低碳钢非对称角焊温度场有限元分析

针对单边开坡口的非对称角根焊中熔透不稳定、成形质量差的问题,对其温度场及熔池成形规律进行分析从而优化焊接参数的选取,改善成形质量.考虑温度、对流、辐射和相变潜热对材料物理性能的影响,利用有限元分析软件建立了低碳钢非对称角焊缝有限元模型,并进行仿真计算.对比讨论了不同结构情况下焊接电流对温度场的影响,重点分析了非对称角焊接参数对背部熔宽的影响.结果表明,非对称角焊缝温度分布不均匀,背部熔宽对电流的变化十分敏感,焊接电流大小对熔池形状影响较大.通过试验得到三组熔透情况不同的焊缝,其热影响区形状尺寸与仿真结果吻合良好,从而验证了理论分析的有效性.     

A finite element analysis of temperature variation in silicon wafers during wiresaw slicing

Temperature variation during slicing can cause undesirable warp and nanotopography on wafer surfaces, especially for large wafers. In this paper, a finite element model is constructed and presented to analyze and synthesize temperature variation of ingot during wiresaw slicing. The heat flux and natural convection boundary condition arising during slicing have been studied and incorporated in the model as well as the material removal. The model is designed to accommodate time-dependent boundary conditions and geometry which are integral to wiresaw slicing process. The results obtained from the model compare very well with the experimental results available in the literature. A method is proposed in order to obtain a relatively flat profile of temperature during slicing in order to reduce warp due to heat generation by intelligent control of boundary conditions. The method is tested using the model developed. The proposed method can be utilized by practitioners in order to obtain wafers with less warp and improved nanotopography due to thermal aspects in slicing using wiresaws.     

基于有限元的管线钢焊接温度场模拟

针对管线钢焊接,考虑了材料热物理性能参数、相变潜热与温度的非线性关系,建立了焊接过程的数学模型和物理模型。利用ANSYS软件的APDL语言编写程序,实现了在移动热源载荷下的焊接有限元计算,分析对比了不同焊接工艺参数对焊接温度场的影响程度。     

Development of a thermo-viscoplastic cutting model using finite element method

In this paper, a cutting model is developed by applying the thereto-viscoplastic FEM (finite element method) to analyze the mechanics of steady state orthogonal cutting process. The model is capable of dealing with free chip geometry and chip-tool contact length. The coupling with thermal effects is also considered. In calculating temperature distributions, the “upwind” scheme is employed to remove spurious oscillations that occur in the solution and therefore it is possible to analyze high speed metal cutting. Orthogonal cutting experiments are performed for 0.2% carbon steel to validate the cutting model. Tool forces are measured and the results are discussed in comparison with the results of the FEM analysis.     

A finite element analysis for the characteristics of temperature and stress in micro-machining considering the size effect

In this paper, a finite element method for predicting the temperature and the stress distributions in micro-machining is presented. The work material is oxygen-free-high-conductivity copper (OFHC copper) and its flow stress is taken as a function of strain, strain rate and temperature in order to reflect realistic behavior in machining process. From the simulation, a lot of information on the micro-machining process can be obtained; cutting force, cutting temperature, chip shape, distributions of temperature and stress, etc. The calculated cutting force is found to agree with the experiment result with the consideration of friction characteristics on the chip–tool contact surface. Because of considering the tool edge radius, this cutting model using the finite element method can analyze micro-machining with a very small depth of cut, almost the same size of tool edge radius, and can observe the ‘size effect' characteristic. Also, the effects of temperature and friction on micro-machining are investigated.     

A comparison of orthogonal cutting data from experiments with three different finite element models

The aim of this study is to compare various simulation models of orthogonal cutting process with each other as well as with the results of various experiments. Commercial implicit finite element codes MSC.Marc, Deform2D and the explicit code Thirdwave AdvantEdge have been used. In simulations, a rigid tool is advanced incrementally into the deformable workpiece which is remeshed whenever needed. In simulations with MSC.Marc and Thirdwave AdvantEdge, there is no separation criterion defined since chip formation is assumed to be due to plastic flow, therefore, the chip is formed by continuously remeshing the workpiece. However, in simulations with Deform2D, the Cockroft–Latham damage criterion is used and elements, which exceed the predefined damage value, are erased via remeshing. Besides this different modeling of separation, the three codes also apply different friction models and material data extrapolation schemes. Estimated cutting and thrust forces, shear angles, chip thicknesses and contact lengths on the rake face by three codes are compared with experiments performed in this study and with experimental results supplied in literature. In addition, effects of friction factor, different remeshing criteria, and threshold tool penetration value on the results are examined. As a result, it has been found that although individual parameters may match with experimental results, all models failed to achieve a satisfactory correlation with all measured process parameters. It is suggested that this is due to the poor modeling of separation.     

A finite element analysis of residual stresses in stretch turning

An analytical method has been proposed in this paper to determine the residual stresses in stretch turning. This is done using the thermal elasto-plastic finite element method to determine the transient temperature distribution, followed by thermal elasto-plastic stress analysis. An attempt to explain the mechanism of stretch turning is made, and the effects of stretch level on residual stresses are also discussed.     

有限差分网格温度载荷向有限元网格的转换

通过对有限差分及有限元网格的零件外形及节点温度的双重检测,开发了有限差分网格温度载荷向有限元网格转换的接口软件,从而可利用现有的商业软件实现温度场后处理显示,以验证所开发模拟软件的正确性.     

A three-dimensional finite element analysis of the temperature field during laser melting of metal powders in additive layer manufacturing

Simulating the transient temperature field in additive layer manufacturing (ALM) processes has presented a challenge to many researchers in the field. The transient temperature history is vital for determining the thermal stress distribution and residual stress states in ALM-processed parts that utilise a moving laser heat source. The modelling of the problem involving multiple layers is equally of great importance because the thermal interactions of successive layers affect the temperature gradients, which govern the heat transfer and thermal stress development mechanisms. This paper uses an innovative simulation technique known as element birth and death, in modelling the three-dimensional temperature field in multiple layers in a powder bed. The results indicate that the heated regions undergo rapid thermal cycles that could be associated with commensurate thermal stress cycles. Deposition of successive layers and subsequent laser scanning produces temperature spikes in previous layers. The resultant effect is a steady temperature build-up in the lower layers as the number of layers increases.     

基于有限元仿真的曲轴内铣加工参数优化

曲轴内铣技术因为其在加工质量和加工效率方面的优势被广泛应用于曲轴粗加工工艺上,但是内铣加工参数的选取缺少相应的标准及方法。通过有限元仿真建立曲轴内铣切削有限元模型,用仿真得到的铣削力进行曲轴变形仿真,从而预测曲轴轴颈圆柱度误差。研究发现:曲轴轴颈圆柱度误差随着刀盘转速增大而逐渐减小,且减小的速率逐渐降低。      

A factorial analysis of input parameters using finite element techniques

A two-level factorial design was performed to evaluate the effect of three key input parameters in a finite element analysis of a forging process. A series of “computer experiments” were performed that simulated the forging of a subscale jet engine disk, and these results were then compared with an actual disk forging.     

渗碳问题有限元模拟收敛性分析

采用Laplace变换法对一维渗碳问题进行了理论求解,在此基础上使用SYSWORLD有限元分析软件进行了渗碳问题有限元模拟收敛性分析。本文用DH表示渗碳影响距离。结果表明,对于一维渗碳问题,以理论解为参考,网格尺寸小于DH/3时,模拟计算值较精确;对于二维渗碳问题,四边形网格的计算精度较三角形网格高些,网格尺寸应小于DH/4;三维渗碳模拟时,网格尺寸应小于DH/5。     

3D finite element method analysis of deformation and temperature rise during equal-channel angular pressing

The material flow, temperature rise of the billet and pressing load during equal-channel angular process （ECAP） were studied by using 3D finite element method for Cu at different comer angle of mold, interfacial friction coefficient between the billet and the mold. As comer angle increases, the magnitude of shear deformation decreases and the strain difference between upper and lower part of the material becomes more apparent. The pressing load and peak temperature rise of the billet become low as the interracial friction coefficient decreases. The effects of the comer angle of mold on the temperature rise of the billet can be ignored, but the effects of the friction coefficient between the mold and the billet must be taken into account. For pressing load, the effect of the friction coefficient is larger than that of the comer angle. A good agreement between the simulated and measured material flow is obtained.     

防护罩砂型铸造模加工与温度场有限元分析

以一种防护罩为研究对象,根据图形的解析几何性质列出特殊点坐标值的非线性方程组,使用二分迭代法建立了方程组求解各值的数学模型。在编程软件中编制计算器,完成特殊点坐标值的计算,并且编写了防护罩砂型铸造模的数控车削加工程序。在有限元分析软件中进行建模,充分考虑铸铁和型砂材料的导热系数、密度等,对整个铸造模型进行了瞬态温度场的有限元模拟,得出了温度场分布云图,根据温度场云图确定了铸件的冷却时间。     

下落料式冲裁凹模刃口结构有限元分析

结合Pro/MECHANICA软件对冲裁凹模刃口的阶梯形刃口和锥形刃口2种结构进行了有限元模拟,从静态分析、疲劳分析、动态冲击分析等三方面对2种刃口所受到的应力、变形、应变及疲劳寿命等进行分析比较,得出2种刃口的不同工作特点,对下落料式凹模刃口结构设计提供理论依据。     

Fictive stress model based finite element analysis for bulk metallic glasses at an elevated temperature

It is important to manufacture micromachine parts and simulate the deformation behavior of bulk amorphous alloys in a superccoled liquid region. For these purposes, a correct constitutive model that can reproduce viscosity results is essential for good predictive capability. In this paper, finite element analyses of nonlinear behaviour in bulk metallic glasses during die compression in the supercooled liquid region have been carried out based on the fictive stress model in conjunction with the Maxwell viscoelastic model. The friction effect between the work piece and the die played an important role in inhomogeneous deformation.     

An application of the finite element method to the prediction of cutting tool performance

In metal cutting tools the are close to the tool point is the single most important region and conditions at the tool point must be carefully examined if improvements in tool performance, through changes in tool design and material, are to be achieved. The paper describes an analysis of cutting tool performance through a determination of the stress distribution within, and at the boundaries of, the tool wedge. The stressanalysis was based on a two-dimensional model as encountered in orthogonal cutting, using a range of cutting geometries including tools with double rake angles. A finite element technique was employed which can be effectively utilised in the solution of metal cutting problems once the boundary conditions have been established. The results presented demonstrate the significance of the chosen boundary conditions to the analysis of metal cutting. Finally it is argued that the deformation of the cutting edge, especially at the clearance face under the stress field set up in the tool, may well be a determining factor in establishing tool life as based on the flank wear criterion.     

板壳单元在焊接热弹塑性有限元计算中的应用

基于有限元软件Abaqus,采用板壳单元对薄板对接焊进行热弹塑性数值模拟. 建立具有截面积分特性的板壳单元二维有限元模型,采用高斯面热源与均匀体热源组合的混合移动热源,考虑材料随温度的变化特性,对薄板的接温度场与变形场进行了计算,并与相当网格尺寸的三维实体单元计算结果进行了对比. 结果表明,板壳单元与实体单元计算所得温度场与变形结果比较一致;采用非均匀板厚模拟加强高的板壳单元能够进一步改进焊接变形预测结果;在保证计算精度的条件下,板壳单元比实体单元具有更高的计算效率,计算结果为改进大型结构焊接变形预测方法提供了参考意义.