Standards for CAD Data ExchangeS.BALAMURUGANASST.PROF (Sr.G)DEPARTEMENT OF MECHANICAL ENGINEERINGSRM UNIVERSITY

CONTENTS

DEFINITIONCLASSIFICATIONFUNCTIONAL FEATURESDESIGN FEATURESMANUFACTURING FEATURE

Standards for CAD Data Exchange

ProductDesign(CAD)Engineeringand Analysis(CAE)CustomerRequirementsProductDatabasesManufacturingDatabasesMaterialsPlanningProcurementInstallationandDistributionFabrication, Assembly & Test OperationsProductInformationManagement Product DesignManufacturing EngineeringSupply ManagementCustomerSuppliersMarketingNeutral I/FNeutral I/FProduct Data ManagementCAD data is used throughoutthe organization

Typical SituationMajor companyuses CATIAMajor supplieruses I-DEASSmall supplieruses AutoCADSmall supplieruses Solid EdgePartner uses Unigraphics

The ProblemEvery CAD system uses its own proprietary data formatDesign data must be converted from one format to the other

Direct Translation between CAD SystemsNeed a translator from every CAD package to every otherFor 4 CAD packages, need 6 translatorsFor 6 CAD packages, need 16 translators!I-DEASUnigraphicsPro/EngineerCATIA

Data Exchange StandardsTo address the problem, many standards for CAD data exchange have been developedCAD systems can import and export to many of these standard formats

InterfacesCAD/CAD CAD/CAMStandardization OrganizationNational & EuropeanInternational ISOIGES

PDDI

SET

VDA/FS

CAD*I

CIM-OSA

EDIFPDESANSI (USA)AFNOR (France)DIN (Germany)ESPRIT (EEC)ESPRIT (EEC)Product Data StructureSTEP( A full data model)USA Electronics Industry Evolution of Data Standards

Current SituationTranslation using IGES is unreliablegeometry is corruptedmuch cleanup required after translationTranslation using STEP is not widespreadSTEP translators only recently availableExisting translators lose informationparametrics and constraintsfeatures and history trees

Short-term SolutionsTo avoid data translation problems, many companies have standardized on a single CAD systemFordall suppliers must use I-DEASChryslerall suppliers must use CATIAGeneral Motorsall suppliers must use Unigraphics

A Better SolutionA better solution is development of reliable data exchange standards, using a neutral interface

Neutral Interface

Requirements of an InterfaceThe interface must be capable of handling all manufacturing dataThere should be no information loss (maintain the semantics during conversion)The system must be efficient to be capable of handling the realtime requirements of manufacturingThe system should be open-ended to permit extensions or contractions

Requirements ContinuedThe system should be adaptable to other standardsThe system must be independent of the computer and architecture usedIt must be possible to form application-oriented subsets of the standard to reduce costsThe interface must be upward and downward compatible in a hierarchical control structure.Test procedures must be provided to verify effectivety.

Initial Graphics Exchange Specification (IGES)Formatted ASCII file formatSupports many 2D and 3D CAD entitiesHas gone through several versions since 1980Widely supported

Problems with IGESMany incompatible flavoursUnreliable translation, particularly for complex geometryNo formal information modelling basisInsufficient support for conformance testing

STEP(Standard for the Exchange of Product Model Data)Uses a formal model for data exchangeInformation is modelled using the EXPRESS languageEXPRESS has elements of Pascal, C, and other languagesIt contains constructs for defining data types and structures, but not for processing dataEXPRESS describes geometry and other information in a standard, unambiguous way

STEP ArchitectureLayer 1: Implementation methods(EXPRESS)Physical filesLayer 2: Resource information modelsLayer 3: Application protocolsConformance testing & test suites

Classes of STEP PartsIntroductoryDescription methodsImplementation methodsConformance testing methodology and frameworkIntegrated resourcesApplication protocolsAbstract test suitesApplication interpreted constructs

Status of STEPSTEP has been under development for many years, and will continue for many moreOver a dozen STEP parts have been approved as international standardsMany others are under development

Other StandardsStandards for technical documentsStandards for imagesInternet and Web standards

Continuous Acquisition and Life-cycle Support (CALS)Developed by US Department of DefensePrescribes formats for storage and exchange of technical dataTechnical publications an important focus

Important CALS StandardsStandard Generalized Markup Language (SGML)document description languageseparates content from structure (formatting)uses tags to define headings, sections, chapters, etc.HTML is based on SGMLComputer Graphics Metafile (CGM)vector file format for illustrations and drawingsIGESalso used for illustrations

Common Formats for Bitmap ImagesStandardsJoint Photographic Expert Group (JPEG)ProprietaryGraphics Interchange Format (GIF)Windows bitmap format (BMP)Zsoft file format (PCX)Tagged Image File Format (TIFF/TIF)Targa file format (TGA)

Web and Internet StandardsHypertext Markup Language (HTML)used to describe web pagesbased on SGMLVirtual Reality Modelling Language (VRML)standard for description of 3D interactive environments and worldsdownloaded and displayed in a web browserwell suited to sharing of CAD data

Other CAD File FormatsDXFde facto standard published by AutoDesk (AutoCAD)STL3D file format used as input for Stereolithography SATsolid model file format used by ACIS-based CAD systems

Thank you

*Today we will discuss the shaded areas in our reference architecture, tools to assist manufacturing engineers, namely Neutral Interfaces, Bill of Materials, Group Technology, Computer Aided Process Planning (CAPP), Shop Instructions, Post Processing, and Line Balancing As stated, the input to this function is the complete product data model presented in a neutral formatThe tools assist manufacturing engineers to manipulate design and process related data into manufacturing instructions for manual and automated operations.Potential Scope of CIM ToolsOur CIM tools cover all types of manufacturing processes starting with the preparation of raw material from base resources (Iron, Steel, Plastics, Silicon, Fabric, etc.).Examples of fabrication/machining processes are: Casting, Forging, Plastic Injection Molding, Forming (Roll & Die), Shearing, Bending, Drawing, Punching, Separating (Milling, Sawing, Turning, Grinding, etc.), and Conditioning (Heating, deposition, etc.).Examples of mechanical & electrical assembly processes are Bonding (Heat, Welding, Soldering, Adhesive, etc.), Mechanical Fastening (Rivets, Screws, Staples, Seaming, Compliant Pin, Wire Wrap) and Finishing (Plating, Coating, Painting).Examples of electrical test processes are Functional and In-Circuit Circuit Board Testing, Modular and System Unit Testing, Electrical Value Testing.Examples of mechanical test operations are Dimensional Measurement, Operational Tests, Chemical Testing, etc.Another dimension to the scope would be process based manufacturing vs discrete manufacturing, petroleum refining vs automobile manfacturing. CIM in the process industry involves a tremendous knowledge of process and facilities design, the latter being very CAD intensive, and process monitoring and control.This course will focus largely on discrete manufacturing having the most potential for CIM, being driven from the CAD product design model. We will touch on process control in a later lecture. The tools we are discussing today are used in discrete manufacturing.

*IGES; Initial Graphics Exchange Specification, The defacto standard for mechanical today.PDDI; Product Definition Data Interface, developed by the US Air Force ICAM projectPDES; Product Data Exchange SpecificationSET; Standard dEchange et de Transfer, a French development for CAD/CAM exchangeVDAFS; Verband der Automobilindustrie; German automobile standard for tramsfar of 3D curves and surfaces for which IGES is unsatisfactory.CAD*I; an EEC initiativeEDIF; Electronic Data Interface, a USA electronic industry CAD standard which is struggling to get inclusion in PDES.STEP; Standard for Exchange of Product Definition Data, finally the emergence of an international standard that has an excellent chance of being universally adopted. *