带台阶厚壁管类工件水淬的计算机模拟

本文以金属淬火冷却过程的连续过冷沸腾换热理论为基础,利用热分析和热结构耦合分析的有限元算法,以有限元分析软件ANSYS为分析工具,对45钢带台阶厚壁管类工件水淬过程进了计算机模拟,得到瞬态温度场、瞬态应力场以及残余应力场分布,并对计算结果进行分析.     

注塑成型冷却过程的数值模拟

采用循环平均假设，忽略模壁温度的周期变化，将模具的传热简化为三维稳态热传导总是，考虑到注射模的结构特点（型腔为狭缝面，冷却孔细长），推导出求解其温度场的边界积分方程；注塑件的传热简化为一维瞬态热传导，给出确定其冷却时间及表面循环平均热流的方法；通过模具及塑件传热的耦合迭代分析，使模具－塑料件界面的温度和热流满足相容条件，最终确定模具型腔的温度分布及塑件的冷却时间。最后通过一个例子说明数值模拟在冷却系统设计中的应用。     

强磁场对微合金钢晶粒细化的作用

近来,关于外加磁场处理对钢材组织性能的影响在国内外受到普遍关注,但有关工作的研究对象大多是合金钢和高碳工具钢,关于外加磁场对低碳微合金钢组织性能影响的研究报道很少.本文主要研究了在微合金钢的热处理冷却过程中外加稳恒磁场的作用.实验结果表明,钢材热处理冷却过程中的磁场处理可以使微合金钢晶粒细化.外加稳恒磁场可诱导奥氏体向铁素体相变,即降低转变势垒,提高转变形核数量,细化相变后的晶粒.在本文的实验条件下,随着磁感应强度的升高,晶粒尺寸减小.当磁感应强度在0.1特斯拉以下时,对晶粒细化的影响不大.磁场产生的晶粒细化作用可使试样相变后铁素体显微组织均匀,这种均匀的金相组织分布明显不同于加速冷却产生的不均匀金相组织.     

7A04铝合金构件深冷处理过程瞬态温度场的数值模拟

建立了7A04铝合金构件深冷处理过程瞬态温度场的有限元模型,对7A04铝合金材料在低温状态下的若干物性参数进行了实验研究,并运用温度场反算法分别得到了铝合金试件与低温（热）介质之间的传热系数。运用ABAQUS6．5有限元软件,对7A04铝合金构件瞬态温度场的数值结果表明,在淬火、深冷与上坡淬火过程中,构件上端部位存在很陡峭的温度梯度。     

大型压力机模座热处理过程模拟及工艺优化

实测并建立了55NiCrMoV7钢的热物性参数数据库和CCT曲线,基于ABAQUS软件建立了不同冷却介质淬火的热力耦合模型.模拟了大型压力机模座油冷和水冷两种淬火过程,获得了温度场和应力场的演化规律.结合模座上不同位置的冷却速度和CCT曲线预测了工作层的组织状态,并预测了模座上的应力分布.结果表明:采用完全油冷方式将在...     

圆柱体工件高压气淬过程中的数值模拟

利用导热微分方程和单值性条件推导了轴对称短圆柱体温度分布的通用数学微分方程,可计算工件上任意点的温度和任意时间的温度分布;采用伽辽金(Galerkin)加权余量法推导了二维轴对称圆柱体瞬态温度场的有限元计算的积分方程;采用大型有限元计算软件ANSYS对5Cr1MoV轴对称实心圆柱体工件淬火过程的温度变化及热应力/应变分布状况进行了模拟计算.     

三维瞬态方形管流的热流固耦合数值模拟

以主动冷却发动机壁板为模型,考虑受均匀热流载荷作用下方形管在流体冷却过程中的共轭传热问题,建立了防热涂层、固体管道和冷却液的三维耦合模型。利用数值离散方法进行了瞬态热流固耦合分析,得到了固体结构和流场的瞬态温度场、界面热流及结构应力分布规律。结果表明:在冷却液的作用下结构温度能达到稳定值,但油冷情况下稳态温度值高于水冷情况;在流固界面处温度沿流向逐渐上升,且壁面热流分布在界面上下表面处随时间变化情况不同,在结构边角处出现较大的应力集中。     

梯度功能材料板瞬态温度场有限元分析

采用有限元法与有限差分法相结合的方法,对梯度功能材料板的瞬态温度场进行了分析,并且通过ＺｒＯ２和Ｔｉ－６Ａｌ－４Ｖ组成的梯度功能材料对本方法的正确性进行了检验,最后给出了加热、冷却过程的瞬态温度场分布。     

磁流变液的流体动力学理论

在外加磁场作用下,磁流变液从牛顿流体变成了Bingham体,超过屈服应力开始流动,其的流变性(弹性、塑性、粘性)、磁化性、导电性、传热性以及其它的机械性质和物理学性质皆发生显著的改变.研究磁流变液在外加磁场作用下,流场分布规律随磁场强度变化的动态特性,建立磁流变液的流体动力学理论,对开发和设计磁流变器械至关重要.本文运用物理学和流体力学的基本理论,结合本构方程,考虑磁场对磁流变液的流动的影响,建立了磁流变液力磁耦合的流体动力学模型,给出了描述磁流变液流动的基本方程组.     

汽车转向节淬火过程温度场数值模拟、淬硬层深度预测与验证

本文采用ANSYS对某汽车40Cr转向节的淬火冷却过程温度场进行了数值模拟、温度场的求解,并考虑了材料热物性参数随温度的变化,得到瞬态温度场,进而对照40Cr的CCT推导组织转变,利用临界冷却速度预测了某些位置的淬硬层深度,并通过金相组织分析和硬度测试进行了验证。模拟结果和实验结果基本吻合。实测淬硬层与预测淬硬层深度相比,其值偏大;实测硬度值与预测硬度值相比,其值偏小。     

基于多维度物理参数影响的超高强钢热成形冷却流场仿真分析

目的 研究关键参数对超高强钢热成形模内淬火效果的影响规律,合理选择模具材料和冷却流场空间结构,达到冷却淬火后材料中条状马氏体含量最大的目的.方法 利用流体仿真软件Star–ccm+对超高强钢热成形模具冷却流场进行有限元模拟分析,采用7种不同热导率的热成形模具材料和直径为15、20、25、30、35 mm的冷却管道管径,...     

磁性纳米制冷剂冷却回路热磁对流特性研究

建立磁性纳米制冷剂Fe3O4-R600a冷却回路的热磁对流特性实验系统,研究了磁场分布、磁场强度、加热功率、冷却温度等对热磁对流特性的影响。结果表明：外磁场对磁性纳米流体热磁对流过程的影响非常明显,可无须机械泵驱动而实现能量的自主传递过程,冷却回路中的磁流体循环流动和传热性能取决于外磁场与温度的协同作用,应用外磁场有效可控制冷却回路的运行特性。     

中厚板加速冷却和直接淬火时冷却能力研究

为了确定加速冷却或直接淬火时实现预期的冷却速率所需的对流换热系数,利用MSC.MARC有限元分析软件对Q345B中厚钢板冷却过程中温度场进行了数值模拟计算.确定了实现直接淬火条件下不同厚度(20 mm)钢板的理论极限冷却速率所需的对流换热系数为15 000 W/(m2·℃),并分析了冷却速率与对流换热系数、钢板厚度之间关系.研究表明,对于同一厚度、材质中厚钢板,其冷却速率随对流换热系数的增加而增大.超快速冷却或直接淬火时,带钢冷却速率随对流换热系数增加而显著增加;对流换热系数大于15 000 W/(m2·℃)时,厚度(30 mm)钢板的冷却速率基本不变,达到其物理极限冷却速率;换热系数增加,厚度方向上温度梯度增加.     

Improved thermal resistance network model of motorized spindle system considering temperature variation of cooling system

In the motorized spindle system of a computer numerical control (CNC) machine tool, internal heat sources are formed during high-speed rotation; these cause thermal errors and affect the machining accuracy. To address this problem, in this study, a thermal resistance network model of the motorized spindle system is established based on the heat transfer theory. The heat balance equations of the critical thermal nodes are established according to this model with Kirchhoff's law. Then, they are solved using the Newmark-β method to obtain the temperature of each main component, and steady thermal analysis and transient thermal analysis of the motorized spindle system are performed. In order to obtain accurate thermal characteristics of the spindle system, the thermalconduction resistance of each component and the thermalconvection resistance between the cooling system and the components of the spindle system are accurately obtained considering the effect of the heat exchanger on the temperature of the coolant in the cooling system. Simultaneously, high-precision magnetic temperature sensors are used to detect the temperature variation of the spindle in the CNC machining center at different rotational speeds. The experimental results demonstrate that the thermal resistance network model can predict the temperature field distribution in the spindle system with reasonable accuracy. In addition, the influences of the rotational speed and cooling conditions on the temperature increase of the main components of the spindle system are analyzed. Finally, a few recommendations are provided to improve the thermal performance of the spindle system under different operational conditions.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0239-4     

Research on key technologies of FEM simulation of temperature field in the process of quenching

In this paper, some key technologies of computing the quenching temperature field are given. According to the characteristics of quenching process, a new method of computing phase-transformation latent heat is presented to ensure the computation accuracy of temperature. The phase-transform latent heat is regarded as the internal heat source because it can result in the rise of temperature in the process of cooling. A new method of self-control and adaptive time-step is presented in this paper. This method can be used to compute the time-step according to maximum and minimum difference values of the temperature field between the previous simulating step and the current simulating step. A finite element method (FEM) software for evaluating the temperature and the phase-transformation is developed by using the methods presented in this paper, the lump parameters method and fine mesh method. The experimental results or analytical values of two cases are used to check the accuracy of FEM simulation. The comparisons show that the simulation results of FEM software are consistent with experimental results or analytical values.     

雾化气体淬火过程耦合流场数值模拟及实验研究

运用计算流体动力学(CFD)的方法在FLUENT平台上建立雾化气体淬火的三维非稳态模型,对介质不同速度工况下淬火过程中试件温度场、流体速度场、流体温度场和流体压力场进行了流固热耦合数值模拟,并将模拟结果与边界条件实验结果进行了对比分析。结果表明,同等工况下,介质进口速度越大,流体的速度也越大;同截面上200m/s速度工况下试件上下表面两区域的压力差值比100m/s速度工况下大;试件放在淬火区淬火80s后,200m/s速度工况下试件的最高温度为299.5℃,100m/s速度工况下试件的最高温度为336℃,由此得出淬火介质进口速度越大,淬火试件的温度下降越快,试件冷却速度越快,冷却效果越好。     

Mathematical model coupling phase transformation and temperature evolution during quenching of steels

Abstract

To calculate the internal stresses in steels during quenching it is necessary to be able to predict accurately the evolution of phase transformations during the cooling process. After a review of published papers, a mathematical model coupling phase transformations with temperature field predictions at each instant during the cooling process is proposed. Incubation and growth periods are treated separately, using Scheil's method and the Johnson–Mehl–Avrami formulation, respectively. Martensitic growth is considered separately using the Koistinen and Marburger law. The temperature field calculation is carried out by the resolution of the heat equation using an implicit finite–difference method. An internal heat source term has been included in the heat equation to take into account the heat generated by the phase transformation. The results of the theoretical calculations are compared with those obtained by experiment, and the validity of the model and the effect of internal stresses on the theoretical predictions are discussed.

MST/13     

Propagation velocity of normal zones in a SC braid

Propagation velocities of normal zones are obtained experimentally in a superconducting (SC) braid which is wound into a coil to simulate the SC pulsed dipole magnet for a synchrotron from the viewpoint of cooling. A numerical calculation to determine this velocity is carried out by using a modified thermal conduction equation. The equation eliminates a troublesome problem on the boundary condition reported previously by defining a new variable of the square of the heat flux along the conductor. A velocity dependent correction factor is used for cooling to take account of the transient effect. The values calculated are a representation of the experimental dependence of the velocity on both current and magnetic field and this indicates that the correction factor is applicable to the winding of the braid if modified properly. Discussion is also made on the transient cooling in the coil.