无网格法及其在金属成形中的应用综述

对无网格方法的定义、分类以及无网格方法在金属成形中的应用进行了综述。无网格方法主要根据函数近似方案和离散方程进行分类。函数近似方案是无网格方法的基础,函数近似方案的近似特征、近似精度和近似效率对无网格方法的分析计算能力具有重要影响。无网格法虽然不如有限元方法成熟,但是其具有很多有限元方法不具备的优点,如：近似函数没有网格依赖性、基函数可以包含反映问题特性的函数系列、采用紧支函数的无网格法具有带状稀疏系数矩阵等。由于无网格法对非线性问题的强大求解能力,使其在金属成形领域具有广阔的应用前景。     

板料成形有限元模拟网格重划及其应用

分析和论述了板料成形有限元模拟中网格重划技术,研究并建立了板料成形有限元网格重划算法,实现了状态参量在新旧网格中的传递,结合DYNAFORM有限元分析软件,对NUMISHEET’93设定的方盒标准考题进行了模拟,结果证实了该技术的可行性。     

A new contact judgement method for sheet metal forming simulation

A new contact judgement method for sheet metal forming simulation is proposed. The method can overcome miss-judgement and error-judgement, and improve numerical stability and computational accuracy effectively. Based on the proposed contact judgement method, a static–implicit FE code is developed. Some typical sheet metal forming processes and the benchmark of NUMISHEET’93 are simulated, and satisfactory results being obtained.     

物理逆向法在优化钣金成形毛坯中的应用

钣金成形中毛坯形状直接影响工件的成形和材料的流动情况,因此优化毛坯设计非常重要,不仅可以得到高质量的零件,而且节省材料和成本。文章介绍了关于‘物理逆向法’的进一步工作,提出了适合生产应用的加热装置。并通过有限元模拟和试验,对比研究了几何法、有限元一步法、物理逆向法确定毛坯的合理性。结果表明,物理逆向法适合毛坯的优化,对于盒形件,该方法与有限元一步法效果接近,而且明显优于几何法。     

Application of the R-functions method to visioplastic analysis in metal forming

This study is concerned with visioplastic analysis of metal forming processes with help of the R-functions method. The method in conjunction with the flow function and stress function methods is used to construct kinematically admissible velocity fields and statically admissible stress fields for regions with complicated boundary shapes. Application of such fields for approximation of the experimentally obtained information allows to determine mechanically correct strain and stress distribution for steady and non-steady-state problems in axisymmetric and plane-strain metal forming processes.     

无网格法及其在金属塑性成形中的应用*

介绍了SPH, RKPM和EFG等几种无网格法的研究进展及其在金属成形问题中的应用情况, 以及无网格法在求解过程中与有限元的主要区别, 最后以平面应变镦粗过程为例, 并和有限元法对比, 说明无网格法在求解金属成形大变形问题中的优越性和存在的主要问题, 并提出今后发展的方向。     

Introduction to sheet-bulk metal forming

Sheet-bulk metal forming as a new class of manufacturing processes is one of the possible answers production processes provide to the increasing demands on functional integration into light weight parts made of high strength steel. Research in this field is carried out in several places. The special issue was initiated by the Transregional Collaborative Research Centre 73. It contains newest results from this research initiative as well as international results in the field of sheet-bulk metal forming.     

Development of general multivariable run-by-run control methods with application to a sheet metal forming process

The problem of flexible-tool sheet metal forming and in-process shape control has been confounded by the lack of available measurements during the process. Run-by-run (rbr) control has been developed to achieve feedback control advantages in processes that do not lend themselves to in-process sensing and actuation. While the process cycle time sampling interval limits the performance, rbr can still achieve zero mean error and predictable variance on the output. This paper demonstrates a novel extension of typically single input–single output (SISO) rbr control to the control of discrete-die sheet metal forming which is a multivariable, regionally-coupled process; one where a single input affects a limited region of outputs and a single output is affected by multiple independent inputs. To this end, an easily calibrated, generic plant model is first reviewed. This model, along with others describing regional coupling, proves to be ill-conditioned for even moderately-sized processes. This renders the direct plant inversion used in SISO rbr control impractical. As a result, three controllers that do not rely on inverting the plant are considered: the linear-quadratic regulator (LQR), linear-quadratic Gaussian (LQG), and H-infinity. All three of these controllers are applicable to both square and non-square plants, and they are not limited to the class of plant explicitly considered in this paper. Next, the concept of robustness is introduced by establishing stability limits through structured singular values. All three controllers are experimentally tested on a discrete-die sheet metal forming press. In this stretch forming process, the traditionally monolithic die is divided into many small segments. These segments can then be rearranged to form a new die shape between sheet metal stretching cycles. The proper rearrangement of these inputs in response to output shape error is the goal of the three controllers. Experimental results are in close agreement with theoretical predictions, showing the validity of the modeling and control approaches.     

The application of the artificial neural network and taguchi method to process sequence design in metal forming processes

This study shows the correlation between the design methodology of the artificial neural network (ANN) and the statistical design of experiments (DOE) approach and is demonstrated for process design in various metal forming processes. After investigating the effect of each parameter upon the characteristics by the Taguchi method which is one of the DOE, orthogonal array (OA) table and characteristics are applied to ANN as experimental data and then opiimal design parameters are established. Using the rigid plastic FEM, the simulations are performed and the results of ANN are confirmed. This technique requires smaller runs than the conventional method to find the optimal condition of design parameters for the design’s aim. This new technique can be used in a wide range of metal forming process designs.     

Development of multistage sheet metal forming analysis method

The multistep sheet metal forming process for axisymmetric shapes has been modeled employing a simplified finite element analysis method. The analysis is based on the idea of dividing the deformation history into several steps while applying the total strain theory of plasticity in each step. An algorithm has been developed which satisfies the potential energy minimization process at the entire nodal point grouping in each step of the forming process. Although numerical solutions have been obtained up to a four-step process, there are no inherent limitations in the basic methodology to extend it to any number of steps. The assumption of proportional loading in each step of forming was carefully examined by comparing the computed principal strain ratios with those of experimentally observed values. It was found that some regions of the sheet material undergo nonproportional straining; consequently, a single-step approximation for a multistage forming process may not give a valid result. Sensitivity of the new model to the number of intermediate steps has also been examined. It is concluded that the new model is a good approximation of the multistage sheet forming process.     

A novel sheet metal forming method—Millipede forming

Millipede forming, a novel sheet metal forming method, has been proposed and developed recently to overcome fundamental limitations in conventional roll forming. For this new method, there are two main aspects: use of an optimal transitional surface and implementation of a method to feed the strip through the transition surface. Achieving the optimal transitional surface involves defining the change of surface shape between a flat strip and a final shaped product conceptualised to the strip's mid-surface, regardless of the strip's thickness.In this paper, one method of implementing a transition surface, Millipede forming, is introduced. A prototype has been built to demonstrate the working principle and can be used to produce some simple profiles, within a short forming length of 200 mm.     

数字图像相关法的板料成形极限研究与应用

为了克服现有板料成形极限测定方法的不足,采用XJTUDIC三维数字散斑应变测量系统,实现了一种基于数字图像相关法的板料成形极限测定新方法.首先,将测量系统架构在杯突试验机上,记录从试验过程初始到破裂的一系列图像,实现应变在线、全场测定.然后,通过对破裂前的最后一张图像进行截线,拟合数据,对颈缩区域插值得到极限应变,从而绘制成形极限曲线图.最后,通过对SPCC36型号碳钢材料板料件成形极限的测量,验证了本文方法的可行性和有效性.     

板料成形中拉延筋的模拟及应用

将拉延筋模型引入到板料成形动力显式有限元分析中,并以汽车前照灯矩形反光镜为应用实例,对其拉延成形过程进行了模拟。     

细观损伤力学及其在金属塑性加工中的应用

简述了细观损伤力学的研究进展,分析了细观损伤力学对金属塑性加工的重要意义.在金属塑性加工中,对大部分塑性成形工序,应抑制损伤的产生与发展,以提高材料的变形能力;对分离工序,应创造合适的断裂条件,以保证获得良好的断面质量.以细观损伤力学在精密冲裁和超塑性成形中的应用为例,分析了材料细观裂纹的形成过程以及材料损伤断裂的原因,提出了细观损伤力学理论和应用上的局限性,以拓宽细观损伤力学的发展和工程应用.     

Sheet metal forming: A review

Developments in the numerical modeling of stamping processes and experimental measurements now make it possible to design stamping processes using sound engineering principles. This article shows how experimental and theoretical contributions have led to the concept of a forming window in strain space that identifies the strains that can be developed safely in a sheet element. It is bounded by failure limits corresponding to localized necking, shear fracture, and wrinkling. A robust stamping process is one in which the strains in the part lie well within the forming window. The nature of the window and the influence of material behavior on its shape can be predicted. Editor’s Note: A hypertext-enhanced version of this article can be found at www.tms.org/pubs/journals/JOM/9911/Hosford-9911.html. For more information, contact W.F. Hosford, University of Michigan, Department of Materials Science and Engineering, 2300 Hayward Street, Ann Arbor, Michigan 48109-2136; (734) 764-3371; fax (734) 763-4788; e-mail whosford@umich.edu.     

Two-step method of forming complex shapes from sheet metal

A two-step method of forming a part and a method of designing a preform shape are being discussed. The part may be formed from lightweight material to an extent that would normally exceed the forming limits of the material if the part were attempted to be formed in one-step conventional stamping die. Critical areas including deep pockets and sharp radius areas of the final part are formed from a preform or intermediate shape part. The first forming step can be conducted by variety of sheet metal forming methods; the preformed blank is further formed in a fluid pressure forming process to a final part shape wherein broad radius areas and pockets of accumulated metal of the preform are formed into deep pockets and sharp corners of the final shape. Electrohydraulic forming technology is employed for the second forming step.     

任意模具形状的金属三维体积成形过程刚塑性无网格RKPM分析方法

将无网格方法引入三维金属体积成形分析,在给出基于刚塑性流动理论的三维无网格再生核质点方法及其基本理论方程的基础上,为了提高分析系统的通用化和自动化,采用网格法来描述任意形状的三维模具型腔曲面,给出了三维无网格法数值模拟系统中动态接触边界自动处理的非线性接触算法,实现了任意模具形状的三维体积成形过程的无网格法数值模拟。对上模为半球形的三维立方体塑性变形过程进行了数值模拟,并与三维刚塑性有限元体积成形商品软件Deform3D的计算结果作了比较,验证了本文方法的正确性。     

A new lubricant carrier for metal forming

A lubricant carrier for metal forming processes is developed. Surfaces with pores of micrometer size for entrapping lubricant are generated by electrochemical deposition of an alloy, consisting of two immiscible metals, of which one metal subsequently is etched away leaving 5 μm layers with a sponge-like structure. The pores will act as lubricant reservoirs during severe forming processes. The deposited microporous layer is evaluated by friction tests in the form of ring compression tests and double cup extrusion tests. Furthermore the anti-seizure properties are investigated by single cup extrusion at high reduction and excessive stroke comparing with conventionally lubrication using phosphate coating and soap.     

Applying numerical Taguchi optimization to metal forming

The central idea behind a numerical approach for parameter tolerance design is the concept that multiple numerical process simulations can be used in accordance with the Taguchi orthogonal experiment arrays to perform parameter sensitivity analysis and for tolerance design using a quality loss function. The quality loss function is analytically defined using a novel material modeling technique based upon the second law of thermodynamics.     

A new upper-bound elemental technique approach to axisymmetric metal forming processes

A new upper-bound elemental technique (UBET) is proposed to improve the ineffectiveness of UBET for solving forging problems that are geometrically complex or need a forming simulation for predicting the profile of free boundary. This method combines the advantages of the stream function and the finite element method (FEM); specifically, the curve fitting property of FEM and the fluid incompressibility of the stream function. The formulated optimal design problems with constrained conditions are solved by the flexible tolerance method. Three forming problems (ring upsetting, closed-die, and backward-extrusion forging) are used to illustrate this method: the results of ring upsetting show a good ability of simulating for predicting the forming profile of a free boundary; the closed-die forging produces a lower upper-bound solution than UBET; and backward-extrusion forging demonstrates the flexible curve fitting property for a complex geometric boundary.