing plates. In this switch back welding method, the torch moves forward and backward with an oscillation frequency of 2.5 Hz. In order to achieve this welding, personal computers control the conventional welding robot, the power source characteristic and the wire feeder unit. During the forward, the torch is weaving on the V groove gap without the weld pool. If the weaving width becomes wider than the proper width, the tip of the wire becomes high and a good back bead cannot be obtained. The weaving width is adjusted so as to get the proper width in the switch back welding. The suitability of the welding conditions for each root gap was verified by observation of the arc, the weld pool and the external appearance of back beads. A good back bead was obtained under V groove welding in 2–4 mm gap.     

TIG焊活性剂对焊缝成形的影响

活性化焊接（A－TIG焊）在90年代末期受到国外的高度重视，同传统的TIG焊（钨极惰性气体保护电弧焊）相比，在相同的规范下活性化焊接能够大幅度地提高生产率、降低生产成本。中针对不锈钢和钛合金材料，研究了在A－TIG焊中单一成分的活性剂和涂敷量对焊缝成形的影响。试验结果表明，与无活性剂的焊缝相比，活性剂CaF2,SiO2,NaF,Cr2O3和TiO3都能够有效地增加不锈钢和钛合金焊缝的 熔深，随着涂敷量的增加，焊缝熔深也相应的增加，熔宽减小。但涂敷有CaF2活性剂的不锈钢焊缝成形不好，涂敷有Cr2O3的钛合金焊缝正面熔宽没有明显的变化。在不锈钢焊接中，活性剂SiO2的作用效果最好；而钛合金的焊接中CaF2的作用效果最好。电弧收缩和熔池表面张力的变化是活性剂增加熔深的主要原因。     

外加横向磁场对高速GMAW焊缝成形的影响

对于高速熔化极气体保护焊接（GMAW）过程,当焊接速度超过临界值后,会出现驼峰焊道,焊缝成形变差.研究证明,熔池中动量很大的后向液体流是产生驼峰焊道的主要原因.研发了外加横向磁场发生装置,通过产生的电磁力来抑制后向液体流的动量,从而抑制驼峰焊道的形成.应用特斯拉计测试和考察了工件上磁感应强度大小及分布的影响因素.通过开展焊接工艺试验分析了不同强度的外加磁场作用下的焊缝成形规律.结果表明,外加横向磁场能明显调控熔池流态,有效抑制驼峰焊道和咬边等缺陷,显著改善焊缝成形,提高临界焊接速度.     

激光焊熔池图像三维形态恢复算法分析

利用熔池图像表面的明暗变化恢复熔池表面三维形态,分析熔高和熔宽等特征与焊接质量的关系.试验装置采用红外激光辅助光源和带有近红外窄带滤波组合系统的高速影像设备实时捕捉熔池动态图像,并根据统计学估计光源位置参数,采用基于单幅熔池灰度图像的明暗恢复形状技术(shape from shading,SFS)中的局部分析算法来恢复熔池三维表面形态,并通过中值滤波和三次样条插值对三维重建后熔池形状进行去噪和平滑处理.结果表明,所采用的方法能有效地恢复熔池表面信息,为大功率盘形激光焊接过程中根据熔池二维图像预测焊缝成形提供了一种方法.     

Mathematical analysis of the role of recoil pressure in weld pool dynamics during laser-MIG hybrid welding

A mathematical model was established to simulate the weld pool development and dynamic process in stationary laser-MIG hybrid welding. Surface tension and buoyancy were considered to calculate liquid metal flow patter, moreover, typical phenomena of MIG welding, such as filler droplets impinging weld pool, electromagnetic force in the weld pool, and typical phenomena of laser beam welding, such as recoil pressure, Inverse Bremsstrahlung absorption, Fresnel absorption were all considered in the model. The laser beam and arc couple effect were introduced into this model by the plasma width during hybrid welding. The role of recoil pressure in the weld formation was discussed. Transient weld pool shape and complicated liquid metal velocity distribution from two kinds weld pool to an unified weld pool were calculated. The simulated weld bead geometry with consideration recoil pressure was in good agreement with experimental measurement.     

高速TIG-MIG复合焊焊缝驼峰及咬边消除机理

搭建了TIG-MIG复合焊试验平台及电参数-高速图像同步采集系统,进行了一系列低碳钢高速TIG-MIG复合焊工艺试验,研究了高速TIG-MIG复合焊的电弧形态、熔滴过渡及熔池行为对焊缝成形的影响,并确定了合适的匹配参数.结果表明,MIG焊电流在240~300 A,且TIG焊电流与MIG焊电流相当时,TIG-MIG复合焊焊接过程稳定,即使在焊接速度高达2.5 m/min时,焊缝仍无驼峰、咬边等缺陷,与传统MIG焊相比,熔深增加,熔宽减小.TIG-MIG复合焊由于电弧间的相互作用,两电弧指向发生偏转,电弧压力减小,焊接过程不产生弧坑,且熔宽变窄,这是避免驼峰和咬边缺陷的主要原因.     

盘型激光焊接状态多传感信息融合分析

针对大功率盘型激光焊接状态,研究一种基于支持向量机的多传感信息融合分析方法. 使用紫外、可视和红外波段的两个高速摄像机同时获取激光焊接过程中金属蒸气、飞溅和熔池动态图像. 通过模式识别技术提取焊接过程多传感信息特征及进行数据主成分特征分析,并以焊缝宽度变化作为衡量焊接状态稳定性的参数. 运用支持向量机融合各特征,通过网格搜索和粒子群算法优化支持向量机参数,建立基于支持向量机的多传感信息融合模型. 结果表明,支持向量机多传感信息融合方法能够有效预测焊缝宽度变化趋势,为大功率盘型激光焊接状态的实时监控提供试验依据.     

三电极高速CO_2双边角焊质量及稳定性分析

对三电极高速CO2双边角焊焊接工艺进行研究,通过LabVIEW电信号采集与高速摄影分析了焊接质量及过程稳定性.结果表明,焊接中引导电流应为最大,且引导焊枪与中间焊枪之间电流差距100A左右可获得理想的焊缝成形,中间焊枪与跟随焊枪的电流差距大小对焊接质量无明显影响,且焊枪指向位置在底板为宜.在同一工艺时,随着焊接速度增大,焊接过程变得不稳定,同一焊接速度时,试验电流400/300/300A组合时焊接过程最稳定.大电流组合时,应增大焊丝之间距离以减小电弧之间的干扰.     

脉冲个数调频对铝合金双脉冲焊性能的影响

在保证焊接热输入不变情况下,利用同时改变强弱脉冲个数的方法实现双脉冲低频的调频,并基于直接的电信号波形、间接的焊缝宏观和微观金相对三组不同频率双脉冲和一组单脉冲进行焊缝质量比较.结果表明,双脉冲对熔池的搅拌作用使得焊缝质量优于单脉冲,同时随着双脉冲低频频率的变化,在调制频率3.8 Hz时接近熔池振荡频率,使振荡加强,焊缝热影响区减小,晶粒组织细化,焊接性能最好.     

焊丝自转式MAG焊焊接过程与接头组织分析

提出了通过焊丝自转搅动熔池进而细化焊缝组织的MAG焊接新方法.试验中采集了焊接过程电信号和熔池形态,分析了焊丝转速对低碳钢表面堆焊接头组织特征的影响.结果表明,焊丝自转可以增加短路过渡的频率,使焊接过程更稳定,熔滴过渡近似熵的计算也证明焊接过程的稳定性可以明显地提高.利用钨颗粒示踪技术可以发现焊丝自转能够显著增加熔池金属流动性,熔池宽度随着焊丝自转速度的改变先变大后变小,焊缝金相组织分析也证明熔池流动性的改变可以有效细化焊缝金属晶粒,减少联生结晶的生成.     

水下高压干式环境下压力及焊接参数对GMAW焊缝成形的影响

开展水下高压干法焊接试验研究,在焊接过程相对稳定的情况下,以环境压力、焊接电流、保护气成分、焊丝伸出长度为变量,探索其对于焊缝截面成形的影响规律. 采用正交试验方法,通过试验确定了焊缝熔深、熔宽及余高随上述变量的变化规律. 结果表明,随着环境压力增大,焊接飞溅增多,熔深增加,熔宽减小,余高增高;高压环境下,随着焊接电流增大,熔宽没有明显变化,熔深增加,余高略有增加;随着保护气中CO₂比例的增加,熔深减小,熔宽增加,余高变化不明显;随着焊丝伸出长度增加,熔深减小,熔宽增加,余高增加.     

MIG焊熔宽模糊控制系统

大双波长滤光片正面实时检测焊缝熔宽技术的基础上建立了焊缝熔宽模糊控制系统。本文对熔宽模糊控制器的结构以及模糊控制变量的选择进行了讨论,在此模糊控制系统中采用双输入单输出的模糊控制器模型,即采用迷惑宽的变化及其变化率作为模糊控制器的两输入量,采用焊接电流作为模糊控制器的输出量。本文给出了熔宽模糊控制系统结构图并详细介绍了熔宽模糊控制器的设计过程,根据用双波长滤光片正面实时检测焊缝熔宽技术得到的焊接电     

填丝脉冲GTAW熔池形状定义和图像处理

在填丝脉冲GTAW过程中,从熔池图像上可以观察到熔池形状的变化,如度、长度、后拖角和表面高度等。熟练焊工可以根据变化的情况实时地调整焊接规范,保证焊缝成形稳定,利用获得的焊接熔池图像,采用一定的熔池图像处理算法可以计算出熔池形状的特征参数,以满足过程建模和实时控制的要求。本针对填丝脉冲GTAW熔池形状变化的特点,提出了统一的熔池形状非线性拟合公式和熔池形状参数。设计了快速图像处理算法,满足在实际焊接过程中提取熔池形状参数的要求,试验结果证明,熔池形状非线性拟合公式准确,图像处理算法有效,为进一步焊接过程的建模和控制奠定基础。     

Control of weld composition when welding high strength aluminium alloy using the tandem process

Abstract

A new cost effective process for generating different weld element compositions has been examined. Utilising tandem welding technology, different series aluminium filler wires were mixed in a single weld pool with the result that the composition of the principal alloy elements, copper and magnesium were accurately controlled. Thermodynamic modelling was then used to predict an optimum weld bead composition for eliminating solidification cracking when welding Al2024. In order to validate the predicted target composition, the tandem process was used to control the composition of the weld bead. The presented results show that using this system to deposit a controlled ternary composition weld, solidification cracking was eliminated when welding highly constrained test pieces. In contrast, cracking was evident when using commercially available binary filler wires under the same conditions.     

Optimization and Prediction of Angular Distortion and Weldment Characteristics of TIG Square Butt Joints

Autogenous arc welds with minimum upper weld bead depression and lower weld bead bulging are desired as such welds do not require a second welding pass for filling up the upper bead depressions (UBDs) and characterized with minimum angular distortion. The present paper describes optimization and prediction of angular distortion and weldment characteristics such as upper weld bead depression and lower weld bead bulging of TIG-welded structural steel square butt joints. Full factorial design of experiment was utilized for selecting the combinations of welding process parameter to produce the square butts. A mathematical model was developed to establish the relationship between TIG welding process parameters and responses such as upper bead width, lower bead width, UBD, lower bead height (bulging), weld cross-sectional area, and angular distortions. The optimal welding condition to minimize UBD and lower bead bulging of the TIG butt joints was identified.     

脉冲熔化极气体保护焊熔池的视觉传感与实时控制

研究对脉冲熔化极气体保护焊（GMAW）熔池过程采用视觉传感与实时控制方法的可行性问题。由于GMAW过程的熔滴过渡现象的复杂性，尝试模拟焊工通过观察熔池变化等因素来调整焊接参数获取满意的焊缝成形的行为。建立了脉冲GMAW过程熔池视觉传感系统，宏观上将熔滴过渡对熔池特征的影响作为黑箱过程处理，根据脉冲GMAW弧光光谱分布和熔池图像特征提取，实现对脉冲GMAW熔池动态过程的实时检测。采用辨识算法建立焊接动态过程的数学模型，进而设计脉冲GMAW熔宽的PID控制器，实现对脉冲GMAW熔池宽度的实时控制。试验表明，建立的视觉传感系统、图像处理算法以及控制器设计检测与控制熔池变化在一定程度上的能够满足脉冲GMAW焊缝宽度的实时性与精度要求。     

Decoupling control scheme for pulsed GMAW process of aluminum

A double-variable decoupling control scheme was proposed for GMAW-P process of aluminum helping to efficiently develop welding procedure. Weld pool width and arc length were both measured through vision sensing in welding process. Weld bead shape was improved by changing the current waveforms to adjust the heat input while the arc length was controlled to stabilize the welding process. An experimental system was developed to sense, observe and control the welding process real-timely. Experiments were conducted to verify the effectiveness of the scheme. The results show that good weld bead shape and stable welding process can be obtained through the double-variable decoupling control scheme without complex metal transfer control and considerable trial and error to identify suitable combinations of welding parameters in GMAW-P. This control scheme provides an alternative to obtain proper weld quality for GMAW-P.     

Influence of process variables on weld bead quality in two wire tandem submerged arc welding of HSLA steel

Two-wire tandem submerged arc welding process involves simultaneous depositions from two electrode wires with the leading wire usually connected to a DC power source and the trailing wire connected to a pulsed AC power source. The weld bead profile and mechanical properties in the tandem submerged welding are significantly affected by the leading and trailing wire current transients and the welding speed. We present here a detailed experimental study on the influence of leading wire current, trailing wire current pulses, and welding speed on the weld bead dimensions and mechanical properties in single-pass tandem submerged welding of a typical HSLA steel. It is realized that the weld bead penetration is primarily influenced by the leading wire current while the weld bead width and the reinforcement height are sensitive to the trailing wire current pulses. Greater magnitude of trailing wire current pulses and shorter negative pulse duration increase the weld pool volume leading to reduced cooling rate and poor mechanical properties as the formation of the strengthening phases like acicular ferrite is inhibited. In contrast, increase in welding speed reduces the rate of heat input thereby enhancing the cooling rate and the weld bead mechanical properties. A set of empirical relations are developed to estimate the weld bead dimensions and mechanical properties as function of the welding conditions. The predictions from the empirical relations and the corresponding measured results are observed to be in fair agreement.