共查询到18条相似文献,搜索用时 243 毫秒
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建立了空心阴极真空电弧焊(Hollow Cathoda Vacuun Arc Welding,HCVAW)焊接TC4钛合金板(5mm)熔池中流体流动和传热过程动态行为的物理,数学模型,并对焊接过程进行了数值模拟计算和工艺试验,通过计算,找出了爆接速度和爆接电流等工艺参数对爆缝成型的影响规律,并计算出焊接过程中工作上的温度场分布和熔池中的流场分布,计算结果与实验结果基本相符。 相似文献
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目的 研究等离子弧焊接穿孔过程中熔池内部的金属流动情况和小孔动态变化过程。方法 通过“传热-熔池流动-小孔”之间的相互耦合关系,建立了等离子弧焊接穿孔过程的数值分析模型,通过VOF方法追踪了小孔界面,采用FLOW-3D软件模拟了等离子弧焊接熔池和小孔的形成过程,定量计算了等离子弧焊接温度场、熔池流场及小孔形状;分析了等离子弧焊接熔池和小孔行为;并通过等离子弧焊接实验数据验证了模拟结果。结果 当焊接时间为0~1.0 s时,小孔深度曲线与熔深曲线几乎相同,小孔底部紧贴熔池底部;在2.8 s以后,小孔深度曲线与熔深曲线有一定距离,小孔深度曲线在一定范围内波动,等离子弧焊接电弧挖掘作用到达极限,电弧压力与其他力达到平衡状态。模拟的焊缝熔深为8.04 mm、熔宽为13.20 mm,实验测得的焊缝熔深为8.00 mm、熔宽为13.42 mm。结论 构建的随小孔动态变化的曲面热源模型和电弧压力模型可以描述等离子弧焊接过程中的电弧热-力分布;模拟出了等离子弧焊接熔池和小孔动态演变过程;模拟得到的等离子弧焊接焊缝形貌与实验测得的焊缝形貌基本吻合。 相似文献
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为了更深入地探究电子束焊接过程中的机理问题,利用数值软件Fluent,对10mm厚的2219铝合金电子束焊接熔池进行三维瞬态模拟。分析电子束焊接进入准稳态后熔池中涡流的变化规律和产生原因,并结合电子束与匙孔壁面相互作用进行讨论。结果表明:电子束焊接进入准稳态后熔池呈周期性波动;根据液态金属流动情况可将焊接熔池分为3个区域,区域Ⅰ中的液态金属维持了熔池体积的稳定,区域Ⅱ中的涡流起到扩大熔池表面的作用,区域Ⅲ中的涡流促使匙孔坍塌;通过对电子束与匙孔壁面的耦合分析可知,电子束在匙孔壁面上并不是均匀分布的,这造成了匙孔底部具有一定的滞后性。 相似文献
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焊接过程中焊接熔池内部的流体流动传热过程对熔池的形状、气体及夹杂物的吸收、聚集和逸出等影响很大,尤其影响元素在熔池中的分布。研究发现,熔池内流体主要受表面张力、浮力和电磁力的作用,其中表面张力对熔池形状起主导作用;焊接热输入、功率、焊接速度均对焊接熔池的形成有不同程度的影响。在焊接过程中,不同材料在交界处会发生元素互扩散,不同的元素扩散系数相差较大,而同种元素在不同扩散深度处的扩散系数却相差不大。由于焊缝中元素分布是否均匀直接关系到焊接接头的质量,因此元素在熔池熔化过程中具体的扩散形式以及在熔池凝固后元素的偏析情况是未来的研究热点。 相似文献
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在“中国制造2025”、美国《国家先进制造战略计划》、欧洲航天局《惊奇计划》、日本《增材制造科研计划》、新加坡《工业增材制造项目》以及欧盟《3D打印标准化路线图》等全球新型制造技术迅猛发展的机遇下,金属激光3D打印融合了计算机辅助设计、材料加工与成形技术,以数字化模型文件为基础,通过软件与数控系统将特制材料逐层堆积固化,制造出实体产品,该技术日益成为国内外专家学者的研究热点。它与传统的对原材料进行切削、组装的加工模式不同,是通过材料累加的原理,从无到有地制造产品的新型技术工艺。也正是由于增材制造的这种技术特点,使得它受到全球的广泛关注,将可能会给传统的制造业带来一系列深刻的变革。其中同轴送粉式金属激光3D打印技术因具有成形尺寸大、可利用材料范围广、成形件的材料性能优异等特点,在航空航天、交通、医疗与能源等领域有着广阔的应用前景,成为金属增材制造主流的工艺技术。 3D打印熔池中存在着传热、对流、传质、气-液界面冶金反应以及固-液界面扩散等复杂的动态物理冶金过程。熔池的流体力学行为直接影响材料组织的均匀性以及致密性,因此,如何通过流体力学方法对熔池的流体动态过程进行模拟,建立熔池温度和流场的三维非稳态模型,并定量分析浮力、表面张力、粉末冲击力以及综合作用对3D打印过程温度场、速度场和熔池形态的影响是需要解决的关键问题。 数值仿真模拟是研究同轴送粉式金属激光3D打印熔池动力学过程的重要手段之一。目前,在关于同轴送粉式金属激光3D打印数值模拟和激光焊的数值模拟研究中,已包含较为全面的多尺度数值模型,例如光-粉耦合作用数值模型、熔池气-液界面和固-液混合区界面追踪模型、熔池瞬时变化的热场和流场分析模型、熔池中合金元素的分布过程介观模型以及基于相场法的熔池形貌和显微组织凝固元胞自动机模型等。 本文主要阐述国内外研究学者对同轴送粉式金属激光3D打印仿真模拟的研究进展,主要集中在3D打印过程中熔池瞬时变化的热场和流场分析、合金元素的分布过程以及熔池形貌和显微组织凝固等方面。由于数值模拟方法具有一定的通用性,为了更全面地介绍与同轴送粉式金属激光3D打印技术相关的数值模拟方法,本文也涉及了少量送粉式激光熔覆以及激光电弧填粉焊接等过程的数值模拟工作。 相似文献
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Numerical Simulation of Current Density Distribution in Keyhole Double-Sided Arc Welding 总被引:2,自引:0,他引:2
Junsheng SUN Chuansong WU Min ZHANG Houxiao WANGNational Key Laboratory of Advanced Welding Production Technology Harbin Institute of Technology Harbin ChinaKey Lab. of Liquid Structure Heredity of Material Minisity of Education Shandong University Jinan China 《材料科学技术学报》2004,20(2):228-231
In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process. Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole. 相似文献
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A three-dimensional friction stir welding (FSW) process model has been developed based on fluid mechanics. The material transport in the welding process has been regarded as a laminar, viscous, and non-Newtonian liquid that flows past a rotating pin. A criterion to divide the weld zone has been given on the basis of cooperation of velocity field and viscosity field. That is, the η 0-easy-flow zone that existed near the tool pin corresponded to the weld nugget zone; the area between the η 0-easy-flow zone and η 1-viscosity band is corresponded to the thermal-mechanical affected zone (TMAZ). The model gives some useful information to improve the understanding of material flow in FSW through the simulation result of velocity distribution. In order to appraise the friction stir pin design, three kinds of pin geometry, one is column pin, the second is taper pin, and the last one is screw threaded taper pin, were used in the model. The pin geometry seriously affected the simulation result of velocity distribution in the η 0-easy-flow zone. The velocity distribution in the η 0-easy-flow zone can be considered as the criterion of optimizing friction stir tool design. This study will benefit to direct the friction stir tool design. 相似文献
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Three-dimensional transient governing equations were developed based on conservation laws of energy, momentum and mass. These equations described physical phenomena of convection in weld pool and heat transfer in workpiece during variable polarity vertical-up plasma arc welding process. Boundary conditions for the developed governing equations were given. Welding energy input for variable polarity vertical-up plasma arc welding process was quantitatively expressed. Free surface deformation of the keyhole molten pool was coupled into calculation. Effect of wire filling on the geometry of molten pool and weld reinforcement was considered in the simulation. Correlations of temperature and thermophysical properties for aluminum alloy 2219 were quantitatively established. A control volume based finite difference method was used to solve the discrete governing equations. Moreover, dynamic evolutions of geometrical profile, dimension and fluid flow for the molten pool and keyhole were simulated through the developed computational routines, which achieved transient solution of fluid flow field coupling with thermophysical properties, temperature field and weld pool free surface deformation. Besides, the effect of the workpiece thickness on the moments of keyhole formation and stable keyhole establishment was analyzed, and thermal cycles for the main welding stage were calculated. In addition, experiments via variable polarity vertical-up plasma arc welding technique were conducted, and the established models were experimentally verified through weld cross-section profiles. 相似文献
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The mechanism of the increasing of A-TIG welding penetration is studied by using the activating flux we developed for stainless steel. The effect of flux on the flow and temperature fields of weld pool is simulated by the PHOENICS software. It shows that without flux, the fluid flow will be outward along the surface of the weld pool and then down, resulting in a flatter weld pool shape. With the flux, the oxygen, which changes the temperature dependence of surface tension grads from a negative value to a positive value, can cause significant changes on the weld penetration. Fluid flow will be inward along the surface of the weld pool toward the center and then down. This fluid flow pattern efficiently transfers heat to the weld root and produces a relatively deep and narrow weld. This change is the main cause of penetration increase. Moreover, arc construction can cause the weld width to become narrower and the penetration to become deeper, but this is not the main cause of penetration increase. The effects of flux on fluid flow of the weld pool surface and arc profiles were observed in conventional TIG welding and in A-TIG welding by using high-speed video camera. The fluid flow behavior was visualized in real-time scale by micro focused X-ray transmission video observation system. The result indicated that stronger inward fluid flow patterns leading to weld beads with narrower width and deeper penetration could be apparently identified in the case of A-TIG welding. The flux could change the direction of fluid flow in welding pool. It has a good agreement with the simulation results. 相似文献
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Dong Honggang Gao Hongming Wu Lin 《International journal for numerical methods in engineering》2006,65(10):1673-1687
Double‐sided arc welding process powered by a single supply is a type of novel high‐production process. In comparison with the conventional single‐sided arc welding, this process has remarkable advantages in enhancing penetration, minimizing distortion and improving welding production. In this paper, a three‐dimensional steady numerical model is developed for the heat transfer and fluid flow in plasma arc (PA)–gas tungsten arc (GTA) double‐sided keyhole welding process. The model considers the surface tension gradient, electromagnetic force and buoyancy force. A CCD camera is used to observe the size and shape of the keyhole and weld pool. The acquired images are analysed through image processing to obtain the surface diameters of the keyhole on the two sides. A double‐V‐shaped keyhole geometry is then proposed and its characteristic parameters are derived from the images and cross‐section of weld bead. In the numerical model, the keyhole cavum within the weld pool is treated as a whole quality, whose temperature is fixed at the boiling point of the workpiece material. The heat exchange between the keyhole and weld pool is treated as an interior boundary of the workpiece. Based on the numerical model, the distributions of the fluid flow and temperature field are calculated. A comparison of cross‐section of the weld bead with the experimental result shows that the numerical model's accuracy is reasonable. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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《Materials Science & Technology》2013,29(12):1427-1432
AbstractA mathematical model is developed to assess the solidification behaviour of the weld pools. To do so, during gas tungsten arc welding of commercial pure aluminium, equations of conversation of mass, energy and momentum are numerically solved considering three-dimensional steady state heat transfer and fluid flow conditions. The weld pool geometry, weld thermal cycles and various solidification parameters are calculated using temperature and velocity fields acquiring from the utilised model. The solidification behaviour of the weld pool at the weld centreline and the fusion line is then studied using the solidification parameters including temperature gradient G, solidification rate R and the combined forms G/R and GR. In order to verify the predictions, welding experiments are performed and geometry of the weld fusion zone is measured. The calculated geometry of the weld fusion zone is found to be in good agreement with the corresponding experimental result. The predictions show that the cooling rate GR increases toward the centreline while the other solidification parameter G/R shows a different behaviour. In addition, it is found that under the employed welding conditions, as the welding speed increases temperature gradients both at the weld centreline and at the fusion line are reduced. 相似文献