喷射成形圆柱坯的计算机模拟与工艺设计

建立了描述喷射成形圆柱坯形状演化过程的数学模型，找到了一种较为简便的计算屏蔽系数的方法，研究了圆柱坯的生长规律．模拟结果表明，雾化参数、沉积盘的下拉速率和起始偏心距等是影响沉积坯形状演化的重要因素；喷射角主要影响上部过渡区的形状；而沉积盘转速在一定范围内变化时，对沉积坯形状演化几乎没有影响．喷射成形开始一段时间后，沉积坯顶点的生长速率将等于沉积器的下拉速率．在其它参数一定的情况下，通过适当选取起始偏心距，可以缩短沉积坯进入稳态生长的时间．模型结果与实验结果吻合较好．提出了喷射成形圆柱坯工艺的设计思路．     

往复式喷射沉积管坯制备中喷射高度的闭环控制

分析了往复式喷射沉积制备大壁厚管坯的工艺原理,研究了喷嘴喷射高度在线检测及闭环控制方法及技术。喷射高度控制系统包括漏包提升执行机构、沉积层厚度在线测量、基于PLC的喷嘴高度控制。提升执行机构采用伺服电机驱动的丝杠螺母机构,针对沉积层间断增长的特点,采用间断提升控制方式;研究了沉积层厚度在线测量方法,分析了收集基底形状误差对测量及控制精度的影响并提出多点测量方案。理论分析表明,采用三点测量法可消减基底形状误差的影响。对不同内径及壁厚的管坯进行了喷射实验,喷射高度累积误差低于5%,较好地满足了大壁厚管坯制备对稳定的喷射高度的要求。     

Plasma Spray Deposition on Inclined Substrates: Simulations and Experiments

In the plasma spray coating process, the coating’s profile and overall thickness are dependent on the number of overlapping traverses of the torch, the shape of the particle spray plume, the spatial distribution of the in-flight parameters of the particles within, and the orientation of the substrate. In this paper, a semi-empirical methodology for predicting three-dimensional deposits by the plasma spray process is developed. It comprises of three stages: first, spatial distributions of the in-flight parameters of multi-sized particles within the spray plume are determined by Computational Fluid Dynamics simulations. The size and shape parameters of the splats formed when individual droplets impact and spread out are obtained by experiments. Finally, a computer program is developed to integrate the particle parameters distribution and the empirical splat geometric data to generate a three-dimensional profile representing the deposit. The procedures predict the deposition volumes and thicknesses for different substrate inclinations with good agreement to experimentally sprayed deposits.     

管状喷射沉积坯成形过程数值模拟

喷射成形是一种近终形材料加工技术,针对管状沉积坯的成形过程进行了模拟。首先建立了管状沉积坯成形过程的数学模型,然后模拟了沉积坯厚度变化过程。结果表明：沉积器平移速度、沉积器半径、喷射距离对沉积层厚度均产生影响;而沉积器旋转速度超过30r/min时,该参数对沉积层厚度影响可以忽略。     

Droplet splashing during arc spraying of steel and the effect on deposit microstructure

The mechanism by which droplet deposition occurs is important when filling substrate features for the electric arc spray forming of steel tooling. Particle image velocimetry and high-speed video imaging techniques have been used to observe droplet deposition, particularly with regard to the behavior of droplets originating from splashing. Droplet splashing on deposition has been seen to be significant, and splash droplets form a large proportion of the overspray. The splash droplets are smaller and, when first created, move slower than the parent droplet. When spraying into deep features, the lateral and upward movement of splash droplets acts as a mechanism for deposit formation onto surfaces in shadow from the main spray. Microstructural study has shown that oxidation of the splash droplets before redeposition leads to a deposit with a high fraction of oxide. Simultaneous growth of deposit formed directly from the spray, and from splash droplets, results in a banded microstructure containing elongated macropores. A mechanism for such microstructural evolution is proposed.     

基于显著性的薄壁铝合金管小弯曲半径数控弯曲工艺参数优化(英文)

薄壁铝合金管小弯曲半径数控弯曲是个多因素耦合、多模具约束下的复杂过程。提出以有限元模拟为基础,基于显著性的工艺参数优化方法,即采用析因因子设计分析工艺参数对成形质量,即最大壁厚减薄率和最大截面畸变变化率影响的显著性,获得影响显著的参数,即管与防皱模间间隙的最优值,并确定其他影响不显著的参数值,包括管与模具间的间隙和摩擦、芯棒伸出量和助推速度。结果应用于规格为d50mm×1mm×75mm和d70mm×1.5mm×105mm(管外径D0×管壁厚t0×弯曲半径R)的铝合金管弯曲,获得了合格的管件。     

双金属复合无缝钢管冷轧成型过程的数值研究

采用非线性有限元法对不锈钢/碳钢双金属复合钢管的冷轧成型过程进行了数值模拟,得到了钢管在整个冷轧成型过程包括稳定轧制阶段和钢管冷轧脱模以后的位移场和应力应变场.计算结果显示,冷轧成型过程的应力分布十分复杂,在环向没有对称性.本文根据计算结果绘制了钢管的径向、环向及轴向应力分布图.在稳定轧制阶段,径向应力在内层钢管内壁,减径量越大,径向应力越小;环向应力在碳钢和不锈钢界面位置和内层不锈钢管的内壁,减径量越大,环向应力越小;轴向应力与减径量的大小成反比关系.采用冷轧成型工艺生产双金属无缝钢管,成品钢管的直径精度较高,壁厚精度低于直径精度.参数研究表明,计算直径接近理论值,受减径量的影响相对较小;计算壁厚与理论值有一定误差,钢管壁厚精度随减径量的增加而降低.对于本文计算的外径为φ202 mm,壁厚为11 mm的双金属复合管,在减径量为2 mm时的壁厚相对误差仍小于5％.同时,双金属复合管外层碳钢钢管壁厚变化量相对较大而内层不锈钢管的壁厚变化相对较小.论文的研究成果对于双金属复合钢管冷轧成型工艺设计、孔型和轧辊设计具有参考价值.     

Effects of vacuum plasma spray processing parameters on splat morphology

Several statistical tools (i.e., Gaussian and Weibull distribution analyses, the t-test, and analysis of the variance) were used to examine relationships between vacuum plasma spray processing parameters and the morphology of flattened particles (splats) on a smooth, polished substrate. Astroloy, a nickel-base powder, was vacuum plasma sprayed onto polished copper substrates under various processing conditions. Different flattened particle shape factors, including equivalent diameter, elongation factor, and degree of splashing, were determined using image analysis. The spray parameters (i.e., current intensity, chamber pressure, argon mass flow rate, etc.) strongly influenced splat formation and morphology and thus deposit microstructure and properties.     

Atmospheric Plasma-Sprayed Hydroxyapatite Coatings with (002) Texture

Hydroxyapatite (HA) coatings are being widely used in biomedical applications owing to their excellent biocompatibility and osteoconductivity. Recent studies have demonstrated that the crystallographic texture plays an important role in improving the chemical stability and mechanical properties of HA coatings. In this study, optimized APS parameter was selected to deposit HA coatings with strong (002) crystallographic texture, high phase purity and enhanced melting state. Cross-sectional SEM images show uniformly distributed columnar grains perpendicular to the coating surface. To study the formation conditions of columnar grains, coatings with distinct microstructure were deposited with different spray parameters. Moreover, HA coatings were deposited on substrates with varying temperatures such as 25, 300 and 600 °C at a long stand-off distance to evaluate the role of the substrate temperature in the formation of columnar grains. The results indicate that completely molten in-flight particles and slow cooling rate are necessary conditions to form a strong crystallographic texture. The present study suggests that the crystalline structure of HA coatings deposited and formed by APS could be well controlled by modifying spray parameters and substrate temperature.     

不锈钢管件无模拉伸实验研究

对不锈钢管件无模拉伸变形时壁厚变化进行了实验研究 ,分析了不锈钢管件无模拉伸时壁厚变化的影响因素及影响规律。确定了不锈钢管件无模拉伸时壁厚变化经验公式。实验结果发现 ,不锈钢管件无模拉伸时 ,壁厚变化tf/t0 与Dif/Di,D0 f/D0 ,1-RS的值成正比 ,即 :tf/t0 =k1Dif/D0 =k2 D0 f/D0 =k3 1-RS。对于薄壁不锈钢管件 (当t0 /D0 <0 1)无模拉伸时 ,k1=k2 =k3 =1。     

聚氨酯橡胶硬度对薄壁三通管内高压成形的影响

以外径为Φ24 mm、壁厚为1.5 mm、长度为120 mm的H85黄铜管为例,以壁厚增减量不超过30％为合格品作为前提,以生成最大支管胀形高度的橡胶硬度为最佳参数,结合胀形实验和有限元仿真共同分析了60～90 HA范围内7种不同硬度的聚氨酯橡胶棒对等径三通管成形质量的影响.研究结果表明:随着橡胶硬度的逐渐增大,支管胀...     

基于MSC.MARC的TP2铜管材液压胀形数值模拟

利用有限元分析软件MSC.MARC,建立了变径铜管材模型,完成了管材液压胀形过程的模拟,对成形后的管材进行了壁厚和等效应变分析.得出了轴向进给和管内高压的较合理的匹配关系,得出了壁厚减薄率和应变的最大区域是在管材两端倒角和胀形最大区域的连接处.     

纵波斜射探头检测厚壁高压无缝钢管

在大口径厚壁钢管的超声波检测中,由于受第一临界角的限制,采用接触法纯横波周向检测只能检测壁厚与外径之比〈0．2的管材。通过理论分析,采用入射角为10°的纵波斜射探头,对壁厚与外径之比〉0．2的钢管进行接触法周向检测,并根据折射纵波和折射横波的声压往复透射率（波高）及其在仪器荧光屏上的水平位置加以区分。实践证明,该方法实用可行。     

Microstructure and mechanical properties of a spray-formed Ti-based metallic glass former alloy

A Ti_45.8Zr_6.2Cu_39.9Ni_5.1Sn₂Si₁ composite plate was spray deposited on a copper substrate. From the bottom substrate-contact surface to the upper free surface of the deposit, a layered microstructure evolution in the order of fully amorphous (for the region 1-2 mm perpendicularly away from the substrate), amorphous/nanocrystalline (3-4 mm from the substrate), ultrafine-grained crystalline (5-6 mm from the substrate) and micron-sized crystalline phases (7-8 mm from the substrate) was observed. The oversprayed powders bellow 50 μm exhibit fully amorphous structure, while the ones above 50 μm show certain crystallization behavior. The fracture strength of 1.58-1.85 GPa with obvious plastic strain can be achieved under compressive tests for the spray-formed deposit. Spray forming can therefore produce bulk-sized high strength Ti-based alloy which evolves gradually from certain non-equilibrium towards equilibrium during deposition, which were considered to be attributable to the chill effect at the bottom substrate-contact surface and the following heat entrapment from the successively deposited droplets or powders.     

腔内约束电热爆喷涂涂层的形成

在内径为7 mm的聚乙烯爆炸腔进行钼丝的电热爆喷涂试验,用扫描电镜观察涂层的表面和截面形貌、涂层厚度,分析涂层与基体的结合情况.结果表明,爆炸腔内钼丝的爆炸产物在基体上会形成一个喷涂圆面,由中心涂层区和外围粘结层组成.中心涂层区在喷涂距离5～8 mm时,所得涂层致密、厚度均匀,与基体结合良好,局部界面附近存在元素扩散现象;外围粘结层随喷涂距离的增大而消失.大面积喷涂层可由单个喷涂圆面的合理搭接来形成,通过多次喷涂可增加涂层的厚度.     

Effects of process parameters on numerical control bending process for large diameter thin-walled aluminum alloy tubes

Numerical control(NC) bending experiments with different process parameters were carried out for 5052O aluminum alloy tubes with outer diameter of 70 mm, wall thickness of 1.5 mm, and centerline bending radius of 105 mm. And the effects of process parameters on tube wall thinning and cross section distortion were investigated. Meanwhile, acceptable bending of the 5052O aluminum tubes was accomplished based on the above experiments. The results show that the effects of process parameters on bending process for large diameter thin-walled aluminum alloy tubes are similar to those for small diameter thin-walled tubes, but the forming quality of the large diameter thin-walled aluminum alloy tubes is much more sensitive to the process parameters and thus it is more difficult to form.     

结构对连续熔化与定向凝固用冷坩埚磁场的影响(英文)

为了提高连续熔铸与定向凝固用冷坩埚的工作效率和优化结构设计,基于实验验证,建立了不同结构的电磁冷坩埚的3D有限元模型,并研究了坩埚结构对其内部磁场的影响规律。电磁冷坩埚的结构变量包括坩埚内径、坩埚壁厚、开缝形状以及水冷铜环。结果表明:随着坩埚内径的减小、开缝宽度和横截面积的增大以及水冷铜环的去除,坩埚内分瓣中点和开缝处的磁场随之增强。此外,当外径一定时,存在一个最差的坩埚壁厚使得坩埚内磁场值最低。     

V形面喷涂成膜数值模拟

目的 建立V形面喷涂成膜仿真模型,深入研究V形面喷涂成膜特性,为优化喷涂喷枪轨迹及获取理想涂膜提供理论支撑。方法 采用欧拉–欧拉方法建立包含喷雾流场模型和喷雾沉积模型的V形面喷涂成膜模型,结合动态自适应加密技术和SIMPLE算法,求解分析喷雾流场规律和涂膜厚度分布特性及形成机理,开展喷涂实验验证所建模型及成膜特性的正确性。结果 随着Z轴距离的增大,喷雾流场横向雾形由椭圆形变为长条状,纵向雾形在长轴方向上近壁面时与平面喷涂差别较大。相较平面喷涂,外壁喷涂喷雾覆盖范围广,内壁喷涂结果相反,且喷雾横向扩展程度与Z轴坐标值均呈线性关系。V形面内外壁喷涂涂膜均呈椭圆形,且膜厚均沿径向递减。外壁喷涂涂膜光环宽度最大,涂膜厚度值普遍低于平面喷涂;内壁喷涂涂膜光环宽度最窄,短轴方向涂膜厚度值普遍高于平面喷涂。随着V形面角度变大,涂膜中心厚度不断增加。涂膜厚度值在短轴方向均呈单峰分布,而在长轴方向上,外壁喷涂涂膜厚度均呈双峰分布,内壁喷涂涂膜厚度分布随角度变化有差异。结论 建立的喷涂成膜模型用于V形面喷涂成膜过程仿真是有效的,V形面较大地改变了喷涂过程中的喷雾流场特性和涂膜厚度分布特性。     

基于数值模拟的薄壁管冷弯成形工艺研究

薄壁管冷弯成形过程中最常见的缺陷有管坯内侧失稳起皱、外侧减薄破裂,为获得质量良好的某车用水冷管接头冷弯件,采用数值模拟方法分别研究了芯棒伸出量e、防皱块与管坯间隙c以及芯棒直径d等工艺参数对冷弯成形质量的影响.结果表明:随着芯棒伸出量e增大,管坯外侧壁厚减薄率γ增大,管坯内侧起皱趋势先减小再增大;随着管坯与防皱块的间隙...     

Processing Conditions Affecting Grain Size and Mechanical Properties in Nanocomposites Produced via Cold Spray

Cold spray is a coating technology based on aerodynamics and high-speed impact dynamics. In this process, spray particles (usually 1-50 μm in diameter) are accelerated to a high velocity (typically 300-1200 m/s) by a high-speed gas (pre-heated air, nitrogen, or helium) flow that is generated through a convergent-divergent de Laval-type nozzle. A coating is formed through the intensive plastic deformation of particles impacting on a substrate at a temperature below the melting point of the spray material. In the present paper the main processing parameters affecting the microstructural and mechanical behavior of metal-metal cold spray deposits are described. The effect of process parameters on grain refinement and mechanical properties were analyzed for composite particles of Al-Al₂O₃, Ni-BN, Cu-Al₂O₃, and Co-SiC. The properties of the formed nanocomposites were compared with those of the parent materials sprayed under the same conditions. The process conditions, leading to a strong grain refinement with an acceptable level of the deposit mechanical properties such as porosity and adhesion strength, are discussed.