基于PGWO-BP神经网络的管材自由弯曲精确成形参数预测

为了提高管材自由弯曲成形技术的加工精度，针对平面弯管加工精度的成形参数开展精确预测工作，通过建立成形参数预测模型的方法使弯曲半径和弯曲角的实验值与设计值一致。首先，建立有限元仿真模型并通过管材加工实验进行修正，采用优化后的仿真模型建立预测的样本数据库，以有限元仿真得到的弯曲半径和弯曲角作为输入，以弯曲半径和弯曲角的设计值作为输出，结合BP神经网络和灰狼优化算法搭建成形参数预测模型。结果显示，改进后的PGWO-BP神经网络预测的弯曲半径和弯曲角的最大误差不超过2%,同时利用该预测模型开发了管材精确成形的工艺参数确定软件。     

AZ31B镁合金电流辅助旋压回弹角预测及工艺参数优化北大核心CSCD

在金属旋压工艺中,回弹是一种无法避免的成形缺陷,为了减小旋压制件的回弹,在电流辅助旋压的基础上,以AZ31B镁合金旋压件为研究对象,通过正交实验探究了电流强度、主轴转速、旋压轮进给速率与回弹角的关系,对实验结果进行了极差分析和方差分析,得到了工艺参数对回弹角的影响规律及最小回弹角的工艺参数组合。以实验数据作为训练样本,建立了BP神经网络模型进行回弹角预测,将实验得到的工艺参数组合作为输入,进行回弹角预测及实验验证,结果表明:BP神经网络模型的预测结果与实验结果的相对误差小于3%,能够较准确地预测回弹角,为实际生产和进一步的实验研究提供了理论指导。     

6061-T4薄壁铝合金管数控弯曲回弹规律(英文)

以规格为50.8mm×0.889mm(管材外径×管材壁厚)的高性能薄壁6061-T4铝合金管为对象,采用单因素实验分析和基于全过程三维有限元模拟的正交方法,获得多个弯曲成形参数对6061-T4薄壁铝合金管数控弯管回弹的影响。结果表明:1)弯管回弹角随弯曲角度的增大而总体呈线性增大;2)影响弯管回弹的显著性因素从高到低排列为:芯棒管材间隙,弯曲半径,压模管材摩擦,防皱块管材间隙,压模管材间隙,助推速度,芯模管材摩擦和芯球个数;3)显著性成形参数对回弹的影响规律与不锈钢和钛合金相似:回弹角随弯曲速度、芯棒管材间隙、相对弯曲半径、防皱模管材间隙、压力模摩擦系数、压力模相对助推速度的增大而增大,随芯棒伸出量、芯球个数和芯棒摩擦系数的增大而减小。     

小直径LF6铝合金管数控弯曲回弹规律

航空用小直径铝合金管在数控弯曲卸载后会产生比较明显的回弹现象,影响零件的几何和形状精度。基于有限元软件AUTOFORM,建立了LF6铝合金管数控弯曲弹塑性有限元模型。利用该模型,研究了弯曲角度与卸载后回弹角度之间的关系,并通过正交实验分析了工艺参数对小直径LF6铝合金管数控弯曲回弹的影响规律。结果表明,回弹角随着弯曲角度的增大而线性增大;回弹角随芯棒伸出量的增大而减小,随芯棒与管材间隙和管材与压块间摩擦系数的增大而增大,压块相对助推速度小于1时,回弹角增大。     

基于ABAQUS有限元模拟铝合金小弯曲半径的内压推弯成形

内侧起皱、外侧壁厚减薄及横截面畸变等是管材弯曲成形过程中主要缺陷,对于小半径弯曲成形的管材尤为严重。采用有限元技术对φ32 mm×1 mm的LF2M铝合金管材在1倍相对弯曲半径时的推弯成形过程进行了数值模拟,得到了内压力、管坯与凹模之间摩擦系数等工艺参数对管件成形质量影响规律。结果表明,合理增加管坯与凹模之间摩擦系数能降低壁厚减薄,同时内压大小对控制截面畸变有重要影响,在摩擦系数0.06和15MPa内压成形工艺参数时能得到较好成形效果。     

0Cr18Ni9管材大曲率无芯弯曲回弹研究

为了提高管材回弹后的质量,初步建立了管材大曲率无芯弯曲回弹角的预测模型。同时建立了管材弯曲回弹模拟模型,基于ABAQUS数值模拟和实验对0Cr18Ni9管材进行大曲率无芯弯曲(相对弯曲半径为1. 5),验证了模拟模型的可靠性。研究了弯曲角、弯曲速度及壁厚等工艺参数对管材弯曲回弹的影响。结果表明:管材弯曲回弹是一个应力释放的过程,弯曲角对回弹影响最大,壁厚次之,弯曲速度影响最小;回弹角随弯曲角度的增大而增大;回弹角随壁厚增大而减小;弯曲速度与回弹角成正相关关系,回弹角随弯曲速增大而增大。     

考虑金属黏性的弯管滞后回弹分析

研究材料黏性对金属管材弯曲滞后回弹的影响,选取双层黏弹塑性模型描述材料力学行为,对06Cr19Ni10不锈钢进行一系列单轴拉伸和应力松弛实验,获得与黏性相关的材料性能参数。应用ABAQUS仿真分析软件仿真分析管材弯曲滞后回弹过程,获得60天内各时间节点的滞后回弹角度数据。选取06Cr19Ni10无缝管进行管材弯曲滞后回弹实验,应用三坐标精密检测仪测量管材各采样节点的滞后回弹角度。对比实验结果和仿真数据,二者的滞后回弹角度差值小于10%,证明仿真结果具足够的预测精度,在工程中有一定的指导意义。     

TA18高强钛管数控弯曲回弹工艺参数影响的显著性分析

高强钛管数控弯曲卸载后会产生显著回弹现象,这严重影响着管件的几何和形状精度。基于ABAQUS平台建立了TA18高强钛管数控弯曲、抽芯及回弹三维弹塑性有限元模型,并进行可靠性评估。通过虚拟正交试验,研究工艺参数对TA18高强钛管数控弯曲回弹的影响显著性及规律。结果表明,影响回弹的显著工艺参数依次为:芯棒伸出量、弯曲模-管子摩擦系数、压块-管子间隙、压块相对助推速度和芯棒-管子间隙;其影响规律为回弹角随芯棒伸出量的增大而减小,随弯曲模-管子摩擦系数、压块-管子间隙和芯棒-管子间隙的增大而增大,当压块相对助推速度小于1时,回弹角明显增大。并采用多元逐步线性回归方法建立了回弹角与显著工艺参数之间的预测模型,经对比验证,对于规格为φ12mm×t1mm×R36mm的TA18高强钛管,此模型预测结果与虚拟试验结果之间误差不超过5%。     

BP神经网络在铝合金板材激光弯曲成形中的应用

在铝合金板材的激光弯曲成形中,工艺参数(激光功率、扫描速度和扫描次数)的不同组合使板材的弯曲角度也不同,而且从试验数据中很难得出激光工艺参数与弯曲角度之间的规律。本文用BP神经网络技术对铝合金板材的激光弯曲成形结果和工艺参数进行了预测。结果表明,预测值与真实值之间的误差都稳定在10%以内。精度比较高,说明运用BP神经网络对激光弯曲角度进行预测是可行的。     

基于BP神经网络的管材材料参数逆向识别

管材材料塑性本构参数是研究管材弯曲成形的关键因素之一。对于大直径管材的力学性能,可通过取样拉伸试验测得材料的应力应变曲线与弹性模量;对于小直径管材的材料参数,则较难直接通过实验测得。该文利用ABAQUS有限元软件,对小直径厚壁管材绕弯成形及回弹过程进行数值模拟,提出基于BP神经网络算法与数值模拟仿真实验相结合的管材材料参数逆向识别的方法,实验数据的对比表明,该方法能够有效的预测管材材料参数。     

Springback of thin-walled tube NC precision bending and its numerical simulation

The springback is one of the key factors which affect the forming quality of thin-walled tube NC precision bending. The elastic-plastic finite element method was proposed to study the springback process of thin-walled tube NC precision bending and the combination of dynamic explicit algorithm and the static implicit algorithm was proposed to solve the whole process of thin-walled tube NC precision bending. Then, the 3D elastic-plastic finite element model was established based on the DYNAFORM platform, and the model was verified to be reasonable. At last, the springback rule of thin-walled tube NC precision bending and the effect of geometry and material parameters on the springback rule of thin-walled tube NC precision bending were studied, which is useful to controlling the springback of thin-walled tube NC precision bending, and the numerical simulation method can be used to study other effect of parameters on the forming quality of thin-walled tube NC precision bending.     

Springback After the Lateral Bending of T-Section Rails of Work-Hardening Materials

This paper studies the springback after the lateral bending of T-section rails, considering the work-hardening materials. A linear-hardening model and an elastic-plastic power-exponent hardening model of the material are adopted and compared with the real experimental stress-strain curve obtained from the uniaxial tension tests. The analytical formulas for the springback and residual curvatures are given. The numerical results indicate that the material hardening directly affects the accuracy of springback prediction compared with the experimental results. Besides, springback prediction is not sensitive to hardening parameters in the beginning of elastic-plastic bending deformation. Although there is an apparent yield stage in the true stress-strain curve, the adopted hardening models can achieve an allowable relative error, if hardening parameters are properly selected.     

基于BP神经网络的铝合金板料弯曲回弹控制研究

针对铝合金板料在弯曲成形后回弹的现象,分析了板料弯曲时回弹的力学原理,采用变压边力法,利用数值模拟软件对板料弯曲的回弹进行了模拟。利用BP神经网络技术对变压边力下,板料的弯曲回弹量进行了预测。通过优化后的神经网络模型,找到了最佳的弯曲成形工艺参数。与实际情况对比,预测的板料弯曲回弹量具有一定的准确性和适用性。     

Springback Prediction Model Considering the Variable Young’s Modulus for the Bending Rectangular 3A21 Tube

Springback is inevitable for thin-walled rectangular 3A21 tube in rotary-draw bending process, and Young’s modulus is a crucial material property parameter affecting springback simulation. Therefore, to improve the springback prediction precision, the variation of Young’s modulus with plastic deformation for 3A21 material is studied through a repeated loading-unloading experiment, and a piecewise linear function is given out to describe the relationship between Young’s modulus and plastic strain, which is considered into a new material constitutive model combined with the Von-Mises yield function and the Swift isotropic hardening rule. Furthermore, a finite element springback prediction model is established by means of this new constitutive model for rotary-draw bending process of thin-walled rectangular 3A21 tube, and its reliability is validated experimentally. Comparisons between simulation results and experimental data show that, the accuracy of springback prediction can be improved significantly by 18.02% when the variation of Young’s modulus is considered. On the basis of the established model, the stress distribution field of thin-walled rectangular 3A21 tube in the whole rotary-draw bending process is obtained and analyzed.     

Springback characterization and behaviors of high-strength Ti–3Al–2.5V tube in cold rotary draw bending

Stress-relieved Ti–3Al–2.5V bent tube in hydraulic bleeding systems improves the overall performance of advanced aircraft and spacecraft due to its unique high specific strength. However, the high ratio of yield strength to Young's modulus may induce significant elastic recovery after unloading. The precision bending of the high strength Ti-tube (HSTT) depends on the understanding of the springback features and mechanisms. Using the plasticity deformation theory, the explicit/implicit 3D-FE and the physical experiments, the springback behaviors of the HSTT under multi-die constrained cold rotary draw bending (RDB) are addressed. The results show that: 1) The elastic recovery of the HSTT should be characterized by the significant angular springback, the radius growth and the sectional springback; Both the angular and radius springback should be compensated, while the sectional one decreases the cross-section flattening; 2) Among multiple parameters, both the material properties (Young's modulus, strength coefficient and anisotropy exponent) and the geometrical dimensions (bending angle and bending radius) dominate the unloading; Both the angular and radius springback values decrease with the smaller bending radii; The angular springback increases linearly with the larger bending angles, while the radius growth fluctuates little with the increasing of the bending angles at the later bending stages; Both the springback values of the HSTT are far larger than the ones of the 5052O Al-alloy tube and the 1Cr18Ni9Ti tube; The maximum variations of the angular and radius springback with changing of the processing parameters are 78% and 62.5% less than the maximum ones under different material properties and geometrical ones, respectively. 3) A two level springback compensation methodology is proposed to achieve the precision bending in terms of both springback angle and radius.     

薄壁U形圆管多道次绕弯成形性分析

详细分析了薄壁管的绕弯成形过程及其变形特点,采用LS-DYNA软件对U形薄壁圆管的2道弯曲工序的绕弯成形过程进行仿真,重点对从预成形仿真、回弹仿真到考虑回弹量的过弯成形仿真的仿真方法进行探讨。与实验结果进行比较分析表明,采用该文提出的薄壁圆管绕弯成形方法仿真结果与实验测量值吻合较好,圆管弯曲角外侧厚度过量减薄和内侧材料堆积引起的起皱以及弯曲角回弹,是薄壁管类零件绕弯成形的主要缺陷。     

薄壁管纯弯曲塑性成形分析及回弹计算

回弹是薄壁管数控弯曲常见的质量缺陷。文章基于薄壁管弯曲变形微体受力分析,建立了薄壁管圆周方向上力的平衡微分方程和切向应力在薄壁管横截面上的分布函数。由此可确定中性层的位置,求出外加弯矩,并用虚功原理解得回弹角度。论文针对不同几何参数的薄壁管进行了数控弯曲实验,分析了弯曲角度和相对弯曲半径对回弹角度的影响规律,并验证了理论计算结果与实验结果基本相符。利用该文介绍的计算方法可在实际弯曲之前计算出回弹补偿量,以提高管件弯曲成形精度。     

基于显著性的薄壁铝合金管小弯曲半径数控弯曲工艺参数优化(英文)

薄壁铝合金管小弯曲半径数控弯曲是个多因素耦合、多模具约束下的复杂过程。提出以有限元模拟为基础,基于显著性的工艺参数优化方法,即采用析因因子设计分析工艺参数对成形质量,即最大壁厚减薄率和最大截面畸变变化率影响的显著性,获得影响显著的参数,即管与防皱模间间隙的最优值,并确定其他影响不显著的参数值,包括管与模具间的间隙和摩擦、芯棒伸出量和助推速度。结果应用于规格为d50mm×1mm×75mm和d70mm×1.5mm×105mm(管外径D0×管壁厚t0×弯曲半径R)的铝合金管弯曲,获得了合格的管件。     

基于响应面法的U形件弯曲成形回弹优化

U形件弯曲成形过程中比较突出的问题是回弹,通过将响应面法(RSM)与有限元仿真软件Dynaform相互结合,基于NUMISHEET’93的U形弯曲标准考题,将凹模圆角半径选定为Rd=8 mm,以模具间隙、摩擦系数、冲压速度3个参数作为影响因素,竖直方向的回弹位移作为优化目标,建立17组试验方案,对U形件弯曲成形过程进行仿真模拟。借助Design-Expert8. 1对17组数据进行拟合处理,得到关于优化目标的二次非线性回归方程与优化的参数组合,即模具间隙为1 mm、摩擦系数为0. 15、冲压速度为800 mm·s^-1。优化的参数组合代入有限元软件再次仿真得到回弹位移为0. 731 mm,其与方程拟合值0. 738 mm相差约1%,并在前人研究基础上将回弹位移进一步减少了26. 2%,最后进行了实物弯曲验证。RSM与Dynaform的结合减少了有限元模拟的次数,有效地提高了板料弯曲的成形精度与质量。     

三层复合管弯曲成形数值模拟及实验

针对核能用含有致密体和粉末体异种材料的三层复合管模型的复杂性,采用有限元数值模拟软件MSC.Marc对三层复合管建立模型,实现其带有从动的弯曲成形模拟,并分析其回弹及椭圆度等;根据模拟结果,设计模具,进行物理实验。模拟结果与物理实验有较好的一致性,得到成形质量较好的弯曲件,验证了有限元模型建立的可靠性。