金属成形过程中热力耦合分析技术的研究

金属成形过程中，温度对金属的变形行为具有很大影响，尤其是高温成形过程。基于有限元的热力耦合分析是研究金属变形的有效方法，本文对热力耦合分析技术进行了系统的研究，推导了有限元公式，提出了耦合分析的计算模式。开发了通用的分析二维金属成形过程的有限元分析软件Ｓ—ＦＯＲＧＥ。通过对圆柱体镦粗实验的模拟，说明了该方法和软件的正确性。     

采用TiH2粉末和造孔剂NH4HCO3烧结多孔钛（英文）

采用 TiH2和造孔剂 NH4HCO3混合粉末,利用粉末烧结法制备了多孔钛。研究表明,NH4HCO3的添加对于烧结的多孔钛的相组成几乎没有影响。多孔钛的孔隙度、平均孔隙尺寸、压缩强度和压缩弹性模量随 NH4HCO3添加量的增加而急剧下降。多孔钛可用添加不同量的造孔剂来调整孔隙结构和力学性能。独特的孔隙结构和适宜的力学性能满足多孔植入材料的基本要求。表明烧结的多孔钛是有前景的多孔植入候选材料。     

一种冷冲压复合模具优化设计

分析某变电器开关压圈结构特点,提出一种合理优化的成形工艺设计。在一次成形过程中,只需一副复合模具,既实现不同3种工序的复合,又实现3种不同类别工件的冲压复合,模具经现场生产使用,工作稳定可靠,制件质量满足要求,满足现代智能制造高精度、低成本、高效率的要求。     

阳极氧化法制备TiO2多孔膜

通过对TiO2多孔膜阳极氧化制备工艺的研究，提出了其成膜机理。实验以硫酸为电解液，以纯钛(TAl)为阳极，铜片为阴极，采用了恒压和恒流2种阳极氧化方式，在纯钛的表面获得TiO2多孔膜。用FESEM观察其孔径分布在100nm～200nm之间，并且随着阳极氧化电压和电流密度的增加，多孔膜的孔径有增大的趋势。最后，讨论了在硫酸电解液中TiO2多孔膜的形成机制。     

EIS characterisation of Ti anodic oxide porous films formed using modulated potential

Titanium, due to its excellent corrosion resistance, good mechanical properties and biocompatibility has been employed in many fields, such as in biomedical and dental implants. A passive oxide film formed on titanium surface is responsible for its high corrosion resistance. In the present study, oxide films were grown on titanium surface employing an anodising procedure using modulated potential, in a hydrofluoric acid solution. Electrochemical impedance spectroscopy was used to study the electrochemical behaviour of anodised Ti surface in a NaCl solution. The dependence of oxide film characteristics on forming conditions was analysed employing equivalent circuits. Samples were observed by scanning electron microscopy, in Jeol-JSM-5900LV microscope of the LME/LNLS, Campinas. It was observed that final anodising potential has an influence on the porous layer film morphology and that the anodising procedure with the chosen solution produces a double layer porous anodic film.     

半固态金属触变塑性成形上限法

在高固相率时,半固态金属的力学模型可简化为连续多孔体力学模型。针对半固态金属触变塑性成形的特点,本文发展了上限法理论在半固态金属触变塑性成形分析中的应用。提出速度间断值不仅要包括切向分量,还要包括法向分量。速度间断的法向分量是由金属通过速度不连续面时,材料固相率的变化而引起的。由此建立了半固态金属触变塑性成形的上限分析模型和理论方法,导出了上限功率的计算公式。为在实际触变塑性成形工艺分析中的进一步应用奠定了理论基础。     

板材数字化成型机计算机控制系统

介绍了一种新兴的金属板材成型技术———板材数字化成型技术的原理 ,论述了板材数字化成型机的计算机控制系统 ,说明了该控制系统的各项功能 ,以及该控制系统的硬件和软件结构 ,并着重讨论了基于WINDOWS操作系统的控制系统软件的设计     

An investigation of the high-temperature corrosion (burning) of an automobile exhaust valve

An automobile exhaust valve fabricated from 21-4N austenitic steel and burnt out during normal operation has been examined using conventional metallographic techniques and electron probe microanalysis. In the burnt-out region a thick porous outer oxide has developed, containing oxides of chromium, manganese and nickel; but there is no sign of a healing Cr₂O₃ layer forming. In contrast, regions remote from the burning form a thin dense, adherent oxide apparently comprising three layers: an inner chromium-rich oxide, an intermediate layer containing chromium and manganese, and an outer layer containing iron. The metal beneath the burnt region is depleted in chromium and manganese, but is enriched in nickel. A thin layer contains internal sulphides; some of the larger particles appear to be essentially FeS containing significant amounts of chromium and it seems likely that many of the finer particles are chromium and manganese sulphides. The porous layer contains phosphorus, sulphur and lead: the lead is always associated with phosphorus, and probably with sulphur, presumably as lead phosphate or a mixture of this with lead sulphate. However, much of the sulphur in the scale is not associated with lead: it seems probable that this is sodium sulphate, the sodium (and much of the sulphur) probably entering with the intake air.There is clear metallurgical evidence of a considerable temperature rise associated with the burning out of the valve.It is concluded that the reaction is similar to the sodium sulphate induced hot corrosion encountered in boilers and gas turbines operating in marine environments; the presence of lead oxide, and the cyclic variation of the oxygen potential of the atmosphere can be expected to accelerate this form of attack. There is no evidence of a carburization/oxidation attack.     

过滤用粉末烧结梯度多孔材料

梯度多孔材料具有高过滤精度大透气系数的特点,作为过滤器大大降低了压降,从而降低了生产成本。粉末烧结是制备过滤用梯度多孔材料的主要工艺方法。本文综述了国内外过滤用梯度多孔材料的现状,包括其分类、表征以及常用的梯度成型技术和粉末烧结技术,对比了过滤用梯度多孔材料的经济优势。同时,也表述了其中存在的问题和一些解决方法。     

金属扣挤压成型模具设计

介绍了一种金属扣挤压成型模具，该模具结构简单、使用方便，模具采用“吸气-密闭压缩-气动顶出”的顶出方式，保证了产品质量，提高了模具的使用寿命。     

点阵结构金属多孔材料制造技术

本文综述了点阵结构金属多孔材料的主要拓扑形态及其制造技术,并对目前广泛采用的变形成型法、金属丝编织法,以及随后发展起来的快速成型和注射成型等技术进行了对比分析.最后,对点阵结构金属多孔材料研究的努力方向提出了一点建议.     

制多孔不锈钢过滤片的试验研究

通过以水雾化0Cr18Ni9不锈钢粉为原料,以钢模压制或等静压制成形,在真空中或纯氢中烧结制取多孔不锈钢过滤片的试验,提出了制品的气泡试验最大孔径与水雾化不锈钢粉末颗粒平均尺寸关系的经验公式,并针对不锈钢粉末粒级、成形压力和添加剂对多孔不锈钢过滤片的孔隙度、气泡试验最大孔径、相对透气系数和拉伸性能的影响进行了研究。研制的多孔不锈钢过滤环片已批量生产,取得了明显的经济效益。     

模具参数对楔横轧铝合金轧件内部空洞的影响(英文)

通过分析楔横轧内部空洞(疏松)缺陷的物理性质和形成特征,将内部空洞视为多孔材料,利用多孔材料的刚塑性有限元方法,建立7075铝合金坯料内部空洞缺陷的数值模型。采用相对密度研究成形角、展宽角、断面收缩率对内部空洞缺陷的影响规律。结果显示:内部空洞的扩展主要发生在展宽段,楔入段对它的影响很小。展宽角是影响内部空洞产生的主要因素,而断面收缩率的影响较小。成形角、展宽角、断面收缩率越大,越不易发生内部空洞缺陷。在模具设计时,为了防止铝合金坯料轧制后产生内部空洞缺陷,断面收缩率应选择在55%～65%之间,展宽角在8°～10°之间,成形角在29°～32°之间。     

外缘外曲翻边毛坯尺寸计算方法

通过对外缘外曲翻边应力应变状态的分析，提出了预规变形区的变形和对毛坯尺寸进行修正的方法，从而提高翻边成形精度。     

气动卡扣冲压机的设计

为了改变钢管打包时包装带卡扣的制作工序多、劳动强度大、效率低等状况,凌源钢铁集团有限责任公司钢管厂设计制造了一次成型气动卡扣冲压机,提高工作效率 3倍多,减轻了劳动强度,而且操作简便,易于维修。     

微挤压成形系统的设计与实现

针对微挤压成形工艺要求,设计开发了一种微挤压成形系统,该系统装置采用压电陶瓷为驱动器,以实现成形速度的精确控制;利用压簧-楔块机构实现自动进给,减少了人工操作步骤;通过计算机控制系统与传感器,实现对微挤压成形过程的实时控制及数据采集。在室温条件下,使用该成形系统对铅丝坯料进行微挤压实验研究,结果表明,成形装置受力形变对挤压结果产生的影响可以通过适当的预紧力得到改善,从而成形出轮廓清晰的微型齿轮,验证了该研究方案的可行性,为后续的微型金属零件成形研究提供技术依据。     

Processing and microstructure of SiC laminar composites

Porous laminar materials and alternate laminates of dense and porous layers in silicon carbide have been elaborated by tape casting and liquid phase sintering (YAG-alumina eutectic) processing. Porosity was introduced by the incorporation of pore forming agents (PFA) (5–50 vol%) in the slurry. Two types of PFA with a narrow size distribution have been used (corn starch and polyamide powders). The effects of size, content, type of PFA on tape casting processing, sintering characteristics, porosity control and microstructure are investigated. For each PFA, the porosity attains a maximum value dependent on the PFA nature (41 vol% with corn starch). Only for starch, the volumetric shrinkage was unaffected by the PFA content up to 45 vol%. Homogeneous distribution of porosity has been obtained for both monolithic and composite laminates. An equiaxed and homogeneous silicon carbide microstructure has been obtained and was unaffected by PFA. Layered structures without defects have been obtained with parallel layers and uniform thickness (dense layer: 70 μm; porous layer: 80 μm).     

Experiments with a Low-Cost Hot Isothermal Pressing Machine Developed for Superplastic Forming

Hot isothermal/isostatic pressing machines are technically good candidates for superplastic forming (SPF) of otherwise hard-to-shape materials such as superalloys. These machines are, however, very expensive so that small or medium-size enterprises can not afford them. This has impeded widespread use of SPF processing. In an attempt to alleviate the problem, the authors have developed a laboratory model of an affordable hot isothermal pressing machine with differential gas pressure as the forming medium. Careful selection of process parameters such as temperature, gas pressure, strain rate, and process time as well as monitoring of thickness changes in a workpiece has a pivotal role in successful operation of such machine. It has been illustrated in this article that SPF can be successfully performed with this machine on the basis of process parameters estimated with existing analytical relations. The performance of this machine has been verified by several experiments on SPF of titanium-based sheets, as reported in this article.     

Influence of tool parameters on internal voids in cross wedge rolling of aluminum alloy parts

The internal void of cross wedge rolling (CWR) part can be treated as porous material due to their similar physical property and deformation characteristics. Aiming at the CWR process of aluminum alloy 7075 workpiece, the numerical simulation model for internal void was established by means of the rigid-plastic FEM method for the porous material. The relative density was used to research the influence of three primary parameters on the internal void in CWR process, including the forming angle α₁, the stretching angle β and the area reduction ΔA. The experimental results show that the expansion of internal void occurs in the stretching zone, and the knifing zone just has a little influence on it. The stretching angle has a great influence on the internal void, while the area reduction has a small influence on it. The size of internal voids decreases with the increase of area reduction, stretching angle and forming angle. When designing the CWR tool geometry and operating conditions, to prevent the internal void, the area reduction is suggested to be 55%–65%, the stretching angle to be 8°–10°, and the forming angle to be 29°–32°.     

Synthesis of nanosized CuCrO2 porous powders via a self-combustion glycine nitrate process

The glycine nitrate process has been successfully employed to prepare nanosized, porous, stoichiometric, homogeneous CuCrO₂ powders without ambient control. In this method, a precursor solution was prepared by mixing glycine with an aqueous solution of blended (Cu-Cr) metal-nitrates in their stoichiometric ratios. The glycine-mixed precursor solution was first heated in a beaker to evaporate excess water for forming a viscous bluish semi-transparent gel. The beaker was then covered with a metallic mesh, and the temperature increased slowly to 170 °C to auto-ignite the material. The combustion was self-sustaining and very rapid, producing gray colored powders. The as-prepared powders were nanosized (∼20 nm) into a spherical shape and crystallized in a delafossite structure. The powders showed a very large surface area of 30.92 m²/g, as determined by BET surface area measurements. The SEM/TEM studies on these powders confirmed their nanosized nature and porous structure.