Prediction and verification of melting front in GTA weld pool of full-penetration

A thermal conduction model is applied to speed up the numerical analysis of the temperature distribution and the weld pool geometry of full penetration in gas tungsten arc （GTA） welding. With considering both top and bottom flee surface deformation of full-penetrated weld pool, three-dimensional weld pool with melting front and solidification front is predicted. Welding experiments are conducted to measure the melting front curves at the top surface and the longitudinal section of the weld. It shows that the predicted and measured results are in good agreement.

Mechanism of pool separation and stratification in laser remelting and cladding

The laser remelting with a two-layer material system (upper material was Al-30 % Ti-20 % Ni alloy,substrate was commercial aluminum alloy) and the laser cladding of a commercial 45 steel with copper Powder (including 25%SiC) were carried out using a 2kW continuous CO2 laser. For the case of laser remelting, a upper Pool in the alloying layer and a lower Pool in the substrate separated by the unmelted Al-Ti-Ni alloy were observed. For laser cladding, a stratified Pool was observed, whose top layer was Cu alloy liquid and bottom was Fe alloy liquid. The mechanism of laser Pool separation and stratification is illustrated by numerical calculation of heat transter process of the two-layer system, combining with material physical properties (especially mixed enthalpy). A classification criterion for laser Pool with the two-layer material system has been presented and four types of the laser Pool are divided into unique Pool, separated Pool, mixed Pool and stratified pool,which provides a theoretical basis for obtaining a excellent surface coating.

Simulation and experimental analysis of melt pool evolution in laser engineered net shaping

In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made.Then,the establishment process of the multi-physical field model of the melt pool is introduced in detail.It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile,space temperature gradient,and time temperature gradient.Meanwhile,some parameters,such as the 3D morphology and surface fluid field of the melt pool,which are not obtained in the online measurement experiment,are analyzed.Finally,the influence of changing the scanning speed on the profile,peak temperature,and temperature gradient of the single-line melt pool is also analyzed,and the following conclusions are obtained:With the increase in scanning speed,the profile of the melt pool gradually becomes slender;The relationship between peak temperature and scanning speed is approximately linear in a certain speed range;The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed,and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.

三维互穿结构Cu-W触头抗熔焊机理

触头闭合回跳电弧引起的开关电器动熔焊问题,直接影响大功率接触器的电寿命和可靠性。为此设计了2种三维互穿有序结构的四边形和菱形十二面体的Cu-W复合材料触头,围绕触头动熔焊过程中的电弧、熔池、液滴溅射及凝固相变降温等问题,建立触头熔池流体动力学模型和冷凝降温数学模型,研究了2种有序结构和商用无序结构的触头阳极在闭合回跳电弧作用下熔化温度分布、熔池喷溅形貌和接触区域金属凝固过程,通过模拟熔焊实验平台进行了熔焊力验证。结果表明,通过调节三维互穿有序W骨架结构,能够有效抑制熔池扩散和液态金属喷溅,并降低熔焊力,从而提高Cu-W复合材料的抗熔焊性能。

不锈钢激光选区熔化单道成形表面介观模拟与实验验证

目的为了获得不锈钢激光选区熔化单道成形质量好的加工参数,提高成形质量。方法对于316L不锈钢材料的激光选区熔化(SLM)成形,采用离散元方法(DEM)构建颗粒随机分布的三维介观模型,采用流体体积法(VOF)动态追踪SLM成形过程熔池传热、流动和凝固等行为,该模拟考虑相变潜热、热物性参数随温度非线性变化、Marangoni效应,研究了温度梯度引起的表面张力和蒸汽反冲力等现象对熔池液态金属流动和凝固的影响,并对不同激光参数和扫描速度对熔池温度场和内部流动的影响规律进行了分析。结果当激光功率为150 W、扫描速度为400 mm/s时,激光能使不锈钢粉末充分熔化,凝固后的轨迹形貌连续光滑。通过提高激光扫描速度和降低激光功率使得热输入减小,熔道表面成形出现球化等缺陷。结论通过单道成形实验观察和分析熔池与熔道的三维尺寸与形貌,有效验证了数值模拟的正确性,较好地预测出SLM过程中的缺陷种类,为深入理解SLM过程中的复杂物理现象和优化工艺参数提供了参考。

含铜污泥搭配发热危废协同处理及综合利用技术

本文介绍了富氧侧吹熔池熔炼炉协同处理含铜污泥和发热危废的技术,该工艺具有金属回收率高、熔炼强度大、一次能源消耗低,实现了含铜污泥的有价金属的综合回收和发热危废的无害化处理。生产实践表明:处理量10万吨/a含铜污泥和发热危废,可降低煤率约10%,节约成本770万/a,产出约4000t/a的多金属合金(其中含铜55%、含镍11.9%),为企业提质增效打开了的突破口。

选区激光熔化镍基合金IN625数值仿真热源模型比较研究

热源模型的选取对数值模拟增材制造过程中准确预测温度场分布和熔池形貌至关重要。本文选取面热源模型、体热源模型和双椭圆热源模型进行对比分析。3种热源模型被汇编成用户自定义子程序嵌入Abaqus/Standard仿真软件中用于镍基高温合金IN625选区激光熔化过程中最高温度和熔池形貌的预测。仿真与实验结果对比表明,双椭圆模型可以较好地预测熔池几何形貌,而体热源模型在预测最高温度值时准确度更好。相比之下,面热源模型在预测最高温度和熔池形貌时准确度最差。研究结果表明,在开展深入研究之前,热源模型的校准修正是提高效率和模拟准确性的前提。

激光选区熔化铜合金多道成形的熔池行为和缺陷机理

目的针对激光选区熔化成形铜合金零件中孔隙缺陷的质量问题,研究不同扫描间距下多道熔池的动力学行为,以及不规则未熔合孔隙缺陷的生成机制。方法构建多物理场的高保真数值模型,采用离散元法搭建粉末床,结合两相流法追踪金属相自由表面,并通过射线追踪算法研究多道成形时的全局吸收率,深入分析扫描间距对熔池演变以及未熔合孔隙缺陷的影响。结果前一熔道的扫描对后一熔道有预热效果,因此第2熔道的宽度和吸收率总是大于第1道。随着扫描间距的增加,热积累效应减弱,第2道熔池的宽度和深度随之减小。扫描间距小会增加熔道间的重叠部分,不利于提升零件的构建速率,但无限地增加扫描间距会导致未熔化孔隙缺陷。通过对比70、100、130μm扫描间距下的成形熔道发现,70μm熔道的搭接率接近50%,100μm能形成良好的搭接,且没有缺陷生产,而130μm熔道有明显的孔隙缺陷及未完全熔化的粉末。结论扫描间距的变化会造成液态熔体流动、传热和传质的改变,进而改变激光选区熔化铜合金多道成形的熔池动力学行为与吸收率,最终影响成形件的质量。选用合适的扫描间距可以有效地避免未熔合缺陷,并保证相邻熔道间有良好的搭接率。

激光熔覆熔池动态演化及缺陷工艺调控研究进展

激光熔覆是一种高能束增材修复技术,具有热影响区小、组织性能可控性强、材料选择范围广等系列优势,目前已广泛应用于能源动力等领域关键金属构件的增材制造成形与受损零部件的修复再制造中。激光熔覆是以“激光”为热源的能量沉积技术,包括高能激光束冲击、表面熔池熔化快凝及熔覆表面层形成等多种物理、化学过程,其中熔池内金属热流体动力演化行为与熔覆层缺陷及表层组织性能调控密切相关。金属熔池具有“急热骤冷”的凝固特征,其内部对流、传热和传质等行为决定了熔覆层中温度及应力分布状态,是诱导熔覆层内气孔、裂纹等组织内部缺陷形成的关键因素。从激光熔覆过程中熔池内部对流、传热与传质的动态物理特性出发,论述了激光热源的理论模型设计、动态熔池中“流场+温度场+应力场”的多物理场数值模拟等方面的相关研究。在此基础上,分析了激光熔覆层典型缺陷-裂纹和气孔的形成机理及特征,总结了“材料-工艺-熔凝行为-涂层缺陷”的内在关联机制。同时,针对单一工艺方式调控熔池内熔凝过程的局限性,概述了多种复合能量场调控技术对熔覆层内部缺陷的作用机制与调控效果。最后,总结了当前激光熔覆层缺陷动态形成过程中存在的问题,并对其发展趋势进行了展望。

基于改进CeiT的GTAW焊接熔透状态识别方法

针对熔池信息与背景相似度高、噪声多、预测实时性差、识别精度低等问题,提出了基于改进CeiT网络模型的GTAW焊接熔透状态识别方法.首先通过MobileNetV3对Image-to-Tokens模块进行轻量化改进,提升预测的实时性能;其次设计DGCA模块改进LeFF模块来增强特征间的远程依赖关系、丰富类标记中所包含的分类信息;最后将LeFF模块中的底层特征和高层语义特征进行融合,提高模型对熔池特征的表示能力.仿真结果表明,与MobileNetV3,ResNet50,ShuffleNetV2,DeiT和CeiT模型相比,所提出的模型获得了更高的准确率和较快的检测速度.

光束倾角对激光深熔焊304不锈钢焊缝力学性能及熔池流动的影响

在激光深熔焊接中光束倾角会直接影响匙孔形态,光束倾角对熔池流动也具有一定的影响.采用激光深熔焊接白板试验结合“半三明治”熔池流动直接观测试验,以激光倾角作为变量,研究其对304不锈钢激光深熔焊接焊缝力学性能及熔池流动的影响.结果表明,在焊缝的力学性能上,不同激光倾角对焊缝上、中部的影响差异性较小,对下部的影响较大,焊缝底部拉伸件出现较多气孔缺陷,正激光入射角下的焊缝抗拉强度和断后伸长率小于负激光入射角.正激光入射角下“上小下大”的匙孔形貌使其底部易产生涡流,不利于气泡的排出,且匙孔坍塌频率较负激光入射角大,导致熔池稳定性较差,焊缝气孔缺陷的形成概率呈现为正激光入射角高于负激光入射角态势.

激光选区熔化316 L不锈钢熔池面积对力学性能的影响

为了探索激光选区熔化316 L不锈钢熔池对力学性能的影响,本研究通过激光选区熔化技术打印4组不同工艺参数的12个样品,并对样品进行室温拉伸和微观结构表征,提出了基于Matlab工具箱以及改进Canny算法提取熔池面积,同时观察每组的熔池面积与每组对应抗拉强度的变化曲线。结果表明:熔池面积逐渐增大的同时,其样品抗拉强度也随之增大,两者具有同样的变化趋势,不仅如此,当熔池面积达到最大值0.042 mm^(2)时,抗拉强度达到最大值509.46 MPa。

超声振动方向对激光定向能沉积Inconel 718性能影响研究

目的面向激光定向能沉积表面改性及再制造发展需求,揭示超声振动方向对激光定向能沉积Inconel 718零件的影响机制,为超声辅助激光定向能沉积高质量成形提供参考。方法开展多方向超声振动辅助激光定向能沉积Inconel 718零件试验,结合原位熔池监测技术,研究沉积方向、搭接方向和扫描方向超声振动对熔池流动行为、微观结构和力学性能的影响。结果不同方向超声振动显著影响了熔池的动态流动行为,其中搭接方向超声振动使熔池润湿面积提高了86.4%,并且形状更为规则,拖尾现象得到改善。微观组织细化方面,扫描方向振动效果最佳,晶体直径细化了46.9%,水平方向的晶体等轴晶转变优于沉积方向,而在沉积方向振动下,Laves相点球化和减少最为明显。相较于对照组的显微硬度210.4HV0.2,添加沉积、搭接和扫描方向超声振动后分别提高到了232.5HV0.2、230.9HV0.2和233.9HV0.2,变化趋势与晶体直径变化趋势基本一致。水平方向超声振动影响下,特别是扫描方向的超声振动在提高材料强度的同时,还在一定程度上保持了材料的延展性;在搭接方向上,超声振动辅助显示出较好的各向异性消除能力,获得了优异的硬度、强度和塑性匹配。结论不同方向超声振动,通过不同方向的惯性力和热流改善了熔池的动态流动性,其中搭接方向超声振动在扩大熔池润湿面积和改善熔池动态形状方面具有优异的综合能力。由于超声强度方向性传播衰减和引起不同的声压梯度,微观组织细化和Laves相的细小点球状消减分别在扫描方向和沉积方向上最为显著,这些变化引起了显微硬度和拉伸性能的相关性提升。超声振动还均衡了材料的力学性能,提高了抗拉强度、屈服强度和延展性,尤其在搭接方向上,显示出较好的各向异性消除能力。可根据具体需求目标,选用相应的超声振动方向或者复合使用,以获得优异的Inconel 718零件熔池流动、微观形貌和力学性能匹配。

激光线能量密度对75W-FeCoNiCr合金微观组织及力学性能的影响

利用FeCoNiCr高熵合金为黏结相,并采用激光定向能量沉积(L-DED)方法制备新型75W-FeCoNiCr合金,研究激光线能量密度对合金相组成、相对密度、微观组织及力学性能的影响。研究结果表明,在线能量密度为157.14~325.00 J/mm时,不同线能量密度下的合金相组成没有明显变化,均由BCC-W相、TCP金属间化合物析出相Co_(7)W_(6)相和FCC-FeCoNiCr黏结相组成。随着线能量密度的增大,成分过冷度增加,析出相长大速率加快,其形态由板状/胞状向树枝晶状转变,并且粒径从1μm增加到8μm左右。随着线能量密度的升高,合金的致密度、显微硬度和压缩强度均呈现先升高后降低的趋势。当线能量密度为166.67 J/mm时,析出相主要为均匀胞状结构,此时,合金的致密度、显微硬度和压缩强度均达最高值,分别为98.4%、656 MPa和2261 MPa。

COPRA双层熔池湍流模型优选

为了预测下封头内双层熔池的流动和传热过程,基于不同湍流模型,同时采用凝固熔化模型对堆芯熔池研究装置(corium pool research apparatus,COPRA)双层熔池实验进行计算流体力学(CFD)数值模拟,通过数值计算获得准稳态下熔池的温度、沿壁面的热流密度与内壁面壳层的分布,将模拟结果与实验值进行比较,评价不同湍流模型的适用性和准确性,并进行湍流模型优选。结果表明,壁面模化大涡模拟(WMLES)湍流模型对下封头内双层熔融池流动与传热模拟的准确性和适用性最好;基于WMLES湍流模型,氧化层温度随着熔池高度增大而增大,氧化层上部存在强烈的湍流,在熔池底部的壳层最厚。

电子束熔炼用水冷铜坩埚研制

电子束熔炼作为一种优异的真空冶炼技术,其核心部件水冷坩埚的结构设计尤为重要,坩埚的冷却性能将直接影响电子束熔炼的效果及安全。通过理论分析、数值模拟、试验考核,研究了坩埚水道结构、熔池形貌对坩埚冷却能力的影响。通过坩埚选材、熔池利用率分析、能量损耗分析和冷却计算确定了坩埚结构,建立了数值仿真模型,采用模拟计算方式对比了两种熔池形貌的坩埚在不同装料量下的冷却性能,并针对性能优异的坩埚开展了试验考核。结果表明:模拟不同锭厚条件下,坩埚B的冷却水温度和坩埚表面温度较坩埚A均偏低,坩埚B的熔池形状和水道结构匹配更合理,散热效果更好。试验考核过程中坩埚B状态稳定,满足设计要求。

Towards implementation of alloy-specific thermo-fluid modelling for laser powder-bed fusion of Mg alloys

Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBF).However,its capabilities for being implemented as a reliable tool for material design,where minor changes in material-related parameters must be accurately captured,is still in question.In the present research,first,a thermo-fluid computational fluid dynamics(CFD)model is developed and validated against experimental data.Considering the predicted material properties of the pure Mg and commercial ZK60 and WE43 Mg alloys,parametric studies are done attempting to elucidate how the difference in some of the material properties,i.e.,saturated vapor pressure,viscosity,and solidification range,can influence the melt pool dynamics.It is found that a higher saturated vapor pressure,associated with the ZK60 alloy,leads to a deeper unstable keyhole,increasing the keyhole-induced porosity and evaporation mass loss.Higher viscosity and wider solidification range can increase the non-uniformity of temperature and velocity distribution on the keyhole walls,resulting in increased keyhole instability and formation of defects.Finally,the WE43 alloy showed the best behavior in terms of defect formation and evaporation mass loss,providing theoretical support to the extensive use of this alloy in L-PBF.In summary,this study suggests an approach to investigate the effect of materials-related parameters on L-PBF melting and solidification,which can be extremely helpful for future design of new alloys suitable for L-PBF.

扫描速度对激光选区熔化Ti6Al4V熔池流动行为的影响

为了研究Ti6Al4V钛合金激光选区熔化制造过程的熔池演变特征及流动行为,采用数值分析方法讨论了扫描速率对熔化温度及流场的影响。结果表明:熔池大小和熔池存在的时间随扫描速度增大而减小,当扫描速度较低时熔池的后部固/液相界面极易形成波浪状突变。对于500 W激光功率,当扫描速度为0.004 m/s时熔池最大流动速度约为0.42 m/s。随扫描速度的增大,熔池流速呈近似线性减小。这可能是扫描速度减小使柱状晶向等轴晶转变的原因。

Anisotropy in mechanical properties and corrosion resistance of 316L stainless steel fabricated by selective laser melting

The corrosion behavior and mechanical properties of 316 L stainless steel(SS) fabricated via selective laser melting(SLM) were clarified by potentiodynamic polarization measurements, immersion tests, and tensile experiments. The microstructural anisotropy of SLMed 316 L SS was also investigated by electron back-scattered diffraction and transmission electron microscopy. The grain sizes of the SLMed 316 L SS in the XOZ plane were smaller than those of the SLMed 316 L SS in the XOY plane, and a greater number of low-angle boundaries were present in the XOY plane, resulting in lower elongation for the XOY plane than for the XOZ plane. The SLMed 316 L was expected to exhibit higher strength but lower ductility than the wrought 316 L, which was attributed to the high density of dislocations. The pitting potentials of the SLMed 316 L samples were universally higher than those of the wrought sample in chloride solutions because of the annihilation of MnS or(Ca,Al)-oxides during the rapid solidification. However, the molten pool boundaries preferentially dissolved in aggressive solutions and the damage of the SLMed 316 L in FeCl3 solution was more serious after long-term service, indicating poor durability.

In situ monitoring methods for selective laser melting additive manufacturing process based on images-A review

Selective laser melting(SLM)has been widely used in the fields of aviation,aerospace and die manufacturing due to its ability to produce metal components with arbitrarily complex shapes.However,the instability of SLM process often leads to quality fluctuation of the formed component,which hinders the further development and application of SLM.In situ quality control during SLM process is an effective solution to the quality fluctuation of formed components.However,the basic premise of feedback control during SLM process is the rapid and accurate diagnosis of the quality.Therefore,an in situ monitoring method of SLM process,which provides quality diagnosis information for feedback control,became one of the research hotspots in this field in recent years.In this paper,the research progress of in situ monitoring during SLM process based on images is reviewed.Firstly,the significance of in situ monitoring during SLM process is analyzed.Then,the image information source of SLM process,the image acquisition systems for different detection objects(the molten pool region,the scanned layer and the powder spread layer)and the methods of the image information analysis,detection and recognition are reviewed and analyzed.Through review and analysis,it is found that the existing image analysis and detection methods during SLM process are mainly based on traditional image processing methods combined with traditional machine learning models.Finally,the main development direction of in situ monitoring during SLM process is proposed by combining with the frontier technology of image-based computer vision.