ZQQTB磨球凝固过程数值模拟及工艺优化

针对Φ125mm ZQQTB中锰合金铸铁磨球的铸造工艺,利用华铸CAE模拟软件对磨球的浇注凝固过程中流动场和温度场进行数值模拟,预测了Φ125中锰合金铸铁磨球在铸造中可能产生的缺陷位置,并对磨球内部产生缩孔、缩松的原因进行了分析。通过增加上铁模及砂套,缩短内浇道尺寸等对浇注系统进行了修改和优化,并对浇冒系统优化前、后的铸造方案进行了温度场的数值模拟对比。结果表明,优化后的浇冒系统实现了顺序凝固,缩孔缺陷从磨球内部转移到了冒口内,模拟结果与实际浇注结果相符。     

基于表面网格的塑料注射成型浇口位置优化

直接利用表面网格的几何信息计算最佳浇口位置,可显著提高浇口位置优化算法的计算速度与有效性。基于流动平衡的定义和权值流动长度,建立了优化目标函数。根据一定假设条件,将表面网格转化为带权值的无向图,结合遗传算法与爬山算法的优点,建立了Generic-Hillclimbing(GH)浇口位置搜索方法,并利用最短路径算法求解目标函数值。与Moldflow浇口优化功能相比较的实例表明,该方法能够高效准确地得到优化的浇口位置。     

等效源方法的适用性判定及源的优化布置

采用等效源方法建立了辐射体表面法向振速到场点声压的传递函数,实现了声场的数值预报。以相对速度误差为评价指标,对等效源法的求解精度进行了先验判定,提出了以1/2速度误差限制线来确定等效源法适用的频率范围,进一步以声辐射效率为指标对声压计算结果的合理性进行后验判定。分别针对单个频率点、多个频率点对等效源的位置进行优化,结果表明存在最优等效声源位置以满足辐射体表面法向振速的最佳匹配。将等效源的优化方法应用于具有声反射面的脉动球源及锥-柱组合壳体的辐射声场预报,预报结果与解析解及边界元法计算结果吻合较好,说明等效源法在工程上应用是可行的。     

基于等效辐射声功率和形貌优化的车身结构噪声控制

以某车型白车身为研究对象，首先建立白车身结构有限元模型并验证其有效性；随后通过对模型进行等效辐射声功率分析，得到白车身关键板件对车内的辐射噪声水平，并识别贡献量较大的结构位置；再根据分析结果构建白车身形貌优化模型并进行计算求解；最后将优化前后白车身等效辐射声功率进行对比，优化后辐射噪声在分析频段内整体降低，且最大响应峰值降低3.8 d B。研究结果表明，在汽车白车身设计阶段，基于等效辐射声功率分析和形貌优化设计可以有效地抑制结构的辐射噪声。该方法和思路可为工程领域相关的结构噪声分析和控制提供参考。     

单轴位置转台轴系特性分析

转台作为检测与评价惯性导航仪器仪表的主要设备,其轴系静态刚度、动态特性和控制精度等直接影响到检测的可靠性和置信度。本文针对单轴位置转台,对轴承和驱动电机等关键部件进行了等效处理,利用软件ANSYS建立了有限元模型,通过静力学分析得到了转台简化模型的变形情况;通过模态分析得到其固有频率和振型,结果表明转台结构刚度较大,其固有频率远大于外部激励频率,可以避免共振,并为后续的结构优化打下基础。     

物理可视化技术在聚合物模塑成型分析中的应用

为了克服传统注塑成型过程的不可见性,在模具或者注塑机的料筒上人为添加视窗,在视窗位置用石英玻璃代替传统的金属材料,使用摄像机来记录聚合物的填充或塑化过程。主要介绍了物理可视化技术在模塑成型中的应用:利用高速摄像机拍摄得到熔体的充模过程,选取一定数量的图片,根据图片的时间差和流动前沿的位置变化,可以获得熔体流动前沿的填充形态和填充速度;利用椰果壳活性炭颗粒作为示踪粒子,可以得到熔体内部流场的流动轨迹和流动速度等重要参数;利用物理可视化技术结合模具关键位置的温度压力传感器,可以直观地解释填充不平衡现象产生的原因和规律。     

镁合金典型构件等温成形数值模拟及优化

运用DEFORM-3D软件对镁合金箱盖的等温成形过程进行了有限元数值模拟分析。根据箱盖结构特点,初步设计3种形状的预制坯,依据数值模拟结果,优化得到最终预制坯,并分析了等温成形过程中箱盖的等效应力、等效应变、速度、载荷-行程曲线等。研究结果,Ⅲ型预制坯金属在各个部位的流动相对较均匀,流动自然平滑,无拉伤、折叠等缺陷发生。综合分析,得出Ⅲ号预制坯的成形效果最好。     

T形截面实腹型钢砼梁抗弯承载力计算方法探讨

对于《钢与混凝土组合结构设计施工手册》中关于T形截面实腹型钢砼梁抗弯承载力的计算假定提出了若干改进建议：按照中和轴与组合截面相对位置的不同，给出了较为完整的中和轴位置的判定准则：采用等效应力法计算此类构件抗弯承载力，得到了相关计算式。     

汽车空调暖风机热交换器的优化设计

提高汽车空调性能的主要方式是提高热交换器的换热效率. 由于汽车内部空间的限制,不能单纯依靠增加热交换器体积的方法来提高热效率,因此对热交换器结构优化设计将具有现实意义. 利用Flnent求解和正交设计的方法对汽车暖风机热交换器进行优化设计. Fluent软件可以模拟热交换器的流动和传热过程,正交设计的方法可以建立回归方程,因此可以得到出口温度的数学模型,该模型定量地描述了翅片间距、翅片高度及水管间距对换热效率的影响,优化汽车暖风热交换器的结构,最后通过试验证明了优化设计结果的准确性.优化热交换器的结构参数：翅片间距为1.1 mm,翅片高度为6.9 mm,管距为5.2 mm.根据Fluent模拟仿真得到出口温度的回归方程：Y=307.308+2.333X₁ +0.677X₂+0,561X₃-2.501X₁²,影响出口温度的因素依次为翅片间距、翅片高度和水管间距.Fluent模拟仿真和正交试验设计相结合的方法有助于产品结构分析和优化设计.     

船舶管路系统弹性支承在冲击作用下的位置优化设计

在强冲击作用下 ,船舶的管路系统会发生剧烈的振动 ,从而导致管路系统的破坏。本文拟采用不同边界条件的直梁模型 ,模拟管路系统 ,利用等效最优控制特性法建立系统的状态方程 ,进而得到直梁模型在多约束情况下的动态响应。经过对该模型冲击作用后在持续性周期荷载、随机荷载作用下的振动响应优化分析指出 ,合理布置弹性支承位置可以有效的避开共振区 ,改善弹性支承的减振效果。本文所得图表和结论对于管路系统弹性支承的位置设置提供了理论上的参考依据。     

Branch and bound search to optimize injection gate locations in liquid composite molding processes

In liquid composite molding (LCM) processes the resin is injected into a mold cavity containing pre-placed reinforcement fabrics through openings known as gates, and the air leaves the mold through openings called as vents. The gate and vent locations play a crucial role as to whether the resin covers all empty spaces between the fibers in the mold, which dictates the quality and the properties of the final product. Optimization methods are used to find the gate and vent locations that will create a favorable flow that will prevent dry spots. In this paper, branch and bound search is adapted to mold filling in LCM processes and is used to find the optimal injection gate location that fulfill two different objectives. First, to find the gate locations that will yield the shortest fill time. Second, to find the auxiliary gate locations that will counteract a disturbance during filling and minimize the size of the dry spot. In each case, three geometries have been studied. The results are compared with exhaustive search and genetic algorithms results to illustrate the efficiency and accuracy of branch and bound search method.     

Gate elements at injection locations in numerical simulations of flow through porous media: applications to mold filling

Mold filling in polymer and composite processing is usually modelled as a special case of Darcy flow in porous media. The flow pattern and the time necessary to fill the mold depend on the ‘gate’ locations where resin is injected into the closed mold. In composite manufacturing, these are commonly outlets of small tubes transporting resin from a reservoir and their diameters are several orders of magnitude smaller than the mold dimensions. Similar size issue is also encountered in other applications of flow through porous media, such as oil and water pumping and drilling. Traditionally, these inlets are modelled by pressure or flow rate boundary condition as applied at a node of the finite element mesh that represents the injection gate. The omission of the inlet radius in the model results in a mathematical singularity as the mesh gets refined. The computed pressure or flow field depends on the mesh size and does not converge to the accurate solution, as the finite element mesh is refined. It is possible to deal with this phenomenon by modelling the inlet geometry more accurately but this approach is inefficient, as it requires additional degrees of freedom and, above all, significantly complicates the modelling process if the inlet location is not fixed a priori. This paper presents a more efficient alternate solution. It uses special ‘gate’ elements embedded in the mesh around the injection locations. Instead of adjusting the geometrical modelling of the injection location, the adjacent elements use modified shape functions to accurately model pressure field in the neighbourhood of small radial inlet. The proper pressure field shape‐functions for ‘gate’ elements based on linear finite elements are derived. The implementation in an existing mold filling simulation and how the ‘gate elements’ are automatically selected is described. An example to demonstrate the use of ‘gate’ elements and convergence towards the accurate solution with mesh refinement is presented. Copyright © 2004 John Wiley & Sons, Ltd.     

Optimum arrangement of gate and vent locations for RTM process design using a mesh distance-based approach

Resin transfer molding (RTM) is considered a promising manufacturing process for high performance composite materials. In the RTM process, gate/vent location is one of the most important variables in process design. It has a great impact on mold filling time and resin flow pattern, thus affects the process efficiency and product quality. Many studies have been conducted on optimization of RTM mold filling process to determine the locations of gates and vents. Most of them approached the optimum process design problem via numerical method-based process simulations. Due to the extensive computations involved, such approaches are difficult to be implemented for large and complex parts. This paper introduces a new approach to optimum arrangement of gates and vents for two-dimensional or two and a half-dimensional parts based on the mesh distance concept. With the assumption that the resin first fills the nodes closest to gates, the vent locations that minimize the area of trapped air can be determined. With the objective of minimizing the maximum distance between gates and vents and avoiding dry spot formation, genetic algorithm was employed to carry out the gate location optimization. The new RTM process design approach was tested on numerous cases obtained from the literature. It was found that the new approach was very efficient and effective in finding the optimal locations for gates and vents. The resulting gate and vent locations lead to satisfactory process performance as indicated by the optimal process performance index. The computational time required by the new approach was only a fraction of that reported by those simulation-based methods in the literature.     

Use of Centroidal Voronoi Diagram to find optimal gate locations to minimize mold filling time in resin transfer molding

In Resin Transfer Molding (RTM) processes, liquid resin is injected into a dry reinforcement structure to create a composite part within given time limits. To reduce the fill time, resin may be injected into the mold through multiple gates. The minimum number of gates and their locations needs to be determined. To reduce the number of scenarios to be simulated, an iterative method is implemented for multiple-gate injection optimization. The inlet nodes on the mesh surface are used to generate a Voronoi Diagram of the mold geometry. Then the optimal Centroidal Voronoi Diagram (CVD) of the mold surface is searched iteratively. It is shown that the generation points associated with the optimal CVD correspond with the gate locations that yield the shortest fill time. The results are compared with exhaustive search and genetic algorithms results to illustrate the efficiency and accuracy of CVD method.     

树脂传递成型加工注射口位置的快速优化法

树脂传递成型加工工艺是一种先进复合材料加工的方法。虽然计算机数值模拟的研究已经取得了很大进步,但计算机数值模拟非常耗时间。本文中提出了一种树脂传递成型工艺注射口位置的快速优化方法。该法假设树脂首先注满离注射口近的节点,再根据溢料口的位置安排要求避免干点的出现这一点来决定溢料口位置;如果设计的溢料口数量比计算出来的必须的溢料口数量少,则会出现干点区。把干点区的面积作为罚函数加入目标函数中,目标函数的主体是从注射口到溢料口的距离。因此,笔者是在固定溢料口和注射口数量的前提下优化注射口的位置,获得注射口位置后,经过计算将获得溢料口位置。由于注射口位置是在离散的节点位置上,优化的变量是节点编号,所以优化方法采用功能很强的遗传算法来进行。针对五种模型进行了优化,优化的结果说明了本方法的可行性。     

笔记本电脑电池盖进浇方案MOLDflow分析

为了减少笔记本电脑电池盖产品的注塑缺陷和提高一次试模的成功率,提出在模具设计阶段改善产品成型质量的模具结构优化方案.应用MOLDFlow软件对电池盖产品的进浇方案进行仿真分析,分析了浇口尺寸、模具温度和成型工艺参数对填充时间、熔接线、气穴位置的影响,证实了所提改善方案的正确性,并得到优化的成型工艺参数,从而解决了电池盖的注塑缺陷问题,提升了生产效率,为模具设计人员进行模具设计以及注塑工艺人员进行工艺参数的调整提供依据.     

RTM工艺注模过程边缘效应模拟分析

RTM工艺需将纤维预制体预置到模具中,由于纤维预制体结构不均匀性和模具形状、尺寸等影响,极易产生边缘效应。边缘效应会严重影响树脂流场发展和压力场分布。本文作者采用等效渗透系数方法模拟边缘效应,得到了其影响下的树脂流动前峰曲线和压力场。研究表明:一方面边缘效应可能导致不期望的树脂流场发展而形成工艺缺陷——干斑;另一方面可以利用边缘效应提高工艺效率:常流率注射时减小合模压力和注射压力,常压力注射时可以减少注模时间。      

Effect of gate size on the melt filling behavior and residual stress of injection molded parts

This paper studies the effects of gate size on the cavity filling pattern and residual stress of injection molded parts. A total of three rectangular gates with different sizes were used. Experiments were carried out by using a dynamic visualization system. A flow visualization mold was specially designed and made for this study. A high-speed video camera was used to record the mold filling phenomena of cavities with different gate size and different processing parameters. In addition, a Stress Viewer was used to characterize the residual stress of molded samples. It was found that the undersized gate has many adverse effects on the filling behavior and residual stress of molded parts. With a larger gate, the cavity will be filled faster and residual stress of parts may be smaller. The result of the study also indicates that nozzle temperature and injection rate can significantly affect the above two aspects.     

Temperature and pressure evolution in fast heat cycle injection molding

An accurate mold temperature control during injection molding processes allows obtaining objects with better surface finishing, more accurate surface replication, and reduced frozen-in orientation. The control of these properties is particularly important when the thickness of the molded part is very small as in the case of microinjection. In this work, thin multilayer heaters are adopted to obtain a very fast mold surface temperature evolution during the process of an isotactic polypropylene (iPP). The effect of mold temperature history on the pressure developed inside the cavity is analyzed and correlated to both gate solidification and mold deformation. Results confirmed that, with a fast control of the cavity surface temperature, a reduction of the injection pressure is achieved, without affecting the cycle time. The understanding of the phenomena that occur during the fast temperature evolution on the cavity surface can allow the microstructural calibration of the molded parts.