Correlative spatter and vapour depression dynamics during laser powder bed fusion of an Al-Fe-Zr alloy

Spatter during laser powder bed fusion(LPBF)can induce surface defects,impacting the fatigue performance of the fabricated components.Here,we reveal and explain the links between vapour depression shape and spatter dynamics during LPBF of an Al-Fe-Zr aluminium alloy using high-speed synchrotron x-ray imaging.We quantify the number,trajectory angle,velocity,and kinetic energy of the spatter as a function of vapour depression zone/keyhole morphology under industry-relevant processing conditions.The depression zone/keyhole morphology was found to influence the spatter ejection angle in keyhole versus conduction melting modes:(i)the vapour-pressure driven plume in conduction mode with a quasi-semi-circular depression zone leads to backward spatter whereas;and(ii)the keyhole rear wall redirects the gas/vapour flow to cause vertical spatter ejection and rear rim droplet spatter.Increasing the opening of the keyhole or vapour depression zone can reduce entrainment of solid spatter.We discover a spatter-induced cavity mechanism in which small spatter particles are accelerated towards the powder bed after laser-spatter interaction,inducing powder denudation and cavities on the printed surface.By quantifying these laser-spatter interactions,we suggest a printing strategy for minimising defects and improving the surface quality of LPBF parts.

Analysis of high-power disk laser welding stability based on classification of plume and spatter characteristics

Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Characteristic parameters such as the area and number of spatters, the average grayscale of a spatter image, the entropy of a spatter grayscale image, the coordinate ratio of the plume centroid and the welding point, the polar coordinates of the plume centroid were defined and extracted. Karhunen-Loeve transform method was used to change the seven characteristics into three primary characteristics to reduce the dimensions. Also, K-nearest neighbor method was used to classify the plume and spatter images into two categories such as good and poor welding quality. The results show that plume and spatter have a close relationship with the welding stability, and two categories could be recognized effectively using K-nearest neighbor method based on Karhunen-Loeve transform.

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.

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.

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.

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.

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.

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 effective for on-line predicting spatter rate of its corresponding welding condition.

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。

基于OCT原位测量的可调环模激光焊飞溅定量评价

为了快速准确定量评价金属飞溅以优化工艺和保证焊接质量,采用1060铝合金可调环模(variable beam profile,VBP)激光焊为研究对象,搭建了基于光学相干层析成像(opticalc coherence tomography,OCT)的激光焊匙孔深度原位测量系统,并提出了一种1DCNN-BiLSTM复合深度学习模型,该模型利用两种网络单元的特性对匙孔深度信息进行局部和全局时序特征挖掘,实现了飞溅状态的定量评价.结果表明,该模型的飞溅识别准确率达到99.69%,为VBP激光焊工艺优化和质量控制提供了指导依据和闭环反馈.

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。

基于电阻点焊过程与形貌的飞溅成因分析及控制方法

【目的】在汽车白车身制造生产过程中,电阻点焊是板件连接的主要焊接工艺,但电阻点焊焊接过程中焊渣飞溅对白车身焊接质量影响较大,还会导致设备故障等问题,进而增加返修成本并降低生产效率。因此,该文对降低电阻点焊白车身的飞溅成因分析与控制方法展开研究。【方法】提出了一种飞溅成因分析与控制方法的操作流程,从多维度分析焊接过程与焊接形貌,进而针对性地实施措施,并在实际生产中验证飞溅成因分析与控制方法的操作流程。【结果】在验证过程中。通过对焊装车间飞溅率较高的工位基于分析结果进行优化,使得车间整体飞溅率由14%降低至6%,飞溅率低于优化前50%,有效减少预打磨工位的工作量和飞溅引起的故障率。【结论】飞溅成因分析与控制方法的理论体系保证了白车身焊接质量,提高了生产效率,并为后续工作提供思路指导与经验借鉴。焊接飞溅率是焊装车间主要控制指标之一,在生产过程中还需要不断监测、调整和保持,从而制定更有效的标准流程,减少飞溅对白车身质量的影响。

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。

430铁素体不锈钢薄板激光焊接背面飞溅和熔池动态的数值模拟

薄板的激光焊接对离焦量敏感,很小的离焦量偏差就会导致熔池不稳定。本文采用数值模拟的方法,研究了离焦量对0.6 mm厚430铁素体不锈钢薄板激光焊熔池动态行为的影响,分析了形成焊道背面飞溅的原因。结果表明,在目前所用的焊接工艺参数条件下,离焦量决定着激光热输入在熔池中的位置和分布。熔池中匙孔的深度随着离焦量的降低而增大,负离焦(-0.1 mm)形成穿透的匙孔,零离焦(0 mm)和正离焦(+0.1 mm)形成的匙孔尺寸较小。不同离焦量均形成具有束腰结构的熔透熔池,熔池表面和匙孔表面的流速最大。熔池高度方向上存在由中间束腰部位向上下表面流动的两个涡流,液体金属在熔池上表面由熔池后方向前方流动。匙孔中的蒸发作用力和表面的高流速使匙孔不断闭合,在底部形成封闭的气泡。背面飞溅只在负离焦条件下形成,零离焦和正离焦不产生背面飞溅。负离焦条件下,熔透熔池形成的初期在焊道背面形成小颗粒的滴落型飞溅,主要是由熔池重力和表面流动导致;在穿透匙孔形成的末期因为气泡破裂形成大颗粒的喷射型飞溅。正离焦条件下熔池的形态、流动较为稳定,预测的焊道横断面轮廓与实验结果吻合良好。

TO型外壳封焊边缘金属飞溅的控制

储能焊作为TO型外壳主要密封工艺,在TO型外壳封焊过程中能量分布不均容易造成封焊边缘处产生金属飞溅。为解决金属飞溅外观异常问题,以TO8型金属外壳为例,分别研究储能焊密封工艺参数及管帽结构对TO型外壳密封后外观状态的影响。通过优化密封气压、电压、焊接时间及改良管帽结构的方法解决了TO型外壳封焊处金属飞溅问题,降低了TO型外壳封焊边缘缺陷,保证了产品外观满足相关标准要求。

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。

Welding characteristics of AZ31B magnesium alloy using DC-PMIG welding

Direct current pulsed metal inert-gas （DC-PMIG） welding was carried out on AZ31B magnesium alloy to obtain continuous welding joints of 3 mm and 8 mm thickness with 1.6 mm diameter of filler wire. The behavior and mechanism of metal transfer, the parameter ranges of stable welding process, the microstructure and mechanical properties of magnesium alloy were investigated. The results show that the metal transfer form of magnesium alloy using DC-PMIG welding is realized in modes of globular transfer, projected transfer and spray transfer. Welding spatter with a large size will be produced in the mode of globular transfer, and high-quality joints with few spatters can be obtained in the mode of projected transfer and spray transfer when the linear energy of filler wire is 242-27l J/cm, droplet diameter is 1.6-0.9 mm tensile strength of weld beads is 94.2% of that of base metals. and transition frequency is 30-69 Hz. The average ultimate

GMAW工艺仰焊咬边缺陷的研究分析与控制

对电站锅炉膜式壁管排鳍片与管子角焊缝采用熔化极气体保护焊(GMAW)仰焊位置易产生咬边缺陷进行了试验研究,根据不同材料焊接生产出现咬边的几率,对材料成分进行了统计与分析研究。仰焊时由于重力因素会加剧熔化金属下坠,使熔化金属脱离焊趾而流向熔池中心,导致仰焊更容易产生咬边缺陷。结果表明,焊接速度是影响产生咬边的关键因素,通过降低焊接速度可以有效地减小和消除咬边缺陷;Mn/S比较低的材料,产生咬边缺陷的几率较高,焊接时应严格控制焊接速度。