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Open CASCADE Helps STEP to Attain Industrial Objectives

As an active member of CAX-IF, Open CASCADE works to promote the STEP standard and improve data exchange in key areas like transfer of large assemblies, multi-representation of the CAD model and gathering of data in mixed file formats (STEP files plus files in a native format).

Open CASCADE participated in the latest CAX-IF forum, TR9J, held in Asheville, North Carolina, from March 19th to 21st. Part of the PDES initiative devoted to the promotion of the STEP standard in industry, this forum was organized in conjunction with the PDM-IF forum and other meetings on STEP topics.

The general trend of developments is towards more complex and realistic exchanges, reflecting the growing, daily utilization of STEP in industry.

In addition to exchanging basic BRep geometry and topology with other systems via STEP, Open CASCADE 4.0 now addresses data exchange based on assembly structure data (recognized for PDM and used for large assemblies) and group descriptions (internal to CAD models). Models can be defined either as assemblies or as final parts, thereby facilitating the exchange of very large assemblies under PDM control. Validation properties that allow checking correct exchange and color attributes are also included.

Open CASCADE 4.0 thus allows integration of assembly descriptions from outside systems. An example of this type of Open CASCADE-based application is ANATOLE software from EADS CCR, designed to verify tolerance between the parts of large Airbus assemblies.

Assembly import is only one of the topics that interest both STEP and Open CASCADE users. Another important area of work during the coming months concerns multi-representation of the CAD model (for analysis, to distinguish nominal and idealized shapes, for PDM, as wireframe plus solid, etc.). Other topics include material properties, in particular density (allowing higher-level exchanges); coloring of internal assembly instances; and dimensional tolerancing.

In another area, related to the PDM-IF forum, Open CASCADE will consider data exchange with mixed files. These would consist of main files in STEP format with sub-files in a native format such as CATIA.

Actions planned for the mid-term could have a significant impact on STEP compatibility and coverage. Edition 2 of AP203 (the general CAD standard) is in preparation and will adopt a more modular approach, incorporating advances in areas such as PDM, construction history, and property attachment. Open CASCADE works to meet these challenges and also participates in work on parameterized assemblies, an item initiated by ISO.

As STEP use increases, being able to exchange data which share common definitions becomes more and more important. These definitions concern primarily geometry, topology, and assembly structure. Although AP203 and AP214 (automotive CAD) already interoperate on a broad scale for CAD exchanges, even greater performance is the goal of AP203 Edition 2.

CAX-IF members have tested interoperability between AP203-AP214 and other protocols. Open CASCADE participated in testing, as well as in the resolution of issues within the framework of ad hoc forums on AP210 (electromechanics), better integration between CAD and PDM, and AP209 (the analysis application protocol). For AP209, interoperability will first involve geometry and the product life cycle, then nodal points and meshing.

Together with CAX-IF, the PDM-IF team and the Analysis team (which manages AP209) agreed on a common approach to areas of mutual interest in order to harmonize definitions and practices between these domains, as well as to fit together exchange and industrial data flow.

For questions on Open CASCADE activity within the STEP initiative, contact us.

For an example of a STEP assembly, see:

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