共查询到19条相似文献,搜索用时 671 毫秒
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金属直薄壁件激光直接沉积过程的有限元模拟Ⅱ.沉积过程中热应力场的模拟 总被引:5,自引:0,他引:5
建立了按激光光斑直径逐点沉积热力耦合的热应力有限元分析模型.316L不锈钢直薄壁件沉积过程的热应力模拟结果显示,拉应力区出现在基板与沉积部分界面处(界面拉应力区)和沉积部分顶部(顶部拉应力区);拉应力区的位置随激光束的运动不断变化.实验证明,沉积过程中的开裂分别发生在沉积部分顶部(顶部开裂)和基板与沉积部分界面处的边缘部位(边缘开裂).顶部开裂出现在顶部拉应力区,边缘开裂出现在界面拉应力区中拉应力最大的边缘部位.有限元模拟结果很好地解释了实验中的开裂现象. 相似文献
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李素丽 《稀有金属材料与工程》2017,46(12):3645-3650
金属熔滴均匀连续沉积是一种新型的3D打印技术和快速原型(RP)技术。本文系统研究了铝熔滴连续沉积到基板表面的瞬态传热传质现象,沉积机理主要包括金属熔体的毛细现象及固液界面的传热、凝固、搭接和重熔。采用VOF方法对连续沉积的金属熔滴在水平固定铝基板表面沉积进行3D建模。针对凝固传热过程中不同参数下熔滴在铝基板表面沉积、凝固进行了研究,通过数值计算与实验验证,各种工艺参数的影响,如喷射速度、基板温度、熔滴直径与碰撞最大铺展因子的影响,显示了很好的一致性。基于上述研究,成形形貌和内部微观结构之间的定量关系进一步验证了金属熔滴连续沉积、凝固重叠工艺的可行性。此工艺为金属微沉积制造实施有效的过程控制提供指导。 相似文献
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晁艳普 《稀有金属材料与工程》2016,45(8):1924-1930
翘曲、分层、开裂是7075铝合金微熔滴沉积制造过程中常见的缺陷,其原因主要是沉积制造过程中存在较大的温度梯度和热应力集中。为了探究热变形、翘曲和开裂的形成机理,采用有限单元法和单元生死技术,通过APDL(ANSYS)编程,建立了气动按需熔滴沉积成形温度和热应力计算模型,分析了7075铝合金微熔滴逐点、逐层沉积三维制件过程中温度和热应力的动态演变规律。并使用7075铝合金微滴,在相同初始边界条件和工艺参数下进行了沉积试验,模拟结果与7075铝合金制件微熔滴沉积试验结果基本吻合,较好地反映了实际成形过程中零件的温度和热应力场变化规律,为减少或消除铝合金微熔滴沉积制造过程的缺陷提供了理论依据,从而促进了该技术在高熔点合金零件制备中的应用。 相似文献
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金属铜电沉积过程中分形研究 总被引:14,自引:0,他引:14
以环形金属铜片作为阳极,细铜丝作为阴极,研究了酸性电解液条件下金属铜电沉积过程中的二级枝晶生长现象,测定了沉积时间-电流关系曲线,对外加电压,电解液中硫酸铜浓度等对金属铜的电沉积产物形貌及其分维数的影响进行了观测,分析。研究发现,沉积过程中,电流随沉积时间的增加而变大,沉积产物的分维数随电解液中硫酸铜的增加而变大,随外加电压的变动而波动。 相似文献
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Jun Luo Le-hua Qi Song-yi Zhong Ji-ming Zhou He-jun Li 《Journal of Materials Processing Technology》2012,212(10):2066-2073
A pneumatic drop-on-demand (DOD) system has been applied to solder complex and dense interconnects of modern micro electronic devices. Initial parameters of uniform droplets were first measured. Then influences of experiment parameters, such as the crucible temperature, the substrate temperature and the droplet velocity on spread of solder droplets, were investigated experimentally and theoretically. The results showed that effects of impact velocity on the spreading could be negligible and the solder spreading process was driven by capillary forces because of the low Weber (We) number of depositing droplet. The influence of initial droplet temperature on the droplet spreading was not regular. The contact diameter of solder droplets on copper substrate increased when the substrate temperature increased from 443 K to 493 K. At last, copper cables were successfully soldered to pins of a flexible circuit using the direct solder deposition and re-melting process. The soldering results showed the feasibility of the data-driven soldering technique using the pneumatic DOD deposition technology. 相似文献
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Han-song Zuo He-jun Li Le-hua Qi Jun Luo Song-yi Zhong Hai-peng Li 《Journal of Materials Processing Technology》2014,214(11):2566-2575
Micro metal droplet is the basic building block of three-dimensional metal parts fabricated by micro droplet deposition manufacturing (MDDM) technique. In this paper, the effect of wetting behavior between liquid metal and spray nozzle on the generation of micro aluminum droplets produced by pneumatic drop-on-demand (DOD) technique was investigated by simulation and experiment. A finite element model of liquid–gas flow was established based on the improved level set method (LSM). Then the generation of micro liquid aluminum droplets under different wetting conditions was simulated. A series of spraying experiments were also performed on micro droplet deposition experiment platform. The results show that the generation and flight of micro aluminum droplets are influenced by wetting condition between liquid metal and the nozzle surface significantly. Additionally, the effect of wetting behavior on the droplet size was analyzed to achieve the smallest building block. It was found that the droplet radius decreased with the increase of contact angle exponentially, which agreed with the numerical calculation and experiment results. On this basis, a wettability criterion was proposed for selecting nozzle materials. These works would be helpful for the processing optimization and equipment improvement of MDDM technique. 相似文献
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Modeling and characterization of metal droplets generation by using a pneumatic drop-on-demand generator 总被引:1,自引:0,他引:1
Jun LuoAuthor Vitae Le-hua QiAuthor Vitae Ji-ming ZhouAuthor Vitae Xiang-hui HouAuthor VitaeHe-jun LiAuthor Vitae 《Journal of Materials Processing Technology》2012,212(3):718-726
A 2D axisymmetric model has been proposed to study the mechanism of the droplet generation by using a pneumatic drop-on-demand (DOD) generator. A proprietary pneumatic DOD generator was also applied to conduct droplet generation experiments. The validity of the proposed model was verified through the simulation results of droplet pattern, breakup length distance and droplet diameter, which were in good agreement with the experimental ones. Theoretical studies were conducted to characterize the metal droplet generation using pneumatic DOD technique. Theoretical analyses show that metal droplets break away from jets in front of the sphere ends due to the increase of the capillary disturbance at a very small Ohnesorge number (Oh < 0.01). This capillary disturbance is caused by the action of surface tension. Shapes of droplets do not significantly change because of the relatively low pressure inside droplets. The droplet diameter decreases when the nozzle diameter decreases to 100 μm, while the ratio of droplet diameter to nozzle diameter increases rapidly. An external disturbance with high frequency should be introduced to accelerate the metal jet breakup for further decreasing the droplet size. This work offers a useful guide for choosing appropriate parameters to generate metal droplets using pneumatic DOD technique. 相似文献
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本文利用均匀凝结理论,以气动系统中典型的充放气系统为研究对象,给出了该系统在放气过程中凝结的计算方法,分析了凝结现象的本质过程。 相似文献
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Research on lateral instability of the uniform-charged droplet stream during droplet-based freeform fabrication 总被引:3,自引:0,他引:3
Jun Luo Le-Hua Qi Xiao-Shan Jiang Ji-Ming Zhou Hua Huang 《International Journal of Machine Tools and Manufacture》2008,48(3-4):289-294
A droplet initial displacement assumption was made and a dynamic model of the charged droplets was developed to understand the lateral instability of the uniform-charged droplet stream for freeform fabrication. The distribution of charged droplets depending on deposition distance was obtained based on this dynamic model after the droplet charge was calculated by the FEM. Then, a droplet charging and depositing apparatus is set up to generate the uniform-charged droplet stream. The droplet charge was measured and the droplet distributions at different distances were collected in the experiment. The results show that the theoretical radius of droplet distribution area agrees well with the mean experimental value at the deposition distance of 50 cm. The theoretical trend of droplet stream dispersion fits well with experimental result. The maximum accurate deposition distance within which the radius of distribution area is less than one droplet diameter is about 27 cm according to the prediction of droplet distribution, which provides the basis for further accurate metal droplet deposition. 相似文献
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Yan-pu ChaoAuthor Vitae Le-hua QiAuthor Vitae Yuan XiaoAuthor Vitae Jun LuoAuthor Vitae Ji-ming ZhouAuthor Vitae 《Journal of Materials Processing Technology》2012,212(2):484-491
Metal micro-droplet deposition manufacturing technique is a novel direct metal rapid prototyping for building the miniaturized parts. In this paper, the novel direct metal rapid prototyping was proposed to fabricate micro thin-walled metal parts. A direct droplet fabrication experimental system was developed based on the forming principle of micro-droplet deposition manufacture. Several deposition experiments were conducted to investigate the influences of process parameters on the formed wall thickness and deposition accuracy of droplets. The experimental results show that the proper deposition distance Hs for obtaining high deposition accuracy of droplet ranges from 1 mm to 20 mm; the formed wall thickness W can be controlled by selecting different nozzle diameters D and formed angle of deposited droplet θ. According to the experiment results, a micro thin-walled structure with wall thickness of 400 μm was fabricated by adjusting the process parameters. The above research works show that it is feasible to fabricate the micro thin-walled metal parts by micro-droplet deposition manufacturing technique. 相似文献
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《Acta Materialia》2008,56(7):1588-1596
A numerical model has been developed to simulate the dynamic shape evolution of Ni superalloy rings during spray forming. The model comprises: (1) a droplet primary deposition model, simulating droplet primary deposition at a deposition surface; (2) a droplet splashing model, simulating the droplet splashing/scattering behaviour; and (3) a droplet redeposition model, simulating the redeposition of the scattered droplets onto the deposition surface. The model has been validated against experiments of spray forming large diameter IN718 alloy rings, and for the first time, the effects of droplet splashing and redeposition on the dynamic shape evolution of spray forming IN718 alloy rings and the deposition yields have been investigated and quantified. The model serves as the basis for a thermal dynamic model that is described in Part 2 of this publication. 相似文献
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Development of a welding system for 3D steel rapid prototyping process 总被引:10,自引:0,他引:10
0 IntroductionWeldingrapidprototypingisanovelproductionprocessinwhichasolidcomponentareformedbyweldingdepositionaccordingtoathree dimensionalCADmodel.Inthisprocess ,athree dimensional( 3D)objectisslicedbyCAD ,andcorrespondingoutlinecurvesofeachlayerareobta… 相似文献
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目的优化电化学沉积法制备氢氧化铜纳米结构的实验参数,探究不同润湿性表面冷凝液滴尺寸分布规律。方法采用正交试验法,综合考虑电解液浓度、反应温度、极化时间、电流密度对接触角的影响,并通过SEM分析其表面形貌。同时,基于MATLAB软件,提出一种能快速精确识别、提取并统计冷凝液滴特征值的图像处理方法。结果正交试验最优参数为浓度0.5mol/L、温度5℃、时间2000s、电流密度4 mA/cm^2,此时样品表面接触角高达168.8°,滚动角小于3°。冷凝实验结果显示,在超疏水表面,冷凝液滴会频繁的合并自移除,液滴平均粒径最小,粒径在1~10μm范围内的液滴占比维持在50%左右;而在疏水与亲水样表面,冷凝液滴仅能发生合并现象,液滴平均粒径显著增大;冷凝后期,超疏水、疏水与亲水样表面冷凝液滴密度分别稳定在2000、1000、360 mm-2左右。结论纳米针结构能最大限度地降低固液接触面积,降低冷凝液滴粘附力,提高冷凝液滴合并自移除频率,减少冷凝液滴直径,提高冷凝液滴更新率,有望实现高效冷凝传热。同时通过与Image-J图像处理结果比对,验证了该冷凝液滴尺寸分布图像处理方法的可行性。 相似文献