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.     

考虑材料参数变化的高强钛管数控弯曲回弹行为研究

目的研究钛管数控弯曲回弹角、回弹半径的变化规律,揭示回弹角和回弹半径变化特征的形成机制。方法基于有限元软件平台,建立考虑收缩应变比-弹性模量变化的Ti-3Al-2.5V钛管数控弯曲成形及回弹全过程的有限元模型。结果回弹角随弯曲角和相对弯曲半径的增加而增加;回弹半径在弯曲角小于30°时,随弯曲角的增加而先变化很小,后显著增加;弯曲角大于30°时,回弹半径随弯曲角的增加而逐渐减小。回弹半径随相对弯曲半径的增加而增加。弯曲角越大,应力分布区域越大,回弹变形越大;相对弯曲半径越大,弯管中处于弹性变形的区域占总变形区域的比例较大,回弹变形越大。结论考虑两参数变化时对回弹角和回弹半径的变化趋势无显著影响,但获得的回弹角和回弹半径均大于忽略两参数变化时的值;考虑收缩应变比-弹性模量变化时,弯曲变形区沿外脊线的拉应力大于忽略两参数变化时的拉应力,卸载回弹时,管材发生大的弹性恢复,表现为回弹角和回弹半径的增加。     

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.     

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.     

Process parameter design of spring-back and spring-go in V-bending process using Taguchi technique

Bent parts of complex shapes with high precision are increasingly required. To achieve a high precision of parts, especially the required bending angle, a suitable design of process parameters is strictly considered. In this study, process parameters of bending angle, material thickness and punch radius were investigated. The finite element method (FEM), in association with the Taguchi and the analysis of variance (ANOVA) techniques, was carried out to investigate the degree of importance of process parameters in V-bending process. The results revealed that the degree of importance of process parameters in V-bending process depended on the spring-back and spring-go. The material thickness has a major influence on the spring-back. In contrast, in the case of spring-go, the bending angle has a major influence and closely followed by the material thickness. In addition to predicting the degree of importance of process parameters by the combination of the FEM simulation, the Taguchi technique, and the ANOVA technique, by facilitating an improvement in the quality of the required bending angle was strictly considered by optimization of these process parameters corresponding with the spring-back and spring-go.     

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。     

材料参数对3A21矩形管弯曲回弹的敏感性分析

为了解材料参数波动对3A21铝合金薄壁矩形管弯曲回弹的影响,基于动态显式有限元软件ABAQUS,借助多因素敏感性分析方法,建立了薄壁矩形管弯曲回弹敏感性分析模型,对材料参数影响回弹的规律进行了敏感性分析.结果表明：弹性模量是影响3A21薄壁矩形管回弹最敏感的因素,其次分别为强度系数、初始屈服应力及硬化指数;弹性模量对回...     

复杂空间弯管三维自由弯曲成形有限元模拟及试验

目的以一复杂空间弯管为例,开展三维自由弯曲成形实验研究。方法首先提出三维自由弯曲成形工艺解析方法,然后通过有限元模拟与实际试验相结合的方法进行研究。结果有限元模拟所得到的弯管与CAD模型相比,弯曲半径偏差值不超过2%,吻合度较高。实际成形出的弯管与CAD模型对比显示,第1个弯曲段的实际弯曲半径为118 mm,设计值为120 mm,实际值与设计值偏差1.67%;第2个弯曲段的实际弯曲半径为133 mm,设计值为130 mm,实际值与设计值偏差2.30%,2个弯曲半径的偏差值均不超过3%。结论验证了三维自由弯曲成形工艺解析方法的可靠性,有限元模拟较好地指导了实际成形试验。     

Numerical simulation of hot stamping of quenchable boron steel

Quenchable boron steel is a new type of ultra-high-strength steel used for automotive parts to reduce the weight of automobiles and maintain the safety requirements. On the basis of experimental data of mechanics and thermal physical properties, a material model under hot stamping condition of quenchable steel was set up, and the numerical simulation to the whole hot stamping process of hot forming, quenching and spring-back of bending parts was made with ABAQUS software. The results show that the springback of hot stamping parts increases when the blank-holder force (BHF) decreases; and it increases when the clearance between punch and dies increases and when the die radius increases. The simulation results are basically in agreement with experimental results.     

Bending stiffness loss of paperboard at conversion — predicting the bending ability of paperboard

The ability of paperboard to resist bending has been investigated. Paperboard is often bent in converting and packaging machines. The paperboard is bent over rolls and thus formed to certain curvatures. If the roll diameter is small the paperboard will be highly curved. This means that high tensile stresses occur on the convex side and high compression stresses on the concave side. If these stresses are too high the paperboard will be damaged by fractures and wrinkles on the surfaces. The bending stiffness of the board will also be reduced. The importance of certain parameters, such as roll diameter, angle of wrap, board thickness, board compression strength and others, have been investigated. In this study seven qualities of paperboard were investigated. It has been shown that the bending force–bending angle curve can be used to obtain information about the ability of different board qualities to be bent to certain curvatures without being damaged. © 1998 John Wiley & Sons, Ltd.     

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.     

Coupling effects of material properties and the bending angle on the springback angle of a titanium alloy tube during numerically controlled bending

The significant springback after the numerically controlled (NC) bending of a titanium alloy tube has an important influence on the precision of the shape and size of the bent tube. This springback depends on the material properties of the tube, the bending angle, and especially their coupling effects. The influence of some material properties and the bending angle on the springback angle in the NC bending of a TA18 tube were investigated using a three-dimensional (3D) elastic–plastic finite element model. Using multivariate and stepwise analyses, the coupling effects of the bending angle and the material properties on the springback angle during NC bending were revealed. It was observed that Young’s modulus, yield stress, the strain hardening coefficient and exponent, and the thickness anisotropy exponent, as well as interactions of these parameters with the bending angle, have a significant influence on the springback angle. The bending angle, yield stress, and hardening coefficient have positive effects on the springback angle, and Young’s modulus, the hardening exponent, and the thickness anisotropy exponent have negative effects. The influence of the material properties of the titanium alloy increases with the bending angle. Young’s modulus and the strain hardening coefficient and exponent have the greatest influence on the springback angle. The results will be very useful in predicting, compensating for and controlling the springback of titanium alloy tubes during NC bending.     

高强TA18钛管微观织构对拉伸力学性能与弯曲成形性能影响研究

目的 揭示高强钛管微观织构强度与宏观各向异性指标CSR值的定量关系,阐明微观织构对钛管拉伸力学性能与弯曲成形性能的影响,为高强钛管冷轧微观织构及性能精确调控奠定重要基础。方法 选取不同轧制工艺条件下获得的高强钛管进行单向拉伸测试及EBSD表征,分析微观织构对管材拉伸力学性能的影响;选取具有典型微观织构分布状态和CSR值的高强钛管进行数控绕弯试验及成形质量测试。结果 单向拉伸力学性能测试结果表明,当CSR值为0.65~2.43时,随着CSR值的增大,颈缩阶段管材的应变与整体伸长率不断增大;数控绕弯试验结果表明,当高强钛管CSR值从1.27提高到1.48时,其断裂前最大弯曲角度从20°提高到110°,当CSR值增大到1.71时,可以成功实现120°的弯曲,并且随着CSR值进一步增大到2.14,弯管件的截面畸变率和壁厚减薄率不断减小。结论 建立了可以准确描述宏观CSR与微观织构强度指标之间定量关系的双曲函数表达式,高强钛管径向织构强度的增强会提升高强钛管变形过程中抗壁厚减薄的能力,并有利于管材弯曲成形质量的提升。     

基于数值仿真的冲压成形界面接触压力

为探究冲压成形过程中板料-凹模圆角区界面接触压力,采用有限元静力算法建立了U形件小圆角半径弯曲成形过程的数值仿真模型,完成了板料和模具界面接触压力数值模拟,并参数分析了钢板强度、相对圆角半径、压边力和摩擦系数对板料界面接触压力分布的影响.研究表明:与压边力和摩擦系数相比,钢板强度和相对圆角半径更明显地影响着板料界面接触压力,并随着材料强度增加和相对模具圆角半径减小界面接触压力明显增加;随着压边力和摩擦系数的增加,界面接触压力宽度也随之增大.     

材料参数对高强不锈钢管数控绕弯成形失稳起皱的影响

目的研究材料参数波动对管材数控绕弯成形失稳起皱的影响规律。方法基于ABAQUS有限元平台,建立了21-6-9高强不锈钢管数控绕弯成形过程三维弹塑性有限元模型,并验证了模型的可靠性;采用该模型模拟分析了材料参数波动对其数控绕弯成形过程失稳起皱的影响规律。结果随着厚向异性指数、屈服强度的增大或弹性模量、硬化指数的减小,弯管的起皱趋势增大,泊松比和强度系数对弯管起皱趋势的影响较小。结论材料参数对弯管起皱趋势影响的大小依次为:屈服强度、弹性模量、厚向异性指数、硬化指数、强度系数和泊松比。     

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.     

Simulation and experiment of curve irradiated laser bending process of titanium alloy sheet

Abstract

Laser bending along a curve scanning path is a complex 3D forming process. To analyse the deformation behaviour of the process and the effect of process parameters on the bending angle of sheets, numerical simulation becomes indispensable. In this paper, non-linear transient heat transfer and dynamic structural computational models including thermal mechanical coupling analysis, in which the temperature dependence of the thermal and mechanical properties of the material are taken into account, have been developed. The temperature, stress, and strain fields as well as the effect of process parameters on the bending angle were calculated on the basis of models using the finite element method. Meanwhile, an experimental parameter investigation was also carried out. The results showed that, compared with the linear laser bending, curve irradiated laser bending has a significant reduction of the bending angle and the bending angle decreases with increasing path curvature. The bending angle increases with increasing laser power and decreasing spot diameter, and decreases roughly with decreasing scanning velocity. Good correlation was found between the numerically simulated results and the experimental data.     

低模量高强度钛合金的研究进展

介绍了近年来低模量高强度钛合金的成分选择、设计方法及研究进展，讨论了合金元素添加量对合金力学性能的影响，并对这种低模量高强度钛合金的应用前景作出了展望。     

型材拉弯的力学与回弹分析

回弹是弯曲成形中普遍存在的现象,是由卸载过程中内力重新分布引起的,回弹的存在直接影响弯曲件的成形精度.本文针对转台拉弯成形过程,对等边型材等曲率拉弯进行了应力-应变分析,并按照卸载预拉力与不卸载预拉力两种情况对工件回弹进行了研究与探讨,得到两组半径回弹率理论曲线.通过与试验结果对比,不卸载拉力计算的结果与试验值比较吻合.     

钛合金在航天飞行器上的应用和发展

主要介绍了高强韧钛合金、高温钛合金、低温钛合金和铸造钛合金及钛合金的先进成形技术在航天飞行器上的应用,指出了钛合金发展现状和趋势。其中对粉末冶金技术和超塑成形/扩散连接(SPF/DB)技术做了较详细的介绍。重点介绍了美国和俄罗斯的粉末冶金技术发展现状和我国粉末钛合金技术在多种型号产品研制中的应用情况。同时指出超塑成形/扩散连接新技术为克服钛合金成形昂贵又难以加工而受到限制的问题提供了新途径。