激光拼焊板成形过程数值模拟技术现状及趋势

由于焊缝性能与母材存在较大的差异以及焊缝自身形状的特点,激光拼焊板在成形过程中的数值模拟分析可以采用不同的建模方法。介绍了国内外对激光拼焊板数值模拟采用的不同建模方法,比较了不同焊缝模型对计算结果的影响,并利用ABAQUS／Explicit动力显示积分模块分别采用忽略焊缝以及考虑焊缝采用壳单元时的建模方法对U形件的弯曲成形过程进行了数值仿真,结果显示焊缝模型对模拟结果影响较大,采用忽略焊缝的建模方法得到的焊缝移动量较小。     

True stress–strain analysis on weldment of heterogeneous tailor-welded blanks—a novel approach for forming simulation

This paper presents a novel experimental method of analysis to determine the tensile properties of weldment of the heterogeneous tailor-welded blank (TWB) and its base metal. A real-time microscopic recording system was developed to acquire the true stress–strain data of the weldment during tensile testing. Specially designed tensile specimens of the weldment were cut from the prepared stainless steel (AISI 304) TWBs with a thickness combination of 1 mm/1.2 mm. With the aid of a newly developed measurement system, the real-time deformation of laser-marked circular grids on the surface of the tensile specimens was captured. The deformation recorded made possible the determination of the stress and strain values of the weldment based on the assumption of plastic incompressibility. The accurately measured tensile data of the weldment is used to determine the localized necking based on the vertex theory. The localized necking criterion is implemented into a computer program, LS-DYNA, which is critical in the numerical simulation of the TWB forming. The simulation makes it possible accurate determination of the strain distributions in TWBs along the centerline perpendicular to the weldment. The predicted strain distributions were compared with those measured and found to be satisfactory, thus demonstrating the validity of the proposed experimental method to accurately determine the true stress–strain values of the weldment and the parent metals.     

基于成形应力极限的管材液压成形缺陷预测

基于塑性应力应变关系及Hill79屈服准则,推导出极限应力与极限应变间转化关系,进而建立2008T4铝合金的成形应力极限图(Forming limit stress diagram,FLSD)。采用LS-DYNA软件对三通管液压胀形过程进行模拟,应用FLSD预测胀形过程中破裂的发生及成形压力极限,并与传统成形极限图(Forming limit diagram,FLD)结果进行了对比。研究表明,FLD与FLSD预测结果中破裂缺陷位置相同,但极限内压力值存在很大差别,而FLSD预测结果与物理试验结果较吻合。考虑到FLD受应变路径影响显著的因素,将FLSD作为管材液压成形等复杂应变路径下的成形极限的判据更加方便可靠。     

One-step FEM-based evaluation of weld line movement and development of blank in sheet metal stamping with tailor-welded blanks

Currently, more and more tailor-welded blanks (TWBs) are used in the automobile industry. It is very important to locate the weld line and predict its movement during the forming process. The initial weld line can be predicted by one-step finite-element analysis according to the desired weld line in the final workpiece. Meanwhile, weld line movement during the deformation process can be evaluated in advance. In this paper, the procedures of finite-element analysis of one-step FEM with TWBs are established. The contact between tool and blank and the effect of restraining forces under the blankholder due to drawbead and blankholder pressure are considered as well. Forming limit diagram (FLD) is used to show not only the tendency of reduction in thickness and fracture but also of increase in thickness and wrinkle. Hydraulic controlled pads used to clamp the weld line during the deep drawing process are simplified as static external force to eliminate the movement of the weld line. In order to speed up and ensure the convergence of Newton-Raphson iterations, energy-based 3D mesh mapping algorithm is introduced to obtain the initial solution. The above-mentioned methods have been implemented in the authors’ in-house one-step FEM code InverStamp. A rectangular cup drawing case demonstrates that this approach can be easily implemented to evaluate weld line movement and develop initial blank in sheet metal stamping with tailor-welded blanks.     

Optimization of drawbead design in sheet forming using one step finite element method coupled with response surface methodology

In a sheet forming process, drawbead plays an important role on the control of the material flow. In this paper, a numerical procedure for the design of forming processes is described. It is based on the coupling of an optimization technique and the simplified one step finite element method (also called inverse approach). The optimization technique allows adjustment of the process parameters so that specified criteria are fulfilled. Response surface methodology (RSM) is a global approximation method, which is ideally suited for solving highly nonlinear optimization problems. The finite element method, in addition to predicting the response of the process to certain parameters, allows assessment of the effect of a variation in these parameters on this response. The authors utilize the one step method at the preliminary design stage to supply stress or strain information for the following optimization using RSM. The procedure for this optimization process is fully described. The front fender for Numisheet 2002 is presented and the real defect free workpiece is produced to demonstrate the usefulness of the proposed optimization procedure. A comparison between the two forming limit curves (FLC) before and after optimization and results obtained using the precise incremental commercial software DYNAFORM based on the explicit dynamic approach verify that the optimization design method of drawbead could be successfully applied in designing actual tools of auto body cover panels.     

激光拼焊板成形极限图的理论建立方法

由变形不均引起的颈缩或破裂是激光拼焊板的成形难题,工程中迫切需要了解拼焊板的成形性能.成形极限图是一种评价板料成形性能的有效手段,通常可以由试验法和理论计算法获得.目前试验法成本高,费时费工:理论计算法尚不完善,需进一步研究改进.提出一种新的拼焊板成形极限图理论计算模型,结合HOSFORD屈服准则,获得了高强度IF钢等厚激光拼焊板的成形极限图,计算结果与试验数据吻合较好,证实拼焊板成形极限图的理论建立方法的正确性.基于拼焊板成形极限图的理论建立方法,可在已知拼焊板焊接区材料性能参数的条件下快速获得拼焊板成形极限图.     

基于数值模拟技术的吸塑模成型工艺优化

介绍了吸塑成型工艺过程,对吸塑成型的关键技术进行了阐述,包括运动函数的建立和成型时间的预测。基于Polyflow软件平台,以冰箱门体内胆吸塑模为例,通过对吸塑模成型过程的分析,对吸塑成型工艺过程进行了数值模拟分析。模拟结果表明:在整个真空吸塑成型过程中,吹泡时间的长短是控制制件成型质量的关键。吹泡时间过短会导致制件厚度局部变薄不均匀;而吹泡时间过长,则会出现局部折皱和折叠。结合数值模拟技术和运动函数,实现了吸塑成型工艺参数的优化。     

Optimization of tool geometry parameters for turning operations based on the response surface methodology

This investigation focuses on the influence of tool geometry on the surface finish obtained in turning of AISI 1040 steel. In order to find out the effect of tool geometry parameters on the surface roughness during turning, response surface methodology (RSM) was used and a prediction model was developed related to average surface roughness (Ra) using experimental data. The results indicated that the tool nose radius was the dominant factor on the surface roughness. In addition, a good agreement between the predicted and measured surface roughness was observed. Therefore, the developed model can be effectively used to predict the surface roughness on the machining of AISI 1040 steel with in 95% confidence intervals ranges of parameters studied.     

Simulation of dissimilar tailor-welded tubular hydroforming processes using EAS-based solid finite elements

Developments in the numerical simulation of the hydroforming process of tubular metallic components, tailor-welded before forming, are presented. Both technologies, tailor-welded joining operations and hydroforming processes, are well known in industry, although most commonly separately used. Tailor-welded joining operations are usually encountered in plain sheets, subsequently formed by stamping. Tube hydroforming processing, on the other hand, is frequently associated with parts consisting of uniform thickness, material properties, and dimensions. The present analysis focuses on the influence of process parameters, such as the position of the weld-line and initial thickness values, in the innovative process of combining tailor-welded tubes (with distinct thickness values) and hydroforming. Particular attention is posed on the relation of imposed axial displacement vs. imposed hydraulic pressure into the tube, forming parameters that are not known a-priori in the manufacturing of a new part. Another point of practical interest is the numerical simulation of the weld-line movement, after forming is complete. The finite element method is directly employed in the numerical simulation by means of innovative solid elements suited for incompressibility applications, and included by the authors into the commercial program ABAQUS as user-elements. The obtained results can then lead to a better understanding, along with design tools, for the process of hydroforming of tailor-welded tubular parts, accounting for dissimilar thickness of the basic components.     

Determination of forming limit diagrams of sheet materials with a hybrid experimental-numerical approach

A new methodology is proposed to obtain the forming limit diagram (FLD) of sheet materials by utilizing routinely obtained experimental punch load versus displacement traces from hemispherical punch stretching experiments and by analyzing strain history of the test samples from finite element simulations of the experiments. The simulations based characteristic points of diffuse and localized necking are utilized to obtain the limit strains. The proposed method for FLD determination considers out-of-plane displacement, punch-sheet contact and friction, and avoids using experimental strain measurement in the vicinity of the neck on the dome specimens and the rather arbitrary inhomogeneity factor to trigger localization such as in the commonly used Marciniak-Kuczynski method. A criterion of maximum in the ‘pseudo’ major strain acceleration for the onset of localized necking, proposed earlier by the present authors, is utilized to determine the limit strain in FE simulations as well as in FLD verification experiments. The proposed overall approach for obtaining FLD is rapid and accurate and could be implemented for routine FLD generation in a laboratory setting with significant reduction in cost, effort and subjectivity.     

Optimization of drawbead restraining forces and drawbead design in sheet metal forming process

This paper presents an optimization procedure of drawbead restraining forces in order to improve the sheet metal formability in deep drawing process. A simplified finite element method called inverse approach (IA) has been developed for sheet forming analysis with the consideration of the drawbead restraining forces. This IA is combined with a mathematical programming algorithm to optimize the restraining forces and then to design the drawbeads. The obtained optimization procedure is very efficient due to the simplified assumptions of the IA and the analytical sensitivity analysis. The Square cup of Numisheet’93 and the Renault Twingo dashpot cup are presented to demonstrate the usefulness of the proposed optimization procedure for industrial applications. Verifications of the obtained results have been carried out using a precise incremental commercial code OPTRIS^TM based on explicit dynamic approach to show the effectiveness of our approach.     

Effects of plastic anisotropy and yield criteria on prediction of forming limit curves

The effects of yield criteria on predictions of the right-hand side of forming limit diagrams (FLDs) are investigated. Predictions of limit strains are determined from an initial imperfection model based on the early work of Marciniak and Kuczynski (1967). Particular attention is placed on the effect of normal plastic anisotropy on limit strains during biaxial sheet stretching. The anisotropic yield criteria investigated in this paper include Hill’s (1948) quadratic criterion, Hosford’s (1979) higher-order criterion, and case 4 of Hill’s (1979) non-quadratic criterion. Several important characteristics of the yield surface shape are discussed and a new parameter that quantifies some of these aspects is introduced. Similar to the work of Barlat (1987), this parameter is based on the relative position of plane strain on the yield surface and can be used to predict the various effects of yield criteria on limit strains. Results indicate that predictions of FLD are very sensitive to selection of yield criteria.     

Calculation of forming limit diagrams using Hill's 1993 yield criterion

Based on the analysis proposed by Jones and Gillis (JG), forming limit diagrams (FLDs) are calculated from idealization of sheet deformation into three stages: (I) homogeneous deformation up to maximum load, (II) deformation localization under constant load, and (III) local necking with precipitous drop in load. In the calculation, Hill's 1993 yield criterion is used. Using this yield criterion and the JG model, effects of materials parameters such as ratio of uniaxial to equi-biaxial yield stress, strain hardening, strain rate sensitivity and plastic anisotropy on the shape and level of forming limit curves are studied. In addition, the capability of the JG model to predict limit strains is demonstrated through comparison of calculated results with experimental data for the interstitial free (IF) steel and aluminum alloys 3003-O and 8014-O. It is concluded that although the model predicts the effect of material parameters reasonably well, the calculated limit strains are higher than the experimental FLDs. The observed discrepancy may be attributed to the assumption of planar isotropy, cavitation and the nature of texture present in the sheets. Due to the overestimation of the predictions, care must be taken when using this approach for industrial purposes.     

多点数字化拉形成形性能的数值模拟分析

以鞍形曲面蒙皮件为例,对多点数字化拉形过程进行了数值模拟分析.通过模拟所得到的最佳水平预拉力与实际拉形工艺中通过经验公式确定的值相符,验证了算法的准确性.从材料、板厚、曲面形状和变形程度等方面入手分析多点数字化拉形的成形性能,结果表明:随着板料厚度减小、变形程度增大,板料起皱的趋势增大,并且不同的曲面形状及材料对板料的成形结果都有影响.同时给出了临界变形量极限图.研究结果为多点数字化拉形技术的实用化提供了重要依据.     

Fungal assembly of L-asparaginase using solid-state fermentation: a review

Because of its antitumor therapeutic-activity, as well as its application in food industries to improve the quality,L-asparaginase has attracted considerable attention from several investigators. In recent years, fungi have occupiedadvanced rank among microorganisms in the production process of the enzyme. This review is spotting the light onthe advantages of fungal enzyme and its applications in the food industry and medications. The solid-statefermentation was discussed as the wide alternative and most accepted biosynthesis technique. However, some lightswere also spotted to the statistical experimental design of the fermentation process, mainly on the methodology of theresponse surface for L-asparaginase biosynthesis by fungi. Finally, the immobilization of the enzyme and the featuresof the widely used solid substrates for the maximization of the production process were explored.     

智能控制在模具温控成形中的应用

模具的温度控制和调节是高效而经济地生产高质量成形零件的必不可少的条件.介绍了智能控制在模具温控成形过程中的应用现状,指出数值模拟对温控成形过程温度场的研究有助于控制成形过程,实现对模具温度的智能控制,使零件的质量得到充分保证.     

基于响应面法的麦弗逊悬架优化设计

用响应面法对麦弗逊悬架结构参数进行优化设计。基于多刚体动力学软件ADAMS构建麦弗逊悬架模型;在ADAMS/Insight模块中用析出法得到影响各定位参数的主要因子;接着,采用响应面法建模的中心组合设计法仿真得到响应面模型方程。并依据结果进行悬架系统的优化研究。     

Formability evaluation of friction stir welded 6111-T4 sheet with respect to joining material direction

In order to evaluate the formability of friction stir welded (FSW) automotive TWB (tailor-welded blank) sheets with respect to base material direction, the aluminum alloy 6111-T4 sheet was joined with three different types of combination: RD||RD, TD||RD, TD||TD (Here, RD and TD mean the rolling direction and transverse direction, respectively). Formability performance was experimentally and numerically studied in three applications including the simple tension tests, hemisphere dome stretching and cylindrical cup drawing tests. For numerical simulations, the non-quadratic orthogonal anisotropic yield function, Yld2004-18p and the isotropic hardening law were implemented into the material constitutive model. As for the failure criterion, the forming limit diagram (FLD) was utilized to determine the failure strain.     

板料拉深成形数值模拟中动态边界条件的处理

针对板料拉深成形过程中工件与模具接触边界的动态变化,将模具表面离散为若干个三角形单元,并用参数方程来描述工件节点及模具三角形单元的运动情况,将工件与模具的接触问题转化为空间直线与平面的动态求交问题。在此基础上,通过实际的模拟分析,证明该处理方法的可行性。     

基于智能布点技术的近似模型优化研究及其在冲压成形中的应用

针对基于统计学原理试验设计方法的缺陷,采用一种基于设计变量边界条件以及最优样本信息的智能布点方法,并结合移动最小二乘的响应面近似模型优化方法对非线性问题进行求优。为了验证该方法的有效性,采用该方法对非线性测试函数进行了极值求解。同目前主流的试验设计方法相比,其求解精度以及响应面拟合精度都有一定的提高。将该方法应用于薄板冲压成形体系中拉延筋的优化,得到预期的结果,并成功地用于实际产品成形。