水火弯板温度场理论分析和数值模拟

水火弯板工艺是船体外板弯曲的一项关键的流程,前人对钢板的温度场已进行过相关的研究。高斯热源热流密度模型被广泛用于水火弯板的温度场的分析,其参数的选取和定义,是水火弯板数值模拟中一个关键问题。本文采用高斯热源热流密度模型对水火弯板中的气体火焰热源和钢板的温度场展开了研究,并提出了高斯热源热流密度模型的不足和改进方法。     

快速再制造成形温度场模拟中的热源模型对比研究

介绍了基于快速成形的熔覆快速再制造系统,对成形温度场模拟中的两种热源模型,即高斯热源模型和双椭球热源模型,使用单元生死技术模拟熔覆区动态成形过程,并做了相应的成形试验,采集了温度数据,将两种热源下的温度场数据进行对比.研究结果表明,双椭球热源模型的模拟结果更加接近试验结果.     

镍基合金熔接涂层与基体温度场的有限元分析

建立镍基合金熔接涂层和基体的三维有限元分析模型,基于ABAQUS软件采用生死单元法对其进行温度场分析,研究了镍基合金熔接涂层和基体之间的温度场变化规律。结果表明:熔接涂层与基体之间的温度场呈阶梯状分布;热源附近的熔接涂层温度场呈均匀分布;移除热源后,熔接涂层的降温速率高于基体的降温速率。     

工艺参数对无模成形温度场的影响

采用有限元法对不锈钢棒材无形温度场进行了数值分析，分析了工艺参数如冷热源速度、冷热源间距以及变形程度对温度场的影响，该分析结果很好地反映了各项工艺参数对温度场的影响规律。     

挖掘机动臂板焊接温度场模拟及影响因素分析

利用有限元方法对挖掘机动臂平板对接焊温度场进行了分析,采用Goldak椭球热源模型,应用DFLUX子程序定义热源模型的位置、大小、热输入以及焊接速度等参数来模拟瞬态温度场的分布及其变化,在此基础上通过改变焊接热输入、热源模型参数和焊接速度来分析其对温度场分布的影响规律.研究结果表明,由于焊接热源具有集中移动的特点,焊接热源模型参数以及焊接速度对焊缝区和热影响区的温度分布影响比较明显,热输入的变化与最高温度的变化大致呈线性关系.运用有限元法,选取Goldak椭球热源模型通过DFLUX子程序可有效进行挖掘机动臂平板焊接的数值模拟.     

一种应用于大直径药芯焊丝堆焊的热源模型

为准确地模拟出大直径药芯焊丝堆焊时的焊缝形状,提出了一种新的旋转叠加高斯曲面体串热源模型。分别建立经典的高斯热源模型和新的热源模型,利用高级编程语言C#在visual studio 2010平台上进行解析法计算,得到试件温度场分布和焊缝横截面轮廓,并进行试验验证。结果表明,与经典高斯热源模型相比,使用新模型可以更准确地模拟焊接温度场;同时,通过分析两种热源模型模拟结果,可以了解新热源模型与高斯热源模型的不同特点,为正确选择热源模型、进行高效数值模拟提供依据。     

6061-T6铝合金搅拌摩擦焊温度场的数值模型和参数影响分析

针对带圆柱搅拌针的搅拌头,推导了一种搅拌摩擦焊热源模型的一般表达式,按照滑动摩擦、粘着摩擦和混合滑动摩擦与粘着摩擦3种机制计算其中的摩擦应力,得到3种热源模型。采用ABAQUS软件,通过子程序实现热源模型并进行加载,建立了12.7 mm厚6061-T6铝合金板的搅拌摩擦焊温度场数值模型。数值模拟结果与实验结果的对比表明:基于粘着摩擦和混合滑动摩擦与粘着摩擦的模型能较好地预测温度场,两者给出的焊接稳态温度场基本一致,而基于滑动摩擦的模型预测的温度场偏高。通过改变模型参数的取值,系统地研究了边界条件、预热时间、焊接参数、搅拌头结构尺寸对温度场、产热功率和搅拌头所受力矩的影响,得到一系列规律和指标。     

2219铝合金激光电弧复合焊接及其温度场的模拟

研究了在激光电弧复合焊接条件下,2219铝合金的焊接工艺参数及其温度场的变化。通过调节激光功率、焊接速度等,得到了最佳焊接工艺参数;利用ANSYS有限元软件,采用均匀分布的高斯分布热源、柱体热源与椭球热源模型相叠加的组合热源模型,对6 mm厚2219铝合金的激光-MIG复合焊接温度场进行了数值模拟。实验所得焊缝接头平均抗拉强度为155 MP,达到铝母材的51%;且数值模拟结果与焊缝截面尺寸基本一致,表明了所选热源模型可适用于2219铝合金激光-MIG复合焊接温度场的数值模拟。该研究为铝合金的激光-MIG复合焊接的工艺研究以及数值模拟提供了有益的参考。     

镗铣加工中心主轴箱热特性仿真及试验研究

对镗铣加工中心主轴箱进行三维建模,依据工况确定热源,计算得出热源发热量并作为热载荷,以计算得出的各换热面对流换热系数作为边界条件,对主轴箱温度场进行了模拟分析,得到温度场分布以及稳态、瞬态温度场变化规律。依据温度场模拟结果,进行了热-结构耦合分析得到主轴箱热变形。通过主轴箱温度测试实验对温度场模拟结果进行了验证,并对实验与仿真结果的误差进行了分析。研究结果为建立热特性分析模型以及热误差的补偿提供参考。     

球罐环焊缝接头残余应力的三维非线性有限元分析

建立了球罐环焊缝焊接温度场和焊接应力应变场三维移动热源有限元分析模型,考虑了材料的热物理性能和力学性能随温度而变化,应用单元生死技术模拟焊接填充过程,模拟计算出移动热源作用下的温度场,以及以温度场为基础的环焊缝接头焊接应力应变场的分布规律:温度场结果表明,由于焊接的热输入和速度不同,以及热源加载体积不相等,每道焊接的最高温度均不相等。应力场的分析结果表明,在球罐内表面的焊缝及近缝区,呈现双向残余拉应力(经向和周向),而在外表面的对应区域,经向残余应力是压应力,周向残余应力为拉应力。     

Residual stresses due to a moving heat source

An analytical model based on finite element method is presented for determination of the residual stresses of thermal and mechanical origin due to surface grinding process. The temperature field within the workpiece is determined as the quasi-steady state temperature distribution due to the moving heat source. An iterative procedure is employed for evaluation of the step-by-step movement of the temperature field and the force, in order to simulate the movement of the grinding wheel over the workpiece. Computation of the elastic-plastic stress history culminates in the residual stress state of the workpiece. Influence of the magnitude of mechanical force, the rate of heat input and the speed of movement of workpiece on the residual stress distribution, are discussed.     

基于瑞利分布的平面磨削温度场的仿真研究

考虑磨粒在砂轮表面随机分布对接触区热流密度分布的影响,基于未变形磨屑厚度的瑞利分布理论,假定流入工件的热流密度呈瑞利分布,建立了瑞利分布热源模型。采用基于有限元法的瑞利分布热源模型对典型磨削工况进行仿真计算,将计算结果与矩形分布及三角形分布仿真结果进行对比,系统地分析了热源模型、磨削液对温度场的影响规律。结合磨削实验测量值,发现基于瑞利分布的热源模型仿真结果与实验测量值吻合较好。     

基于ANSYS的平面磨削温度场的有限元仿真

通过确定移动热源的加载方式,运用ANSYS软件的热分析模块对磨削温度场进行仿真分析,得到了不同载荷步的温度场分布以及不同深度的节点的温度变化曲线,验证了越靠近热源磨削温度越高以及工件下层材料温升显著低于工件表面。通过改变砂轮线速度、工件进给速度和磨削深度,得到了主要的磨削参数对磨削区温度场的影响状况,证明了钛合金磨削存在临界磨削速度。在临界磨削速度附近某一区间磨削温度出现回落,因此适当的磨削速度、高的工件进给速度和小的磨削深度可以有效的减小磨削温度。     

成形铣齿加工过程中的切削热模型

为了获得铣齿切削时切削区域的温升分布,在分别对铣削热产生和传出的机理,以及刀具和工件之间几何关系分析的基础上,得出包含对应虚拟镜像热源的热源模型。考虑到剪切面热源和刀屑接触面摩擦热源对工件、切屑和刀具的温升作用效果的不同,根据傅里叶导热定律推导出顶刃切削时相应热源的温升计算公式,分别对3者的温升分布进行计算可以获得整个切削区域的温升分布。结果表明,铣削过程中温度随切削的深入而升高,在不改变工件和刀具材料的情况下,进给速度是影响切削温度的主要因素,改变刀盘转速对温升的影响不大。     

TEMPERATURE DISTRIBUTION DURING ELECTRO-DISCHARGE ABRASIVE GRINDING

The objective of this work is to develop a finite element method (FEM) based mathematical model to simulate the hybrid machining process of grinding and electric discharge machining (EDM), named as Electro-discharge abrasive grinding (EDAG), for temperature distribution in the workpiece. Two different finite element codes have been developed to calculate the temperature distribution due to grinding heat source and EDM heat source separately. The transient temperature field within workpiece due to cut-off grinding is determined due to moving rectangular heat source. Gaussian heat distribution of power within a spark has been considered in the calculation of temperature distribution due to EDM. Temperature distribution in the workpiece due to combined process is obtained by using superposition. The simulation shows a sudden rise in temperature at the spark location. The predicted results can be used for calculation of thermal stresses, which play a major role as far as high-quality product requirements are concerned.     

TEMPERATURE DISTRIBUTION DURING ELECTRO-DISCHARGE ABRASIVE GRINDING

The objective of this work is to develop a finite element method (FEM) based mathematical model to simulate the hybrid machining process of grinding and electric discharge machining (EDM), named as Electro-discharge abrasive grinding (EDAG), for temperature distribution in the workpiece. Two different finite element codes have been developed to calculate the temperature distribution due to grinding heat source and EDM heat source separately. The transient temperature field within workpiece due to cut-off grinding is determined due to moving rectangular heat source. Gaussian heat distribution of power within a spark has been considered in the calculation of temperature distribution due to EDM. Temperature distribution in the workpiece due to combined process is obtained by using superposition. The simulation shows a sudden rise in temperature at the spark location. The predicted results can be used for calculation of thermal stresses, which play a major role as far as high-quality product requirements are concerned.     

Prediction of heat transfer process in helical milling

This paper represented a three-dimensional heat transfer model which describes the temperature distribution with the time variation in solid with conduction-convection boundary during the helical milling process. On the basis of the kinematic mechanisms of helical milling, two types of heat sources were presented; one was the first heat source (FTHS) resulting from the peripheral cutting edge, and the other one was the second heat source (STHS) resulting from the bottom cutting edge. Both effects of the FTHS and the STHS on the temperature distribution of the workpiece were investigated. The FTHS was defined as one semicircle which acted on a helical path; the STHS was defined as one straight line and the movements of which consisted of three ways: rotating around the axis of the tool, turning around the center of the hole, and moving along the axial direction. In order to accurately study the heat transfer model, a stationary coordinate established in the hole and a moving coordinate established in the heat source were developed. The transformation of coordinates and the trajectory of the moving coordinate had been illustrated. Under the two coordinates, a nonhomogeneous partial differential equation (PDE) containing heat source term was derived and was solved using the Green function approach. The heat source term was depicted using the Dirac delta function. A series of experimental tails for Ti-6Al-4V were organized. The experimental results agreed well with the data calculated using the model. The effects of different cutting parameters on the temperature rise were also investigated.     

Quadratic curve heat flux distribution model in the grinding zone

In order to estimate temperature distribution and the influence of grinding parameters on grinding temperature in the grinding zone, a theoretical model used for calculating and simulating the grinding process must be established. Many simplified heat source models developed previously have some errors compared with the actual heat flux to the workpiece. Therefore, based on the triangular heat flux distribution model and temperature distributions measured, an inverse method for the heat transfer mechanism in the grinding zone was investigated and a quadratic curve heat flux distribution model was developed to determine the heat flux distribution and predict the surface temperature of the workpiece. From the theoretical expression of heat flux to the workpiece, it has been found that the quadratic curve heat flux is the superposition of square law heat flux, triangular heat flux, and uniform heat flux in the grinding zone. By comparison of theoretical analysis with the experimental results, it has been demonstrated that the solution using a quadratic curve heat flux can improve the grinding model by decreasing the error, although the uniform and triangular heat fluxes can explain the condition of the heat flux to the workpiece along the grinding zone.     

叶序排布磨粒对砂轮的磨削温度场效应

在砂轮磨削过程中,磨削热影响工件表面完整性,而磨粒排布是影响磨削温度场的重要因素之一。针对磨粒叶序排布的砂轮,采用有限元法对磨削温度场进行了计算模拟分析,获得了叶序系数对工件磨削温度场的影响规律。研究结果表明,随着叶序排布系数的增大,被磨工件的表面温度和温度梯度减低。     

Numerical and experimental studies on the temperature field in precision grinding of SiCp/Al composites

During precision machining of SiCp/Al composites, the temperature of the workpiece surface directly affects the machining quality. In this paper, a triangle heat source model was used to calculate the heat flow during grinding of SiCp/Al composites, then, a three-dimensional finite element method was employed to investigate the temperature distribution at different process parameters, i.e., grinding depth and feed speed of the worktable. In addition, the temperature measures using embedded thermocouple were applied to compare with predictions from the thermal model. The results indicate that the grinding temperature predicted by the finite element method agrees well with the experiment data, and the triangle heat source model was suitable for estimating the workpiece temperature of precision grinding.