Application of an integrated CAD/CAE/CAM system for stamping dies for automobiles Bor-Tsuen Lin & Chun-Chih Kuo
Abstract
The globalization and competition in the automobile industry makes it necessary to reduce the time spent on product development. Therefore, computer aided product development has become one of the most important techniques in the automobile industry. According to the concurrent engineering concept, an integrated CAD/CAE/ CAM system for automobile stamping die development is established. The system is based on 3D surface construction CAD software STRIM, CAD/CAE software CATIA, stamping formability analysis software DYNAFORM, CAM software CADCEUS, a stamping design knowledge- based system, and a product database. This paper uses the development of trunk lid outer panels as an example to showcase the power of the system, in which the different development stages can be performed simultaneously. The system can greatly reduce the development time and cost, improve the product quality, and push products into the market in a relatively short time.
1 Introduction
Since stamping parts have considerable potential because of their competitive productivity and performance, they have been widely used in the automotive industry. However, the manufacturing industry has three major goals: to improve product quality, to reduce development cost, and to reduce the time spent on development. In order to achieve these goals, we need to bring in new technologies.
From the manufacturing viewpoint, the major requirement for most applications of sheet metal is good formability [1]. Given that part surfaces have become more and more complex and sharp-edged, we need to take advantage of formability analysis to understand their stamping properties. In 1963, Keeler and Backofen [2] introduced the concept of forming limit diagrams (FLDs).
They analyzed the shape and size for an etched circle-grid of sheet metal after it had been stamped. This technique has been widely used in sheet metal formability analysis since then. Recently, software that uses a finite element method has been used to analyze and simulate sheet metal formability. Chen and Liu [3] combined circle-grid analysis with formability analysis to identify an optimal die face, so that the split defect at the drawn-cup wall in the rear floor panel could be avoided. Makinouchi [4] used formability analysis software to analyze four stamping parts—fenders,trunk lid outer panels, side frame outer panels, and tire disk wheels—and to predict their blank geometry, springback, sheet thickness, residual stress, and common defects after stamping. Bigot et al. [5] developed a methodology to validate the modeling of an aluminum forming process based on dimensional characterization and finite element comparison. Taking advantage of artificial neural network, knowledge based systems and finite element analysis, Pilani et al. [6] proposed a method for automatically generating an optimal die face design based on die face formability parameters.
Since die structures are becoming more and more complex and large-sized, we must use a solid model in die design to avoid any potential interference among the various components. Moreover, the solid model can be used for building dissolve models and estimating the fragile section of die structures. Therefore, it is necessary to use a 3D CAD/CAE/CAM system to build solid models, to
develop CNC tooling path programs, and to analyze the stress of die structures when developing stamping dies. Nahm and Ishikawa [7] utilized the set-based design approach with the parametric modeling technique to handle the uncertainties that are intrinsic at early stages of the design. Park et al. [8] combined a CAD/CAM system with a knowledge-based system to develop deep drawing dies of
the motor housing. Cheng et al. [9] used Visual C++ programming to create CAD software for the conceptual design of the scroll compressor, and fabricate a real orbiting scroll part on a CNC machining center.
The globalization and competition in the automotiveindustry makes it necessary to reduce the time spent on product development. Networks are widely used nowadays.As a result, Kao and Lin [10] designed a system that uses a local area network and the Internet to allow two geographically dispersed CAD/CAM users to simultaneously work on the development of products. Kong et al. [11] developed an Internet-based collaboration system for a press die design process for automobile manufacturers to shear design models and analysis results. Moreover, an integrated CAD/CAE/CAM system can tremendously improve productivity. Xu and Wang [12] used the multi-model technology and an integrated CAD/CAE/CAM system to develop cylinder head. Yue et al. [13] took advantage of the concurrent engineering concept and developed an integrated CAD/CAE/CAM system to develop die casting dies for water pumps, which successfully reduce the development time and cost, and improve product quality. Ferreira [14] developed an integrated CAD/RP/FEA system to improve the manufacturing process for Zn casting.
This paper illustrates an integrated CAD/CAE/CAM system for designing stamping dies of trunk lid outer panels for automobiles using concurrent engineering (CE).
2 Procedures for developing stamping dies for automobiles
Once receiving the surface model of a stamping part from an automobile manufacturer, the die manufacturer initializes the development process, which is shown in Fig. 1.
Die face design is a process that uses CAD software to create 3D die faces, which include stamping part surfaces, addendums, drawbeads and binder faces, and analyzes their stamping properties using formability analyzing software. Taking possible common defects into consideration, designers keep modifying the 3D surfaces until they obtain an optimal drawing die face, which will be used in designing dies and designing NC programs for processing die faces.
Layout diagram design is the process of developing the die layout diagram based on its surface model, which includes the following sub-tasks: identifying the central reference point, identifying the press direction, identifying the responsibilities of each process, designing drawing die faces, suggesting die height and indicating press lines.
Since automotive stamping dies can be very large in size, they are processed by casting in order to minimize their weight and cost. 3D CAD/CAE software must be used to design the solid model to avoid any potential interference among various components, which includes cavity, punch,strengthened ribs, functional units and/or standard parts for upper and lower die sets, and blank-holder (BH).
After the die design process is finished, designers will perform motion and interference analysis on the 3D solid models and modify them if any problem is identified. Moreover, the stamping force is very large, modification and enhancement should be made to the die structural models where necessary through structural analysis.
Die manufacture includes dissolve dies manufacture, die dimension manufacture and die face manufacture. Dissolve dies are needed because die bodies are processed by casting. After identifying the information needed to construct 3D solid models, designers should develop NC tooling path programs to make dissolve dies using CNC machines. Then, the die bodies are cast through dissolve dies.
Die dimension manufacture is responsible for making all reference planes and holes, such as die base planes, guiding planes, stopper planes, assembling planes, positioning holes and bolt holes. Die face manufacture generates all surfaces that will be completed in all subsequent sub-tasks. Designers use 3D CAM software to design tooling paths, including roughing, finishing, and corner finishing paths. Moreover, cutting simulation needs to be conducted to ensure the feasibility of the process. After the tooling paths have been identified, they will be posted into NC code to allow further processing by CNC machines.
When the dies have been manufactured and assembled, CMM (coordinate measuring machines) will measure the dimensions of the dies. If no faults are found, die tryouts will be produced. If the tryouts meet all requirements and specifications, mass production ensues.
3 The integrated CAD/CAE/CAM systems
Figure 2 shows the scheme of the integrated CAD/CAE/CAM system for stamping dies. This system includes a set of CAD die face design software, a set of stamping formability analyzing software, a set of CAD/CAE software, a set of CAM software, a stamping die design knowledge-based system, and a product database.
Die face design is the process of designing various supporting surfaces around the stamping part surfaces. These supporting surfaces are not part of the stamping part surfaces. Therefore, the die manufacturer is responsible for the die face design. In order to ensure consistency between the stamping part’s surfaces and its supporting surfaces, specialized surface design CAD software must be used.Commonly used commercial software includes Icem Surf by Icem, STRIM by SGI, and CATIA by Dassault.
The surfaces of automotive parts are very complex and sharp-edged. Their formability cannot be predicted using previous experience. In order to ensure product quality, designers need to perform formability analysis on die faces before designing stamping die. Currently, this kind of software includes DYNAFORM by ETA, PAM-STAMP by EDS, and AUTOFORM by AFE.
Automotive stamping die structures include structural subcomponents, such as punch, cavity, strengthened ribs, functional units, and cam mechanisms, which are used to change the stamping direction and reduce die sizes. The die faces of punch and cavity are made up of thousands of surfaces. These components also make the design job extremely complex. When designing layout diagrams designers use plane diagrams to illustrate layouts of dies. When designing dies, designers use solid models to construct dies that are identical to real dies. Moreover, designers use motion and interference analysis to avoid any potential interference among various components. In the meantime, structural analysis is performed to understand their stresses and strains. Related software that is available in the market includes CATIA by Dassault, PRO/ENGINEER by PTC,and UNIGRAPHICS NX by EDS.
Due to the complex structure of automotive stamping dies, CNC machines should be used to manufacture stamping dies. Therefore, CAM software should be able to assist designers to generate tooling paths and provide cutting simulation. There are many CAM software packages that can support the aforementioned features, including POWERMILL by DELCAM and CADCEUS by UNISYS.
The construction of a stamping design knowledge-based system includes layout design and die design. The layout design includes the empirical formula for surface forming parameters, such as the thickness of sheets, die clearances, fillets radii and spring backs, and material parameters, such as modulus of elasticity, strain-hardening indices and anisotropy. The die design includes the design procedures of designing dies, and design criteria and design standards of each component and standard part.
Information that is needed throughout the process is stored in the product database, which can be accessed by all software in the system via the local network. In addition, in order to allow users to accurately and efficiently access data, all information is stored in a structured database and includes detailed information, including file names, versions,dates, and formats.
In the system, all the CAD/CAE/CAM software and astamping design knowledge-based system were installed on the personal computers with a Pentium 4 3.4 GHz CPU,1024 MB RAM, 128 MB graphics, and Windows XP operating system. The product database was built on the IBM server with a Pentium 3 1.0 GHz CPU, 1024 MB RAM, 128 MB graphics, and Windows NT operating system. The network connection is a 1 GB LAN (local area network).
In this paper, we use the trunk lid outer panel scaled 1/4 as an example to illustrate how to develop stamping dies.We use STRIM 100 to construct 3D surfaces for die faces.DYNAFORM 5.1 is used to perform formability analysis.CATIA V5 R13 is used to conduct die layout diagram design, die design, motion and interference analysis, and structural analysis. We use CADCEUS V5 R1 for tooling path generation and simulation, where NC programs are obtained. CNC machines use these NC programs to manufacture dies. At the same time, a stamping die design knowledge-based system is used to assist the layout design and 3D die design. Since all CAD/CAE/CAM software accepts IGES formats, we use them as communication formats between those software and the product database.
Furthermore, the same 3D solid model is used throughout the entire development process, where different development stages can be conducted simultaneously. Therefore, the development time is fundamentally reduced.
一个集成的CAD/CAE/CAM系统在汽车冲压模具中的应用
摘要
汽车制造业的全球化与竞争，使其在产品开发上的时间缩短。因此，计算机辅助产品开发已成为汽车工业的重要技术之一。根据并行工程的概念，汽车冲压模具开发CAD/CAE/CAM集成系统建立了。该系统是基于三维表面结构CAD/CAD／CAE软件，冲压成形性DYNAFORM分析软件，CAM软件CADCEUS，冲压设计知识和产品数据库为基础的系统，本文以行李箱盖外板的开发为例，展示了系统在不同的发展阶段可以同时进行的功能。该系统可以大大降低开发时间和成本，提高产品质量，并缩短将产品推向市场的时间。
关键词：整合 CAD/CAE/CAM 并行工程 冲压模具 汽车模具
1 引言
由于冲压件具有很大的潜力，因为其生产和性能具有竞争力，在汽车工业中得到了广泛的应用。然而，制造业有三个主要目标：提高产品质量，降低开发成本，减少开发时间。为了实现这些目标，我们需要引进新的技术。
从制造业的角度来看，大多数板材得到应用的主要原因是其良好的成形性。鉴于零件表面变得越来越复杂，我们需要利用成形性分析来了解其冲压性能。在1963，基勒和巴科芬]介绍了成形极限图的概念（FLDS）。他们分析了一个蚀刻已加盖圆形网格的金属板。该技术已广泛应用于金属板材成形性分析中。最近，有限元软件已被用于分析和模拟金属板材成形性中。陈、刘结合圆网成形性分析，确定最佳模面，从而避免了后底板上杯壁上的分裂缺陷。牧野用成形性
软件对四个冲压件的挡泥板、行李箱盖外板、侧围外板、车轮和轮胎的磁盘分析，预测冲压后其毛坯几何回弹、板料残余应力等常见缺陷问题，并在三维特性和有限元比较的基础上利用人工神经网络、基于知识的系统和有限元分析等等开发了一种建模方法来验证铝的形成过程。提出了一种基于模面成形性参数自动生成最佳模面设计方法。
由于模具结构越来越复杂和大型化，在模具设计中避免各种部件之间的潜在干扰必须使用一个实体模型。此外，固体模型可以用于建筑脆弱溶解模型部分的模具结构。因此，使用3D CAD / CAE / CAM系统建立实体模型，开发数控加工路径方案，并分析冲模结构在冲压模具开发中的应力是很有必要的。在设计的早期阶段，纳姆和石川利用集合建模技术设计方法去处理内在不确定因素，以知识为基础的计算机辅助设计系统开发电机壳体拉深模具。在数控
加工中心，用Visual C++编程CAD软件为涡旋压缩机设计制作一个真正的轨道滚动部件。
汽车制造业的全球化与竞争，使其在产品开发中缩短花费的时间是有必要的。今天网络的广泛应用，作为一个结果，高林设计了一种使用局域网和互联网让两个地理上分散的CAD / CAM用户同时工作的产品开发系统。多哥等开发了一种基于网络的汽车制造企业的冲压模具设计过程的协同系统，以剪切设计模型和分析结果。此外，CAD/CAE/CAM集成系统可以极大地提高生产率。徐和王采用多模型技术和CAD / CAE / CAM集成系统开发缸盖，利用并行工程的概念，开发了一个CAD / CAE / CAM集成系统开发水泵压铸模具，成功地减少了开发时间和成本，提高产品质量，费雷拉为提高锌铸件的制造工艺开发了一个计算机辅助设计/快速/有限元分析集成系统。
本文采用并行工程概念为汽车行李箱盖外板冲压模具设计CAD/CAE/CAM集成系统（CE）。
2 汽车冲压模具的开发过程
汽车制造商生产一个冲压件从建立表面模型到模具制造过程，如图1所示。
模面设计是一个利用CAD软件建立三维模面，包括冲压件表面，补遗，拉延筋和胶面，并分析了其冲压性能及使用性能的过程。在模具设计加工模具的数控加工程序，出于可能出现缺陷的考虑，设计师需要不断修改三维表面，直到获得最佳的模具型面。
版图设计是以其曲面模型为基础，开发模具版图的过程，包括以下子任务：确定中心基准点，确定冲压方向，确定每个过程任务，设计图纸面，指出模具的高度，并标注尺寸线。
由于汽车冲压模具的尺寸是非常大的，需要通过铸造加工，以尽量减少他们的重量和成本。使用三维CAD／CAE软件设计实体模型，以避免各个组成部分潜在干扰，包括腔体、冲床、加强筋、功能单元和/或标准零件上下模具、压边（BH）。
模具设计完成后，设计人员将三维实体模型进行运动分析，如果有问题则需要修改知道正确位置。此外，冲压的力量是非常大的，通过对模具模型结构分析修改和加强是有必要的。
模具制造包括模具分散制造、模具尺寸制造和模具表面制造。模具在铸造加工需要溶解模具，在构建三维实体模型时确定所需的信息后，设计人员应该开发出使用数控机床的数控加工程序，使之溶解模具，然后，通过溶解模具铸造模具。
模具尺寸制造需要设置基准面和孔，如模底面、导向面、止动架、装配平面、定位孔和螺栓孔。模具表面的制造会产生所有的表面，将完成在所有随后的子任务。设计师使用三维CAM软件设计加工路径，包括粗加工、整理、和清角加工路径。此外，还需要进行切割模拟，以确保加工过程的可行性。在工具路径已经确定之后，路径将被张贴到数控代码中，让数控机床进一步加工。
当模具组装完成后，三坐标测量机（坐标测量机）将测量模具的尺寸。如果没有发现故障，模拟将继续进行，如果使用符合规格要求，则可以批量生产。
3 CAD / CAE / CAM集成系统
图2显示了CAD/CAE/CAM集成系统模具冲压方案。该系统包括一套CAD模面设计软件，一套冲压成形分析软件，一套CAD／CAE软件，一套凸轮软件，一个以冲压模具设计为基础的系统，和一个产品数据库。
模面设计是在冲压件表面设计各种支承面的过程。这些支撑面不是冲压件表面的一部分。因此，模具制造商负责模具的端面设计，为了保证冲压件表面及其支承面之间的一致性，使用.专门平面设计软件。常用的商业软件F包括ICEM、STRIM、SGI、达索和CATIA等。
汽车零件表面非常复杂和锐利。它们的成形性不能凭靠以前的经验来预测。为了保证产品的质量，设计冲压模具前需要对模具进行成形性分析。目前，这类软件包括DYNAFORM的ETA，PAM-STAMP的EDS等。
汽车冲压模具结构包括用来改变冲压方向和减少模具尺寸的结构组件，如冲压、型腔、加强筋、功能单元，和凸轮机构。冲孔模和腔模面由上千个表面组成，这些组件也使设计工作变得非常复杂，设计布局图时，设计师用平面图来说明模具的布局，设计人员在设计模具时，使用类似真正模具的固体模型构建模具，此外，设计人员使用组件模拟分析，以避免各种组件之间的任何潜在干扰。在此期间，进行结构分析，以了解它们的压力和应变。在设计中相关的软件包括达索CATIA，Pro/E和UG NX的PTC等。
由于汽车冲压模具的结构复杂，数控机床被广泛应用于冲压模具的制造中。因此，CAM软件能够用来协助设计人员生成加工路径，并提供切削模拟，有许多CAM软件包，可以支持上述功能，包括 DELCAM的POWERMILL和UNISYS的CADCEUS。
冲压设计知识体系的构建包括版图设计和模具设计。版面设计包括表面成型的经验公式，
如板材厚度、模具间隙、圆角半径和表面弹性，材料参数包括如弹性模量、应变硬化指数。模具设计包括模具的程序设计和各部件的设计标准。
在整个过程中所需要的信息被存储在产品数据库中，该数据库可以通过本地网络访问系统中的所有软件此外，为了让用户准确、高效地访问数据，所有详细信息都存储在一个结构化的数据库中，包括信息、文件名、版本、日期和格式。
在系统中，所有的CAD / CAE / CAM软件和基本冲压设计知识系统可以安装在4 3.4 GHz奔腾处理器，1024 MB RAM，128 MB图形，XP操作系统的个人电脑上。产品数据库是建立在与Pentium 3 CPU 1 GHz的IBM服务器，1024 MB内存，128 MB图形，和Windows NT操作系统。网络连接是一个1GB的本地网（局域网）。
在本文中，我们使用的缩放4 / 1行李箱盖外面板作为一个例子来说明如何开发冲压模具。我们使用STRIM 100去构建模具三维表面，用DYNAFORM 5.1来进行成形性分析，用CATIA V5 R13进行模具布局图设计、模具设计、模拟干涉和结构分析，在
数控程序使用CADCEUS V5 R1刀具轨迹生成与仿真，数控机床通过这些程序来制造模具。同时，采用以知识为基础的冲压模具设计系统，以辅助设计和三维模具设计，因为所有的CAD / CAE / CAM软件接受IGES格式，我们使用他们的软件和产品数据库之间的通信格式。此外，在整个开发过程中，使用相同的三维实体模型，在不同的发展阶段，可以同时进行，因此，从根本上减少了开发时间。
