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.     

铝合金轧制过程中的热力耦合分析

通过铝合金在Gleeble-1500上的实验数据,建立了本构方程.根据弹塑性热力耦合大变形有限元理论,获得了热轧过程中的数值仿真模型,分析了压下率、轧制速度以及接触传热系数等参数对温度和流动应力变化规律的影响,并与某铝厂热轧板带生产过程中不同压下率下的力能参数变化进行了对比,计算结果表明模拟值与实测值吻合较好,误差低于15%.     

基于流面条元法的热带钢连轧仿真分析

根据流面条元法 ,对 145 0mm六机架热带钢连轧进行了数值仿真。得到了各道次单位轧制压力、前后张应力和出口横向位移的分布。仿真结果表明 ,轧后带钢侧面呈鼓形 ,与实际情况一致。各道次的后张应力和前张应力有类似的分布规律。各道次总轧制压力的计算值和实测值很接近。仿真实例表明 ,流面条元法是一种模拟板带轧制三维变形的实用的工程数值方法。它具有计算量较少 ,适用范围较宽的特点。仿真结果对热带钢连轧工艺规程的制定具有指导意义。     

Prediction of influence parameters on the hot rolling process using finite element method and neural network

In the present investigation, a hot rolling process of AA5083 aluminum alloy is simulated using the finite element method. The temperature distribution in the roll and the slab, the stress, strain and strain rate fields, are extracted throughout a steady-state analysis of the process. The main hypotheses adopted in the formulation are: the thermo-viscoplastic behavior of the material expressed by Perzyna constitutive equation and rolling under plane-deformation conditions. The main variables that characterize the rolling process, such as the geometry of the slab, load, rolling speed, percentage of thickness reduction, initial thickness of the slab and friction coefficient, have been expressed in a parametric form giving a good flexibility to the model. The convergence of the results has been evaluated using experimental and theoretical data available in the literature. Since the FE simulation of the process is a time-consuming procedure, an artificial neural network (ANN) has been designed based on the back propagation method. The outputs of the FE simulation of the problem are used for training the network and then, the network is employed for prediction of the behavior of the slab during the hot rolling process.     

热连轧铝温度场数值模拟及工艺参数影响分析

采用二维交替差分法建立了铝热连轧轧件温度计算模型,同时采用粒子群算法对模型参数进行了优化。经验证,优化后模型的计算精度在10℃以内;利用建立的温度模型研究了铝板带在热轧生产过程中的温度场变化规律,并分析了工艺参数对轧件终轧温度场的影响。研究结果表明,粗轧区轧件温度分布主要由接触导热与轧件内部的热生成两者共同决定,而精轧区还要受到乳液喷淋的影响;轧制速度越大,轧件终轧温度越高,横向温差越大;处于相同机架间的冷却集管的冷却能力几乎相同,而处于不同机架间的冷却集管,随着机架数的增加,冷却能力增强,横向温差随着开启度的增大而减小;轧件宽度对轧件终轧温度的影响很小,而横向温差随轧件宽度的增大而增大;随着乳化液温度的升高,轧件终轧温度升高,而乳化液温度对轧件横向温差没有影响。     

Neural network modeling for the prediction of texture evolution of hot deformed aluminum alloys

Commercial aluminum rolling mills operate under very restricted thermomechanical conditions determined from experience and plant trials. In this paper we report results for four-stand tandem mill rolling simulations within and beyond the thermomechanical conditions typical of a rolling mill by plane strain compression (PSC) testing to assess the effect of deformed conditions on the texture of the hot deformed aluminum strip after annealing. A neural network modeling study was then initiated to find a predictive relationship between the observed texture and the thermomechanical parameters of strain, strain rate, and temperature. The model suggested that temperature is the prime variable that influences texture. Such models can be used to evaluate optimal strategies for the control of process parameters of a four-stand tandem mill.     

Optimization of deformation parameters of dynamic recrystallization for 7055 aluminum alloy by cellular automaton

In order to simulate the microstructure evolution during hot compressive deformation, models of dynamic recrystallization (DRX) by cellular automaton (CA) method for 7055 aluminum alloy were established. The hot compression tests were conducted to obtain material constants, and models of dislocation density, nucleation rate and recrystallized grain growth were fitted by least square method. The effects of strain, strain rate, deformation temperature and initial grain size on microstructure variation were studied. The results show that the DRX plays a vital role in grain refinement in hot deformation. Large strain, high temperature and small strain rate are beneficial to grain refinement. The stable size of recrystallized grain is not concerned with initial grain size, but depends on strain rate and temperature. Kinetic characteristic of DRX process was analyzed. By comparison of simulated and experimental flow stress–strain curves and metallographs, it is found that the established CA models can accurately predict the microstructure evolution of 7055 aluminum alloy during hot compressive deformation.     

随焊碾压防止铝合金焊 接热裂纹的云纹模拟和试验研究

本文提出了一种新的防止铝合金焊接热裂纹方法－－随焊同步碾压法，阐述了其原理，用云纹法模拟了随焊碾压产生的应变场，并进行了随焊碾压防止铝合金焊接热裂纹的试验研究。研究结果表明，随焊碾压可有效地防止铝合金的焊接热裂纹。     

冷轧带钢温度演变及影响因素研究

为了探究冷轧过程及轧制工艺参数对带钢温度的影响及演变规律,采用有限元方法对冷轧带钢进行建模,利用温度场反算的方法确定了带钢和轧辊间的传热热流密度,在此基础上通过改变模型参数对带钢温度场进行了模拟计算。结果表明,带钢温度在前4架轧制区呈阶梯式增长趋势,而在末机架出口呈下降趋势;此外,带钢出口温度随轧制速度、道次压下率、摩擦因数、变形抗力等的增加而升高。     

热轧低碳铝镇静钢表层粗晶缺陷原因分析及控制措施

针对低碳铝镇静钢热轧带钢生产时易出现表层粗晶缺陷的问题,对缺陷形貌及分布情况进行了分析,结合该钢种的CCT曲线及轧线实际生产工艺参数,研究了其表层粗晶的产生原因。结果表明,带钢边部温降导致其处于两相区轧制是造成表层粗晶的关键因素。因此,通过提高终轧温度,加强轧线冷却均匀性控制,对轧辊辊身温度监控,精轧采用升速轧制等措施,可以改善带钢长度方向的温度均匀性、减少带钢边部温降,避免带钢进入两相区轧制,可有效控制带钢表层粗晶缺陷。     

基于“应变重构”的热轧带钢C翘缺陷调控研究

由残余应力不平衡所导致的C翘缺陷是热轧带钢生产过程中难以回避的板形问题,但实际生产中缺乏有效的调控手段。采用基于弹性断裂力学原理的裂纹柔度法,研究了平整加工过程残余应力的演变规律,提出了基于加工过程金属流动性特征的“应变重构”方法,高效、便捷地改善了热轧带钢的平直度缺陷及应力问题。应用上述原理,分析了热轧生产中普遍存在的C翘缺陷的改善机制,并给出了现场应用案例。     

高速列车框架焊接的双椭圆柱高斯分布热源模型

根据高速列车车体结构焊接工艺特点,分析并改进常用高斯热源,提出适用于铝合金惰性气体保护焊接（MIG）的双椭圆柱-高斯分布热源模型.该热源模型基于焊接速度移动,形成的熔池表面为双椭圆形状,热流密度沿厚度方向均匀分布,在径向呈高斯-双椭圆分布.基于热源模型的数学表达,以有限元方法实现了热机耦合的焊接过程仿真,与薄板试验结果比较,温度场分布与降低趋势较好地吻合;拉应力峰值出现在熔合线和热影响区,仿真值、试验值分别为88.8,85 MPa.结果表明,该热源模型有效地模拟焊接温度场时域上的变化过程,准确地预测结构变形、残余应力分布规律,应用于高速列车头车框架结构焊接工艺优化及残余应力评估,为高速列车焊接质量控制及焊接工艺参数选择提供理论指导.     

A multiscale coupled Monte Carlo model to characterize microstructure evolution during hot rolling of Mo-TRIP steel

A multiscale modelling framework has been proposed to characterize microstructure evolution during hot strip rolling of transformation-induced plasticity (TRIP) steel. The modelling methodology encompasses a continuum dislocation density evolution model coupled with a lumped parameter heat transfer model which has been seamlessly integrated with a mesoscale Monte Carlo (MC) simulation technique. The dislocation density model computes the evolution of dislocation density and subsequently constitutive flow stress behaviour has been predicted and successfully validated with the published data. A lumped-parameter transient heat transfer model has been developed to calculate the average strip temperature in the time domain. The heat transfer model incorporates the effect of plastic work for different strain rates in the energy conservation formulation. A coupled initial value problem solver has been developed to integrate the system of stiff ordinary differential equations in the time domain to predict dislocation density and temperature profiles simultaneously. The temporal evolution of microstructure during hot rolling of TRIP steel is simulated by the MC method incorporating thermal and dislocation density data from the continuum models. Simulated microstructural maps, kinetics of recrystallization and grain size evolution have been generated in a 200 × 200 lattice system at different strain rates and temperatures. The simulation code has been implemented in a high-performance grid computing network. The predicted temporal evolution of grain size, recrystallized fractions and flow stress have been validated with the published literature and found to be in good agreement, confirming the predictive capability of the integrated model.     

热轧带钢头尾卷取温度分析及其补偿研究

热轧带钢卷取温度是反映热轧带钢性能指标的重要参数。针对某热轧厂层流冷却系统的具体情况,基于实时数据,应用数据挖掘工具,从理论和工艺的角度分析了控冷过程中头、尾部温差大的原因,得出了热轧带钢头、尾部卷取温度的规律,并以此建立温度补偿模型进行实验研究。文中的研究对提高控冷精度、优化生产工艺具有一定意义。     

Friction evaluation in hot strip rolling by direct measurement in the roll gap of a model duo mill

Using a model duo mill, and model material and lubricants, the hot strip rolling process has been simulated. The normal roll pressure, the shear stress and the shear-stress angle in the roll gap of the mill was measured by load tranducers, the purpose being to evaluate assumed frictional influencing factors, such as: strip reduction, rolling velocity, lubrication and different materials rolled. In order to improve the present simple-friction model for force calculation in hot strip rolling that uses just an average friction value, three friction models were evaluated: the friction laws by Coulomb, Tresca and Wanheim-Bay. The best model was then chosen on the basis of the measurements made in this study. Finally, suggestions for the improvement of the model of strip rolling is made.     

Numerical simulation on microstructural evolution during multipass hot-rolling of aluminum alloys

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纺织机针用工具钢带（T9A）的开发

研究了纺织机针用工具钢带的技术条件及热轧、冷轧、热处理工艺。结果表明，热轧的终轧温度及冷却速度能影响网状碳化物的级别，采用多道次冷轧和球化退火，可使成品钢带获得良好的性能。     

Investigation of rolls size effects on hot ring rolling process by coupled thermo-mechanical 3D-FEA

Hot ring rolling is a significant branch of ring rolling characterized by high nonlinearity, 3D deformation, continuously progressive forming, unsteady-state, asymmetry, etc. with coupled thermo-mechanical behaviors which have significant effects on the deformation behavior, microstructure and mechanical properties of the ring. Changing the sizes of forming rolls including mandrel and driver rolls will considerably affect the roll gap deformation zone which is in close relation to the feed amount of both forming rolls and thus affects forming quality of the ring as well as power parameters. In this study, a reliable coupled thermo-mechanical and 3D rigid-plastic finite-element (FE) model for hot rolling of large rings is established. Then, based on the stable forming condition of the ring rolling process and comprehensive numerical simulations, the size effects of forming rolls on strain and temperature distributions and their uniformity, stress distribution, side spread and power parameters were investigated by 3D coupled thermo-mechanical FE simulation. The results show that there are optimum sizes of mandrel and driver rolls under which the strain and temperature distributions of ring and thus its microstructure are the most uniform where fishtail coefficient and power parameters have reasonable values. The achievements obtained can not only serve as a guide to the design of rolls sizes, optimization and quality control of the hot ring rolling process, but also clarify the plastic deformation and heat transferring of hot rolling of large rectangular-section rings.     

Microstructural evolution on streamlines during hot strip rolling using internal state variables

In this work, a numerical-based model has been proposed to calculate distributions of temperature, strain and strain rate during hot rolling as well as the subsequent microstructural changes after hot rolling of an aluminum alloy. For doing so, a transient finite difference analysis together with a stream function method have been coupled to calculate temperature distribution and velocity field within the rolling metal. A new approach considering internal state variables method has been employed to predict the kinetics of static recrystallization after hot rolling. The predicted results were then compared with the experimental ones and a good consistency was observed between the two sets of data.     

铝板带连铸连轧工艺装备及工程建设综述

比较了铝板带三种主要热轧生产方式的优点及各自的局限性,说明了连铸连轧工艺在铝板带生产中的独特优点,以及连铸连轧工艺的发展情况,分析了连铸连轧工艺在我国铝板带加工行业的应用前景.结合正在建设的国内首条Hazelett铝板带连铸连轧生产线,对铝板带连铸连轧生产线的技术参数、设备组成及工程建设情况等进行了介绍和讨论.