An upper bound solution for closed die sinter forging of hexagonal shapes

The paper reports on an investigation into the various aspects of closed die cold forging of hexagonal powder preforms, which have been compacted and sintered from atomized powder. It is found that for certain dimensional ratios of the preform, the die pressure is minimum. An attempt has been made determine the die pressures developed during the closed die forging of the hexagonal powder preform by using an upper bound approach. The results so obtained are discussed critically to illustrate the interaction of various process parameters involved and are presented graphically     

Geometric mapping of yarn structures due to shape change in 3-D braided composites

The internal yarn structure in 3-D braided preforms possesses a certain topological character which is unique to the braiding method used. Hence, preforms of different shapes but braided by the same method have topologically similar yarn structures. This unique property offers the possibility that the yarn structure in preform of one shape may be geometrically mapped to that in another shape, and vice versa.

This study discusses a geometric mapping methodology, the objective of which is to obtain the appropriate mapping which analytically links the yarn structures in two preforms of different shapes; if the yarn structure in one preform is known, the yarn structure in the other can be determined by the derived geometric mapping.

Two broad classes of mapping are discussed. The first concerns mapping between two preforms that are braided directly in two different shapes; the second concerns mapping between the initial and final shapes of one single preform which is deformed after braiding. In each case, the mathematical forms of the desired mapping functions are obtained, satisfying the geometric constraints imposed by the internal yarns in the respective preforms. The determined mapping functions are then used to investigate the braidability and/or deformability of the considered preforms. Specifically, limiting windows for the braiding parameters that insure the braidability and/or deformability of the preforms are obtained using the appropriately derived mapping functions.

The 4-step 1 × 1 braiding method is used throughout this paper to illustrate the general mapping procedure; rigorous and explicit geometric relationships are derived leading to mapping functions between preforms of rectangular and curvilinear cross-sections. Numerical examples involving mapping between preforms of rectangular and tubular cross-sections are investigated in detail, along with examination of the preform braidability and/or formability.     

基于可视化的型坯拉伸吹胀模式的研究

在型坯再加热条件不变的情况下，通过全透明模具和数码摄像机研究了两步法拉伸吹塑中拉伸与吹气的时序（即预吹气延迟时间t0）对型坯拉伸吹胀模式的影响。研究表明，t0是影响拉伸吹胀模式的一个关键因素，随着t0的增加，型坯预先被拉伸的轴向长度也增加，这时瓶肩的厚度减小，瓶底的厚度增大。实验观察到型坯的拉伸吹胀存在海豚型、积沙型和截圈型3种模式。以海豚型模式成型时，型坯在轴向和径向同时得到充分地拉伸，成型瓶壁厚分布最合要求，积沙型次之，而以截圈型得到的瓶子不合要求。     

金属预成形优化设计及凝聚函数方法

研究了金属预成形设计中的形状优化设计问题及相应的求解算法,并讨论了凝聚函数在这类问题中的应用。金属预成形设计在本质上是一类反问题,给出采用形状优化设计方法求解这类问题的数学模型,讨论了目标函数构造方法对数值计算收敛性的影响。提出采用凝聚函数将∞-范数形式的形状误差函数转化为光滑可微的目标函数,显著提高了求解以金属预成形设计为背景的优化问题的收敛性。采用流动模型描述金属材料高温下的变形过程,利用基于梯度的数学规划方法求解了金属预成形优化设计问题。数值算例验证了所提出方法的有效性。     

预制坯形状对扭力梁内高压成形的影响分析

针对复杂截面扭力梁内高压成形容易出现咬边和开裂的问题,以轿车V型扭力梁为例,采用数值模拟和试验方法,分析了预制坯形状对扭力梁内高压成形的影响,重点研究了压下量（Y）和侧向宽度（B）对预制坯形状和内高压成形的影响.结果表明,当Y、B分别为0.83D（D为管材直径）、0.73D和0.78D、0.78D时,得到的预制坯形状在...     

基于有限元灵敏度分析的预锻模具形状优化设计

在控制锻件几何形状的前提下 ,采用有限元灵敏度分析方法 ,对预锻模具形状进行优化设计 .针对下模速度为零时 ,速度灵敏度边界条件为零 ,其形状在优化迭代过程中得不到优化的情况 ,对速度灵敏度边界条件提出改进措施 ,使上下模具形状同时能够得到优化 .最后给出了优化设计实例 ,验证该方法的可靠性 .     

基于SCM的光纤预制棒气相沉积机床控制系统

在了解光纤预制棒加工工艺的基础上,选择MCVD法为研究对象.考虑到光纤气相沉积技术要求控制系统高度自动化和可靠性,研制了以单片机为处理芯片的控制系统,设计了包括微处理器模块、过程通道模块、人机接口模块等硬件组成以及控制系统软件的实现方法.实现了性能合格的光纤预制棒产品的生产.     

纯碳坯渗硅制备反应烧结碳化硅的研究

以石油焦粉制备纯碳素坯高温渗硅的方法制备了反应烧结碳化硅陶瓷。研究表明 ,素坯的碳含量 (或孔隙率 )对材料的最终物相组成有决定性的影响 ;合成 Si C时的热效应以及反应过程中的体积效应 ,是影响石油焦坯体烧结的根本原因 ;烧结时间短使晶粒细化 ,是材料强度提高的主要原因。 90 %理论碳含量的素坯渗硅后 ,所得材料的密度为 3.0 8～ 3.12 g/ cm3,强度为 (5 5 0± 30 ) MPa     

New thermoplastic composite preforms based on split-film warp-knitting

A newly developed type of dry thermoplastic textile preform incorporating non-crimp glass fibre reinforcements and matrix material in the form of split-film is presented. Weft-inserted warp knitting has been chosen as a textile production technique for its low cost. A specialized glass fibre/polypropylene matrix system has been proven to perform favourably in melt impregnation and to provide good composite properties. Some of the processing techniques to be applied to the new textile preform are presented, one of which is the QUIKTEMP concept for fast heating and cooling of tools for thermoplastic moulding. Composite plates produced from preliminary split-warpknit structures reveal a good potential for cost-saving while reasonable mechanical properties can be maintained.     

中国光纤光缆产业的历史、现状与前景

近年来国产光纤的市场份额正逐步上升,但国内光纤生产企业在原材料上受国外制约较大,光纤预制棒严重依赖进口,而且国内光纤光缆产业联系松散,在5家光纤光缆一体化企业中,仅有两家拥有完整产业链。中国正式加入WTO后,国内光纤光缆企业的整合在所难免,他们应积极进行产业升级,形成多个具有完整产业链的大集团。