Creo Simulate > Getting Started with Creo Simulate > Planning and Modeling Considerations > Building Part and Assemblies > Assembly Considerations
Assembly Considerations
Your model can consist of parts or assemblies. Modeling parts is simpler and faster than modeling assemblies. Modeling assemblies requires additional consideration of how the parts interact or interface with each other. Each case has certain limitations and advantages to consider. You should bear the following in mind as you work:
When you model assemblies, you are working with nonmoving entities. Regardless of the appearance or behavior of the assembly in real-world conditions, Structure and Thermal mode treat all assemblies as nonmoving.
All the parts in the assembly must use the same system of units. You must ensure that all dimensioning in your assembly is consistent. If you use a different system of units for some of the parts, the software automatically converts the part's units so that the units of measure are the same.
Up to the point when you run an analysis or study, your assembly is treated as a collection of individual parts. Thus, during the model development phase, you add modeling entities to parts, rather than to the assembly as a whole.
After you start a run, Creo Simulate merges the individual parts into a single, multivolume body, where individual parts are either connected or unconnected.
If you want Creo Simulate to treat your assembly as a set of shells, you must first define shells or shell pairs for each part in the assembly. You define shells and shell pairs on a part-by-part basis by accessing Creo Simulate after opening the individual parts.
After you have defined shells and shell pairs for each of your parts, you can work with the assembly as a whole. For more information on shells and shell pairs, see About Shells.
If you use midsurface compression for any parts in your assembly that are made up of shells or shells and solids, gaps can form in your model where the curves (edges) or surfaces (faces) are mated or have assembly constraints applied to them. Connections are created between these gaps so the parts deform together as if they are one entity.
If the components are "welded" or bonded together, you must model the components using bonded interfaces.
If the components are free to separate, you must model the assembly using contact interfaces.
Although Creo Simulate uses shell, surface region, beam, mass, and spring definitions from the individual parts that make up an assembly, it ignores any modeling entities and idealizations you added to the parts while working in part mode. Consequently, you need to assign new modeling entities and idealizations when you work with the assembly.
Creo Simulate disregards all beam section dimension and Creo Parametric parameters defined at the part level in assembly mode.
For assemblies, you cannot place loads or constraints on geometry that is merged during a run. If a portion of a merged surface is free, for example, two volumes that have mated surfaces, but one surface is larger than the other, you can create a surface region on the free area and then apply the load or constraint to that surface region.
Creo Simulate allows preprocessing of an assembly in an exploded view. You can mesh the model in the exploded view in FEM mode but not in the native mode. In native mode, the assembly is returned to the unexploded state when running an analysis or creating a mesh.
When you use family table instances in assemblies, note that any modeling entities you create are stored with the assembly rather than with the part.
In addition to opening full master representations of models, you can also open assemblies as simplified representations. The simplified representations can include lightweight representations like graphics, light graphics, geometry, symbolic, or boundary box representations. These representations are not included in simulation analyses and appear translucent in the model.
You can open and modify non-native parts and assemblies in Creo and assemble them as heterogeneous assemblies with mixed content. You can create simulation entities for these non-native heterogeneous assemblies, create and run analyses, and view results in Creo Simulate.