Theoretical analysis on the effects of crystal anisotropy on wiresawing process and application to wafer slicing

Most of the crystals sliced using wiresaw are anisotropic to an extent. The effect of crystal anisotropy on the process of slicing using wiresaw is studied and presented in this paper. A method is proposed to determine the direction of approach (DOA) which will give a better surface finish and reduce deviation from the desired surface normal by maintaining symmetry in material removal rates on the two sides of the wire. The effect of cleavage anisotropy on wiresaw slicing is also studied. If the DOA is perpendicular to a cleavage direction, then the longitudinal direction of the wire aligns with the cleavage direction which increases the tendency of wafer breakage, resulting in lower yield of the wafers. This can be easily avoided by choosing an appropriate DOA. Theoretical analysis is carried out using the proposed methods for slicing silicon wafers. Recommendations are made for three most commonly sliced orientations of silicon: (100), (110) and (111). DOA can be any direction for (100) and (110) wafers from the symmetry point of view but preferred DOAs do exist for these wafers from cleavage point of view. For (111) crystal there are exactly six DOAs with symmetry. However, these six DOAs do not lie in the preferred zones suggested by cleavage criterion. It is suggested that in such situations the symmetry criterion should be given precedence over the cleavage criterion during wiresawing process, as the semiconductor industry has strict tolerances in place for surface normal deviation and flatness.     

Modeling transient fluid flow and heat transfer phenothena in stationary pulsed current TIG weld pool

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A three-dimensional finite element method for a nonisothermal aluminum flat strip rolling process

The purpose of this study is to develop a three-dimensional coupled thermo-elastic-plastic finite element model of nonisothermal rolling and analyze the strip curvature caused by the difference in the heat transfer boundary conditions of the upper and lower rollers. The difference in the rotation speed between the upper and lower rollers was utilized in an attempt to correct the aforementioned curvature in hot rolling due to unsymmetrical cooling conditions. In addition, the changes in shape, temperature field, and strain field of the strip during the various stages were analyzed and can be used to obtain the lateral plastic flow of the strip. As for the aspect of heat transfer, the various possible boundary conditions in the actual hot rolling were considered, which include the convection boiling of the air and water, and the radiation loss. Then, the three-dimensional finite difference heat transfer equation is derived according to the concept of heat balance. As for the determination of the direction of tangential friction force, this study also developed a modification algorithm to adjust to the three-dimensional rolling process. After a comparison with the experimental data in Ref 8 and 15, and the simulated temperature distribution in Ref 17, the partial results obtained from the computation by the numerical analytical model verify that the theoretical model and computer programs established in this study are reasonable. This study shows that hot rolling can greatly reduce the rolling force and strain rate with the early appearance of plastic deformation, and the distribution of temperature field is basically affected by the heat transfer boundary conditions. However, unsymmetrical heat transfer boundary conditions will cause unsymmetrical rolling forces of the upper and lower rollers and cause strip curvature; this condition can be corrected by the difference in the rotation speed of the rollers.     

Abrasive electrochemical multi-wire slicing of solar silicon ingots into wafers

To meet the growing demands of the global photovoltaic (PV) industry, preparing large scale and ultra-thin solar wafers becomes one of the key issues. This paper presents the preparatory investigations of slicing solar silicon ingot into wafers by an abrasive electrochemical method based on a multi-wire saw system. The anodic passivation on silicon can be controlled by applying an anodic potential during the mechanical slicing process, which improves the surface integrity and material removal rate remarkably. This new hybrid machining method has no influence on subsequent cleaning of wafers and preparing the solar cells, and the average photoelectric transformation efficiency is >17.5%.     

Hybrid modelling of 7449-T7 aluminium alloy friction stir welded joints

Abstract

Many finite element models use adjustable parameters that control the heat loss to the backing bar, as well as the heat input to the weld. In this paper, we describe a method for determining these parameters with a hybrid artificial neural network (ANN) coupled thermal flow process model of the friction stir welding process. The method successfully determined temperature dependent boundary condition parameters for a series of friction stir welds in 3·2 mm thick 7449 aluminium alloy. The success of the technique depended on the method used to input thermal data into the ANN and the ANN topology. Using this technique to obtain the adjustable parameters of a model is more efficient than the conventional trial and error approach, especially where complex boundary conditions are implemented.     

薄板TIG堆焊屈曲变形的预测

针对TIG堆焊所引起的薄板复杂屈曲变形问题,采用基于热弹塑性理论的有限元法建立薄板焊接变形预测模型,提出了数字图像相关法对预测屈曲模型进行试验验证并设计了薄板焊接变形检测试验装置. 结果表明,基于数字图像相关技术的非接触变形检测方法能够全场动态获取堆焊屈曲变形数据,全面验证了焊接变形有限元预测模型,基于高斯热源模型、非线性瞬态热传导边界条件、材料高温性能参数等的热?力耦合热弹塑性预测模型具有较高的精度.薄板焊接变形冷却后呈马鞍形,结合动态温度场与应力场,对揭示焊接马鞍形屈曲变形机理具有重要的意义.     

A New Approach in Optimizing the Induction Heating Process Using Flux Concentrators: Application to 4340 Steel Spur Gear

The beneficial effects of using flux concentrators during induction heat treatment process of spur gears made of 4340 high strength steel is demonstrated using 3D finite element model. The model is developed by coupling electromagnetic field and heat transfer equations and simulated by using Comsol software. Based on an adequate formulation and taking into account material properties and process parameters, the model allows calculating temperature distribution in the gear tooth. A new approach is proposed to reduce the electromagnetic edge effect in the gear teeth which allows achieving optimum hardness profile after induction heat treatment. In the proposed method, the principal gear is positioned in sandwich between two other gears having the same geometry that act as flux concentrators. The gap between the gear and the flux concentrators was optimized by studying temperature variation between the tip and root regions of gear teeth. Using the proposed model, it was possible identifying processing conditions that allow for quasi-uniform final temperature profile in the medium and high frequency conditions during induction hardening of spur gears.     

INFLUENCE OF NITROGEN ON THERMAL WARPAGE IN CZOCHRALSKI SILICON WAFERS

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游离磨料线切割硅晶体中的磨粒力学行为研究综述

游离磨料线切割具有切割效率高、切口材料损耗小、表面损伤程度浅、厚度小、切割噪声小等优点而广泛应用于半导体和光伏产业.本文阐述了游离磨料线切割的原理,对游离磨料线切割过程中磨粒力学行为的理论模型研究进行了综述,主要包括磨粒压入力学模型、流体动压滚动力学模型、切削变形力学模型.此外,还从多磨粒的压入效应、切割液的运动方式上...     

钢包静置过程中传热现象的数值模拟

研究钢包静置过程中温度变化规律对控制钢液温度及后续连铸工艺有重要影响。利用ANSYS软件,建立三维钢包传热模型进行瞬态模拟,讨论了4%、6%和8%精炼渣厚度对钢包速度场、温度场以及钢包耐火材料壁温度分布的影响。计算过程采用两相流(钢液-精炼渣)模型,将精炼渣黏度设置为与温度有关的函数,渣-气自由表面和耐火材料表面施加对流和辐射混合边界条件。结果表明,增加渣层厚度可以有效减缓钢液速度场循环,起到保温作用,但会加剧钢液温度分层。钢液的散热功率主要集中在侧壁及钢渣界面,占总量的90%左右。渣层厚度由4%增加至6%,钢渣界面散热功率降低17.42%,继续增加至8%时,又降低了19.96%。     

热处理数值模拟进展之一——扩展求解域热处理数值模拟

金属热处理是复杂的多场耦合非线性物理过程,本文简要归纳前人有关"耦合换热"的研究成果,在此基础上首次提出了扩展求解域的热处理模型。它将温度场的求解域扩展到加热或冷却的热处理工件及其周围环境。用壁面函数法处理流场与固体之间换热,多物体多表面之间的辐射热交换用离散坐标法处理。各物体(子域)界面上的热流密度和温度是耦合换热的计算结果而不是预设定的边界条件。避免了现有的热处理模型中预先设定工件表面的边界条件所遇到的困难和不确定性,有助于更接近于实际生产的情况。本文以新型罩式渗氮炉的设计为例,运用扩展求解域的热处理数值模拟方法成功地进行了设备虚拟设计,证明了该模型具有巨大的优越性。     

Analytical and numerical solutions of transient heat conduction in monolayer-coated tools

The heat generation during metal cutting processes affects accuracy of the machined surface and strongly influences tool wear and tool life. Knowledge of the ways in which the tool material affects the temperature distribution is therefore essential for the study of thermal effects on tool life and workpiece quality. Many studies have been done on simulation temperature distribution in coated cutting tools by means of the finite element method or the finite difference method.In this study, a thermal analytical model is firstly developed to determine temperature distribution in monolayer-coated cutting tools during orthogonal metal cutting. In the analytical model one equivalent heat source applied on the coating layer boundary substitutes for the heat generation introduced from the primary deformation zone, the secondary deformation and the frictional zone along the tool–chip interface as well as the tertiary or the sliding frictional zone at tool–workpiece interface. A mathematical model of the transient heat conduction in monolayer-coated tools is then proposed. The temperature distribution formulations in monolayer-coated tools are obtained using Laplace transform. The influence of different parameters including thermophysical properties of tool coating and tool substrate and thickness of the coating layer on temperature distribution in monolayer-coated tools is lastly discussed and illustrated.     

Enhanced method for the evaluation of the thermal impact of dry machining processes

From today’s point of view the modelling of machining operations is a promising tool to extend the productivity and the precision of future industrial manufacturing. The importance of predictive simulation and compensation of thermally induced workpiece deformation during machining is especially important in dry machining because of the absence of cooling lubricants. Since the simulation results mainly depend on the boundary conditions of the model, a detailed knowledge of them is necessary. In this case the most important boundary condition is the intensity and possibly the distribution of the surface heat flux representing the heat flow into the workpiece resulting from the chip formation. The surface heat flux cannot be measured directly. One possible way to determine surface heat fluxes is to employ a thermal model of the machining process and match simulated and measured time and space dependent temperature fields. This procedure is time-consuming and is in most cases subjective because the congruency of temperature fields is rated manually, e.g. by the position of single isotherms. Therefore an enhanced method for the determination of surface heat fluxes is proposed in this paper. The method is based on nonlinear optimisation techniques and a simple finite difference scheme for numerical solution of the heat equation (WORHP-FDM). The procedure is objective between repeat measurements and works in a fully automated manner. The implementation is validated by the comparison to an analytical solution of the moving heat source based on the model of Carslaw and Jaeger and then applied to measured thermal images from milling experiments.     

Thermal modelling of the multi-stage heating system with variable boundary conditions in the wafer based precision glass moulding process

In the precision glass moulding process, the heat transfer and the resulting transient temperature distributions of the molten glass are of great importance because they significantly affect the productivity as well as the thermally induced residual stresses in the final product. Thermal modelling of the heating system in the glass moulding process considering detailed heating mechanisms therefore plays an important part in optimizing the heating system and the subsequent pressing stage in the lens manufacturing process.The current paper deals with three-dimensional transient thermal modelling of the multi-stage heating system in a wafer based glass moulding process. In order to investigate the importance of the radiation from the interior and surface of the glass, a simple finite volume code is developed to model one dimensional radiation–conduction heat transfer in the glass wafer for an extreme case with very high temperature difference considering temperature dependant thermal conductivity and heat capacity. Afterwards, by using three-dimensional FEM modelling along with a predefined experimental test, the equivalent glass–mould interface contact resistance is determined for two different pressures. Finally, the three-dimensional modelling of the multi-stage heating system in the wafer based glass moulding process is simulated with the FEM software ABAQUS for a particular industrial application for mobile phone camera lenses to obtain the temperature distribution in the glass wafer. In the numerical modelling, the interface boundary conditions for each heating stage are changed according to the determining heat transfer mechanism(s). Numerical results are compared with experimental data to show the validity of the numerical modelling. The obtained results show that the right thermal modelling is highly dependent on the proper choice of thermal boundary conditions in different stages according to the real physical phenomena behind the process.     

电火花沉积WC-12Co涂层单脉冲温度场数值模拟

为了确定电火花沉积WC-12Co涂层的温度场,通过选用合适的热源和热边界条件,建立电火花沉积WC-12Co涂层热传导模型. 利用ANSYS有限元软件进行数值模拟,得到了电极材料及工件材料的温度等值面、温度分布曲线以及温度随时间变化曲线. 通过设置温度场等值线确定了材料熔化和气化区域大小. 同时文中研究了工艺参数对熔化和气化区域的影响,并预测最佳工艺参数的范围. 通过电火花沉积试验验证了模拟预测结果的正确性,得到了可以获得良好沉积形貌涂层的最佳工艺参数.     

三维非线性有限元在热处理炉CAD中的应用研究

提出了一个描述热处理炉三维瞬态非线性温度场的有限元模型，该模型综合考虑了辐射，处理热物性参数的边界条件等复杂因素，根据此模型，使用大型非线性有限元软件MARC，对72kW井式渗氮炉温度场进行模拟计算，模拟结果与实测结果吻合较好，由此提供了一种良好的热处理炉虚拟生产手段，可以作为知识热处理CAD的核心技术之一。     

高速压力机温度场的有限元仿真及实验研究

通过确定高速压力机的运动动力参数,分析计算了高速压力机的热源分布和对流换热系数,并获得了压力机的热边界条件.以有限元方法为基础,建立高速压力机的三维分析模型,进行了温度场变化的分析研究.分析及实验结果表明,所建立的三维压力机温度有限元模型能正确的模拟运行过程中的压力机温度场分布,为压力机热误差分析设计提供了数值分析及实...     

多道激光熔覆温度场的有限元数值模拟

分析了激光熔覆过程中温度场的主要影响因素,在主要考虑边界条件和热源数据的基础上,建立了送粉式激光熔覆多道搭接情况下温度场的有限元计算模型,并对板材上搭接三道熔覆层的熔覆温度场进行了三维数值模拟,得到了每道熔覆层上中心点的温度变化规律.结果表明,在激光熔覆过程中每道熔覆层中心点上的温度随时间延长呈锯齿状变化,且每个中心点所能达到的最高温度并不相同.此外,搭接情况下,熔覆层中心点每次升温前的最低温度是随着熔覆顺序的进行而逐渐升高的,且升高趋势类似于抛物线.此计算结果合理,为研究应力场和应变场的变化规律打下基础.     

不锈钢管冷旋压热力耦合有限元模拟

针对316不锈钢管建立了三维热力耦合有限元模型，对其冷旋压过程进行模拟。在模拟的过程中施加了对流和热传导边界条件，计算了成形过程中的受力特征、运动轨迹、接触特征以及温度场的情况。通过有限元模拟可以为分析不锈钢管冷旋压成形及组织状态提供有力依据，进而有效地指导生产实践。     

中间包传热边界对钢液流动及传热计算的影响

以某厂T型中间包为例,建立了中间包内钢液流动、传热数学模型。针对数值模拟中存在的传热边界条件的准确性问题进行探讨,引入了中间包包衬散热计算模型,得出关于中间包包衬结构的热流散失与内壁温度的关系,作为中间包内钢液流动、传热计算的边界条件。利用商用Fluent软件模拟计算,并比较分析了不同边界条件对中间包内钢液流动、传热的影响,结果表明提出的边界条件模型法使计算模拟结果更符合实际。