What is an SLDASM file?
SLDASM is one of the three main SOLIDWORKS file formats, alongside SLDPRT for parts and SLDDRW for drawings. An SLDASM file records which components make up a product, how they are placed relative to one another through mates, and properties such as color, visibility and suppression for each instance.
Most SLDASM files reference external SLDPRT and SLDASM files rather than embedding their geometry, so the whole set of files is needed to open the complete product. Since SOLIDWORKS 2020, assemblies can also contain components imported from other formats and stored inside the assembly file itself.
What data does an SLDASM file contain?
| Data | Description |
| Assembly structure | Component instances, sub-assemblies and virtual components stored inside the assembly |
| Mates and placement | Relationships and transforms that position each component |
| Configurations | Several variants of the same assembly in one file, with their own suppressed components and properties |
| Instance properties | Names, color, transparency, hidden and suppressed states |
| Metadata | Summary properties, custom properties, configuration-specific properties and units |
| Annotations | PMI, including DimXpert dimensions and tolerances |
What Is SLDASM Used For? Applications and Industry Use Cases
SOLIDWORKS is one of the most widely used mechanical CAD systems, so SLDASM files circulate throughout industrial machinery, consumer products, medical devices, tooling and many other sectors. Engineering teams, suppliers and manufacturing partners exchange them to share complete products, and multi-CAD projects often mix SOLIDWORKS assemblies with data from other systems such as CATIA.
For software developers, reading SLDASM files lets CAM, CAE, additive manufacturing, metrology, robotics and visualization applications open a whole SOLIDWORKS product, not just individual parts, and work with it outside SOLIDWORKS. Configurations, instance properties and metadata help these applications reproduce the product exactly as the designer intended.
Challenges or Common Pitfalls
Like other assembly formats, SLDASM depends on its referenced files. Missing parts, or sub-assemblies edited without rebuilding and saving the parent assembly, lead to incomplete or outdated results. Configurations add another layer of complexity: parts re-saved in a newer version may not contain geometry for their inactive configurations until each one is activated and saved again.
Some SOLIDWORKS features have no direct equivalent outside the application. SpeedPak configurations, assembly features and assembly-level sketches are typical examples, and neutral files imported into SOLIDWORKS and saved as SLDASM can also cause problems unless their links are broken and the file saved again.
Color can also differ from what users expect when the same sub-assembly is used several times with different appearances, or when color is set on the root assembly itself.
How Spatial Helps
Our 3D InterOp SDK reads SLDASM assemblies and their referenced parts, from SOLIDWORKS 98 to recent releases, with a choice between a direct translator and a Parasolid-based translator. The assembly can be kept as a hierarchy or flattened, depending on the target, and written to 3D ACIS Modeler, Parasolid or an XML E-BOM.
3D InterOp imports exact B-rep geometry, including analytic, B-spline, offset, spun and swept surfaces, along with instances, sub-assemblies, virtual components and components stored in sub-folders. Configuration names, hidden and suppressed instances (on request), instance names, color and transparency, user-defined and configuration-specific attributes, units and part-level material properties are all available. Since Release 2026 1.0.1, summary properties such as author, title and keywords can be read as well.
For downstream manufacturing, 3D InterOp also reads DimXpert PMI, reference work planes and points, sketches and manufacturing features such as holes and patterns. For more on SOLIDWORKS annotations, see SOLIDWORKS model-based definition.