多步逆成形有限元法中间构型初始解预示算法

在逆成形有限元法中,为考虑加载路径的影响,针对不同成形类型阶段引入中间构型,整个过程被划分为多阶段成形过程,即多步逆成形有限元法,一个好的中间构型初始解的构造是其中的关键问题之一。针对中间构型初始解的构造,提出一种基于滑移约束曲面的节点反向映射法：利用板材的纯几何弯曲效应构造出弯曲构型,经过伪最小面积法优化后生成空间滑移约束曲面;投影展平的最终构型网格面到展平滑移约束曲面网格中,利用面积坐标计算出所有投影节点的坐标;投影节点反向映射回到空间滑移约束曲面上,构造出对应中间构型的初始解。另外,针对中间构型初始解构造中可能出现部分节点无投影区域的问题,给出一种扩展空间滑移约束曲面轮廓的解决方法。零件的数值算例验证相应算法的可行性与有效性。     

冲压模具设计两例

板料的冲压成形是靠凸模和凹模一对冲压副完成的,然而在设计模具时只要充分掌握工件的成形特点和要求,使工件的变形达到一定的成形要求就可以了,不一定要完全与工件形状一致。这样,可简化模具凹、凸模形状的设计,便于零件的制造加工。下面是我们具体应用的两个例子。     

筒形件颗粒软凹模拉深成形试验研究

分析了颗粒软凹模成形的工艺特点,设计了筒形件颗粒软凹模拉深成形试验模具,对筒形件颗粒软凹模拉深成形进行了试验研究,成形出了质量良好的圆筒零件.颗粒软凹模拉深成形零件各部分的厚度均减小,而且随着拉深高度的增加,减薄量增大.与刚性模具拉深工艺相比,该工艺可有效提高板材的拉深成形极限.颗粒软凹模拉深成形和刚性模具拉深筒形件各部位表面微观形貌的对比分析表明:颗粒软凹模成形可抑制凸模圆角区域微裂纹的产生.     

汽车覆盖件模具凸型面拉延方法

针对汽车覆盖件这种具有复杂曲面特征的零件,在传统的全型面拉延成形方法基础上提出一种新的凸型面拉延成形方法。该方法根据拉延成形过程中凸、凹模工作型面上只有凸型面接触板料的特点,通过成形仿真获得全型面拉延的成形极限图(Forming limit diagram, FLD)和凸、凹模与板料的接触区域分布。然后将板料相对凸、凹模工作型面上的起皱区域及双面接触区域所对应的单元剔除,将单面接触区域中面积较小且形态狭长的单面接触区域合并转化为双面接触区域,同时将未转化的单面接触区域外周节点拟合成曲线后导入到CAD中对凸、凹模工作型面进行分割获得所需的凸型面。算例表明该方法在保证拉延成形质量的前提下可以有效地减小凸、凹模工作型面的面积,降低拉延模具的生产成本。     

基于多点成形的液压成形工艺关键技术的研究

介绍了基于液压成形和多点成形原理的板材成形新工艺.该工艺凸模用液体代替,凹模采用多点基本体调形而成.并用凹模垫技术提高多点成形技术中板材面轮廓度形状精度.对该工艺的液压系统、基本体的调形及压边圈等关键技术问题进行了深入研究.研制出了成形装置,并进行模拟试验.     

方盒形件拉深成形无网格法模拟

针对板材冲压成形有限元模拟存在的不足,采用一种新的数值方法——无网格法对方盒形件拉深成形进行数值模拟研究。建立基于无网格法的板材冲压成形力学控制方程。采用材料形函数避免影响域和形函数的频繁更新。通过改造无网格形函数获得动可容形函数,该形函数具有插值性,通过对全域内的节点形函数进行重新构造,可精确施加复杂问题的本征边界条件。利用模具上分布的节点建立矩阵,利用矩阵的特性可实现接触搜索。在此基础上,为提高接触搜索效率,提出建立稀疏"矩阵"数据结构加快接触搜索。编写板材冲压成形无网格模拟程序,实现方盒形件拉深成形无网格法模拟。通过盒形件冲压成形无网格数值模拟考察压边力对盒形件冲压成形过程的影响,获得厚度分布和应力应变分布,通过数值模拟结果与试验结果的比较,表明采用无网格法模拟板材冲压成形是有效的。     

电机罩盖冲压工艺及模具设计

某罩盖是汽车电机产品上的一种阶梯形拉深件,其形状较为复杂,由大、小两部分圆筒组成,存在与拉深外径相差悬殊的小直径凸台,需要采用冲裁、拉深、成形等多种冲压工艺制成,成形较困难。根据零件的结构特点及技术要求,结合该零件的冲压工艺难点,同时考虑到零件生产效率的提高以及制造成本的降低,制订了5种冲压成形工艺方案,经分析比较,选出了最佳的零件成形工艺方案,并设计了落料、拉深复合模以及拉深、成形、冲孔、挤边复合模。生产验证说明,该工艺能成功解决该类两阶梯直径相差悬殊的小直径凸台成形问题,得到质量合格的罩盖零件。     

阶梯形件液压凸模拉深成形装置的设计及试验

针对阶梯形件在刚模拉深成形中易出现起皱、破裂、壁厚偏差大等缺陷以及普通液压拉深易出现的变形不均匀、不充分等问题，开发了一种简单实用、在拉伸机上就能实现板材预胀充液拉深试验的液压凸模拉深成形装置，该装置采用了液压凸模、刚体凹模的拉深方法。通过不同高度的垫板控制移动凹模的位置，并以1060-O态铝板为材料进行相关试验，利用预胀充液拉深原理，得到阶梯形件。结果表明：该装置可合理匹配预胀压力和凹模预胀位置并显著的提高零件的成形高度和成形质量。     

聚氨酯胀形增补模具

<正> 图1所示的零件材料为A3,料厚为1.2mm。此零件以前是采用两半冲压成形后再焊接的工艺,因零件曲面多,焊接和打光都比较费时,效率很低,满足不了生产需要。后来我们改为先把板料卷成圆筒再焊接打光后采用聚氨酯橡胶模冲压成型。起先我们采用的模具结构是中间凸模为聚氨酯橡胶,两端采用钢凸模垫,在成形过程中,零件的中间部位成形比较好,但两端的喇叭口部位成形不好,没有达到尺寸要求。经分析,其主要原因是由于中间凸模体积小变形量不够所     

机油泵盖板连续模设计

图1所示,为一摩托车机油泵盖板,材料为45钢板。分析零件形状尺寸,若能在一套模具上完成该件的冲孔、成形、落料工步,则功效高、效率好。若采用复合模,模具制造相对简便,但模具凸、凹模芯受零件形状尺寸的影响,最小壁厚难以满足强度要求,模具寿命和可靠性也无法保证,为此,设计采用连续模结构。     

Directional Multiscale Analysis and Optimization for Surface Textures

Surface texturing has a potential to become a cost effective and easy way to improve the tribological performance of lubricated interfacing surfaces. Effects of surface textures on the performance of machine elements as frictional pairs have been investigated over the past two decades. However, despite this research only a limited number of analytical solutions have been proposed as the majority of studies have been experimental and results obtained have not been optimal. This is because the commonly used surface characterization methods are not able to quantify surface textures over a range of scales at different directions and the optimization methods used work only for relatively simple textures and specific constraints imposed on pressure, film thickness, sliding velocity and lubricant rheology. Previous studies have addressed these issues, to some degree, by developing directional fractal signature methods and unified computational approach for texture optimization. In this article, recent advancements in the development of fractal methods and optimization of surface textures are presented.     

齿轮箱流体动压滑动轴承的多目标优化

建立了流体动压径向滑动轴承优化设计的数学模型,借助Matlab优化工具箱,对齿轮箱径向滑动轴承进行了优化设计,结果表明该方法能够获得比常规设计更佳的设计参数。     

H∞ sliding mode control of discrete switched systems with time-varying delays

The finite-time boundedness issue for a class of discrete switched systems with time-varying delays is investigated via sliding mode control (SMC) approach. By employing the Lyapunov functional and average dwell time method, new sufficient conditions are derived to guarantee the finite-time boundedness of the dynamic system in the novel sliding surface. By solving an optimization problem, the sliding mode controller is synthesized such that the discrete reaching condition is satisfied and the chattering is reduced. A simulation example tests the feasibility of the provided SMC scheme.     

Formation of ordered groups of quantum dots during Ge/Si heteroepitaxy

A new approach to the creation of circularly ordered Ge nanoislands by epitaxy on the surface of a heterophase structure consisting of a Si(100) substrate with premade seeds in the form of SiGe nanodisks or SiGe nanorings is developed. It is shown that the spatial configuration of islands in the group is due to the nucleation of the islands in the area of local minima of the elastic energy density on the surface of a circular seed. On the basis of this approach, a number of multilayer structures with vertically aligned ring groups of quantum dots were grown. The elemental composition and luminescent properties of the ordered structures are studied.     

Optimization of Surface Texturing for Contact Between Steel and Ultrahigh Molecular Weight Polyethylene Under Boundary Lubrication

In this study, we developed a design method for surface texturing optimization and evaluated it experimentally. Square patterns composed of different fractions of pore shapes were prepared by using a nanosecond pulse laser on AISI 1045 steel surfaces. A pore diameter of 75 μm was used to design the area densities. The area density was 5–25 %, and the pore depth was 20–75 μm. Different area densities and pore depths were examined for optimization, and pin-on-disk sliding tests were performed using ultrahigh molecular weight polyethylene pins. The results showed that all of the coefficients of friction of the textured specimens were reduced regardless of the area density and aspect ratio. Optimization was performed according to the measured dimensions of the pores, and the optimized area density and pore depth under the current sliding conditions were found to be 25 % and 25 μm, respectively.     

Surface behaviour of as-Cast Al–Fe intermetallic composites

In order to produce energy-efficient material for tribological applications, Al–Fe inter-metallic composites have been produced by liquid metallurgy route. Iron content of the composites varies from 1.67 to 11.2 wt.%. These composites have been tested for their wear properties at different parameters. Debris and wear tracks have been studied in detail to see the surface effects during dry sliding and have been correlated to wear properties. Observations show that low loads and sliding velocities are dominated by oxidative debris and largely covered wear track surface with smooth oxide layer is observed. Whereas metallic debris dominates at higher loads and sliding velocities and highly deformed wear track surface with deep grooves and gross delamination were observed. Further, wear rate is seen to increase continuously with load whereas with sliding velocity it attains a minima after initial decrease and then increases continuously. Low solubility of iron supports the formation of FeAl₃ and an increase in hardness from 95 to 179 VHN continuously improves the wear resistance with increase in percentage iron.     

Metamodel-based global optimization using fuzzy clustering for design space reduction

High fidelity analysis are utilized in modern engineering design optimization problems which involve expensive black-box models.For computation-intensive engineering design problems,efficient global optimization methods must be developed to relieve the computational burden.A new metamodel-based global optimization method using fuzzy clustering for design space reduction(MGO-FCR) is presented.The uniformly distributed initial sample points are generated by Latin hypercube design to construct the radial basis function metamodel,whose accuracy is improved with increasing number of sample points gradually.Fuzzy c-mean method and Gath-Geva clustering method are applied to divide the design space into several small interesting cluster spaces for low and high dimensional problems respectively.Modeling efficiency and accuracy are directly related to the design space,so unconcerned spaces are eliminated by the proposed reduction principle and two pseudo reduction algorithms.The reduction principle is developed to determine whether the current design space should be reduced and which space is eliminated.The first pseudo reduction algorithm improves the speed of clustering,while the second pseudo reduction algorithm ensures the design space to be reduced.Through several numerical benchmark functions,comparative studies with adaptive response surface method,approximated unimodal region elimination method and mode-pursuing sampling are carried out.The optimization results reveal that this method captures the real global optimum for all the numerical benchmark functions.And the number of function evaluations show that the efficiency of this method is favorable especially for high dimensional problems.Based on this global design optimization method,a design optimization of a lifting surface in high speed flow is carried out and this method saves about 10 h compared with genetic algorithms.This method possesses favorable performance on efficiency,robustness and capability of global convergence and gives a new optimization strat     

磨粒微观滑动接触过程热效应的有限元分析

利用ANSYS有限元软件分析了磨粒与被磨损材料表面滑动接触过程中,在摩擦热和力场的耦合作用下,接触区表现出的局部温度变化、应力变化等特性。结果表明,在磨粒滑移过程中,磨粒相当于接受固定热源作用,接触区温度逐渐上升,温度存在起伏波动现象,瞬现温升最高点在磨粒接触区两侧,反映出接触状态的不连续性,接触区状态的非稳定性;被磨材料表面的各点在进入接触前、经历接触时、脱离接触时,接触区温度存在先升高再下降的变化过程,同时,接触区的应力、剪应力、接触压力也发生变化。磨粒滑动过程的热效应问题研究将有助于揭示接触过程中材料表面损伤机制。     

大排量柱塞泵滑靴副底面结构优化设计

滑靴副作为大排量柱塞泵的重要摩擦副,其底面结构是影响大排量柱塞泵综合性能的关键因素。为设计一种适用于大排量柱塞泵的滑靴底面结构,改善大排量柱塞泵滑靴副的综合性能,通过构建剩余压紧力条件下滑靴副总效率数学模型,以滑靴副总效率为优化目标,引入黑洞-蚁群优化算法对大排量柱塞泵滑靴底面结构参数进行优化设计。通过仿真的方法分析了不同柱塞腔压力以及不同转速对优化前后滑靴副总效率的影响,结果表明,基于黑洞-蚁群优化算法得到的滑靴底面环结构有着明显的效率提升。