金属液滴垂直搭接成形工艺研究

通过研究铝合金熔滴的垂直搭接过程中不同工艺参数下的对成形表面形貌和内部质量的影响规律。通过对单一金属液滴沉积行为研究,建立了垂直搭接沉积数值模型,并对多个熔融液滴垂直重叠形态的进化和温度变化过程进行分析和实验验证。实验表明：数值模拟与实验结果有良好的一致性,从而得到了最优参数。该研究对实现金属微液滴垂直搭接生产的有效过程控制至关重要,为制造复杂金属提供了技术支持和参考。     

金属熔滴连续沉积、凝固重叠工艺及实验验证

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。     

金属熔滴连续沉积、凝固重叠工艺及实验验证（英文）

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,采用流体体积法(VOF)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。     

挤压轮转速对大管径电缆铝护套连续包覆成形的影响

挤压轮转速是大管径电缆铝护套包覆成形过程中的一个重要工艺参数,其对工装模具使用寿命、产品质量及生产效率具有直接的影响。基于SSLB500型双轮立式连续包覆机,采用有限元法,通过对Φ180 mm×4 mm电缆铝护套连续包覆过程进行数值模拟,分析在不同挤压轮转速下金属成形过程中的速度场、温度场及压力的分布状况,得到了挤压轮转速对电缆铝护套连续包覆成形过程的影响规律;基于相同模具结构,进行了转速分别3和7 r·min-1的铝护套连续包覆实验,实验结果与数值模拟所得规律相符,证明所建立的有限元模型正确。研究结果可供大管径电缆铝护套连续包覆工艺参数选择时参考。     

金属熔融涂覆成形工艺数值模拟与实验验证

针对金属熔融涂覆增材制造工艺,基于VOF函数和分段线性界面重构方法建立熔融涂覆沉积过程熔体热流场数值计算模型,分析了成形过程中沉积层表面的热力学行为及沉积层形貌的演变行为,利用该模型可获得熔凝区形态及温度场信息。研究了成形质量、沉积层形貌与冶金缺陷间的关系,并对数值计算模型进行了实验验证。结果表明:沉积层形貌计算值与实验值吻合较好,熔融涂覆沉积过程数值计算模型能有效地描述涂覆沉积过程中熔体内的铺展流动和凝固行为。采用热成像系统可实时监测沉积层表面温度信息。沉积层之间重熔结构及内部质量良好,无明显孔隙等缺陷。上述研究为深入理解金属熔融涂覆成形工艺中的复杂物理过程和成形工艺参数的优化提供理论指导。     

微液滴现象与大气腐蚀——Ⅰ.微液滴的形成与扩展

采用改变相对湿度、无机盐粒/金属组合和环境气氛等参数的方法研究了微液滴形成、生长的特征及其与大气腐蚀过程的关系.结果表明,微液滴形成和生长与气氛中氧和相对湿度及盐粒/金属组合密切相关.在大气环境中,微液滴形成和生长需要两个前提条件:第一,环境相对湿度须高于盐粒水解液滴液面的饱和蒸气压;第二,水解液滴下的金属应能被液滴腐蚀.     

金属熔体沉积实验装置研究

金属熔体沉积成形涉及金属熔体的产生,形态演变,流动,凝固等热物理过程。根据金属液流断续特性要求,设计开发了金属熔体沉积装置。结果表明:通过此实验装置研究实现了金属熔体沉积过程关键参数(脉冲压力、扫描速度、熔体温度、基板温度等)的监测与控制,为后续深入研究熔体沉积成形技术提供了必要的实验软硬件基础。     

熔渣中金属液滴沉降过程流体力学模拟（英文）

建立熔炼渣中金属液滴沉降过程的数学模型，研究不同粘性模型下金属/熔渣界面张力对液滴沉降速度以及拖曳力的影响。结果表明：对于较小直径的液滴，Laminar模型和RNG k-ε湍流模型能够准确预测液滴最终沉降速度；界面张力对液滴沉降速度有影响，且影响作用随着液滴尺寸增大而逐渐增大；“RNG+CSS”模型可以准确描述液滴沉降过程和液滴沉降速度的变化。结合数学模型和实验数据，推导出耦合界面张力作用下拖曳力系数计算公式。该模型揭示熔炼渣中金属液滴沉降过程机理，为实际生产中降低渣中有价金属含量提供理论指导。     

三维打印技术中7075铝合金液滴沉积铺展过程的模拟(英文)

采用基于流体体积法的三维模型研究按需喷射三维打印技术中均匀合金液滴的连续沉积和凝固过程。模型中使用的7075合金具有较大的相变温度范围。模拟结果表明:该模型可以很好地模拟出7075合金均匀液滴的连续沉积和凝固过程,模拟出的液滴形状和在相同条件下实验得出的SEM图像相吻合。液滴沉积和凝固的影响导致液滴表面出现垂直和"L"形的脊状突起,液滴的快速凝固使搭接处出现细小的枝晶。     

金属流固耦合沉积方法综述

金属熔体喷射断裂成小液滴后,通过与运动平台装置的协同运动,可在基板上准确沉积,以达到制件成形要求。然而受到不同因素干扰的毛细金属熔体容易出现偏斜、中断,甚至无法断续等问题,难以控制熔融金属沉积过程。因此需要对金属熔体喷射流固耦合特性进行系统的研究。     

金属熔滴碰撞、铺张数值分析

基于金属熔滴沉积成形的3D打印技术,其成形质量与金属熔滴及基板参数有很大关系。本文对金属铝熔滴在不同参数下,比如：熔滴直径、滴落速度、比热、导热系数、潜热以及基板温度等,其凝固过程中的最大铺展因子关系进行了研究。采用VOF对自由表面进行追踪的方法,建立包括对流和相变的计算方程和能量方程的仿真模型,耦合水平集函数,跟踪熔融粒子与周围空气之间的接口,获得的最大传播因子之间的关系,与在文献中出现的实验数据吻合。     

不锈钢0Cr18Ni9熔滴沉积参数优化

在熔融沉积成型(FDM)过程中,为保证熔滴与基板之间有较好融合,本文首先对送丝速度、焊炬不同姿态以及焊炬与基板距离等参数下的熔滴沉积质量以及与基板融合变形过程进行了分析,采用VOF方法对熔滴的自由表面进行跟踪和修正,通过数值计算分别模拟了熔滴以一定速度撞击基板后铺展、融合的过程。通过模拟与试验验证得到可视化结果,表明不锈钢0Cr18Ni9熔滴沉积融合变形过程受多种因素影响,与实际相吻合。     

不同工艺参数对金属熔滴沉积成形影响

采用数值计算与试验分析相结合的方法,深入研究了不同工艺参数(沉积距离、扫描速度、熔体温度、基板温度、喷嘴直径等),单颗金属熔滴的沉积、铺展变化,验证了当前模型的正确性.通过对单颗金属熔滴沉积行为的研究,建立了单道/多道水平搭接成形数值计算模型,探索了金属熔滴在小空间、大温度梯度环境下沉积成形中熔体流动、铺展、凝固成形机理,结果表明,在典型特征截面上搭接成形时,通过优化工艺参数,可以获得熔滴沉积中的主要特征因素与成形形貌、内部质量之间的影响规律,为后续复杂金属件的熔滴液流沉积成形提供了技术支持和参考依据.     

Effect of wetting behavior on generation of uniform aluminum droplets obtained by pneumatic drop-on-demand technique

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.     

Numerical simulation of splat formation dynamics in plasma spray forming

Plasma spray forming shows overwhelming advantages in rapid fabricating parts and moulds. The coating microstructure is strongly dependent on the splat morphology and inter-splat contact nature. Therefore, it is necessary to investigate the splat formation mechanism in order to analyze the coating properties. A dynamical process of a single fully molten droplet impacting onto a smooth surface was investigated. At the same time, the interaction between the two molten droplets in the horizontal and vertical directions was also simulated. Finally, the simulations of impact of a molten droplet on an inclined plane and a sharp edge were presented. It is concluded that the relative distance of the two droplets strongly influences the dynamics of the two droplets interaction. The various surface conditions have direct effects on the dynamics of splat formation. When a droplet impacts onto an inclined surface and a sharp edge, the splat morphology changes obviously and the phenomenon of break up is observed.     

Remelting and bonding of deposited aluminum alloy droplets under different droplet and substrate temperatures in metal droplet deposition manufacture

Micro-void and cold lap are the most common defects of 3D components in aluminum alloy droplet deposition manufacture, which have been found to be associated with the poor remelting and metallurgical bonding between droplets under inappropriate droplet and substrate temperatures. To address this problem, the appropriate temperature condition for achieving good metallurgical bonding between droplets was analyzed and the relationships among surface temperature (T_surf), substrate temperature (T_b), droplets temperature (T_drop), droplets deposition frequency (f) and height of deposition layer (h) were estiblished by one-dimensional (1D) heat transfer analytical model. On this basis, a three-dimensional (3D) transient finite element mode was developed to simulate the thermal behavior during metal droplet deposition component using element birth and death technology. The distribution and variation of surface temperature of previously deposited droplets (T_surf) were predicted and analyzed under different process parameters in fabricating aluminum alloy 3D components. And then, a series of deposition experiments were conducted with different droplet temperatures (T_drop) and substrate temperatures (T_b). The experimental results show that the good remelting and metallurgical bonding between droplets were obtained with the appropriate combination of T_drop (700 °C) and T_b (450 °C). The micro-void and cold laps were not observed in the interior of formed samples, indicating that experimental results basically agree with the theoretical analysis and simulation results. The work provides a useful theoretical and experimental guide for metal droplets deposition manufacture.     

Shape and surface texture of molten droplets deposited on cold surfaces

When a molten droplet impacts on a cold surface, the interaction between solidification and fluid dynamics can lead to different shapes and surface textures of deposited droplets. This article presents an experimental study on deposition of small droplets (39 μm diameter) of molten wax ink on solid surfaces. Our results show that both the final shape and the surface texture of deposited droplets are extremely sensitive to deposition conditions, which include initial temperature of droplets, type of substrate surface and distance between substrate and printhead. Different surface textures are observed and shown to depend on the thermal and flow histories of ink droplets during the process of impact. A test using crystalline wax reveals crystallization as one of the major factors in determining the final texture.     

气体放电热源喷涂技术的数值模拟研究现状∗

热喷涂技术是表面工程领域中极为重要的一种装备强化修复技术，其中以气体放电形式为热源的喷涂技术包括等离子喷涂和电弧喷涂，两者更是占据热喷涂领域的绝大市场份额，采用数值模拟可以解决一些在试验上较为棘手的重点研究问题， 如等离子体流场和熔滴传热传质行为等，以期实现工艺参数的准确调控和优异涂层的制备。研究电弧及等离子喷涂模拟的模型差异化问题及流场速度、温度、电磁性质，归纳相关模拟的发展历程，并调查试验与模拟的吻合程度。结果表明：电弧喷涂中丝材原料会使阴阳极产生温度差，水平速度分布较发散，熔滴模型也多未考虑熔滴群间相互作用；等离子喷涂研究中常用的三维瞬态双温模型已十分贴近实际工况，对熔滴飞行中的加热、加速过程及破碎行为的研究已较为完备，但仍存在湍流模型计算精度不够、对鞘层弧柱区的研究不够深入等问题。后续应重点在电弧喷涂多液滴模型、等离子体电磁作用和等离子丝材喷涂工艺的数值模拟等方面进行深入研究。