X形管内高压成形过程的加载路径优化北大核心CSCD

加载路径对X形管内高压成形质量至关重要,只有加载路径的各参数匹配得当,才能获得合格的成形件。利用DYNAFORM软件模拟不同加载路径下X形管的成形性能。并基于Box-Behnken Design试验设计和响应面法,以内压力、轴向进给量、背向位移量以及摩擦因数为试验因素,分别建立以最小壁厚、支管高度和极限圆角半径为目标的响应面模型。通过方差分析和回归方程分析,对X形管内高压成形过程的加载路径进行设计和优化,有效地改善了壁厚分布、减小了极限圆角半径、提高了支管高度。采用软件的数值优化功能筛选出最优的加载路径,并在此加载路径下对X形管内高压成形模拟结果和试验结果进行对比,发现误差在5%以内,并且壁厚分布具有一致性,说明了该加载路径优化方法具有较高的准确性和较好的可行性。     

On process parameter estimation for the tube hydroforming process

Tube hydroforming is a forming process where an inner pressure combined with axial feeding deforms the tube to the shape of a die cavity. One of the main concerns when designing such a process is to avoid burst pressure, i.e. the process state where the hardening of the material is unable to resist the increase in inner pressure and wall thickness reduction. The success of a hydroforming process strongly depends on the choice of process parameters, i.e. the combination of material feeding and inner pressure. Especially in hydroforming processes, where the free forming phase is substantial, the process is proved to be very sensitive to the inner pressure. By transforming the problem into a deformation controlled rather than a force controlled process, the results from the process parameter estimation become more reliable but on the other hand less intuitive. In this context, three distinct parameter estimation procedures are suggested. Firstly, a self feeding based procedure is proposed with the intention of being a fast method to be used as a first estimate of suitable process parameters. Secondly, an iterative optimization problem set up is presented. Thirdly, and finally, an adaptive simulation procedure based on process response approximations is proposed, which only requires a limited number of simulation runs.     

异形截面管充液成形工艺及过程优化

异形截面管件广泛应用于汽车底盘结构件领域,它不仅可以充分利用材料的强度和刚度,而且是实现结构轻量化的重要措施之一。对汽车底盘变截面管件进行研究,利用有限元软件Dynaform建立了QSTE340低碳钢管材充液成形的有限元模型。研究了充液成形过程中管材预制坯形状、初始屈服压力、整形压力及推头轴向进给量对成形结果的影响,并通过试验验证了仿真分析的准确性。研究结果表明:在异形截面管零件成形过程中,管材预制坯各截面周长与最终零件各截面周长相近时,可以提高成形质量;当初始屈服压力为70 MPa、整形压力为200 MPa、轴向补料量为25 mm时,可以成形出合格零件。     

Optimization of loading conditions for tube hydroforming

Tube hydroforming is a developing technology with advanced features of lightness and unified part. This study investigates the best possible regulation for loading conditions between the internal pressure and the axial feeding by hydroforming of a T-shape metal tube. Using conjugate gradient method with finite element method, a program module is generated to check the hydroformed tube quality about its thickness uniformity and the geometry accuracy. Thereby, a batch mode and a sequential mode to optimize the loading conditions of the tube hydroforming process are created and investigated. Regarding the tube quality from the simulation results, the hydroforming process, which follows the loading curve generated by the sequential mode, is better than by the batch mode. The optimal loading procedure generated by this article can offer another possibility for engineer by determining the internal pressure and the axial feeding in tube hydroforming.     

主要工艺参数对T型管液压成形性能的影响研究

为研究主要工艺参数对T型管液压成形性能的影响,文章提出一项综合评价指标,以评定T型管的成形质量.并采用正交试验设计与有限元仿真分析相结合的方法,研究模具过渡圆角半径、内压力加载路径和支管平衡冲头平衡力等主要工艺参数对T型管液压成形性能的影响,进而通过对试验结果的分析比较,找出最佳成形工艺方案.采用该方案进行实际加工试验,获得成形良好的T型管产品,且试验结果与数值模拟结果基本吻合,说明所用评价指标和试验设计方法在实际生产中有一定的参考价值.     

管件液压成形中加载路径的优化设计方法研究

确定合理的加载路径是管件液压成形工艺设计的关键。文章较为系统地介绍了管件液压成形中加载路径的优化设计方法,比较分析了各种方法的优缺点与适用对象,讨论了研究过程中存在的主要问题和研究的发展方向。     

Numerical/experimental investigations for enhancing the sheet hydroforming process

In this work the authors present some results of their research activity aimed to enhance the sheet hydroforming process. The main focus is the adoption of a movable inferior plate through which the control of the blank forming is realised. Tests on hemitoroidal parts using an innovative equipment with a movable die were carried on at the Institute of Metal Research (Chinese Academy of Sciences) in cooperation with the Aalborg University, putting in evidence main defects and fracture causes. Finite element simulations of the modified hydroforming process using a movable inferior plate were performed at the Centre of Excellence for Mechanical Computation (Polytechnic of Bari), with the aim of evaluating critical strain values and their location, strain paths, load curves and stress maps were analysed. Specimens with proper geometrical shape were designed to avoid possible ruptures and to reduce material thinning in the critical regions.     

不规则四边形截面管件内高压成形数值模拟

以不规则四边形截面管件为研究对象,作内高压成形.基于dynaform软件平台,建立了内高压成形有限元模型,利用该模型研究了内压和轴向进给对不规则四边形管材内高压成形的成形形状、角充填情况及壁厚减薄情况的影响规律,分析了管材破裂和起皱缺陷产生的原因.模拟结果显示,适当减小内压力,同时增大轴向进给量,可以有效地防止破裂的发...     

薄壁管件液压成形工艺改进与疲劳寿命分析

通过对现有U形薄壁管件液压成形工艺的分析,提出应对壁厚不均和疲劳寿命短两方面进行改进;在基于被动液压成形理论分析计算的基础上,提出具体工艺改进方案,并对被动液压成形加载曲线合理区间进行了分析;基于LS-DYNA动力显式有限元分析软DYNAFORM5.6,对薄壁管被动液压成形进行模拟仿真,对改进前后工艺进行对比分析,并结合仿真结果,对改进前后成形工艺加工工件的疲劳寿命进行对比,分析对比结果表明,改进后工艺可显著提高工件的疲劳寿命。     

圆管液压成形过程有限元模拟及失效分析研究

选择圆管中间膨胀的液压成形为研究对象.应用LS-DYNA软件,实现圆管液压胀形的模拟仿真过程,为具体的成形实验提供了参考.管件液压成形过程的三种主要的失效形式有弯曲、褶皱、破裂,而液压成形控制中最主要的参数就是压力,轴向给进力以及材料性质.研究中针对不同加载路径所得到的不同成形效果与失效进行分析,得到的模拟结果与相同条件下的真实实验结果比较接近.研究表明,成形工艺中加载路径(内压力与轴向给进的配比关系)的重要性,同时也说明了该液压成形模拟仿真具有一定的准确性.     

Prediction of forming limits and parameters in the tube hydroforming process

Determination of process limits and parameters for hydroforming was conducted applying widely known plasticity, membrane and thin-thick walled tube theories. Analytical predictions were compared with experimental findings. Simple but useful analytical models to predict buckling, wrinkling and bursting as well as axial force, internal pressure, counter force and thinning in tube hydroforming were verified with experimental results.     

Application of two dimensional (2D) FEA for the tube hydroforming process

Use of FEM in the metal forming process has been a proven analysis tool. Two-dimensional FEA for simplified sections can help to reduce time and cost in part, tooling and process design in tube hydroforming technology as it is a relatively new process, and the existing experience and knowledge base is not as broad as with other forming processes. Some case studies are presented to demonstrate the use of two-dimensional FEA in the hydroforming process. Upon verification through comparison of FEA predictions with experimental results, further planned simulations are conducted to generate simple design rules on geometrical and process parameters.     

Internal state variable plasticity-damage modeling of the copper tee-shaped tube hydroforming process

This paper presents a parametric finite element analysis using a history-dependent internal state variable model for a hydroforming process. Experiments were performed for the internal state variable model correlation and for validating a 2-in. copper tee hydroforming process simulation. The material model constants were determined from uniaxial stress–strain responses obtained from tensile tests on the tube's material. In the finite element simulations, the mesh and boundary conditions were integrated with the geometry and process parameters currently used in industry. The study provides insights for the variation of different process parameters (velocity and pressure profiles, and bucking system characteristics) related to the finished product.     

计算机控制管件液压成形液压压力机的研制

在分析管件液压成形工艺过程,该工艺过程对成形设备的基本要求和现有成形设备发展状况的基础上,介绍了新型计算机控制管件液压成形液压机的设计方法,工作原理以及机械、液压和控制系统的实现;最后,为验证该液压成形压力机的应用效果,给出简单试验件的试验结果.     

A theoretical and experimental study on forming limit diagram for a seamed tube hydroforming

The purpose of this work is to establish the forming limit diagram (FLD) for a seamed tube hydroforming. A new theoretical model is developed to predict the FLD for a seamed tube hydroforming. Based on this theoretical model, the FLD for a seamed tube made of QSTE340 sheet metal is calculated by using the Hosford yield criterion. Some forming limit experiments are performed. A classical free hydroforming tool set is used for obtaining the left hand side forming limit strains, and a novel hydroforming tool set is designed for the right hand side of FLD. The novel device required the simultaneous application of lateral compression force and internal pressure to control the material flow under tension–tension strain states. Furthermore, the suitable loading paths for the left hand side of FLD by theoretical formulas and for the right hand side of FLD by finite element (FE) simulations are calculated. Finally, a comparison between the theoretical results and experimental data is performed. The theoretical predicting results show good agreement with the experimental results.     

A local heating method by near-infrared rays for forming of non-quenchable advanced high-strength steels

A forming process by local heating using near-infrared rays (NIRs) is proposed to reduce springback of non-quenchable advanced high-strength steels, such as dual-phase steels, that are not suitable materials for hot stamping. NIR lamps show outstanding cost performance, and the width of the heating area can be controlled by designed reflectors. To confirm the advantages of NIR local heating, DP980 sheets were heated by two methods – NIR local heating and furnace heating, which heats the whole material. V-bending and 2D-draw bending were conducted with heated DP980 sheets. Results showed that NIR local heating has advantages over furnace heating in both shape accuracy and hardness.     

A simple experimental tooling with internal pressure source used for evaluation of material formability in tube hydroforming

Material properties have powerful impact on the tube hydroforming (THF) process and the quality of the deformed tube, so it is important to select proper materials and evaluate the material formability prior to conducting the process. A simplified and applied tooling, which has no use for any external hydraulic pressure source but internal one, was designed for charactering the material formability in THF. A pressurized-fluid supplier is automatically established to provide the internal pressure and axial load synchronously required for THF, and the ratio of the two loads is achieved by proper design of the supplier. As a stand-alone hydraulic bulging fixture, the tooling can be worked on a conventional press, even on a single action press. Free bulge forming (FBF), bulge forming with axial loading (BFAL), free and restrained bulge forming (free and fixed ends) can be fulfilled by the tooling, and furthermore, bulge forming with proportional loading to some extend can be realized. Comparative bulge forming experiments under various forming conditions were carried out with the tooling to validate this project and the results suggest that restrained conditions on the tube ends highly affect the FBF, while the ratio of the two loads dominates the BFAL.     

钛合金TC4薄壁波纹管液压成形工艺优化

利用有限元软件进行仿真分析,基于Johnson-Cook本构模型和韧性损伤模型,模拟了钛合金波纹管液压成形过程。分析了液压大小、模具圆角尺寸和模片间距对波纹管液压成形的影响规律,并获得了优化的工艺参数。针对管材外径为Φ21.5 mm,壁厚为0.16 mm,成形后最大直径为Φ31.5 mm的钛合金管材,液压成形波纹管的最佳模片圆角半径为4t(t为管材壁厚)、液压大小为42 MPa、模片间距为8 mm。将仿真结果和实验结果进行对比发现,最大减薄率波峰处有2%~3%的差异,管端部有1%~2%的差异,这是由于假设仿真过程中全部采用润滑而实验过程中未必全部润滑,摩擦系数越大减薄率越大造成的,实验验证了仿真的准确性。     

基于正交试验的钛合金盒形件液压成形工艺优化

基于Dynaform软件平台,建立了TC2钛合金盒形件液压成形的三维有限元模型.以液压力、压边力、凸模圆角为因子,成形深度、最小壁厚以及最大增厚率为评价指标,设计了3因素5水平的正交试验方案.通过极差分析,确定了各因素影响评价指标的主次顺序,并运用综合平衡法和方差分析,获得了优选的因素水平组合.