铝合金型材拉弯成形回弹的有限元模拟

对回弹进行有效预测与控制是提高型材弯曲件精度的关键.为了分析轴向作用力对拉弯制件回弹的影响,采用动力显式有限元仿真软件Pam-Stamp2000对中空矩形截面铝型材AA6082(T5)转臂式拉弯成形过程进行了数值模拟,并与实验结果进行了对比.结果表明:增加预拉可以减小制件的回弹,但预拉达到一定水平后,继续加大预拉力对减小回弹将基本不起作用;当预拉不充分时,增加补拉同样有利于减小制件的回弹,但过大的补拉力对于减小回弹几乎没有任何帮助.可见,型材拉弯成形制件的回弹不仅与加载顺序及加载程度密切相关,同时也受到材料应变硬化特性的制约.     

铝合金矩形管拉弯成形过程的数值模拟

采用动力显式有限元程序Pam-Stamp2000对铝合金矩形管的一种拉弯成形过程进行了模拟,分析了模具最大作用力、管材截面畸变、成形件回弹的变化规律.模拟结果和文献给出的实验结果相当吻合,即模具最大作用力、管材截面畸变均随预拉力的增加而增加,而成形零件的回弹随预拉的增加而减小;相同预拉状况下,增加壁厚有利于减小截面畸变.此外,数值模拟给出了模具对管材作用力及管材夹持端轴向拉伸作用力随模具行程的变化规律,揭示了本文的拉弯实质上是一种非恒定轴向作用力(呈渐增趋势)的拉弯成形方式,这与本文的解析结果高度一致.     

平面应变板料拉弯成形回弹理论分析

基于平面应变假设,采用服从Hill平方屈服准则和指数强化材料模型,建立了板料拉弯成形回弹量预测的理论模型。应用该模型计算了一个拉弯成形回弹实例,分析了单位宽度切向拉力、凸模圆角半径、摩擦因数及各向异性参数对板料回弹量的影响。分析结果表明,只有当中性层偏移距离超过板厚的四分之一时,增大切向拉力才能有效地控制板料回弹量,而且弯曲半径越大,增大切向拉力控制板料的回弹量越为有效,然而拉力不能无限制的增大,它的计算准则为板料最外层的等效应变应不大于极限应变。同时还表明,摩擦因数对板料回弹量的影响随切向拉力的增大变得更为显著,而各向异性参数对板料拉弯成形回弹量的影响也较为明显。与有限元数值模拟预测结果的对比表明,理论模型预测板料拉弯成形回弹量与有限元数值模拟结果很接近。     

铝型材构件多点变曲率拉弯制件回弹研究

目的 研究不同预拉伸量和补拉伸量对矩形变曲率构件回弹的影响,以提高柔性三维拉弯成形精度。方法 用有限元模拟了矩形变曲率铝型材三维拉弯成形过程,并用试验验证了有限元模拟的精度,设计了5组不同的预拉伸量参数和补拉伸量进行三维拉弯成形有限元模拟。结果 大曲率和小曲率段试验和有限元模拟的回弹误差小于2 mm,表明有限元模拟分析可以很好地对矩形变曲率构件进行模拟。得出的数据表明预拉伸量对于小曲率弧段回弹的影响比对大曲率弧段的影响更大,当预拉伸量增长到1.0%以后,回弹的下降幅度不再明显;随着补拉伸量的增大,变曲率拉弯制件两段的回弹均得到较好的抑制,当补拉伸量为1.4%时,制件靠近夹钳端出现了缩颈缺陷,产生了较大的质量缺陷。结论 研究证明适量增加预拉量和补拉量能有效减小柔性三维拉弯成形回弹。     

轨道车辆不锈钢拉弯件模具及夹头设计研究

轻量化设计的不锈钢轨道车辆车体结构件大量采用拉弯成形工艺制造。由于型材拉弯后存在弹性变形,卸载后不可避免地会产生回弹现象,拉弯件的弯曲轮廓精度与回弹的控制密不可分。拉弯胎模的工作面也就是外形轮廓设计直接影响拉弯件的轮廓精度,是拉弯胎模设计的关键。本文以先进的位移控制模式下的数控拉弯机为基础,结合型材拉弯工艺设计软件PSBPD和有限元分析,对拉弯模模具轮廓进行考虑回弹量的精准设计。此外,拉弯夹头的咬合力及工作状态的稳定性也是制约拉弯机正常工作获得合格产品的关键之一。结合拉弯现场试验及工艺参数进一步调整优化,得到了满足要求的高精度的拉弯产品。     

基于指数强化模型的预拉力影响角型材拉弯的回弹分析

为从理论上研究预拉力对角型材拉弯回弹的影响,采用指数强化材料模型,在分析角型材截面应力应变分布的基础上,建立了型材转台式拉弯解析模型.分析讨论了预拉力对角型材截面应力分布和加载弯矩的影响规律,并计算得到了回弹角随预拉力变化的规律曲线.与采用双线性强化材料模型的解析计算结果比较表明:采用指数强化材料模型计算的回弹结果与实...     

基于补偿因子的直弯边下陷零件回弹补偿研究

橡皮成形是飞机钣金零件制造的一种重要成形工艺,回弹是橡皮成形过程中主要缺陷之一.为提高钣金零件橡皮成形效率,基于补偿因子对下陷区回弹补偿进行研究,实现钣金零件一步法成形.首先对弯曲回弹公式进行推导,结合弯曲过程中刚度概念引出补偿因子作为直弯边下陷零件回弹补偿公式;然后利用CATIA二次开发功能将补偿公式写入程序并与数据库进行连接,并对直弯边下陷零件进行回弹补偿;采用Pamstamp 2G软件对橡皮成形过程进行有限元模拟,通过实际成形试验对带补偿因子的回弹公式进行验证,最后将模拟值和试验值进行比较.结果表明:有限元模拟过程能够很好的预测回弹,补偿结果达到精准成形要求且误差在0.5°范围内,成形压力对回弹影响很小.对于下陷成形,需要较大的成形压力才能达到一次成形的目的,验证了补偿因子回弹公式的可靠性.     

复杂截面型材力控制拉弯成形数值模拟分析

复杂截面挤压型材的高精度拉弯成形是制造框架式车身的关键技术.本文基于动态显式有限元软件PAM-STAMP,针对一种典型的框架武车身用复杂截面挤压型材,对其力控制方式的直进台面式拉弯成形进行了数值模拟研究,对比分析了两种截面形状的型材截面畸变和回弹随补拉力增大的变形规律,并得到了摩擦系数对成形精度的影响.数值模拟结果表明,增加型材截面的变形刚度,可以显著地减小截面畸变和回弹;增加补拉力,增大了截面畸变但减小了回弹;增大摩擦系数,截面畸变量减小而回弹增加.     

焊管冷弯回弹曲线方程构建及工艺优化

目的 研究316L奥氏体不锈钢板材JCOE弯曲卸载回弹和应力分布特征,对预弯曲量实施相应补偿,以提高弯曲成形精度。方法 基于弹塑性变形理论,利用有限元模拟研究各关键成形参数对板材弯曲卸载回弹的影响规律,将影响指标线性/非线性拟合叠加,构建回弹曲线方程。结果 板料回弹量与上模下压量、下模开口量呈线性关系,与上模下行速度、摩擦因数呈指数关系。结论 优化后的最佳冷弯成形工艺参数如下：上模下压量为12 mm,下模开口量为150 mm,上模下行速度为4 mm/s,摩擦因数为0.15。对于径壁比值≤10的板料成形,理论计算得到的弯曲回弹量与实测平均值吻合较好,构建的模型可以为实际生产奠定理论基础。     

高强 TA18 钛管连续整体多弯成形精度控制

目的研究获得基于多指标的高强TA18钛管整体多弯管件成形精度控制的方法。方法在获得高强TA18钛管数控弯曲非线性回弹和伸长规律的基础上,研究回弹角、回弹半径的补偿方法和伸长控制方法,其次将获得的成形精度控制方法进行多弯模拟应用验证。结果对于回弹角和回弹半径,采用先补偿回弹半径再补偿回弹角的两水平顺序控制方法;对于弯曲伸长,采用预先减少管材下料尺寸和改变弯头位置来控制回弹后直线段长度的控制方法。结论应用上述控制方法,将多弯模拟结果与预成形管件几何尺寸进行对比,获得成形角度、半径和直线段长度的最大相对误差分别为1.00%,5.51%和5.04%。上述误差满足多弯管件装配精度要求,证明所提出的成形精度控制方法是可靠的。     

The study of spring-back of CK67 steel sheet in V-die and U-die bending processes

One of the most sensitive features of sheet metal forming processes is the elastic recovery during unloading, called spring-back, which leads to some geometric changes in the product. This phenomenon will affect bend angle and bend curvature, and can be influenced by various factors. In this research, the effects of significant parameters on spring-back in U-die and V-die bending of CK67 anisotropic steel sheet were studied by experiments and numerical simulations. Comparison between the experimental and the finite element simulation results were also performed.     

Reduction of springback using simultaneous stretch-bending processes

Springback due to the elastic material behaviour can lead to shape errors that cause geometrical and dimensional inaccuracies in sheet metal forming processes, especially in bending operations. In order to reduce springback, the technique of integrating stretching with bending in sheet metal forming processes has been investigated. The object of this paper is to explain how to reduce the effect of the elastic component in the material behaviour using simultaneous stretching and bending so that a method is established for applying plastic forming during the main process, without changing the tool design. This study focuses on three main points: the stretching method, the stretching direction and the stretching length. In regard to swing- and v-bending processes, the springback factor is used as the standard evaluation to investigate these effects using Finite Element simulation. The springback factors are compared for four processes: Bending process without stretching (WS), pre-stretching and bending process (PB), pre-stretching plus simultaneous stretching and bending (PSB) and simultaneous stretching and bending (SB). The simulation results are then verified through experimentation. Based on the validated results, simultaneous stretching can then be subsequently applied to the existing stretch-forming process, which consists of pre-stretching and bending. Using this process, springback was successfully reduced which confirms the efficiency of SB process.     

Investigation of spring-go phenomenon using finite element method

Bending is an application used in the sheet metal forming processes in many industries. One of the main problems of the bending process is the occurrence of spring-back/spring-go. Past research has investigated the spring-back problem. However, the spring-go problem was rarely investigated. In this study, the spring-go phenomenon was investigated using the finite element method (FEM) on the V-bending process. The FEM simulation results clearly and theoretically clarified the spring-go phenomenon on the material flow analysis and stress distribution. The comparison between the spring-back and spring-go phenomena was also clarified.     

Assessment of forming parameters influencing spring-back in multi-point forming process: A comprehensive experimental and numerical study

Like all sheet metal forming methods, one of the main characteristics of parts formed by multi-point forming is dimensional deviation caused by elastic recovery that is known as spring-back. In this paper the effects of material property, sheet thickness and anisotropy ratio along with process parameters such as elastic layer thickness, elastic layer hardness and number of punch elements on spring-back are studied utilizing finite element simulations and experimental tests. Experimental tests are carried out under various conditions by forming V-shaped and Sin-shaped geometries. Aluminum alloy 3105, stainless steel 304 and pure copper were used as sheet materials for experiments. Likewise, black rubber with shore A hardness of 50 and polyurethane with hardness of 65 and 85 were allocated as elastic layers. The Abaqus® commercial code is employed for finite element simulations. The definition of yield behavior of utilized sheet materials is fulfilled by using three yield criteria of Barlat-89, Hill-48 and Von-Mises. Since the Barlat-89 is not adopted in Abaqus, VUMAT and UMAT user defined subroutines are provided and integrated with explicit simulation of forming process and implicit simulation of spring-back phenomenon respectively. The results indicate that parameters such as material property, blank thickness and anisotropy affect spring-back in multi-point forming. Also the thickness and hardness of elastic layers are novel ideas that should be considered in order to minimize the spring-back. In general, using the elastic layer with minimum possible thickness and greater hardness beside the maximum number of pins leads to minimum spring-back.     

Three-dimensional Numerical Study on Temperature Field of Laser Bending of Sheet Metal

Laser bending of sheet metal is a flexible forming technique by using laser scanning. Based of temperature gradsmechanism, the temperature field of sheet metal bending process by using single laser scanning is studied with theANSYS soft. A finite element     

帽形型材绕弯件的曲率一致性

在工业部门广泛应用的各种异型断面的框类零件,由于成形后的弹复变形引起的曲率变化和断面形状畸变等缺陷严重影响制件的质量.此外,沿周向曲率的不均匀性使制件的圆度下降,影响制件的装配性及被加强构件的使用性能.因此,也是这类零件成形时不可忽视的重要问题.本文采用带张力绕弯方法,通过对LY12M帽形材的绕弯试验与分析,得到了主要工艺参数相对弯曲半径R/H、侧压力P、后张力(摩擦力)F对绕弯件曲率不一致性的影响规律.这对提高型材绕弯精度提供了有效的途径.     

Finite element analysis on the coined-bead mechanism during the V-bending process

The coined-bead technique is commonly applied to solve the spring-back problem in the V-bending process. However, the coined-bead mechanism on the spring-back/spring-go feature has not been clearly identified yet. In this study, the finite element method (FEM) and laboratory experiments were used to investigate the coined-bead mechanism and its effects on the spring-back/spring-go feature. The features were clearly identified using a stress distribution analysis. The results revealed that the mechanism of the coined-bead technique not only increases the compressive stress on the bending allowance zone, where the spring-back feature decreases, but also increases the reversed bending zone on the leg of the workpiece, where the spring-go feature increases. Therefore, after compensating for the increases in the compressive stress and the reversed bending feature, the amount of spring-back on the bent part was decreased. The FEM simulation bending force and bending angle results were agreed with those from the experimental results.     

Forming of the titanium elements by bending

Titanium alloys are superior to nearly all metals in terms of a combination of high mechanical strength and low weight. Therefore, titanium is used whenever the construction weight and its strength are essential. Bending is one of the most frequently used methods for forming titanium elements. However, current knowledge of titanium and its alloys forming by cold working is insufficient. Many phenomena, such as spring-back, need to be investigated and explained.This study was undertaken in order to investigate the titanium bending process. A numerical simulation of the bending of a Ti6Al4V ELI titanium alloy bar was carried out with the Adina System, based on the finite element method. The influence of bar diameter, bending radius and bending angle on the strain and stress distribution in the deformed element was analysed. The numerical calculations demonstrated that the spring-back was dependent on the size of the middle material zone, which remained in an elastic state during bending process. This in turn was dependent on the value of the bending radius, bending angle and diameter/thickness of the bent element. Knowledge of the spring-back is very important because it essentially decreases the forming accuracy of the bent elements. This is especially important when vital titanium elements, such as: body implants or aircraft elements, are bent. Therefore, the calculation results were validated experimentally.     

板料数控渐进成形中变形力的研究

研究了板料数控渐进成形变形力的2种计算方法:按照纯剪切变形的方式计算变形力;按照剪切和弯曲综合变形的方式计算变形力。同时,通过实验测量出渐进成形的实际变形力。通过比较,实验测定的变形力与假定剪切弯曲变形计算的变形力相近,可以认为渐进成形是一种剪切弯曲变形。