Convert STP to CATPART

A customer or supplier may provide a neutral .stp or .step model when a CATIA V5 workflow requires a native .CATPart file. Saving the imported geometry as CATPart makes it usable in CATIA part operations and CATIA-based document-management or PLM systems.

What the STP format is

STP, also called STEP, is a vendor-neutral CAD exchange format standardized under ISO 10303. It commonly transfers solid and surface boundary-representation geometry, assemblies, units, colors, layers, and product metadata. It usually does not contain the source system’s parametric feature tree.

Mechanical CAD systems such as CATIA, SolidWorks, Siemens NX, PTC Creo, Autodesk Inventor, Fusion, and FreeCAD import or export STEP files. STEP is used for supplier models, cross-platform design exchange, manufacturing handoff, and archiving geometry independently of a particular CAD application.

What the CATPART format is

.CATPart is CATIA V5’s native part-document format. A CATPart can contain CATIA solid and surface bodies, sketches, parameters, construction geometry, annotations, and feature history.

Converting a STEP model to CATPart normally produces an imported or “dumb” solid or surface body. The CATIA file can be measured, referenced, sectioned, and locally modified, but STEP does not provide the original sketches, constraints, formulas, pockets, fillets, design tables, or feature relationships. Fully parametric CATIA history must be rebuilt manually.

How to convert an STP file to CATPART

CATIA V5 is the most direct desktop option because it performs the native CATPart save operation.

1. Start CATIA V5 and open a suitable part-design or surface-design workbench. The required STEP interface and available import options depend on the CATIA release and installed licenses.
2. Choose File → Open, select the .stp or .step file, and apply the STEP import settings provided by that release.
3. Inspect the resulting specification tree. Confirm that the expected bodies or components were imported, then check units, orientation, colors, assembly placement, and the presence of missing or unwanted geometry.
4. Run CATIA’s available geometry-validation and healing tools. Check for open shells, gaps, invalid faces, self-intersections, and tolerance problems before using the model for downstream design or manufacturing operations.
5. For a single imported part, choose File → Save As, select the CATPart document type, and save a name such as bracket.CATPart.
6. Close and reopen the saved file. Verify that it loads correctly, that no required external references are missing, and that the measured dimensions still match the source STEP file.

A STEP assembly may import as an assembly structure rather than as one CATPart. Preserve it in the CATIA assembly workflow, typically as a CATProduct with component CATParts, or save individual imported components as CATPart files. Do not combine an assembly into one part unless the receiving workflow specifically requires that result.

For repeated jobs, CATIA V5 macros or an enterprise translation pipeline can automate opening STEP files and saving CATPart documents. Automation must account for the CATIA release, licenses, import settings, file naming, assembly structure, and failure reporting.

Online and alternative conversion options

Many consumer online converters translate STEP only to formats such as STL, OBJ, IGES, or PDF; those outputs are not CATPart documents. Use an online service only when it explicitly lists CATIA V5 CATPart export and identifies the supported CATIA release.

For confidential or production CAD, a CATIA V5 installation is preferable. For users without CATIA, use a reputable CAD translation bureau or a vendor-backed cloud translation service, confirm that it produces editable CATPart rather than a mesh, and test a representative file before sending a batch. Uploading supplier or proprietary geometry to an unknown website can expose design data and may leave files in provider storage.

Quality and compatibility limits

• STEP AP203 and AP214 are widely supported. AP242 can carry newer product, PMI, and metadata information, but the result depends on the CATIA release and translator configuration.
• Check the unit system after import. A unit interpretation error can make a model appear 25.4 or 0.03937 times the intended size.
• STEP transfers geometry and selected product data, not the original CATIA design history. Recreate parametric features when future design changes must remain associative.
• Small gaps, trimmed-surface defects, self-intersections, and different modeling tolerances can prevent a closed STEP shell from becoming a valid CATIA solid. Healing or remodeling may be required.
• Imported colors, layers, names, assembly constraints, annotations, and PMI can be incomplete or organized differently after translation.
• CATPart compatibility is release-dependent. A file saved by a newer CATIA V5 release may require a compatible release or conversion before another installation can open it.
• Keep the original .stp or .step file with the CATPart. It provides a neutral reference for auditing dimensions, repeating the translation, or recovering from an unsuccessful repair.