板料数控渐进成形中变形力的研究

研究了板料数控渐进成形变形力的2种计算方法:按照纯剪切变形的方式计算变形力;按照剪切和弯曲综合变形的方式计算变形力。同时,通过实验测量出渐进成形的实际变形力。通过比较,实验测定的变形力与假定剪切弯曲变形计算的变形力相近,可以认为渐进成形是一种剪切弯曲变形。     

金属板材数控渐进成形工艺的研究进展

为了总结过去十几年国内外学者对板材数控渐进成形工艺技术的研究进展,对渐进成形工艺成形机理方面的研究成果进行了综述,分析了其材料变形的特点;全面概述了近年来国内外学者有关成形工艺参数对成形极限、成形精度、表面质量及能耗和效率的影响方面的研究成果,并介绍了国内外金属板材渐进成形装备的研究进展,最后对新兴的板材渐进成形工艺进行了总结概括。现有研究表明,成形件几何精度、表面质量和成形效率等方面的不足仍然是制约该技术广泛工业化应用的关键问题,同时渐进成形件的形性协同控制机理也亟待研究。     

板料渐进成形数值模拟与实验研究

为提高渐进成形的成形效率和成形质量,了解板料渐进成形的变形规律及工艺参数对成形的影响,采用有限元方法对板料渐进成形过程进行了数值模拟研究,分析了斜壁盒形件渐进成形过程应力分布和厚度变化趋势,通过对不同进给量和不同成形路径进行数值模拟,分析了工艺参数对成形的影响.结果表明,斜壁盒形件最大应力和最大厚度减薄发生在底面拐角处;成形过程中工具头运动轨迹应尽量采用走螺旋线的方式,可以提高成形件的成形能力和成形质量.渐进成形实验表明,数值模拟结果与实验结果基本吻合.     

渐进成形A3003铝板减薄带分析及数值模拟研究

研究渐进成形过程中板料减薄带的变化,可以提供合理的加工参数,提高板料的成形性能和加工利用率,减少零件破裂失效.基于渐进成形过程中金属板料轮廓的变化与理想情况下轮廓的区别,对渐进成形初始成形阶段A3003铝板减薄带的产生原因和剪切力的变化过程进行了理论分析,并通过有限元模拟分别从未变形区金属板料的长度和强度两个角度对板料渐进成形过程中未变形区下沉的影响,以及成形角度和杨氏模量对变形区回弹的影响两个方面,对减薄带的产生原因进行研究.结果表明:板料未变形区的下沉和变形区的回弹使板料在初始加工阶段形成一段平缓区域,工具头在平缓区域的变形性质发生了变化,平缓区域发生剪切变形导致了板料在初始加工阶段形成了减薄带;渐进成形时减小板料未变形区的长度,增大板料与垂直方向的角度可以一定程度上阻碍减薄带的产生,模拟结果与理论分析相符合.     

多点复合渐进成形与单点渐进成形的对比分析

为提高金属板材渐进成形的成形质量、成形精度、成形效率和成形极限,了解不同渐进成形工艺对制件成形性能的影响,本文以典型方锥台制件为研究对象,利用有限元软件MSC.Marc对2种渐进成形工艺进行了三维建模,对比分析了单点渐进成形和多点复合渐进成形对制件等效塑性应变、厚度分布和成形精度的影响.数值模拟结果表明:单点渐进成形的等效塑性应变和厚度减薄主要集中在制件相邻侧壁间的拐角处,而多点复合渐进成形的等效塑性应变和厚度减薄均匀地分布在制件成形区;相同成形工艺参数下,相比单点渐进成形,多点复合渐进成形更有利于制件的成形效率、成形质量、成形精度和成形极限的提高,更有利于抑制破裂等失稳现象的产生.2种渐进成形工艺的成形试验表明,数值模拟结果与试验相符.     

硬铝合金半球形零件的渐进成形工艺研究

目的 研究冲压胀形工艺与渐进成形工艺成形半球形零件的区别。方法 使用两种热处理状态的硬铝合金,AA2024-O和AA2024-T4,分别用冲压胀形工艺和渐进成形工艺成形半球形零件。结果 相比较渐进成形零件而言,使用冲压胀形工艺得出的半球形零件的壁厚相对均匀,变形程度可以达到更大;在相同的试验条件下,AA2024-O的成形性能远高于AA2024-T4的成形性能;在本实验所研究的参数范围内,下压量越小,成形高度越大,对AA2024-O进给速率越快,成形高度越大;而对AA2024-T4进给速率越慢,成形高度越大;对于胀形零件,材料在胀形过程中处于双向拉伸应变状态,而渐进成形零件在成形过程中处于平面应变状态;胀形零件的最大应变和最大减薄处是半球的中心,而渐进成形零件的最大应变和最大减薄处是半球的边缘。结论 胀形零件的危险截面在半球的中心,渐进成形零件的危险截面在半球的边缘。     

考虑成形历史的双相钢薄壁结构轴向冲击试验与仿真研究

金属板料塑性成形过程中局部厚度和力学属性将发生变化,进而影响成形结构的最终物理性能。针对双相钢DP590材料,以点焊连接闭口帽型薄壁结构为例,利用落锤冲击试验装置研究了冲压成形条件对结构轴向冲击变形行为的影响,并对该成形—冲击过程进行了数值模拟。试验结果表明:冲压成形构件冲击变形模式为非稳定的混合渐进—欧拉屈曲模式,且随成形压边力增加,构件冲击失稳现象加剧。相应仿真过程发现,引入冲压成形历史信息后,冲击仿真可较为真实地复现物理测试结果,为确保前期冲压成形仿真结果的可靠性,宜采用能够反应三维应力状态的七参数壳单元。     

曲面柔性轧制装置设计与成形工艺分析

采用曲面柔性轧制方法可以实现三维曲面板类件的连续、柔性成形,为了验证该方法的可行性,本文基于曲面柔性轧制原理,设计出成形装置并研究了装置关键部件工作辊的驱动方式,驱动方式可以分为单端与双端两种;进行相关成形实验并对曲面柔性轧制成形工艺进行了分析,探讨了成形过程.结果表明:一次调形成形工艺适用于小变形量情况,成形质量好,效率高;渐进调形成形工艺,以小的压下量逐渐使板料成形,在一定程度上可以消除板料边缘皱褶,减小回弹,利于板料成形;理论上讨论了实时调形成形工艺,该种工艺将会提高成形自动化与效率.对成形件进行了成形精度与厚度分布研究,表明成形效果良好,验证了曲面柔性轧制成形方法的可行性与实用性.     

渐进成形不同热辅助工艺对制件微观结构影响的研究进展

渐进成形作为一种先进的柔性成形技术获得了当今学者的广泛关注,然而传统渐进成形工艺难以对室温环境下整体延展性较差的板料进行加工成形,研究人员提出的不同类型热辅助工艺可以通过提高板料温度环境进而有效改善上述问题。对热辅助渐进成形体系进行了简要概述,按照渐进成形加热方式的不同将热辅助工艺分为热介质加热、电辅助加热、热辐射加热和其他方式加热4个大类,在此基础上综述了不同学者在热辅助渐进成形工艺方面的学术成果,并基于不同类型的热辅助工艺,结合微观层面总结了温度对板料成形性的影响。在热渐进成形加工过程中,材料处在多场耦合作用的复杂情况下,其中热场是导致板料微观组织变化的主要原因,辅助工艺提供的额外热源有利于材料组织发生演变,最终显著改善了材料的成形性,进而提高了零件的成形极限。最后,针对不同类型的热辅助方式在供热范围与温度均匀性等工艺方面不尽相同的问题,作出了简要评价。     

基于随动支撑的板料渐进成形数值模拟

目的 提出了基于随动支撑的板料渐进成形方法,研究基于随动支撑的渐进成形在刀具与随动板之间距离不同时成形精度、厚度、轴向力、等效应变和等效应力的变化情况。方法 通过对厚度为1 mm的6061铝合金板料分别进行普通渐进成形数值模拟、刀具与随动支撑板距离为1 mm和0.8 mm的随动支撑渐进成形数值模拟,分析了板料在成形过程中成形精度、厚度、轴向力和等效应变的变化情况,并将普通渐进成形数值模拟的结果与刀具和随动支撑板距离为1 mm和0.8 mm的基于随动支撑渐进成形数值模拟结果进行对比分析。结果 与普通渐进成形相比,随动支撑渐进成形能够提升成形精度,但当刀具与随动板之间的距离较小时,成形精度较差;随动支撑渐进成形板料侧壁厚度更薄,轴向力的数值及波动范围都更大,且随着刀具与随动支撑板之间距离的减小而增大。此外,当刀具与随动支撑板之间的距离为0.8 mm时,随动支撑渐进成形板料的等效应变会明显增大。结论 基于随动支撑的板料渐进成形在一定程度上可以提高板料成形精度。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。