Convert SLDASM to STP in your application
3D InterOp is a CAD interoperability SDK that lets your software read SLDASM files and write STP, with exact B-Rep geometry carried across and nothing tessellated.
Spatial does not offer an online converter or a desktop conversion app. 3D InterOp is a component that software vendors embed in their own products.
- Reads SOLIDWORKS assembly · Writes STEP
- Exact geometry → exact geometry
- C++ / C# APIs
SLDASM to STP at a glance
Both formats store exact geometry, so the model stays exact. The differences are in the product data each one can carry.
| SOLIDWORKS assembly (source) | STEP (target) | |
|---|---|---|
| Full name | SOLIDWORKS Assembly | Standard for the Exchange of Product model data |
| Standard / owner | Dassault Systèmes SOLIDWORKS | ISO 10303 — AP203, AP214, AP242 |
| File extensions | .sldasm | .stp, .step |
| Geometry | Exact B-Rep (in the referenced parts) | Exact B-Rep |
| Assemblies / structure | Yes | Yes |
| PMI | Semantic (DimXpert) and graphical, SOLIDWORKS 2014 and later | Graphical and semantic (AP242) |
| 3D InterOp support | Read only | Read and write |
What's preserved, what changes
Here is what your application can expect to carry across from SOLIDWORKS assembly to STEP.
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Preserved
Exact geometrySolids and surfaces stay exact B-Rep. The model is never reduced to a triangle mesh.
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Preserved
Product structureThe SLDASM product structure is written to STP.
Why software vendors add SLDASM to STP conversion
Supplier and OEM exchange
STEP is the ISO standard most supply chains specify for exchanging 3D models. Writing it lets your users send data to partners on any CAD system.
Model-based definition
STEP AP242 can carry semantic PMI next to exact geometry, so your users can share models together with their manufacturing data.
Long-term archiving
As an ISO standard independent of any CAD vendor, STEP is widely used to archive product data.
Things to check before you ship
- Written STP versions: AP203, AP214 or AP242 (.stp, .step or .stpx).
- Semantic PMI in STEP AP242 needs a license in addition to the STEP writer.
- Supported SLDASM input: SOLIDWORKS 98 to 2026.
- Test PMI transfer end to end with real SLDASM files from your users.
- Validate a sample of translated files in the target system your users actually work with.
Working with Spatial was a real milestone for us: Thanks to the powerful 3DInterOp library, we were able to successfully bring our complex CAD-based solutions to the cloud while remaining flexible to meet individual customer requirements. For us, Spatial is not just a technology partner, but a true enabler of our product strategy.
Dr. Arno Michelis, Founder, Simus Systems
Read the Case StudyAbout the formats
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Source format
What is an SLDASM (.sldasm) file?
An SLDASM file is a SOLIDWORKS assembly. It defines how parts and sub-assemblies fit together and references the SLDPRT files that hold their geometry.
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Target format
What is a STEP (.stp) file?
STEP is the ISO 10303 standard for exchanging 3D product data between CAD systems. Its application protocols range from exact geometry (AP203, AP214) to full model-based definition with PMI (AP242).
Frequently asked questions
Yes. Both formats store exact B-Rep geometry, so the model is translated without being tessellated into triangles.
3D InterOp reads PMI from SLDASM, and semantic PMI can be written to STEP AP242 with the additional STEP AP242 license.
Yes. 3D InterOp reads the SLDASM product structure and writes it to STP.
The STEP writer supports AP203, AP214 and AP242, with AP214 as the default. Your application sets the version at export; semantic PMI is written to AP242 only.
Yes. If your application uses Parasolid, a Parasolid-based SOLIDWORKS reader is available.
3D InterOp reads SOLIDWORKS 98 to 2026.
No. 3D InterOp reads SLDASM but doesn’t write it. To send data back to SOLIDWORKS users, write a neutral format they can import, such as STEP.
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Building software that needs to convert SLDASM to STP?
3D InterOp is an SDK that lets your application read SOLIDWORKS assembly and write STEP alongside 30+ CAD and BIM formats.