Next generation stamping dies — controllability and flexibility

In sheet metal forming, external energy is transferred to sheet metal through a set of tooling to plastically deform a workpiece. The design of the tooling and its associated forming process parameters play important roles in this manufacturing process since they directly affect the quality and cost of the final product. With increasing demands from customers, government regulations, and global competition, the controllability and flexibility of stamping dies have been challenged. In this paper, we will summarize the research activities conducted at the Advanced Materials Processing Laboratory at Northwestern University in the area of sheet metal forming. An overview of our approach towards the system will be given followed by a summary of individual projects in the areas of failure prediction, design and control of a variable binder force, and the segmented die design with local adaptive controllers.     

Flexible manufacturing of sheet metal parts based on digitized-die

Digitized-die forming (DDF) is a flexible manufacturing technology through which a variety of three-dimensional sheet metal parts can be produced in a DDF system. It eliminates the need to design and produce the conventional die. The central component of DDF system is a pair of matrices of punches, the punches are controlled by computer and the desired shape of die is constructed by changing the heights of punches. Based on the flexibility of DDF, new forming processes are designed that cannot be realized in conventional stamping. In varying deformation path DDF, a sheet part is manufactured along an optimal forming path, and large deformation can be achieved for the material with poor formability. In sectional DDF, a sheet part is formed section by section, and this technique makes it possible to manufacture large-size parts in a small DDF press. A closed-loop forming system was built by combining DDF with rapid 3D-shape measurement system. It is used to compensate for material springback and improve dimensional accuracy of the formed part. And a DDF system with multi-point blankholder control system was developed to control the material flow, thereby to prevent sheet parts from wrinkling and tearing. The DDF integrated system is described, and the detailed forming procedures are explained in the paper. Typical examples are presented showing the applicability of the DDF technology.     

Geometric modelling of drawbeads using vertical section sweeping

This paper presents a swept surface for the geometric model of drawbeads mounted on curved surfaces. Vertical section sweeping is used for the swept surface. The section curves are the cross sections of the drawbeads and the shapes of the section curves are variable. Also, the section planes are normal to the projection of the drawbead curve along the die opening direction. This paper presents a scheme for computing the variable vertical section curves and the smooth endings for the swept surface of a drawbead. The geometric model presented has a no-undercut shape in the die opening direction and easily represents the smooth ending at ends of drawbeads.     

基于NURBS的多点成形CAD系统的研制

介绍了自主开发的多点成形CAD软件系统的基本框架结构,研究了其中一些关键技术的实现,并对该软件在多点成形工艺实验和实际生产中的应用情况作了简单介绍。     

柔性级进模CAD／CAM系统FPDDS

阐述了建立一个柔性级进模ＣＡＤ／ＣＡＭ系统（ＦＰＤＤＳ系统）的重要性以及该系统的组成结构和功能。介绍了基于特征设计技术的板金件构型方法和交互式条料排样的原理。阐述了提高级进模ＣＡＤ／ＣＡＭ系统及效率的有效途径是选择一个合理的装配模型及基于该模型的一个模具标准结构定义工具，并且建立一个与主系统独立的开放式模具标准件建库系统。     

覆盖件成形缺陷的数值仿真实例分析

为研究汽车大型覆盖件成形规律,并分析其缺陷成因,介绍了板料成形动态显式有限元数值仿真技术的应用现状、基本理论及应用步骤.通过实例研究了采用有限无数值仿真技术进行覆盖件成形缺陷成因仿真分析的途径.仿真结果表明,采用数值仿真可以分析覆盖件变形规律,了解冲压过程中应力、应变分布及方向,成形极限图分布及缺陷情况,进而改进模具结构和冲压工艺,消除成形缺陷、提高产品质量.数值仿真技术是解决大型汽车覆盖件成形缺陷问题的有效工具.     

Porting an industrial sheet metal forming code to a distributed memory parallel computer

The parallel version of the sheet metal forming semi-implicit finite element code ITAS3D has been developed using the domain decomposition method and direct solution methods at both subdomain and interface levels. IBM Message Passing Library is used for data communication between tasks of the parallel code. Solutions of some sheet metal forming problems on IBM SP2 computer show that the adopted DDM algorithm with the direct solver provides acceptable parallel efficiency using a moderate number of processors. The speedup 6.7 is achieved for the problem with 20000 degrees-of-freedom on the 8-processor configuration.     

计算机仿真在冲压回弹中的应用研究

该文运用仿真计算的方法，采用板料成型数值模拟国际会议NUMISHEET的标准算例，系统地研究了各种西素对冲压件回弹的影响，比较了它们对回弹抑制的效果，并讨论了回弹的控制方法．这对于生产中制定合理的冲压工艺方案，控制和减步冲压件的回弹．提高产品的尺寸精度有重要指导意义和实用价值。     

Parameter identification for a traffic flow model

In this paper, a macroscopic model is presented which describes the traffic flow on a freeway by a set of nonlinear, deterministic difference equations. The model is deduced from simple physical and empirical considerations and contains a set of free parameters which have to be estimated using real traffic data. This identification procedure is formulated here as a parameter optimization problem which is solved by nonlinear programming. In addition, the sensitivity of the model with respect to parameter changes and structural changes is investigated. Although stochastic events play a role in traffic dynamics, the results demonstrate that the validated model copes surprisingly well with real traffic behaviour.     

基于实体单元的薄板成形模拟

传统有限元分析薄板成形一般使用壳单元进行模拟,忽略薄板沿厚度方向应力应变的变化,这很难反映薄板弯曲变形部分的状况.基于连续介质力学及有限变形理论,借助于计算机仿真技术,利用LS-DYNA软件中的实体单元模拟了低碳钢板深冲成筒形件的过程,得到了薄板在冲压成形过程中的应力应变场,并分析了板料各区域的受力变形情况,发现了凸凹模圆角处薄板沿厚度方向的应力应变分布并不均匀,这些模拟结果对筒形工件的深冲压加工具有一定的指导意义.     

Concurrent manufacturing of parts and tools for the sheet-metal industry

The manufacturing of complex bent parts can be supported effectively by computer-aided planning methods. Software systems are already available for unfolding, laser cutting and bending sequence determination. The paper focuses on methods that support the design of non-standard bending tools and the flexible manufacturing of such tools using laminated object modelling (LOM) technology. The developed system allows for concurrent planning and manufacturing of bending parts and tools. Within the framework of this system, neural networks are applied for automated tool design.     

Robust maximum-likelihood estimation of multivariable dynamic systems

This paper examines the problem of estimating linear time-invariant state-space system models. In particular, it addresses the parametrization and numerical robustness concerns that arise in the multivariable case. These difficulties are well recognised in the literature, resulting (for example) in extensive study of subspace-based techniques, as well as recent interest in ‘data driven’ local co-ordinate approaches to gradient search solutions. The paper here proposes a different strategy that employs the expectation-maximisation (EM) technique. The consequence is an algorithm that is iterative, with associated likelihood values that are locally convergent to stationary points of the (Gaussian) likelihood function. Furthermore, theoretical and empirical evidence presented here establishes additional attractive properties such as numerical robustness, avoidance of difficult parametrization choices, the ability to naturally and easily estimate non-zero initial conditions, and moderate computational cost. Moreover, since the methods here are maximum-likelihood based, they have associated known and asymptotically optimal statistical properties.     

On the frequency domain accuracy of closed-loop estimates

It has been argued that the frequency domain accuracy of high model-order estimates obtained on the basis of closed-loop data is largely invariant to whether direct or indirect approaches are used. The analysis underlying this conclusion has employed variance expressions that are asymptotic both in the data length and the model order, and hence are approximations when either of these are finite. However, recent work has provided variance expressions that are exact for finite (possibly low) model order, and hence can potentially deliver more accurate quantification of estimation accuracy. This paper, and a companion one, revisits the study of identification from closed-loop data in light of these new quantifications and establishes that, under certain assumptions, there can be significant differences in the accuracy of frequency response estimates. These discrepencies are established here and in the companion paper to be dependent on what type of direct, indirect or joint input-output identification strategy is pursued.     

模拟板金冲压成形的计算机软件系统

ＳＭＦＳＳ１由模具设计的ＣＡＤ模块、前处理模块、成形过程仿真模块和后处理模块及接口组成。仿真模块使用有限元方法对成形过程中的接触问题采用了接触搜寻法确定接触对，并使用罚参数法快速准确地求出接触力。前后处理模块使ＣＡＤ系统与仿真模块构成统一的应用系统，应用效率与方便性良好。通过应用实例说明软件的实用性及可应用性。     

三菱A700系列变频器的设计与应用 第5讲 塑料挤出机的无速度传感器矢量控制

无速度传感器变频调速控制系统就是取消了变频调速系统的速度检测装置,通过间接计算法求出传动运行中电机的实际转速值作为转速的反馈信号。本文将着重介绍这种控制方式在塑料挤出机中的设计与应用。