Data Exchange Week 2

Data Exchange Between CAD/CAM Systems

Why do we need Data Exchange?

• Design projects require data to be shared between suppliers • Different companies often used different CAD systems • All CAD systems have their own database formats • They are mostly proprietary and often confidential • Data is stored in different ways e.g. 1.0,2.0,3.0 or X1.0,Y2.0,Z3.0, etc.

• Data conversion between systems becomes necessary

Alternative approaches System B

System A Future System System C

System D

Number of Direct translators = 2 (N-1)

Alternative approaches

System A

System C

Future System

N e u t r a l f o r m a t

System B

System D

Data Exchange Formats • IGES (Initial Graphics Exchange Specification) •1980 US NIST, National Institute of Standards and Technology • DXF • VDA – German Automotive Industry • SET – Airbus • PDES – American fore-runner of STEP • STEP • STL • VRML

3D - IGES • The Initial Graphic Exchange Specification (IGES) format, is the most used neutral format to transfer data between heterogeneous CAD systems. • Users can perform bi-directional data exchange between dissimilar systems with direct and automated access to IGES files.

IGES file structure •

Start section –

•

Global section –

•

Data index and data attribution

Parameter Data Section –

•

System environment information

Directory Entry section –

•

Comment, filename, data name, etc

Real data value(coordinate, parameter value)

Terminate Section

2D - DXF/DWG • DXF/DWG : DXF formats were developed by AutoDesk. • After creating drawings, designers can export data in DXF/DWG formatted files and import the 2D geometric data contained in a DXF/DWG file into other drawing tools.

DXF File Structure • • • •

Header Section Tables Section Block Section Entities Section

STL • STL format was developed by 3D Systems as a neutral format to input geometric data into their 3D printing systems • It represents the geometry as a series of triangular facets • It is now being used for other purposes besides 3D printing • It is simple to create but has little overall structure

VRML • VRML (Virtual Reality Modeling Language) format is also a facetted format • It can represents other aspects besides geometry, e.g. colour • It is widely used for graphics visualisation purposes

STEP • STEP AP203 / AP214 format (Standard for the Exchange of Product model data) • It supports geometry and assembly structures and handles topology (shells, solids) on export and import.

• STEP files are human readable • Other STEP APs are available, e.g. electronics data

Questions to Ask about Data Exchange • Who is the data for?

• What level of data is required (2D/3D, solids/surfaces)?

• What will the data be used for?

• How long will the data be kept?