<Emphasis Type="Italic">In Situ</Emphasis> Characterization of Strength and Distortion During Powder Metal Processing

Thermogravimetric analysis and dilatometry are two common in situ measurement techniques used in powder processing to obtain information regarding thermal debinding and sintering. However, these two techniques provide negligible information regarding critical phenomena such as distortion or cracking. This paper discusses newer characterization techniques used to measure in situ strength evolution to help understand defect generation during the thermal debinding process. The information obtained from these in situ measurement techniques assists in intelligent design of optimal thermal cycles and in selection of binders targeted at manufacturing dense sintered components with minimum defects and distortion. The paper discusses examples of applications developed based on the information provided by in situ characterization of strength and distortion.     

MOGA和FEM相结合实现万能型钢轧机机架圆角的多目标优化

文章把多目标遗传算法(MOGA)和有限单元法(FEM)有机地结合起来,建立了一种新的结构优化方法。用MATLAB遗传算法工具箱函数编制了MOGA和FEM相结合的多目标优化程序,对万能型钢轧机机架圆角进行多目标优化,充分发挥了有限单元法数值计算准确及遗传算法求极值的高效性和全局性的优点。与ANSYS自带的零阶和一阶优化方法相比,本优化方法取得了较好的优化效果,为解决复杂的多目标工程优化问题提供了一种新的更有效的途径。     

基于微观组织优化的锻造工艺预成形及毛坯形状优化设计

以锻件晶粒尺寸细小均匀为目标,以预成形形状设计为对象,提出了锻造成形过程微观组织优化设计方法,构建了晶粒尺寸、锻件形状子目标函数以及无量纲化的总目标函数,确定了预成形形状作为优化过程的设计变量;给出了优化设计的具体步骤,采用微观遗传算法和有限元模拟方法开发了基于预成形设计的锻造过程微观组织优化程序;并对典型的圆柱体镦粗进行了面向微观组织优化的预成形设计,给出了能够获得具有良好微观组织的镦粗成形预成形模具型腔形状。通过分析不同高径比的初始毛坯形状对微观组织优化目标函数值的影响,给出了较为合理的初始毛坯形状高径比取值范围。     

基于遗传算法并考虑质量守恒空化边界的最优织构形状

织构形状对摩擦副的润滑性能具有重要的影响,然而最优织构形状随工况参数的变化规律仍缺乏系统性研究。基于满足质量守恒的JFO(Jakobsson-Floberg-Olsson)空化边界条件,通过求解雷诺方程,结合遗传算法并以油膜承载力最大为目标,建立并简化最优织构形状优化模型,对比分析不同工况下最佳微孔与最优织构的承载力情况,探讨最优织构形状的相关几何参数随摩擦副端面间距、滑动速度与空化压力等参数的变化规律。结果表明：不同工况条件下最优形状织构的承载性能均优于最佳微孔织构,尤其当摩擦副端面间距小、滑动速度大时,性能提升更为显著;简化的最优织构形状几何模型共计3设计变量,即液体流入侧两点X_a、X_g横坐标X₁、X₂及织构深度h_g;随摩擦副端面间距增大,X₁先减小后基本不变,X₂逐渐减小,对应的最优织构深度与面积比增大,量纲一织构深度基本不变;随滑动速度增大,X₁先缓慢增大后基本不变,X₂逐渐增大,对...     

Computer modeling of chemical vapor deposition processes

A general purpose computer model for describing the transport phenomena and resulting rate of deposition has been described. Partial differential equations describing the conservation of mass, momentum, energy, and chemical species are solved by a computer program employing the finite difference method. The system considered in this paper is deposition of silicon in a vertical stagnation flow reactor by the reaction of silicon tetrachloride and hydrogen. The program allows for multiple chemical species and natural convection effects. Predicted silicon deposition rates along the substrate are in reasonable agreement with experimental values available in the literature. The effect of gas inlet configuration on the uniformity of deposition has been studied. The model can be used as a tool for design optimization of such reactors.     

机械优化设计的遗传惩罚复合法

提出了遗传惩罚复合优化方法GPCM，并应用于平面铰链四杆机构设计。结果表明，该法可解决局部最优点和初始点选择问题，改进计算收敛速度和设计误差。为机械优化设计提供了新的参考。     

基于ADAMS的滚筒式输送机构的传动速率优化

传动速率是多级输送机构的一个重要的设计参数，也是输送效率的主要影响因素。构建一种瓷砖生产线的滚筒式输送机构模型，基于多刚体系统动力学理论，利用ADAMS对瓷砖在输送机构上的输运过程进行运动学仿真，得到传动速率对瓷砖输运状态的影响。针对瓷砖在输送过程中出现的堆叠与偏转延时问题，提出了最大自转角度和连续输运两个判据，在此基础上得到瓷砖输送机构的最优传动速率。试验结果表明了优化结果的正确性，为输送机构的传动速率优化设计提供了一定参考价值和理论依据，有较强的实用性。     

面向微观组织优化的锻造工艺预成形优化设计

以锻件晶粒尺寸细小均匀为目标,以预成形形状设计为对象,提出了锻造成形过程微观组织优化设计方法,构建了锻造成形过程微观组织优化目标函数,并确定锻造成形预成形形状作为优化过程的设计变量,给出了优化设计的具体步骤,采用微观遗传算法和有限元模拟方法开发了锻造过程微观组织优化程序,并对典型的圆柱体镦粗进行了面向微观组织优化的预成形设计,取得了较好的效果.     

A systematic approach to design high-performance feed drive systems

A systematic design methodology for the mechatronic system composed of mechanical and control subsystems is proposed to design high-speed and high-precision feed drive systems. Strict mathematical modeling and identification processes of the subsystems are performed in this paper. Parametric studies and circular motion experiments in the x–y table are conducted to investigate the influence of interactions on the performance of feed drive systems. Based on analyses of the system performance according to design and operating parameters, a nonlinear constrained optimization problem including the relevant subsystem parameters of the feed drive system is formulated. The multi-objective optimization procedure and normalization technique are introduced in the design process. A Pareto optimum solution set is applied to investigate the relationships between objective functions. The effectiveness of the proposed design methodology is verified through numerical case studies.     

Optimal process design in steady-state metal forming by finite element method—II. Application to die profile design in extrusion

A new approach to optimal process design in steady-state metal forming is presented. In the approach, optimal process design problems are mathematically formulated and solved using a penalty rigid-viscoplastic finite element method as a tool for carrying out necessary calculations for optimization. The basic formulation is presented and the solution procedure is described with the emphasis on the method of calculating the design sensitivities. The accuracy of the design sensitivities thus obtained is assessed by a series of numerical tests. An iterative scheme for optimizing the design variables based on the predicted design sensitivities is also given.     

High-temperature stability, structure and thermoelectric properties of phases

Polycrystalline perovskite-type CaMn_1-xNb_xO₃ phases (with x=0.02,0.05,0.08 and 0.10) were investigated with regard to their structure, microstructure and thermal stability as a function of temperature. The studied phases revealed a complex microstructure at room temperature with 90° twinned domains. At high temperatures, the manganate phases underwent a structural transition from orthorhombic to cubic symmetry, as confirmed by in situ high-temperature X-ray powder diffraction and electron diffraction data. Thermogravimetric heating/cooling studies showed a reversible thermal reduction/reoxidation process that occurred above a defined transition temperature. A possible mechanism relating the high-temperature structural transition and the thermal reduction process of slightly substituted CaMnO₃ phases was proposed. The thermal reduction process resulted in a change in the Mn³⁺/Mn⁴⁺ concentrations in the Mn sublattice, and therefore in a modification of the transport properties. A comprehensive study examined the impact of both phenomena on the electrical and thermal transport properties.     

面向微观组织优化的锻造工艺预成形优化设计及实验研究

以锻件晶粒尺寸细小均匀为目标,以预成形形状设计为对象,提出了锻造成形过程微观组织优化设计方法,构建了锻造成形过程微观组织优化目标函数,并确定锻造成形预成形形状作为优化过程的设计变量。采用遗传算法和有限元模拟相结合的方法,开发了锻造过程微观组织优化程序,对典型的H型锻件进行了面向微观组织优化的预成形设计,取得了较好的效果。并根据优化设计的结果进行了实验研究,优化结果的晶粒尺寸及其分布趋势与实验结果比较吻合。     

Optimal temperature variable selection by grouping approach for thermal error modeling and compensation

One of the difficult issues in a thermal error compensation scheme is to select appropriate temperature variables as well as to obtain accurate thermal error component models. In this research, an optimization method is presented to overcome this difficulty. The optimization objective function is formulated by a modified model adequacy criterion based on the Mallows' C_p statistic. A new search method is developed for discrete search domains with non-directional or unknown-order variables. The search process includes correlation grouping, representative searching, group searching and variable searching. It not only ensures optimal results but also reduces computational time greatly. One modeling example is presented. The optimal model is found with a 0.982 R²-value using four temperature variables selected from 46 candidates of temperature variables. The largest error residual is reduced down to 2.2 microns from 20.0 microns. The comparison of modeling results from the proposed approach and three other modeling methods is addressed as well.     

Effect of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> doping on the structure,magnetic properties and electrical properties of La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>

The (La_0.7Ca_0.3MnO₃)_1x /(NiFe₂O₄) _x (x = 0 to 0.09) composites were prepared using a conventional solid state reaction method. The structural, magnetic properties, and electrical properties of LCMO/NFO composites were investigated using X-ray diffraction, scanning electron microscopy, field cooled DC magnetization, and magnetoresistance (MR) measurements. The resistivity measured as a function temperature demonstrates that the pure LCMO and x = 0.01 samples display metal to semiconductor transitions. However, the composites of x > 0.03 samples clearly present the electrical behavior as an insulator/semiconductor type behavior. It was observed that the resistivity of the samples increased systemically with an increase of the NFO content. From the MR measurements, it was found that the MR effect is enhanced for x = 0.01 with a NFO composition. In all, the spin-polarized tunneling and the spin-dependent scattering may be beneficial for an improved low-field magnetoresistance effect. These phenomena can be explained by the segregation of a new phase related to NFO at the grain boundaries or surfaces of the LCMO grains.     

Phase equilibria and chemical vapor transport in the system Mo–Ta–As

The phase diagram Mo–Ta–As was studied in two partial isothermal sections at 1050 °C (in the As-rich corner) and at 1400 °C (As-poor alloys) using powder X-ray diffraction and electron probe microanalysis. A complete solid solution was found to exist between isostructural Mo₅As₄ and Ta₅As₄ and the ternary solubility of Mo in Ta₃As at 1400 °C was determined. A ternary phase Mo_xTa_1−xAs with MnP-type structure was found to exist in the As-rich part of the system. Lattice parameters were investigated as a function of composition for (Mo,Ta)₅As₄ and for Mo_xTa_1−xAs. Additional experiments of chemical vapor transport (CVT) from 1000 °C to 900 °C using different ternary source compositions and I₂ and Br₂ (PtBr₂) as transport agents were performed. Only Ta compounds were found in the sink and no ternary transport was observed.     

OPTIMAL DESIGN PROCEDURE BASED ON VISCOPLASTIC MATERIAL BEHAVIOUR

1.IntroductionSafety,functionality,protectionofenvironmentandlowpricemaybenumberedasmayorreasonsformakingofanoptimalproduct.Ontheotherhandoptimalproductmaybedonebyconcurrentlyutilizingalloftherelevantinformation,methods,computerperformances,manufacturingpossibilitiesandofcourseknowledgepotential.Themaintaskoftheoptimalprocedureinthedesignprocessaswellasinthemanufac-turingprocessistofindthebestcombinationbetweentheobjectivefunctionandconstrains.Theobtainedproductwillbeoptimalasthemathematicalid…     

Multiperformance Optimization in Turning of Free-Machining Steel Using Taguchi Method and Utility Concept

This article presents the application of Taguchi method and the utility concept for optimizing the machining parameters in turning of free-machining steel using a cemented carbide tool. A set of optimal process parameters, such as feed rate, cutting speed, and depth of cut on two multiple performance characteristics, namely, surface roughness and metal removal rate (MRR) is developed. The experiments were planned as per L ₉ orthogonal array. The optimal level of the process parameters was determined through the analysis of means (ANOM). The relative importance among the process parameters was identified through the analysis of variance (ANOVA). The ANOVA results indicated that the most significant process parameter is cutting speed followed by depth of cut that affect the optimization of multiple performance characteristics. The confirmation tests with optimal levels of machining parameters were carried out to illustrate the effectiveness of Taguchi optimization method. The optimization results revealed that a combination of higher levels of cutting speed and depth of cut along with feed rate in the medium level is essential in order to simultaneously minimize the surface roughness and to maximize the MRR.     

FCAW process optimization using the multivariate mean square error

Optimization of welding processes is not a trivial task, mainly due to the great number of required and desirable characteristics that must be analysed. Moreover, the optimization of a welding process with multiple characteristics without considering the variance–covariance structure may lead to inadequate optimum. To help with this task, a method of multi-objective optimization based on the multivariate mean square error applied in the study of multiple correlated characteristics of a flux-cored arc welding process is presented. This method characterized by a combined approach based on the response surface methodology, design of experiments, and principal components analysis consisted of an attempt to achieve the nearest values to specific targets, for each characteristic (penetration, deposition rate, deposition efficiency, convexity index of the weld bead, and dilution), considering the welding variables expressed as a result of welding voltage (V), wire feed speed (Va), and contact tip to workpiece distance (d). The results point, to a good adequacy of the proposed method.     

Enhancement of room-temperature magnetoresistance in La<Subscript>0.6</Subscript>Dy<Subscript>0.1</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The samples of La0.6Dy0.1Sr0.3MnO3/(Ag2O)x/2(x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20, 0.25, and 0.30) were prepared by using the solid-state reaction method.Their magnetic property, transport behavior, transport mechanism and magnetoresistance effect were studied through the measurements of magnetization-temperature(M-T) curves, ρ-T curves and the fitting of ρ-T curves.The results indicated that Ag could take part in the reaction when the doping amount is small.However, when the doping amount is compar...