Application of upper bound method to the powder‐forging of cup‐shaped axisymmetric preforms for estimating punch load

This paper is concerned with the analytic derivation of the punch load required to forge cup‐shaped axisymmetric porous preforms. Splitting the two‐dimensional preform domain into three rectangular regions, we assumed the kinematically admissible velocity fields to apply the upper bound method. According to the resulting formulas, we developed an incremental numerical algorithm for computing time‐discretized step‐wise punch loads and preform volumes. In order to illustrate the validity of the proposed estimate, we compared the numerical results obtained by the present analysis with those by the finite element simulation. From the comparison made through different preform dimensions, we observed that the present analysis expects the reliable upper bounds of process step‐wise punch loads. Copyright © 2001 John Wiley & Sons, Ltd.     

汽车六角球头冷锻工艺优化与数值仿真

冷锻成形工艺是一种少无切削的净近成形工艺,以其精度高、生产效率高、低耗节能等优点,大量使用在汽车零配件的生产。六角球头销是汽车转向系统中的关键零件,其六角成形的质量直接影响到产品的使用性能。本文针对六角一次成形发生镦锻失稳问题,基于金属塑性成形理论,分析在镦锻过程中的金属流动,提出采用预成形工艺。根据产品结构,提出了大V锥形、锥形、锥六角形三种预成形工艺方案,采用DEFORM-3D对六角头成形方案进行数值仿真。为了得到最优参数,通过建立优化数学模型,对数值仿真获取的应力应变、损伤值分布、载荷进行优化得到最优方案。结合有限元数值分析对比分析三种方案,得到了预成形为锥形的成形效果最好,材料流动更为合理。经生产试验证明,通过预成形为锥形生产的六角头充填饱满,无不良缺陷,对生产同类型的成形工艺具有一定的参考价值。     

Numerical simulation of forging a ball from a cylindrical billet

Abstract

Rigid‐viscoplastic finite element equations are used for the analysis of metal forming process. With the view of solution accuracy and computation efficiency, the possible overconstraint of the incompressibility condition is avoided by modifying the penalty method in the variational formulation; and both the direct iterative method and Newton‐Raphson iterative method are combined to solve the finite element equations. The forging process of a ball from a cylindrical workpiece is completely simulated by a remesh procedure. The computed results agree well with the experimental measurements. It is shown, during the early stage of plastic deformation, the effect of friction is small, but gradually increases with further plastic deformation. In the finishing stage, the shear plastic deformation is found mainly in the flash portion. As the shape factor of workpiece increases, the filling of the die cavity is more complete, but the required forming energy increases and the variation of microstructure within the final forged product is intensified. The effect of die velocity also improves die cavity filling.     

基于有限元模拟的四通阀体多向模锻工艺研究

针对阀体传统制造工艺效率低、锻件性能差、成本高等问题,本文提出采用先进的多向模锻工艺进行阀体制造,并以一种不等径四通阀体为典型对象,结合Deform-3D数值分析进行工艺研究.首先,根据不等径四通阀体的结构特征,确定了分模面,并依此设计了两种锻件图;其次,根据锻件图设计了 3种不同的多向模锻结构,并分别确定了模具的加载...     

上模压下速度对带阻尼台叶片精锻影响的研究

利用DEFORM-3D,采用刚粘塑性有限元法,建立了带阻尼台叶片精锻过程的三维有限元模型,模拟分析了上模压下速度对带阻尼台叶片精锻过程的影响规律.获得了不同上模压下速度时的等效应力、最大主应力等场变量分布及带阻尼台叶片精锻过程载荷-行程曲线,并根据最大主应力分布提出了对终锻坯料形状设计的建议.研究结果对带阻尼台叶片精锻工艺的制订具有重要的指导意义.     

大弯扭叶片热模压成形有限元模拟及其预制坯的优化设计

采用有限元方法进行了大弯扭叶片热模压成形工艺的数值模拟，并利用模拟结果实现了成形叶片的反向展开，完成了叶片热模压成形的平板预制坯的优化设计，研究并将该方法所得到的展开平板坯与几何展开法和机械压平法的结果进行了对比，研究发现，传统展开方法得到的结果与有限元模拟法得到的结果相差很大，有限元方法考虑了实际成形中温度场的变化、工件定位方式，塑性变形过程，可以得到定位准确、周边余量很小有限元方法考虑了实际成形中温度场的变化、工件定位方式、塑性变形过程，可以得到定位准确、周边余量很小且分布均匀、压形后贴模情况优良的平板预制坯，与目前常见的几何展开法和机械压平法相比取得了显著进步，实验结果表明，采用有限元法设计的预制坯可直接用于生产，无需反复调试，节约了材料，提高了生产效率。     

汽车盘体零件小飞边模锻成形工艺开发及数值分析

汽车盘体零件通常采用机加工成形或者两步锻造成形(预锻+终锻),而机加工成形的效率和材料使用率较低、两步锻造成形的设备及模具成本较高,因此对该盘体零件的一步锻造成形的可行性进行了研究。根据汽车盘体零件的结构特征,设计了3种不同形式的飞边槽结构,并通过有限元分析软件Deform-3D分别进行了建模及数值分析,对比了不同飞边槽结构对汽车盘体零件填充质量、锻造成形力及锻模磨损的影响。最终得出了采用沟式飞边槽结构更优的结论,同时从等效应力分布规律和温度分布规律两方面分析了该结构下锻后零件的质量。结果表明:采用沟式飞边槽结构能得到填充完整、质量好、无瑕疵的汽车盘体零件,并通过生产实践进行了验证,提高生产率的同时有效降低了材料成本、模具成本、设备成本。     

An upper bound limit load for overmatched scarf-joint specimens

A simple kinematically admissible velocity field involving single jump lines is proposed to find an upper bound limit load for overmatched scarf-joint specimens. It is shown that the solution based on the chosen velocity field depends on two dimensionless parameters, while the number of essential dimensional parameters is four. This is a great advantage for engineering applications. The results, for a particular case, are compared with a similar solution for centre-cracked tensile specimens and one which is obtainable from the new solution as a particular case.     

An extended advancing front technique for closed surfaces mesh generation

An extended advancing front technique (AFT) with shift operations and Riemann metric named as shifting‐AFT is presented for finite element mesh generation on 3D surfaces, especially 3D closed surfaces. Riemann metric is used to govern the size and shape of the triangles in the parametric space. The shift operators are employed to insert a floating space between real space and parametric space during the 2D parametric space mesh generation. In the previous work of closed surface mesh generation, the virtual boundaries are adopted when mapping the closed surfaces into 2D open parametric domains. However, it may cause the mesh quality‐worsening problem. In order to overcome this problem, the AFT kernel is combined with the shift operator in this paper. The shifting‐AFT can generate high‐quality meshes and guarantee convergence in both open and closed surfaces. For the shifting‐AFT, it is not necessary to introduce virtual boundaries while meshing a closed surface; hence, the boundary discretization procedure is largely simplified, and moreover, better‐shaped triangles will be generated because there are no additional interior constraints yielded by virtual boundaries. Comparing with direct methods, the shifting‐AFT avoids costly and unstable 3D geometrical computations in the real space. Some examples presented in this paper have demonstrated the advantages of shift‐AFT in 3D surface mesh generation, especially for the closed surfaces. Copyright © 2007 John Wiley & Sons, Ltd.     

The effects of die shapes and additives on the physical and biodegradable properties of biodegradable cushioning extruded foams

In this study, efforts were focused on the effects of the operating parameters, i.e. die shapes (DS), PVA ratio (PR), additives (AT) on the physical and biodegradable properties of the corn/PVA extrudates. We also evaluated the extrudates as cushioning materials. The process variables were the operating, conditions, die shapes (○, ∞, ? and O ), PVA ratio (40%, 50%, 60%) and additives [sodium bicarbonate (NaHCO₃), calcium carbonate (CaCO₃) and calcium hydroxide (Ca(OH)₂)]. The experiment is a 4 × 3 × 3 factorial design. Samples of each treatment were collected and the physical, mechanical and chemical properties were measured and analysed using the PROC ANOVA and PROC CORR of the SAS 6.0 software package. 35 The experimental results indicated that: (a) The change of die shapes (DS) had a significant effect on the longitudinal expansion, bulk density, compressibility and biodegradability properties of the extrudates; (b) the change of PVA ratio (PR) had a significant effect on the longitudinal expansion, bulk density and compressibility, but no effect on the biodegradability properties of the extrudates; and (c) the change of additives (AT) had a significant effect on the longitudinal expansion, bulk density and compressibility, but no effect on the spring index of the extrudates. Copyright © 2003 John Wiley & Sons, Ltd.     

基于土体连续性作用下挡土墙动力响应的显式闭合形式解

挡土墙-土动力相互作用是影响挡土墙地震响应的关键因素.基于连续介质模型分析挡土墙-土动力相互作用是当前主要的研究手段.但当前的连续介质模型无法获得挡土墙-土动力相互作用中各物理量的精确表达式,这对揭示挡土墙地震响应机理产生了阻碍.通过引入最小二乘响应面法改进了一种连续介质模型,并与现有方法进行对比,对地震作用下挡土墙动...     

An inverse finite element minimization-based method for solution of multi-dimensional phase-change and material boundary shapes

An inverse finite element method for solution of unknown multidimensional phase-change and material boundary shapes is presented. The method is based on minimization and requires boundary shape parametrization. The unknown boundary parameters are determined by minimizing the error between a limited number of known (e.g. measured) temperatures and the temperatures associated with the iteratively altered boundary. The algorithm presented is based on the multidimensional downhill simplex minimization method. The inverse method is illustrated and verified using a model of the plasma arc welding process. In particular, it is shown that the technique is capable of accurately determining a specified weld pool capillary interface shape using a limited number of simulated thermocouple measurements. The code's ability to determine the interface shape is investigated under various interface-thermocouple separations, using varying numbers of simulated thermocouples.     

An analytical solution for mechanical etching of glass by powder blasting

Masked erosion of glass by powder blasting is studied and a nonlinear partial differential equation of first order describing the displacement of the glass surface is proposed. This equation is solved by means of the characteristic-strip equations. If so-called transition regions are introduced near the edges of the mask, an analytical solution can be obtained which is in reasonable agreement with measurements.     

花键冷挤压用组合凹模内径收缩量的计算

为研究花键组合凹模压入预应力圈时内径的变化规律,实验研究了轴向压合量对凹模内径变化的影响规律.在理论分析的基础上,推导了组合凹模压合后凹模内径的计算公式,并通过实验进行了验证.研究表明:花键挤压用组合凹模压合时,大径比等直径的圆凹模内径收缩得慢,而小径则比等直径的圆凹模内径收缩得快.     

某型号十字轴精密成形工艺分析

目的研究十字轴闭塞式单向温挤压成形的可行性。方法根据十字轴的结构特点,确定了成形方案,并利用有限元技术对成形过程进行了数值模拟分析,然后结合物理实验对工艺可行性进行了验证。结果有限元分析和试验结果相吻合,锻件成形效果较好,没有出现充不满、折叠缺陷。结论采用闭塞式单向温挤压成形工艺,获得了满足尺寸要求的十字轴锻件,成形过程稳定可靠,成形工艺可行。     

开口回流式汽车风洞结构的声固有特性分析

将开口回流式风洞整体作为研究对象．建立变截面管道回路的声学分析模型,利用管道中的声传播理论,得到确定风洞流道内声空间声固有特性的方法;进而对同类型的某模型风洞的声固有特性进行计算,并与该模型风洞的测量结果和现有的研究方法得出的结果比较,说明本文的研究方法能较全面准确地确定无流或低风速风洞中的声固有特性,从而也较清楚地解释了引起这类风洞低频颤振现象的声响应特性,是对低频颤振机理的进一步探索。     

Possibility of closed loop material recycling for fiber reinforced thermoplastic composites

It becomes significantly important to preserve ecological balance of the earth and protect the environment from getting worse. One of the urgent issues to be tackled will be to develop and establish recycling technology for polymeric composite materials. The expression of recycling technology in this case is that after the life of industrial products of fiber reinforced thermoplastic (FRTP) is completed, instead of being thrown away as wastes, they are reused as a raw material for new applications. An additional goal is that of saving valuable resources and not consuming further energy. This paper deals with a possibility of closed-loop recycling technologies for FRTP. The key factor is the fiber length which is expected to reduce in each recycling step. Materials tested here are continuous FRTPs, long FRTPs, short FRTPs, and powder reinforced plastics. The effect of fiber length on the reinforcing mechanism is first examined. The correlation between outdoor exposure test and accelerated weathering test is the second subject to covered. The third subject is to make clear the influence of crushing and heat history which are inevitable during each recycling stage. Throughout the above investigation, the concept of closed-loop recycling technologies has been established, although it is still in a preliminary stage.Abbreviations FRTP fiber reinforced thermoplastic - C-, L-, S-, P-FRTP continuous-, long-, short-FRTP, powder-RTP - FRP fiber reinforced thermosetting plastic - UD unidirectional - PP polypropylene - CF carbon fiber - GF glass fiber - V _f volume fraction of fiber     

金属粉末选择性激光烧结成形机制的研究

分析了纯金属粉末、预合金粉末和多组分金属粉末的选择性激光烧结成形机制;详细讨论了粉末的化学成分和物理性质,激光功率、扫描速率、扫描矢径、扫描间距等激光参数以及粉层厚度、粉床预热温度、保护气氛等工艺参数对成形机制的影响;并简要讨论了金属粉末选择性激光烧结技术的进一步研究方向.     

Failure analysis of a hot extrusion die used for Al-Li alloy processing

Al-Li alloys being developed as lighter, substitutes for conventional high strength Al alloys are to be processed by routine methods. During extrusion of a 8090 Al-Li alloy, the extrusion die container failed causing some alarm. This failed die container was analysed to examine if the failure was caused by interaction of Li diffusing out of Al-Li alloy with the carbides of die steel. The evidence, although not conclusive, is sufficient to exercise caution during such processing.