Convert STP to SLDASM

A supplier may provide a mechanical model as .stp or .step when the receiving company works in SolidWorks. Converting it to .sldasm is useful when the model must be opened as a SolidWorks assembly, combined with native components, checked, documented, or revised.

What the STP format is

.stp and .step are filename extensions for STEP files, an ISO 10303 exchange format used by mechanical CAD systems. STEP can contain precise boundary-representation geometry, assembly structure, component names, colors, and selected product metadata.

CATIA, Siemens NX, PTC Creo, Autodesk Inventor, Fusion, SolidWorks, suppliers, and manufacturing services commonly use STEP for purchased components, quotations, design reviews, and cross-system data exchange.

STEP is not a native SolidWorks design-history format. An import normally preserves geometry and, when supplied by the exporter, assembly placement and product structure; it does not recover the source sketches, parametric features, equations, mates, configurations, or feature-tree operations.

What the SLDASM format is

.sldasm is SolidWorks' native assembly format. It stores the assembly hierarchy and references external SolidWorks part files (.sldprt) and subassemblies, along with component positions, suppression and visibility states, display states, configurations, mates, and assembly-level data.

An .sldasm file is therefore usually not self-contained: its referenced .sldprt and subassembly files must remain available in the expected locations. A converted STEP assembly can be saved natively, but its imported components generally remain geometry without the original parametric history.

How to convert STP to SLDASM

SolidWorks Desktop is the most dependable option when the output must be a valid native SolidWorks assembly.

1. Copy the source .stp or .step file into a working folder. Use a dedicated output folder because an assembly import can create multiple referenced part files.
2. In SolidWorks, select File → Open, choose the STEP file type, and open the file. The exact STEP type labels and import options vary by SolidWorks release.
3. If the file contains an assembly, retain its product structure. Choose the import setting that creates separate part documents when available instead of combining all components into one multibody part.
4. Review the FeatureManager design tree and graphics area. Check component count, names, colors, orientation, and placement. For defective imported bodies, use Tools → Evaluate → Import Diagnostics where that command is available.
5. Review the 3D Interconnect setting. Keeping the external STEP reference can allow updates from the source file; disabling or breaking that link, when supported by the release and import type, creates a more independent SolidWorks dataset. Confirm the result before deleting or moving the STEP file.
6. Save the opened assembly with File → Save As, selecting SolidWorks Assembly (*.sldasm). Keep every generated .sldprt and subassembly file with it, or use SolidWorks reference-management tools when relocating the dataset.
7. Close and reopen the saved .sldasm. Resolve any missing references and verify critical interfaces, component positions, and assembly behavior.

If the STEP file contains one solid or one multibody part, SolidWorks normally opens it as a part, so saving directly as .sldasm is not the correct operation. Save it as .sldprt, then create a new assembly with File → New → Assembly and insert the part. For a multibody part that needs separate assembly components, use Save Bodies to create part files and then insert those parts into an assembly.

Other conversion options

Commercial translators such as Datakit CrossManager can convert STEP data for workflows that do not have SolidWorks installed, but native assembly output, component references, and supported SolidWorks versions must be confirmed in the current product documentation. CAD Exchanger Desktop or Cloud can be useful for inspecting or translating neutral CAD data, but do not assume that an online service exports a native .sldasm; verify that format explicitly before uploading a file.

Online conversion is unsuitable for confidential engineering data unless the service's security and retention terms are acceptable. Many browser converters output STEP, IGES, Parasolid, or mesh formats rather than .sldasm, and a service that claims native SolidWorks output may package references differently from SolidWorks Desktop.

Quality and compatibility limits

STEP transfers geometry, not the source SolidWorks feature history. Recreate mates, equations, configurations, design intent, and assembly constraints after conversion. Inspect holes, threads, thin walls, fillets, contact faces, moving joints, and other interfaces that affect manufacturing or motion.

AP203, AP214, and AP242 files differ in the product, appearance, and metadata they can carry. The actual result also depends on the exporting CAD system and the SolidWorks release; a newer STEP feature or entity may be ignored or imported imperfectly by an older release.

Large assemblies can take substantial time and memory to import and may create many external files. Preserve the complete referenced-file set, avoid changing filenames casually, and test the saved assembly on another workstation if it will be shared or archived.