Knowledge-based substep deterministic optimization of large diameter thin-walled Al-alloy tube bending

Regarding increasing applications with mass quantities, diverse specifications, and close quality tolerance, the precision bending of large diameter thin-walled (LDTW) Al-alloy tube should be efficiently achieved. However, bending of LDTW Al-alloy tube is a highly tri-nonlinear process with possible multi-defect, needing strict coordination of various bending tools and processing parameters. Considering the coupling effects of various forming parameters on multiple defects, this study developed a knowledge-based substep methodology to solve the deterministic optimization of LDTW Al-alloy tube bending with multi-objective and multi-variable under multiple factor constraints. Considering narrow forming window under small bending radii (R _b?<?2D, R _b—bending radius, D—initial tube diameter), a finite element (FE)-based stepwise iterative search method is proposed to optimize key forming parameters of LDTW Al-alloy tube under small R _b, and the search direction is based on bending knowledge. While for large R _b bending with wide optional ranges of forming parameters, a hybrid optimization approach is used by combining virtual design of experiment, FE simulation, approximate response surface model, sequential quadratic programming algorithm, or genetic algorithm. Using orthogonal experimental method, three-dimensional (3D)-FE simulation, experiential data, and analytical formulae, knowledge on key forming parameters, coupling effects on multiple defects, effect significance, and design rules are obtained as well as initial values and design ranges. By several practical bending scenarios with D up to 100 mm, the proposed substep deterministic optimization methodology for LDTW Al-alloy tube bending is evaluated.     

管材激光成形的数值模拟研究

建立了管材激光弯曲成形的有限元模型,对成形过程进行了数值模拟分析。模拟结果表明对应于加热和冷却阶段,管材的激光弯曲成形分别经历反向弯曲和正向弯曲两个变形阶段。管材加热区与未加热区域之间形成的较大的塑性应变差使得管材整体上产生了朝向激光束的正向弯曲。成形的机理主要表现为增厚机理。未加热区域的管材壁厚基本不变化,不会出现机械弯曲中管材的破裂问题。     

工艺参数对管材激光弯曲成形影响规律的研究

管材激光弯曲成形是一种柔性金属塑性成形方法。将连续的激光光斑简化为一间歇跳跃的方形匀强面热源,并考虑材料性能参数与温度的相关性,建立了管材激光弯曲成形的热-机耦合有限元工艺仿真模型,对成形过程进行了数值模拟。有限元模拟结果表明:在其他条件不变的情况下,激光弯曲角度随激光功率的增大而增大,两者基本上成线性关系;弯曲角度随扫描速度的升高而减小,随光斑直径的减小而增大,但当光斑直径减小到一定程度后,弯曲角度开始减小;弯曲角度随扫描包角的增大而增大,当扫描包角为180°时,弯曲角度达到最大,弯曲角度随扫描包角的继续增大而减小;扫描次数与弯曲角度间成近似的线性关系,且第一次扫描管材产生的弯曲角度最大。     

间隙对薄壁矩形管绕弯成形截面畸变影响的研究

基于ABAQUS/Explicit,建立了铝合金薄壁矩形管绕弯成形过程三维有限元模型,并对其可靠性进行了验证.模拟分析了芯棒与管坯间隙、压块与管坯间隙、防皱块与管坯间隙及弯曲模与管坯间隙对管坯截面畸变的影响规律.研究结果表明:减小芯棒与管坯间的间隙及弯曲模与管坯间的间隙都可减小管坯截面畸变的程度;而压块与管坯间隙及防皱块与管坯间隙的改变对管坯截面畸变率影响不大.     

高聚合物在双螺杆挤出机中预热融化过程的数值模拟

建立双螺杆挤出机预热起动时包括机筒、高聚合物和螺杆在内的非稳态传热模型,用于预测挤出机的温度变化和分布,以及螺槽中的高聚合物融化情况.数值结果表明,受加热通道分布的影响,总体上机筒中部的温度和靠近加热通道的高聚合物温度较高,高聚合物融化越快."8"字孔内表面、高聚合物和螺杆的平均温度随预热时间的增加而升高,"8"字孔内表面的温度在预热初期上升最快,在预热末期最先达到稳态,而螺杆的温度变化趋势与"8"字孔内表面温度变化趋势相反.与温度变化相协同,高聚合物在机筒内的融化速率随预热时间逐渐减小.研究结果对机筒加热通道的设计和优化,以及准确预测安全预热时间具有指导意义.     

管材拉弯工艺及数值模拟分析

拉弯是管材弯曲成形的重要工艺方法,采用有限元分析软件ANSYS/LS-DYNA对不同工艺参数下的管材拉弯成形过程进行了数值模拟,通过改变相对弯曲半径R/D和相对弯曲厚度t/D,分析了拉弯工艺参数对成形过程的影响。研究结果表明:通过增大相对弯曲半径R/D或增大相对弯曲厚度t/D,降低弯曲件的等效应力,可以有效控制弯曲件壁厚的变化,有助于提高管材拉弯成形的质量。     

基于热四极法的涂层刀具切削温度分布研究

为研究涂层在切削过程中对刀具温度分布的影响,建立了涂层刀具的三维瞬态热传导分析模型,发展了基于热四极法的切削过程涂层刀具三维温度场求解算法,得到了涂层刀具的瞬态温度分布。研究了涂层厚度、热对流以及界面热阻对涂层刀具切削温度分布的影响,为切削加工中涂层厚度的确定、切削液的选择以及涂层刀具的失效诊断提供了理论依据。     

A CFD-aided experimental study on bending of micro glass pipettes

This paper presents a study on the temperature profile in the bending process of glass pipettes. To prevent undesirable deformation of the pipette at its bending section, such as kink and constriction, several factors influencing the bending quality are investigated, including the width and temperature of the heating element, heating and bending time. Taguchi method is used to study the key factors and to identify an optimal parameter combination. ANSYS is also employed to study the heat transfer and temperature distribution in the heating zone. It is concluded that the temperature distribution in the bending area is critical to the bending quality, and the width of the heating element decisively determines the temperature distribution.     

微张力减径过程热力耦合有限元模拟

根据某厂十机架微张力减径机组轧制工艺,采用大变形弹塑性有限元法建立了管坯连轧三维热力耦合计算模型,并对实际工艺过程进行数值计算,得到了连轧过程中轧件的温度场、应变场和应力场分布规律。基于计算结果,分析了管坯壁厚分布规律、机架力能参数分布。所得结果与现场设定、实测结果吻合良好,表明了该计算模型的有效性。该模型可为现场张力减径工艺过程离线分析提供有力帮助。     

工艺参数对21-6-9高强不锈钢管数控弯曲壁厚减薄影响的显著性分析

为实现21-6-9高强不锈钢管数控弯曲精确成形,提高其成形质量与成形极限,需要对弯曲过程中壁厚减薄进行有效控制。基于ABAQUS/Explicit有限元软件平台,建立了21-6-9高强不锈钢管数控弯曲三维弹塑性有限元模型,并对其可靠性进行了验证。通过有限元模拟和正交试验,研究了工艺参数对21-6-9高强不锈钢管数控弯曲壁厚减薄影响的显著性及规律。结果表明,影响壁厚减薄的显著性工艺参数依次为芯棒伸出量、管材与芯棒间隙、管材与防皱块摩擦因数、管材与芯棒摩擦因数、管材与压块摩擦因数和弯曲速度,其影响规律为：壁厚减薄率随着芯棒伸出量、管材与防皱块摩擦因数、管材与芯棒摩擦因数、管材与压块摩擦因数、弯曲速度的增大或管材与芯棒间隙的减小而增大。采用多元线性回归方法建立了最大壁厚减薄率与显著性工艺参数之间的回归预测模型,经对比验证,回归预测模型结果与正交试验结果之间的相对误差不超过5%。     

基于数值模拟的线材轧制成形过程研究

通过对线材热连轧过程传热关系进行分析,利用热力耦合弹塑性有限元方法建立了线材与轧辊的三维数值计算模型,结合热轧生产线的实际情况,对高速线材轧制生产线预精轧区六道次轧制过程中的温度场、轧制力与轧制力矩进行了模拟计算。分析了变形区内温度场的分布和变化规律,探讨了轧制过程中所涉及的几何、材料和边界条件等多重强非线性问题,计算结果为生产工艺制度的改进、工艺参数的优化以及微观组织变化规律的研究提供了理论依据,对现场生产也有重要的参考价值。     

Efficient simulation of shell forming by line heating

A simplified thermo-mechanical model for the prediction of angular deformations of metal plates due to line heating is presented. The model utilizes a semi-analytically determined temperature distribution, which incorporates the effects of heat loss and a distributed moving heat source, to find the dimensions of a critical heat-affected region. The dimensions of this region are used to find the angular deformation by an analytic solution method. Predicted values of angular deformation compare well with corresponding values from experimental results. This model is also compared with thermo-mechanical analysis based on the three-dimensional finite element method. The comparisons indicate that the simplified model is fairly accurate and much more efficient in comparison to the finite element solution.     

带壁厚偏差的无缝钢管推压-拉拔复合缩径

通过测量、分析某载重6.5 t胀压成形汽车桥壳用钢管的轴向及周向的壁厚,建立了带壁厚偏差管坯的几何模型及推压-拉拔复合缩径的力学模型,分析了薄壁侧、厚壁侧管坯的受力及变形差异;通过对不同壁厚偏差管坯两侧的推压-拉拔复合缩径进行数值模拟,揭示了壁厚偏差对传力区应力及管坯壁厚的影响规律,并基于传力区不失稳条件给出了初始管坯的周向壁厚偏差的最大值;在专用缩径设备上成功试制出缩径样件,试验结果与有限元模拟所得规律一致。     

T92/12Cr1MoV异种钢焊接温度场的数值模拟

重点介绍T92/12Cr1MoV焊接过程的三维有限元分析模型,得到了多层焊温度场的分布规律,同时通过有限元分析中的关键问题判断和检测,得出如下实验结果：距离焊缝越近的点,加热及冷却速度越快;预热温度提高,加热速度及高温停留时间变化不大,但峰值温度升高,且相变温度以上停留时间变长;焊接线能量增加,t8/5延长,而t8/5过长,促进晶粒长大,使韧性降低,t8/5过短,易生成淬硬组织,因此应严格控制焊接线能量。     

铍材激光钎焊温度场和应力场的数值模拟

在综合考虑激光钎焊熔池表面形状和几何参数的基础上,建立了适合于铍材激光钎焊的表面双椭圆热源分布模型;通过对数值模拟与试验获得的熔深、熔宽等参数的对比,可知计算结果与试验结果吻合较好,说明双椭圆表面热源模型能够较好地模拟铍环钎焊.通过对焊接加热和冷却过程中铍环焊缝附近应力状态变化的比较,发现凝固过程中最大轴向拉应力和最大环向拉应力均位于焊缝中心,这正是焊缝中心较易形成凝固裂纹的主要原因.     

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。     

锅炉受热面热力参数的解析——数值混合计算方法

对锅炉热力过程采用解析——数值混合计算方法建立了计算数学模型。该模型的基础是通过管壁温度的求解解除冷侧流体与热侧流体能量方程之间的耦合关系,然后采用解析——数值混合计算方法分别求解冷热两侧流体能量方程。利用该方法计算了一台600MW超临界直流锅炉冷态启动过程,结果表明计算值与测量值吻合得比较好,而且与迭代解法的计算结果相差不大,但计算时间则大为缩短。     

Analytical model for planar tube hydroforming: Prediction of formed shape, corner fill, wall thinning, and forming pressure

An analytical model for planar tube hydroforming based on deformation theory has been developed. This analytical model can be used to predict hydroformed shape, corner fill, wall thinning, and forming pressure. As the model is based on a mechanistic approach with bending effects included, local strain and stress distribution across the wall thickness can be determined. This includes strain and stress distributions for the outer layer, inside layer, and middle layer. The model is validated using finite element analysis and tube hydroforming experiments on irregular triangular, irregular quadrilateral, and pentagonal hydroformed shapes.     

Numerical analysis of rolling-sliding contact with the frictional heat in rail

Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature field, but few literatures focus on wheel-rail thermal stress caused by frictional heating. However, the wheel-rail creepage is one of important influencing factors of the thermal stress In this paper, a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method. The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration. The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail. The effect of the creepage on the temperature rise, thermal strain, residual stress and residual strain under wheel-rail sliding-rolling contact are investigated. The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact. Both the temperature and thermal strain of rail increase with increasing creepage. The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile. When the creepage is large, the frictional heat has a significant influence on the residual stresses and residual strains of rail. This paper develops a thermo-meehanical coupling model of wheel-rail rolling-sliding contact, and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.     

聚丙烯水下切粒模板温度场的数值模拟

模板是聚丙烯造粒过程中最为关键的设备之一,模板的温度场对切粒质量有重要影响。建立水下切粒模板的三维传热模型,并对该模型进行数值求解,获得模板内部的温度分布。数值结果表明,受导热油加热作用,浅层模板厚度方向剖面的温度分布较为均匀;切粒模板受到冷却水的冷却作用,导致切粒面温度较低;在导热油加热和冷却水冷却共同作用下,切粒面浅层的温度梯度较大。对切粒模板的温度场进行数值模拟和分析,可为模板内部的导热油通道和模孔的设计和优化提供良好的理论支撑。