Experimental Study on Metal Transfer and Welding Spatter Characteristics of Cellulose Electrode

Welding spatter cause many problems during the welding process and this issue is particularly important for cellulose electrode welding. The hot flying spatter balls often deteriorate the working environment, and decrease the welding efficiency. Many factors affect the welding spatter, and metal transfer behavior is one of the main factors. Many studies concerning the spatter mechanism in arc welding process were made; most of them focused on the solid wire welding and the study on cellulose electrode is rarely reported. In this paper the metal transfer behavior and the weld spatter characteristics of three commercial cellulose electrodes were studied experimentally by using a high speed camera for visually capturing the metal transfer. The relationship between the metal transfer and the welding spatter was analyzed experimentally by comparing the spatter loss coefficient, which is for quantitative evaluation of welding spatter, with the statistical analysis of the large droplet transfer mode. The results showed that short circuiting transfer, large droplet spray transfer, fine droplet spray transfer and explosive transfer govern the metal transfer modes in cellulose electrode welding. Weld spatter occurred mainly in the deflection of large droplet process, explosive transfer process and fine droplet spraying process. Different metal transfer modes lead to different spatter. The deflection of large droplet and explosive transfer are the main factors of the spatter formation. Minimizing the droplet size and reducing the deflection of large droplet and explosive transfer leads to the reduction the amount of spatter in cellulose electrode welding.

Effects of current waveform parameters during droplet transfer on spatter in high speed waveform controlled Short-circuiting GMAW

Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.

Welding Polarity Effects on Weld Spatters and Bead Geometry of Hyperbaric Dry GMAW

Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a hyperbaric dry welding experiment system, gas metal arc welding（GMAW） experiments with direct current electrode positive（DCEP） and direct current electrode negative（DCEN） operations are carried out under the ambient pressures of 0.1 MPa, 0.4 MPa, 0.7 MPa and 1.0 MPa to find the influence rule of different welding polarities on welding spatters and weld bead geometry. The effects of welding polarities on the weld bead geometry such as the reinforcement, the weld width and the penetration are discussed. The experimental results show that the welding spatters gradually grow in quantity and size for GMAW with DCEP, while GMAW with DCEN can produce fewer spatters comparatively with the increase of the ambient pressure. Compared with DCEP, the welding current and arc voltage waveforms for DCEN is more stable and the distribution of welding current probability density for DCEN is more concentrated under the hyperbaric environment. When the ambient pressure is increased from 0.1 MPa to 1.0 MPa, the effects of welding polarities on the reinforcement, the weld width and the penetration are as follows： an increase of 0.8 mm for the weld reinforcement is produced by GMAW with DCEN and 1.3 mm by GMAW with DCEP, a decrease of 7.2 mm for the weld width is produced by DCEN and 6.1 mm by DCEP; and an increase of 3.9 mm for the penetration is produced by DCEN and 1.9 mm by DCEP. The proposed research indicates that the desirable stability in the welding procedure can be achieved by GMAW with DCEN operation under the hyperbaric environment.

Investigation into Spatter Particles and Their Effect on the Formation Quality During Selective Laser Melting Processes

During the selective laser melting process,a high-energy laser beam acts on the powder,a molten pool is rapidly generated and the characteristic parameters are constantly changing.Among them,temperature is one of the important parameters in the forming process.Due to the generation of splash particles,there will be defects in the microstructure,which will seriously affect the formation quality of the prepared parts.Therefore,it is necessary to study the relationships between the splash behavior,molten pool characteristics and product quality.The finite element simulation of the transient temperature field was performed by ANSYS software.Time-series images at different frame rates were obtained with a high-speed camera,and the dynamic process of splashing was observed.Using IN718 alloy powder,the influence of the laser energy density on the light intensity of the molten pool was studied.The appearance of splash particles and the deviation of the powder chemical elements caused by the splash were analyzed.The results show that the transient temperature field with drastic change is easy to cause spatter,which is consistent with the experimental results.There are large differences in the splash at different shooting frame rates.Increasing the frame rate can allow the observation of details such as the shape,size and number of splash particles,which is beneficial for studying the process of splash formation.At the moment when the splash occurs,the light intensity of the molten pool always first increases and then decreases,depending on the energy input.The higher the energy input is,the more intense the light intensity of the molten pool and the higher the peak interval distribution.Compared with fresh powder,the contents of Al and Ti in powder reused 5 times were reduced by 0.15%and 0.02%,respectively.The increases of these two elements in the splash were 16.18%and 29.62%,respectively,and the content of Nb even exceeded the standard range.When the energy density decreased from 229.17 J/mm3 to 130.95 J/mm3,the relative density of the part increased from 91.82%to 99.83%.This shows that reducing the energy input can reduce the splash to suppress the generation of defects,along with the weakening of the overall light intensity of the molten pool.These results can provide a basis for feature extraction of the molten pool,which is of great significance for real-time monitoring and online control in manufacturing processes and ensuring product quality.

Elucidation of Metallic Plume and Spatter Characteristics Based on SVM During High-Power Disk Laser Welding

During deep penetration laser welding,there exist plume（weak plasma） and spatters,which are the results of weld material ejection due to strong laser heating.The characteristics of plume and spatters are related to welding stability and quality.Characteristics of metallic plume and spatters were investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW.An ultraviolet and visible sensitive high-speed camera was used to capture the metallic plume and spatter images.Plume area,laser beam path through the plume,swing angle,distance between laser beam focus and plume image centroid,abscissa of plume centroid and spatter numbers are defined as eigenvalues,and the weld bead width was used as a characteristic parameter that reflected welding stability.Welding status was distinguished by SVM（support vector machine） after data normalization and characteristic analysis.Also,PCA（principal components analysis） feature extraction was used to reduce the dimensions of feature space,and PSO（particle swarm optimization） was used to optimize the parameters of SVM.Finally a classification model based on SVM was established to estimate the weld bead width and welding stability.Experimental results show that the established algorithm based on SVM could effectively distinguish the variation of weld bead width,thus providing an experimental example of monitoring high-power disk laser welding quality.

考虑雨强贡献的大型水电站枢纽泄洪雾化影响规律分析

泄洪雾化对两岸边坡的影响一直是水电枢纽长期运行安全关注的重大问题。针对西南水电站枢纽泄洪雾化影响问题,采用随机喷溅数学模型分析了雾化影响规律,并对该模型求解方法进行了改进,在综合考虑复杂地形、水舌风、自然风及水滴飞行过程等因素的同时,以西南地区GS水电站为依托,对不同泄洪工况下的雾化降雨进行预测。结果表明,泄洪方式、地形及自然风在大型水电站雾雨区分布形态中起主导作用。GS水电站不同工况下雾化降雨呈现沿河谷两岸边坡竖向爬升的趋势,暴雨区沿左岸最高扩散至2236 m高程,右岸扩散至2188 m高程,最大纵向长度为815 m,暴雨中心雨强达600~1000 mm/h。研究成果为未来窄河谷、大规模水电站工程泄洪出口处的雾化影响分析提供了参考依据。

高功率激光-MAG复合焊接成形稳定性

采用激光-MAG(Metal active gas arc welding)复合焊接工艺,以焊缝表面成形、焊缝纵截面形貌和熔深波动程度为工艺稳定性评价依据,借助高速摄像系统和图像处理方法,对焊接过程中飞溅和等离子体两种关键过程信息进行特征识别和定量化表征,系统地研究激光功率从5 kW提高到30 kW时,焊接过程关键特征信息与焊接过程稳定性之间的关系。结果表明,随着激光功率的增加,焊缝表面成形出现周期性“上凸-下凹”现象,焊缝内部裂纹和熔深变化特征也随之周期性变化;等离子体面积和飞溅面积均随激光功率的提高呈增加趋势,且两者波动程度和熔深波动程度均呈正相关;等离子体面积增加会导致激光传输过程中能量衰减程度的加剧,使焊缝熔深增加趋势逐渐变缓,其波动程度是影响焊接过程稳定性的关键因素之一。

高温果汁真空冷却特性

为减小真空冷却中液体飞溅并研究不同条件对降温速率的影响,采用控制变量法,通过改变容器的形状、顶部材料与孔径大小、物料的相对装载量、不同初始温度和冷却终温等条件,测定果汁降温过程的质量和温度变化,根据测试结果计算出不同变量下的无效失水率和降温速率。研究表明,降温速率大且无效失水量小的最佳工艺条件为使用相对装载量23.3%、容器顶盖材料为刚性材料、孔径5 mm的长方形容器,由初始温度80℃降至冷却终温为25℃,此时的无效失水率最小,降温速率最快。

A detection algorithm of spatter on welding plate surface based on machine vision

Welding spatter seriously affects the surface quality of the product. Aiming at the automatic detection problem of spatter on welding plate surface, an in-situ detection algorithm of welding spatter based on machine vision is designed. In the extraction process of the welding spatter, the two-dimensional Fourier transform is adopted to obtain the frequency and phase information of image, and the elliptical high-pass filter is introduced to filter the low-frequency signal. The experimental results show that the proposed algorithm has higher extraction rate and extraction accuracy rate of welding spatter than the threshold method, the rectangular high-pass filter and the Canny operator, and it has the characteristics of high efficiency, high precision, and good robustness.

波形控制CO_(2)焊电源电路结构仿真研究

短路过渡型CO_(2)弧焊系统在焊接过程中易产生飞溅,这主要是焊接过程中电弧能量不稳定和熔滴过渡状态不理想所致。为解决这一问题,从弧焊系统主电路结构出发,构建了全逆变和后级加入斩波两种不同控制方式的数学模型。在一定假设条件下,使用MATLAB中的Simulink模块建立两种控制方式的仿真模型,并对两种主电路结构下的输出波形进行对比分析。结果表明,后级加入斩波控制的主电路结构能更有效地满足CO_(2)焊短路过渡低飞溅的需求。这种控制方式能够通过调节电弧能量和熔滴过渡状态,降低焊接过程中的飞溅,提高焊接质量。此外仿真结果还显示,后级加入斩波控制的主电路结构在降低飞溅的同时,还能够有效改善焊接过程的稳定性,提高焊接效率。这对于优化CO_(2)弧焊系统的控制方式和提高焊接质量具有重要的理论意义和实际应用价值。

BDa水电站泄洪雾化数学模型研究

挑流泄洪雾化可能对两岸边坡稳定、交通安全和厂房的安全运行等产生不利影响。采用水滴随机喷溅数学模型,对BDa水电站在无自然风和汛期最不利自然风2种情况下3种典型泄洪工况的雾化影响范围和降雨强度分布进行了分析模拟。研究结果表明,泄洪雾雨受地形影响较大,横向扩散较弱,主要沿边坡爬升,雨强等值线集中;汛期最不利自然风使得雾雨影响范围向左岸偏移,泄洪雾化对左岸山坡的影响大于右岸;泄洪雾化暴雨区范围集中在坝轴线下游195~645 m,横向左岸3 017 m高程、右岸2 988 m高程以下。

Spatter Rate Estimation of GMAW-S based on Partial Least Square Regression

This paper analyzes the drop transfer process in gas metal arc welding in short-circuit transfer mode(GMAW-S) in order to develop an optimized spatter rate model that can be used on line.According to thermodynamic characters and practical behavior, a complete arcing process is divided into three sub-processes:arc re-ignition, energy output and shorting preparation.Shorting process is then divided as drop spread, bridge sustention and bridge destabilization.Nine process variables and their distribution are analyzed based on welding experiments with high-speed photos and synchronous current and voltage signals.Method of variation coefficient is used to reflect process consistency and to design characteristic parameters.Partial least square regression(PLSR) is utilized to set up spatter rate model because of severe correlativity among the above characteristic parameters.PLSR is a new multivariate statistical analysis method, in which regression modeling, data simplification and relativity analysis are included in a single algorithm.Experiment results show that the regression equation based on PLSR is effiective for on-line predicting spatter rate of its corresponding welding condition.

焊丝成分对高氮钢CMT+P焊工艺性的影响

为提升高氮钢焊接质量和优化焊接工艺,研究焊丝氮、锰含量带来的焊接工艺稳定性。采用冷金属过渡加脉冲(Cold Metal Transfer plus Pulse,CMT+P)焊技术对5种高氮钢焊丝进行焊接试验,研究焊丝成分对电信号、熔滴过渡、飞溅率的影响。研究结果表明:氮含量的增加会引起电信号波动变大且分布离散,而锰含量的变化对电信号的影响较小,焊丝中氮含量对高氮钢CMT+P焊接稳定性影响大于锰含量的影响;随着氮含量的增加,熔滴过渡模式由一脉一滴转变为多脉一滴,熔滴形状不规律且尺寸变大,焊丝工艺性变差;当焊丝中氮、锰含量较小,分别为0.42%、7.19%时,焊接工艺稳定性较好;氮逸出、锰蒸发导致高氮钢熔滴剧烈爆炸产生大量飞溅,焊接飞溅率随着氮、锰含量的增加而不断增大。

电弧状态对铝合金激光-电弧复合焊接工艺过程稳定性的影响

焊接过程稳定性是决定焊缝质量的重要因素,而焊接飞溅和焊缝表面形貌是焊接过程稳定性的直接体现。为了得到稳定的铝合金激光-MIG电弧复合焊接过程,本研究采用高速摄影的方法统计焊接飞溅数量,并分析焊缝表面成形质量,对焊接过程稳定性进行了综合定性评价,结合激光焊接与电弧焊接基本原理,探讨了减少飞溅、稳定焊接过程的原理。在本试验条件下,提高纯Ar保护气的流量、电弧弧长和光丝间距,降低电弧电磁收缩力,可以减少飞溅数量。复合焊接飞溅数量减少的主要原因可以归结为两点:激光对熔池的预热作用扩大了熔池前端的面积,使熔滴融入熔池的过程更平稳;工艺优化使电弧对熔滴的作用力保持在合理范围。相关结果为复合焊接稳定的工业应用奠定了工艺基础,指明了工艺优化方向。

15%SiC_(p)/Al复合材料电阻点焊接头组织形貌及焊接飞溅研究

研究了15%SiC_(p)/Al复合材料直接点焊和添加不锈钢片夹层点焊接头的组织差异。对接头显微组织、拉伸剪切断口和焊接飞溅的产生机理进行分析。结果表明:直接点焊接头熔核区出现了SiC颗粒的偏聚现象。在复合材料和电极间添加0.12 mm不锈钢片夹层焊接时,点焊接头熔核区SiC颗粒分布均匀,焊缝区结合致密、无气孔、夹杂和裂纹缺陷;点焊接头撕裂开后的焊点断口呈纽扣型断裂,接头成型良好。焊接工艺参数选择不当时,焊缝液态金属发生明显外溢,出现焊接飞溅。

附加纵向同步磁场下CO_(2)气体保护焊对熔滴飞溅的影响

CO_(2)气体保护焊接工艺具有高效、低成本的优势,被广泛应用于工业生产中。但是CO_(2)气体保护焊接工艺因存在飞溅大、焊缝成形差的问题限制其进一步发展。通过在焊接过程中施加不同参数的同步磁场,利用高速摄像装置对熔滴过渡过程中重要指标参数进行测量分析及参数优选。结果表明:施加纵向同步磁场,当磁场电流控制在2 A和频率2 kHz时,短路时间可达0.65 ms;通过改变磁场参数有效控制焊接飞溅率。在最佳磁场参数2.5 A、70 Hz下,焊接飞溅率最低可达2.68%,表明外加纵向同步磁场能有效控制熔滴过渡短路时间、燃弧时间,并改变熔滴形态,对改善CO_(2)气体保护焊接工艺起到可控作用。

ER70S-6盘条断丝及焊接飞溅原因探讨

通过对气保焊丝用钢ER70S-6盘条用户跟踪及用户交流,就用户反映焊丝钢盘条拉拔断丝及焊接飞溅进行研究,提出焊接用钢盘条ER70S-6改进措施,提高焊接用钢ER70S-6盘条质量。

车身制造中电阻点焊飞溅产生的原因及控制方法

目前国内外白车身焊接广泛采用电阻点焊工艺进行焊接,但电阻点焊过程中受到焊接打点位置、角度、母材板间隙、电极和焊接参数等因素影响,不可避免地会产生大量焊接飞溅,尤其近年来车身镀锌板、高强度钢板的使用,导致飞溅问题尤为严重。通过对点焊飞溅产生的原因进行分析,找出白车身焊接过程中产生飞溅的影响因素,并结合生产实际情况提出相应的控制方法,从而降低了飞溅的发生概率,提高了车身焊接品质。

钢/铝线冲击焊电流参数对引弧和飞溅的影响

利用精密高频逆变冲击焊机进行了钢/铝异种金属线对接冲击焊试验,采集焊接过程的电流信号,并使用高速摄像技术对引弧过程和焊接飞溅进行了研究,分析了焊接电流参数对焊点形貌和抗拉载荷的影响。结果表明,随线圈电流增大,引弧时刻提前,缓升阶梯模式下引弧瞬间电流减小,同时引弧电流上升速度较慢,容易出现引弧失败;三段阶梯模式则不受影响,因为其引弧电流较大,上升速度快,电场较强,能够快速引弧。焊接过程中燃弧间距不足易导致熔滴短路进而爆炸飞溅。增大电磁线圈电流能抑制弹片的回弹幅度,保证燃弧间距,进而减少飞溅的发生。在三段阶梯电流模式下,调整线圈电流为14.5A,减少了焊接过程引弧失败和飞溅现象,获得形貌良好和抗拉载荷稳定的焊点。

防飞溅剂对焊接过程的影响分析

针对焊接防飞溅剂在实际应用中可能出现的使用过量或局部累积现象进行了表面堆焊试验研究,分析不同类型、累积量的防飞溅剂在焊接过程中的状态变化及其对焊接过程中熔池流动性、电弧稳定性以及焊缝成形的影响。结果表明,油基防飞溅剂累积量一旦大于0.045 mL/cm^(2),便会有部分防飞溅剂进入熔池,从而降低熔池的流动性,导致焊丝液态熔敷金属堆积在电弧的后方,同时防飞溅剂会与电弧直接接触。水基防飞溅剂在电弧高温和压力的作用下会向前推进并迅速挥发,即使累积量为0.227 mL/cm^(2)仍不会进入熔池,因此并不会影响熔池的流动性。水基防飞溅剂对应的电弧稳定性明显优于油基防飞溅剂,特别是当累积量小于等于0.09 mL/cm^(2)时,这种差距最为明显。两类防飞溅剂作用下,焊缝整体成形基本一致,仅焊缝熔深较无防飞溅剂的降低约0.5 mm,而焊缝余高和熔宽并无明显变化。