General Information and Techniques for Improving STEP Translation Success

Modeling

• Use entity types that are supported by your translator or defined in exchange agreements

• Wherever possible use basic geometry and primitive solids to create the model

• Avoid modeling practices that can create geometry which cannot be exchanged, as in constructing solids where topological edges converge at a single degenerate point

• Use the highest precision when creating a part

• Most CAD vendors today implement AP 203 (configuration managed 3D design data), Conformance classes 2, 4, and 6

- Class 6 is advanced boundary representation solids

- Class 4 is topologically bounded surfaces

- Class 2 is geometrically bounded wireframe and surfaces

• AP 214 implementations so far have mainly copied AP 203 geometry

• Use b-rep solids since facetted boundary representation solids corresponds with the little-implemented AP 203 class 5

• If you must use wireframe, make it geometrically bounded since topologically bounded wireframe corresponds with the virtually unimplemented AP 203 class 3

Importing STEP Files

• Confirm that files are defined to the agreed standard

• Verify that files have not undergone any conversions that may have corrupted them, e.g. ASCII to EBCDIC conversion can convert special characters, which have a meaning in STEP files

• Ensure that files have not been truncated, e.g. to 80 character records, or in length

Exporting STEP Files

• For assemblies, confirm that all component files are in the same directory

• Make all geometry visible and selectable

• Remove unnecessary geometry, layers, annotation from the file(s)

• Use tools available in the native system to validate geometry prior to export

• Ensure that the STEP translator can support the nature of the data to be exchanged

Unigraphics - General Information

• Prior to export

• Export

UG to CATIA

• Set "Face/Edge B-spline Approx. Tol. (meters) value to ".00001"

• If default CATIA interface value of “.1” doesn’t work, use “.0”, which causes it to defer to the tolerance from the UG model’s STEP file

• Set TOPOLOGY_HEALING "on" in CATIA

• CATIA 4.1.9 can import assemblies from UG v13&14 but CATIA 4.1.8 cannot

• There are practical limits to the size of CATIA models - for UG models > 10 MB:

CATIA to UG

• Change CATIA STEP files, "FILENAME.step" to "filename.stp"

• Translate assemblies one at a time and into separate directories

• Standard "Edge Tolerance (meters)" value of ".0001"

UG to AutoCAD

• At least 100 MB of free space on "C" drive

• Files imported into AutoCAD v14 consist entirely of "blocks" which must be exploded before geometry can be queried

• A patch is available, for Mechanical Desktop v2.0, which allows for the calculation of overall surface area for AutoCAD models

• AutoCAD tolerance of 10^-6 is nearly compatible with UG tolerance of 10^-7

UG to Pro/E

• Using a tight "Face/Edge B-spline Approx. Tol. (meters)" when translating to Pro/E, may improve the exchange but at the cost of a larger file size and longer translation time. Pro/E absolute accuracy must be set at this tolerance and convert tolerance units if necessary

• The selection, "Surface (sheet body) output type" for UG models with sheet bodies, is "as Top Bounded Surfaces".

Pro/E to UG

• Since UG and Pre/E both use the filename extension ".prt", use separate directories to avoid overwriting original Pro/E models

• For a non-assembly Pro/E model set the UG "Edge Tolerance (meters)" equal to the absolute accuracy of the Pro/E model

• With an assembly Pro/E model leave the "Edge Tolerance (meters)" default of "0.00000000"

• Pro/E models that contain solids, surfaces, and wireframe must use separate STEP files for these entities and the separate files can be merged into a wireframe UG model using Parasolid Export/Import function

CATIA to SDRC IDEAS

• Modify UNCERTAINTY_UNIT to match IDEAS’(“.1”)

• Set TOPOLOGY_HEALING "on" in CATIA

SDRC IDEAS to CATIA

• Run autostitch after import

• If prompted to deal with open edges, give tolerance of the original CATIA model

Acknowledgements

The information presented is a compilation of inputs from various sources. PDES, Inc. would like to recognize the following for their contributions:

• General Motors' STEP Translation Center

• Delphi Delco Electronics Systems

• Automotive Industry Action Group ( AIAG )

Other Sources