CAD Exchange Overall Review
CAD data exchange involves a number of software technologies and methods to translate data from one Computer-aided design system to another CAD file format. This PLM technology is required to facilitate collaborative work (CPD) between OEMs and their suppliers.
There are basically three methods of transferring data from one CAD system to another.
- Direct CAD system export/import;
- Direct 3rd party translators;
- Intermediate data exchange formats.
A common method of translation is via an intermediary format. The sending CAD system exports out to this format and the receiving CAD system reads in this format. Some formats are independent of the CAD vendors being defined by standards organisations while others, although owned by a company, are widely used and are regarded as quasi industry standards. It is becoming increasingly common for companies owning these quasi industry standards to further the use of their formats by openly publishing these data formats.
STEP-Files and ISO 10303
STEP-File is the most widely used data exchange form of STEP. ISO 10303 can represent 3D objects in Computer-aided design (CAD) and related information. Due to its ASCII structure it is easy to read with typically one instance per line. The format of a STEP-File is defined in ISO 10303-21 Clear Text Encoding of the Exchange Structure. Most of the CAD software supports STEP importing and exporting.
The ability to support many protocols within one framework is one of the key strengths of STEP. All the protocols are all built on the same set of Integrate Resources (IR’s) so they all use the same definitions for the same information. For example, AP-203 and AP-214 use the same definitions for three dimensional geometry, assembly data and basic product information. Therefore CAD vendors can support both with one piece of code.
AP203 defines the geometry, topology, and configuration management data of solid models for mechanical parts and assemblies. This file type does not manage Colors and Layers. AP214 has everything a AP203 file includes, but adds colors, layers, geometric dimensioning and tolerance, and design intent. AP214 is considered an extension of AP203.
STEP is very modular in its definition, different application protocols may share many common definitions, hence they can interoperate for what is common between them. For a given applicative domain or set of domains, such as 3D CAD, relevant data definitions are taken from some parts, that we can use as reference. If a new domain is to be considered, additional data and constructs come.
AP203 : Configuration Controlled 3D Designs of Mechanical Parts and Assemblies
Scope of AP203 (Edition 1) covers :
- Products as mechanical parts and assemblies,
- Data for configuration control applied to design phase,
- Data related to the documentation of design change process, approval, security classification,
- Geometrical data as : wireframe, surfacic models, faceted models, manifold surfaces and solids (BREP).
It does not cover (in particular) :
- Constructive Solid Geometry (and more generally, Construction History),
- Data which doen’t apply to design phase (such as manufacturing),
- Graphical presentations.
AP214 : Core Data for Automotive Mechanical Design Process
The whole scope of AP214 covers :
- Products as mechanical parts , assemblies, tools used by manufacturing (in principle applied to description of cars),
- Information for process plan, configuration control, applied to design phase,
- Data related to the documentation of design change process, approval, security,classification,
- Geometrical data as : wireframe, surfacic models, faceted models, manifold surfaces and solids (BREP), constructive solid geometry, hybrid models
- References to product data represented in an other format than STEP
- Kinematic structures,
- Tolerance data, Surface conditions.
In regard of this scope, limitations apply. These domains are in practice not covered :
- Parametric representation of shapes,
- Continous kinematics simulations over time,
- Data related to finite element analysis (see AP209),
- Data related to particular technologies such as pneumatic, hydraulic, electric, or electronic.
A second edition of AP214 has been issued in 2003, it introduces various corrections, but no change in the scope.
AP 242: Managed model based 3D engineering
The AP 242 ed2 project aims at defining and using a single integrated ISO standard covering product information interoperability capabilities for: Product Data Management, 3D model based design with PMI (e.g, Geometric Dimensions and Tolerances), Mechanical, Composite, and Electrical harness design.
- AP 209 “Multi-Disciplinary Analysis and design”,
- AP 210 “Electronic assembly, interconnect, and packaging design”,
- AP 233 “Systems Engineering”,
- AP 238 “Application interpreted model for computer numeric controllers”,
- AP 239 “Product Life-Cycle Support”.