外文翻译

广西科技大学

毕业设计外文翻译

文献名称计算机辅助分析和设计金属板料成形过程

第三部分：冲压模具型面设计

学院机械工程学院

专业机械工程及自动化

班级机自Y113

学号 201100103091

姓名黄波稳

Technical report

Computer aided analysis and design of sheet metal forming processes:

Part III: Stamping die-face design

M. Firat*

Department of Mechanical Engineering, The University of Sakarya, Adapazari, Turkey Received 8 September 2005; accepted 31 January 2006

Available online 23 March 2006

Abstract

The finite element simulations of a sheet metal forming process help the methods and tooling engineer designing the forming interface for a stamping part by shifting the costly press shop try-outs to the computer aided design environment. The finite element models used in the sheet metal formability and stamping feasibility assessment studies are commonly based on the ideally rigid die-face design. This hypothesis is in general consistent with the present industrial experience even for large draw-dies of conventional steels. Nevertheless, it may not be practicable in the case of the forming high strength steels of moderate thickness because of the comparable higher press loads required to shape the blank. Consequently, an estimation of the die-face deformations during the forming process may be necessary during the evaluation of potential formability and springback problems and possible compensations should be considered in connection with the usual stamping die design and construction routines before submitting to the production. In this part of the study, an engineering methodology is presented for the structural assessment of the stamping tooling and the die-face designs during the sheet metal forming processes. Using the computer aided analysis and design concepts given previously in Part I and in Part II of this study, the proposed approach is employed in the forming interface design of an automotive stamping part including the complete die construction. The results have indicated the relative merits of the die-face distortions on the formability and springback deformations.? 2006 Elsevier Ltd. All rights reserved.

Keywords: Sheet metal forming; Formability; Springback; Die design

1. Introduction

It is known that a crucial part of the production of a sheet metal stamping die is essentially the development of a die-face design aiming a tooling surface geometry that gives a fully developed blank shape a defect-free stamping form within the necessary quality constraints. The design of stamping tooling elements starts with the part geometry as the basic input data and the methods engineers try to determine the minimum number of operations for a given stamping form in order to reduce the forming tooling costs while satisfying the objective stamping criteria [1]. The methods engineer conducts various try-outs for the forming process design continuing up to the end of workshop try-outs until to the mass production phase of the stamping part. Since both the stamping die-face design and the plastic workability of the sheet metal determine the characteristics of blank deformations, additional care should be paid in the forming of high strength steels to adapt to the lower formability and higher springback deformations [2]. In line with the advancements in the computer aided design and analysis tools the die try-out phase may be carried out reliably in computer generated virtual design environment,and the methods and tooling engineering takes the advantage of the finite element method based simulation in the prediction of the probable formability problems, such as cracks, wrinkles or excessive thinning, related to the dieface designed for a given stamping form. It is also attain- able to estimate the final part geometry after trimming operation and springback deformation. This engineering approach assumes that the die-face deformations during the drawing process are negligible and the industrial practice has proved the validity of this assumption for even large inner panel draw-dies in the case of conventional draw-quality steels [3]. The notion of an ideally rigid draw-die construction, nevertheless, becomes arguable when it comes to the forming of new class high strength steels of moderate thickness because of the bigger die-face distortions because of the relative high forming forces, which may be not considered insignificant anymore [4]. Hence, the die-face deformations and its implications should be considered in connection with the draw die design before submitting to the production.

In this paper, following a short review of the stamping die design practice; a computational methodology is presented for the assessment and control of die-face deforma- tions during the sheet metal forming processes. The proposed approach is employed in the forming process design for a cab body member based on the computer aided design and analysis concepts given in Part I and in Part II of this study. The die-face deformations are taken into account in the computer aided design of the process tooling. The part formability analysis and springback deformations are conducted including the tooling deformations.The relative differences between the ideally rigid and deformable forming interfaces are discussed,

and the assumption of an ideally rigid die-face design is fulfilled by increasing the punch casting wall thickness.

2. Die-face design concepts

The die-face design for a sheet metal forming die may be defined as the composition of a complete surface geometry that deforms a sheet metal blank plastically into a desired stamping shape by ensuring a rigid tooling construction. The design process starts with the part geometry as the basic input data, the methods engineer firstly decides on the drawing direction by tipping the part to the most favorable axis, and eliminating the risk of an undercut. Then,using the material formability and minimum allowable thickness, the amount of stretching deformation is determined and the number of stretch-draw operations is estimated. Using the half-thickness offset geometry of the sheet metal part the designer sets additional surfaces for the punch face by extending the part edges, filleting the sharp edges and by unfolding the flange-type of geometry in the CAD environment. Using the material properties and the amount of maximum stretching deformation, the maximum achievable drawing depth is estimated, and a set of drawbar and counter bar surfaces may be added to both punch and die in order to minimize the deformation gradient during the initial stage of the forming process.After deciding on the press operation type, the binder geometry is generated using a set of flat or developable surfaces, and usually integrating with the draw-bead and con-tra-bead elements in order to restraint the material flowover the punch in an controlled manner [5].

After the creation of punch and binder interface, their geometric counterparts are developed usually by offsetting the surfaces with a clearance amount that is typically a few percent larger than the sheet metal thickness using the CAD software. At this stage using the allowable thinning of the part, the amount of stretch, and the blank size estimate may be done using the volume constancy assumption.Once the methods engineer has createda entire geometric description of the blank and die faces in a CAD environment, the finite element analyses may be performed in order to investigate the process feasibility in terms of the form- ability, part geometry after springback and forming loads byassuming an ideally rigid die construction [6,7]. The finite element simulation of the stamping process is done usually

in two steps. A forming analysis is conducted to determine the metal deformation for a given punch and binder loading and, secondly, the springback deformations following the removal of the tooling is computed with the forming stress distribution and the deformed geometry from the forming step as the inputs along with material thickness distributions [8]. Depending on the relative qualities of the process and material parameters, several virtual try-outs may be necessary in order to reach the optimum tooling geometry and forming elements. At this point,

the forming loads and the type of draw action is determined in accordance with the available press line specifications. Finally, the complete stamping tooling surface is approved and submitted to the draw die construction and manufacturing department. In the automotive industries, the design and construction practice of stamping dies is adopted according to the sheet metal type and draw action in accordance with the type of thechosenmanufacturing press[1,3,9].Usually,anin-house diedesignandconstructionstandardisfollowedinthemate- rialselection forthedieelements includingthedetailedspec.

https://www.360docs.net/doc/a77981389.html,ingthe developed die-face design as the starting dimensions for the punch,upperandlowerbinderelements,theguidelinesgiven

in the in-house standard are employed in the dimensioning and integration of the major structural elements, such as the lower and upper die adaptor plates, punch and binder castings,guidepostandbushingsandwearplates.Additionally,byselectingpresstoolaction,thebolst er–ramgeometry and punch stroke completely define the forming die con-

struction[4,10].TheuseofaCADsystematthisphaseallowsthe design engineer to build a virtual prototype of the upper andlowerhalvesoftheformingdieusinganumberofgeom- etry parameters such as the inner ram shut height and the geometry of the adaptor plate, punch and binder wall thicknessorpositionofblankholderbalanceblocks.Anumberofpositionanalysesofthepunch,diean dblankholderelements duringacompleteformingcycleareconductedtocontrolthe interference and overlap to eliminate any inconsistency between the ram stroke and amount of drawing.

3. The die-face shape control

The sheet metal forming process is a compound system made up of the stamping die and the blank, and involves1312 M. Firat / Materials and Design 28 (2007) 1311–1320 a set of mechanical interactions with the press and the foun dation structure that provide the necessary forming energy [4,5,10,11]. Assuming an ideally rigid die construction connected to the ram and bolster plates of an ideally rigid pressand neglecting all die-face distortions help the methodsengineer designing the forming process following a pure geometric modeling procedure only [2–5]. Otherwise, it would be an enormous engineering effort to include all of these mechanical systems in a computational model that is intended to simulate the sheet metal deformation response during the forming process. It is therefore the most practical approach to isolate the forming interface, i.e., the die-face design and the blank, from the remaining, and to model the blank deformations under the forming forces generated during the frictional contact with the purely geometric description of the die-face design. Moreover, this proposi- tion has found widespread use in the industry for even large inner panel draw-dies in the case of conventional sheet metals. The notion of an ideally rigid draw-die construction, nevertheless, may become questionable when it comes to the forming of high

strength steels due to the higher forming loads needed. In addition, a side trust is generated in the forming of large-scale structural parts with non-symmetric profiles, which may apply remarkably high loads on the bal- ancer blocks and on the wear plates between the punch and binder elements increasing the wear and distortion of guideposts. In these cases the deformations of the production tooling should be included in the computational modeling

of the forming process.

Presently, building a computer model in order to simulate the complete process system is achievable considering the advancements in computer hardware and finite element software, nonetheless it is hardly feasible from an industrial perspective due to the high computer analysis times. Instead a rather simple but a practical engineering approach may be the decoupling the stamping system in to the process-only part composed of the blank plus the die-face design and tooling-only part containing complete draw-die design,

based on the individual characteristics of the deformations experienced during a complete pressing-cycle, respectively. Considering process-only part, there are time-dependent interactions of the sheet metal blank and the forming inter- face bringing about large changes in the blank shape when compared with the scale of die-face distortions. Consequently, the process-only part should be simulated using afinite element formulation based on large-strain and finite incremental deformation theory due to the kinematic characteristics of the blank deformations [8]. On the other hand,small deformation transients superimposed on to the large displacements histories characterize the deformations of the draw-die elements during a single forming cycle. Therefore, a small strain elastic–plastic finite element analysis of the draw-die construction may be appropriate.The interaction of both computational sides is defined in terms of an appropriate data transfer routines (Fig. 1). For the process-only part, the forming simulation uses the geometry information from die-face design as rigid surface Entities and the blank as an elastic–plastic deforming body, and the time-dependent displacement-driven binder and punch motion realize the forming process. The major out- puts are deformed geometry and production stress distribu- tions of the blank after springback and the forming load histories as well as the frictional contact stress distributions over the die-face elements. On the other side, for the tooling-only part, the forming load histories are the basic input for the assessment of the die-face deformation analysis. The finite element analysis of the complete draw-die design for a given press cycle provides the displacements of dieface material points, and the updated die-face design may be fed back to process-only part for the next iteration. Also the computed elastic–plastic stress–strain histories during acomplete press cycle and the contact forces between the punch and binder elements through the wear plates and balancer blocks bring about a significant insight to the interaction of draw-die construction elements.

材料与设计28 (2007) 1311–1320

科技报告篇

计算机辅助分析和设计金属板料成形过程：

第三部分：冲压模具型面设计

作者：Firat

土耳其莎卡里亚啊达铂扎勒大学机械工程学院

2005年9月8日接到，2006年1月31号接受

于2006年三月23号正式启用

摘要

用有限元的方法来模拟分析金属板料冲压成形过程能有效的帮助设计工程师在理论教学和实践加工方面把冲压件从昂贵的车间加工转移到计算机辅助的设计环境来。有限元模型中使用的金属薄板成形性和冲压可行性评估研究通常是基于理想模型设计。这个假设是基于一般符合目前的工业生产经验甚至对于常用的钢也能用于拉延模来分析。然而，对于中等厚度的高强度钢形成的情况不一定可行因为高压负荷所需的坯料形状仍然未知。因此，在成型过程中的模面变形的预测是必不可少的，根据估测值来判断它可变形行的可能性以及回弹性，并且需要结合以前的生产实例紧密分析一般冲压锻模的设计程序。在这一部分的研究当中，从冲压模具和模具型面的金属板成型过程的结构评估中就能够得到一套工程学上的研究理论。利用计算机辅助分析和设计的概念在先前的第一部分和第二部分已经给出介绍，该方法可以使得自动冲压件和完整的模具结构在设计界面中形成。结果表明该模具型面的相对优点是容易锻造成型和回弹性好。

关键词：金属板材成形；成形；回弹；模具设计

1.介绍

众所周知钣金冲压模具生产的一个重要组成部分是关于模面设计模具表面几何形状在必要的质量约束下做出一个无缺陷的冲压毛呸件的发展。设计冲压模具的基本要素是开始以零件几何作为基本的输入数据和方法，工程师试图确定对于给定的操作的最小数量以冲压形式来降低成形模具成本同时满足目标的冲压标准[1] 。该方法工程师用于成形工艺设计直到车间试验结束，持续至冲压部件进入批量生产阶段为止。由两个冲压模面设计和金属板的塑性加工性确定毛坯变形的特性，另外需要注意应保证高强度钢的成形，以适应较低的成形性和较高的回弹变形[2]。在用在计算机辅助设计和分析模具试出阶段可以进行的生产线的模拟并可靠地在计算机生成的虚拟设计环境，

这样的方法和模具设计需要采用有限元法是基于仿真的优点的并且可以预测模具的成形性，如裂纹，皱纹或过度变薄，涉及到的模面设计为给定的冲压特点。这也是可以实现的微调操作，回弹变形后得到最终零件的几何形状。此工程方法假定在绘制过程中的模面的变形可以忽略不计并且工业实践证明这一假设的有效性，即使大的内板拉伸模具中的常规拉伸高品质钢[3]的情况也都一样。作为一个理想的刚性拉伸模具结构的概念，然而，当涉及到中等厚度的材料时就另当别论了，因为相对较高的成形力的新型高强度钢容易形成更大的模面扭曲，这一般都不可能忽略不计了[4] 。因此，模面的变形和其含义应在其提交到生产前的拉伸模设计阶段加以考虑。在本文中，根据以下的冲压模具设计实践和简短的审核计算方法，提出了金属板材成形过程中的模面的变形控制的评估。所提出的方法是采用在成形工艺设计的基础上在第一部分和在本研究的第二部分给出了计算机辅助设计和分析概念的编程器主体部分。在模具的计算机辅助设计环境中考虑应考虑到模面的变形这个问题。这部分的成形性分析和回弹变形处进行，包括模具的理想的刚性和可变形的成形接口之间的缺陷.对这相对差异进行了讨论，并在理想情况下进行刚性模面的设计，通过增加凸模铸件壁厚实现来实现。

2，模面的设计理念

模面设计的板金成型用模具可以被定义为一个具有完整的表面几何形状和塑性变形的片状金属坯料成所需的组合物以确保刚性模具结构冲压形状。设计一开始是以部件的几何形状为基本输入数据，该方法工程师首先通过确定主轴再绘制出其余部分，同时也消除了一定的风险。然后，使用该材料的成形性和最小允许厚度，确定拉伸变形的量，并且估计出能够拉伸的数量。设计人员利用CAD辅助环境将金属板的圆角的尖锐边缘和凸缘部分偏移一定的厚度，用于冲压成型。利用该材料的性能进行最大程度的拉伸变形时，估计可以达到最大的拉伸深度，通过一套牵引装置安装在冲裁面进行冲压，尽量在模具成形的初始阶段减少变形梯度。在决定操作类型之后，使用一组平面或者延生曲面通过与拉伸所结合，通常结合拉延筋把物质约束在一个可以控制的方式上进行冲压。创建冲头和粘结剂界面后，它们的几何同行被抵消表面通常开发具有间隙量，得出的结果比使用CAD软件的金属板厚度大百分之几。在该阶段使用该部分的容许变薄拉伸，完全符合其预算大小使用量恒定的假设。

一旦工程师创造了一整个几何空白的描述和方法在CAD环境里面，有限元分析可以为研究零件的成形工艺性的提供可行性分析，部分几何回弹和成形载荷后分为一个理想的刚性模具结构。有限冲压过程的有限元仿真通常是在两个步骤。进行成型性分析，确定金属变形为一个给定的冲压和粘合剂加载和，其次，回弹变形后对模具的去除应力而形成的力和几何变形的形成步骤随着材料厚度的变化而分析[ 8 ]。根据工艺相对素质和材料参数，可以设置多个虚拟测试为了达到最佳的模具几何的构成要素。在这一点上，成形载荷和动作类型是根据与现有的冲压生产线的规格拟定的。最后，完整的冲压模具表面被批准并报绘制模具结构送往制造部。

3.模面形状控制

金属板材成形过程是由一个复杂系统控制冲压模具和板料的变形，并涉及到M.Firat/《材料与设计》28（2007）1311至1320一组材料和基础机械相互作用的结果，机构提供必要的成形力[4,5,10,11]。假设一个理想的刚性模具结构连接加强了理想的刚性压机板而忽略所有的模面变形面的辅助方法，工程师设计时只遵循纯粹的形成过程几何建模而不结合具体材料分析则会不符合要求。否则，它将是一个巨大的工程，包括所有的这些机械系统中的计算模型，该模型旨在模拟钣金变形影响及采用相应的处理方式。因此，它最接近实用，分离出形成界面，即在模面设计，从剩余空白处进行建模产生下形成势力的空白变形在与纯几何的摩擦接触的模面设计的描述。此外，这种生产理论已经在行业中得到广泛使用，即使大内板拉伸模具在常规片的情况下都可以实施。一个理想的刚性平局，模具结构的概念，不过，有可能成为可疑的，当涉及到所述的高强度钢形成，由于较高的成形负荷需要。此外，一个所产生的大型结构件与非对称成形配置工件，可设计显着高负荷的的平衡块和上冲头之间的耐磨板粘合剂元件增加的办法，磨损和变形。在这些情况下，模具生产的变形应被包括在计算机建模成形过程中。

目前，建立的计算机模型，用来模拟完整过程的系统是可实现的，利用计算机硬件和有限元的先进软件，不过它是从工业的角度来看几乎不可行的由于电脑的分析使之成为可能。用软件模型代替一个相对复杂的，实际的工程方法可以是在冲压系统中分析的过程，只有一部分的坯件加含有完整拉伸模具设计的模面设计和模具仅部分构成的基础上，在一个特征的成型过程中由一个完整的压制循环体系分别变形。考虑到过程的一部分，有金属板的与时间有关的相互作用空并形成界面带来大的变化，在空白形面上，应与模面扭曲变形进行比较。因此，这个过程部分应使用基于大变形和有限的增量变形理论的有限元计算，由数模变形的运动学特性仿真制造。另一方面，变形小的部分采用特征变大来表示变形拉伸量。把整体缩放为单个成形元素。因此，对于拉伸模结构的小应变弹塑性有限元分析也是合适的。

两者的计算方面的相互作用可以用一个适当的数据传输例程来定义（图1）。这个过程只是一部分，成形过程的模拟采用从模面设计为刚性曲面实体和空白面为弹性塑料变形体的几何信息，并随时间变化的驱动的粘合剂和冲压成形过程的运动实现。主要输出是几何变形和回弹载荷是生产成型后的在毛坯上的应力分布以及分布在模面元素上摩擦接触应力。另一方面，只有部分的模具，运用成形载荷的大小对模面变形进行分析和评价。对于一个给定的模具的位移，能够完成拉延模设计的有限元分析，和更新模面设计，同时计算弹塑性应力应变，另外，通过计算在一个完整的压制循环过程中弹塑性应力的应变的一个历史变化情况和通过耐磨板和平衡块的冲头和粘合剂之间的接触力来观察拉伸模运动结构中的相互作用。