焊管冷弯回弹曲线方程构建及工艺优化

目的 研究316L奥氏体不锈钢板材JCOE弯曲卸载回弹和应力分布特征,对预弯曲量实施相应补偿,以提高弯曲成形精度。方法 基于弹塑性变形理论,利用有限元模拟研究各关键成形参数对板材弯曲卸载回弹的影响规律,将影响指标线性/非线性拟合叠加,构建回弹曲线方程。结果 板料回弹量与上模下压量、下模开口量呈线性关系,与上模下行速度、摩擦因数呈指数关系。结论 优化后的最佳冷弯成形工艺参数如下:上模下压量为12 mm,下模开口量为150 mm,上模下行速度为4 mm/s,摩擦因数为0.15。对于径壁比值≤10的板料成形,理论计算得到的弯曲回弹量与实测平均值吻合较好,构建的模型可以为实际生产奠定理论基础。     

基于弯曲实验的DP980力学性能研究

目的 针对仅通过单向拉伸实验无法准确表征金属板材在弯曲成形过程中的力学性能变化的问题,研究通过弯曲实验获取材料力学性能参数.方法 对高强钢DP980展开力学性能测试研究,主要通过弯曲实验对材料弯曲变形过程中形成的弯矩曲率进行测试,将得到的弯矩曲率转化为应力-应变.分别将弯曲和拉伸得到的应力-应变数据导入到三点弯和辊弯成形有限元仿真中,预测板材的成形角度.结果 DP980弯曲变形时的屈服强度要大于轴向拉伸时的屈服强度;分别利用弯曲和拉伸实验测得的应力-应变数据进行仿真,与三点弯实验结果对比发现,采用弯曲实验得到的应力-应变数据对回弹量的预测偏大,而利用拉伸实验得到的应力-应变数据进行仿真,仿真得到的回弹量则偏小,弯曲实验下变形过程中的应变变化数据更加符合真实过程,与辊弯实验对比发现,利用弯曲实验数据进行仿真可以更准确地预测V形板的最终成形角度.结论 相较于单向拉伸实验,通过弯曲实验获取的材料力学性能参数可以更准确地描述材料在三点弯、辊弯成形过程中的力学性能变化.     

工艺参数对辊弯成形金属流动的影响规律

目的提高辊弯成形工艺中工件的最终成形尺寸精度,并为辊弯成形工艺参数的制定提供理论依据。方法以非能动空气导流板辊弯成形为研究对象,对不同参数下金属的流动规律进行研究。建立非能动空气导流板辊弯成形实验和仿真模型,根据模型,分析不同结构参数对金属成形流动规律的影响。结果较大摩擦不利于板材成形,摩擦因数为0.06~0.2之间时成形较好,建议采用塑料润滑;随着板材成形速度的增大,金属的变形抗力增大,板材与轧辊之间出现打滑现象,成形速度为5~10 m/min时成形结果较好;随着轧辊间距的增大,板材刚度降低,不利于板材成形,故其间距取为450~560 mm之间。结论实验结果与仿真结果基本一致,结果表明采用控制成形参数可以有效控制板材的金属流动,从而控制板材辊弯成形以得到更高精度。     

2205/X65双金属管道JCO成形有限元研究

目的研究2205/X65双金属管道JCO成形过程应力应变的演变及其影响因素。方法通过对2205/X65双金属管道JCO成形过程进行有限元模拟,分析了双金属管道成形后应力应变分布与演变情况,得到双金属板材自由弯曲变形特点及不同材料之间的界面应力分布特点,在此基础上研究了最大剪切应力随下压量、下模跨距以及模具半径的变化规律。结果 2205/X65双金属管成形后应力呈分段分布,除了最后一次下压位置,其他各段的应力大小和分布都是一样的,成形后的管坯由圆弧段和直管段相隔循环构成。2205/X65双金属管道成形后中性层在靠近屈服强度更大的2205一侧;在模具下压到最低点时板材上下表面屈服,中性层应力最小;卸载完成后管道厚度方向中间部位有最大残余应力分布,上下表面的环向应力都呈压应力分布。结论不同材料之间界面应力存在大梯度过渡,双金属板材弯曲成形中性层向一侧偏移。2205/X65双金属管道成形过程中最大剪切应力随着下压量的增大呈线性增大,当下压量为30mm时,最大剪切应力达到实验测试的双金属板材的剪切强度;随着下模跨距的增加,最大剪切应力不断减小;随着上模半径的增加,最大剪切应力不断增加,增加幅度较大;随着下模半径的增加,最大剪切应力不断增加,但增加幅度较小。成形后回弹角随着下压量的增大先减小再增大,最后趋于稳定。     

基于六边界优化角度函数的多道次辊弯成形研究

目的 为了提高多道次辊弯成形中板材的成形质量、减少板材纵向弯曲缺陷的产生,提出一种基于新型六边界成形角度分配函数的多道次辊弯成形优化方法。方法 根据翼缘端部水平面投影五次曲线推导出最优辊弯成形角度公式,结合COPRA研究板件峰值纵向应变,以确定最佳成形角度分配区间;在相同条件下,利用Abaquse模拟与实验研究不同成形角度对帽形件辊弯成形纵向弯曲缺陷的影响,并分析辊弯成形工艺参数对板材辊弯过程中应力-应变的影响。结果 新型六边界成形角度分配函数的多道次辊弯成形方法可有效改善板材纵向弯曲缺陷;应力随着成形角度增量的增加而增大,等效塑性应变随成形角度和成形角度增量的增加而增加;实验与模拟结果基本吻合,验证了模拟结果的正确性。结论 优化成形角度分配函数的多道次辊弯成形方法可有效改善板材纵向弯曲缺陷,为提高辊弯工艺精度与板材质量提供一定的理论指导。     

树脂复合钢板V型折弯回弹实验与仿真分析

为了研究模具圆角半径及凸模最大力对树脂复合钢板V型折弯回弹的影响,通过拉伸和搭接剪切试验获得了树脂复合钢板各层的力学性能数据,进行了树脂复合钢板的90°V型折弯回弹实验.对折弯回弹进行了有限元数值模拟,并与试验结果进行对比验证了90°V型折弯回弹有限元模型的可靠性,进一步分析了凸模圆角半径及其下行量对复合钢板折弯回弹角的影响规律,并由此预测出一组最优折弯工艺参数.结果表明:随着凸模下压量的增加,不同凸模圆角半径条件下,折弯回弹后角度大小先几乎直线下降而后有少量回升;将其转化为以凸模最大力为变量时,表现出类似的趋势.     

铝合金板材热成形-淬火一体化工艺研究进展

为解决铝合金室温塑性差和成形后热处理变形的问题,发展起来了一种铝合金板材热成形-淬火一体化新工艺。该工艺是将热处理和热成形在同一工步完成,即固溶后板材快速转移到模具中成形,然后完成模内淬火,最后通过时效来提高其强度。高温成形可提高板材成形性能,模内淬火能够保证其强度和尺寸精度。重点介绍了铝合金板材热成形-淬火一体化工艺关键技术及最新研究进展,总结了铝合金板材热成形-淬火一体化工艺实验研究和数值模拟的研究现状。     

板材激光弯曲成形数值模拟的研究现状及展望

板材的激光弯曲成形是一种利用高能激光束扫描金属板材表面产生非均匀分布的热应力,从而使板材发生塑性变形的金属板材柔性成形新工艺.数值模拟已逐渐成为板材激光弯曲成形研究中的热点内容.综述了近年来国内外对激光弯曲成形过程的温度场及变形场进行数值模拟的研究现状,并对其应用范围和发展前景作了展望.     

航空发动机燃烧室帽罩变压边热成形技术

目的 提出帽罩零件真空环境变压边热成形新技术,解决航空发动机燃烧室帽罩零件冷成形回弹大、精度低、内部应力大,以及热成形壁厚不均、氧化严重等问题。方法 利用有限元仿真和工艺试验相结合的方法,选用GH3625高温合金板材研究变压边热成形过程中压边力加载路径对帽罩成形质量的影响,分析热成形模具热膨胀与回弹变形对帽罩尺寸精度的影响,建立考虑热成形、变压边力加载及模具补偿的成形方案。结果 在900 ℃条件下,帽罩热成形力相比室温下降低约70%,内外径回弹量分别降低约67%和59%。基于几何特征优化的压边力加载路径有助于减小零件型面的回弹。结合回弹变形和热膨胀变形补偿,确定模具总补偿量为内径?0.49 mm,外径?0.62 mm。工艺试验结果表明,采用模拟所确立的成形方案成形的帽罩质量较好,尺寸精度达到IT9级,型面精度在0.2 mm以内,切边后回弹量为0.1 mm,与有限元仿真结果吻合较好。结论 建立的有限元模型和变形补偿方案可以有效地优化帽罩的工艺成形过程,所提出的变压边热成形技术能够显著降低高温合金变形抗力和回弹,可以解决高精度帽罩零件成形制造难题。     

某汽车燃料箱隔热板翻边成形工艺设计及研究

目的 为了成形高质量、少缺陷的汽车燃油箱隔热板.方法 采用整体翻边-局部反拉深的工艺方法,以隔热板曲面凸台圆角处的最大减薄率为试验指标,采取正交试验及极差分析确定最优成形工艺参数,并利用有限元数值软件对其成形过程进行模拟.结果 各因素对曲面凸台圆角减薄的影响主次顺序为:凸模下压速度、摩擦因数、凸模与顶出块夹紧力,最优成形工艺参数组合为:下压速度为10 mm/s、摩擦因数为0.12、夹紧力为40 kN.由等效应变结果分析得出,随着变形量的增加,左侧翻边曲面等效应变分布大于右侧,两侧翻边曲面交接处也积累了较大应变.实际成形件的最大减薄率为凸台位置的17.1％,满足生产要求.结论 在最优工艺参数下生产出合格隔热件,实际成形件的减薄情况与模拟结果基本一致,验证了模具设计和模拟的准确性,这对于成形结构复杂的异形构件具有一定的指导意义.     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.