SOLIDWORKS 2024 added a little-known feature that allows saving an assembly as a multibody part file associatively. This enables powerful workflows for model simplification that can be useful for protecting intellectual property or preparing models for simulation or other downstream applications.

This article will outline the challenges associated with assembly model simplification, a “legacy” workflow for converting assemblies to multibody parts in older versions of SOLIDWORKS, and the enhancements in SOLIDWORKS 2024 and newer versions.

Challenges of Assembly Simplification

Perhaps the most common way to perform model simplification is to utilize SOLIDWORKS configurations; for instance, creating an FEA configuration of a part to be used for Finite Element Analysis and suppressing unnecessary features or details. This can work well for parts and assemblies that feature a relatively flat tree structure, but as the assembly depth (or number of nested subassemblies) increases, it can rapidly become impractical.

The example we’ll be looking at is preparing a 1-ton trailer for analysis. This is not a particularly complex model, weighing in at only around 200 components, but by selecting some components of interest the assembly breadcrumbs reveal a nested structure of six subassemblies.

Figure 1. Assembly structure of trailer.

This means that if we wanted to simplify just the highlighted part and still preserve our original assembly, we may have to create FEA configurations for the part itself as well as each of the six outer subassemblies. Performing many such edits rapidly becomes a problem of combinatorics.

There are times when this type of effort can be worthwhile, but there is a much easier method — particularly when you want to toss away more of the model than you want to keep. In this case for a first-pass structural analysis, there are probably only a couple dozen components that need to be kept.

Save as Multibody Part (Legacy Approach)

A quick and dirty method to perform extreme simplification has been available in SOLIDWORKS for a very long time: simply save the assembly as a SOLIDWORKS part file. It’s very important to pay attention to the “Geometry to save” sub-options here. The “Exterior faces” option may be good for extreme defeaturing or intellectual property protection purposes, but it will only export surface bodies. For finite element analysis or similar applications, we must choose the option “All Components” which will convert the assembly components into bodies in a multibody part.

Figure 2. Saving an assembly as a SOLIDWORKS part.

The downside of this approach is a major one — it is non-associative. With this workflow, we’re creating a distinct copy of the CAD model and any simplifications, geometry preparation or setup we perform from here will have to be repeated if the base model were to change.

Figure 3. Assembly saved as part.

Opening the saved part, we’re presented with a model that looks identical (appearances and all) except it contains 288 solid bodies rather than the hundreds of assembly components.

Now we can perform possibly the greatest model simplification trick in SOLIDWORKS: using the “Delete/Keep Bodies” command with the “Keep Bodies” option. I still remember when this option was introduced 10 years ago, and it continues to amaze me to this day.

Figure 4. Select what you want to keep, throw the rest away.

With this one operation, we’re left with a model simplified down to the bare essentials.

Figure 5. Model structure after Keep Body feature.

The “Delete/Keep Body” feature itself is still feature-based, so if you realize you forgot a component or some reference geometry, you can always edit it or roll up in the tree to see the full model again and extract what you need. I’ve done so here to extract some reference geometry that will be used for the simulation setup.

Now in a matter of minutes, I have a functional finite element model of the trailer.

Figure 6. Meshed model ready for analysis.

To reiterate a note of caution — with this workflow (reducing the assembly to a multibody part with the “Save as Part” method) this whole process is not associative. For this reason, it was a workflow I used to reserve for the most dire of cases. But today there’s a better way.

Converting Assemblies into Multibody Parts (2024+ Approach)

SOLIDWORKS 2024 added a feature called “Make Multibody Part” to the assembly environment (the details of which are covered in the SOLIDWORKS Help Files).

This approach enables a workflow largely identical to everything we ran through above, but associatively, which addresses the main downside that previously caused me to be hesitant to recommend this approach. It’s my go-to method now, with the only remaining caveat being that you’re okay with having a separate CAD file to represent your simplified model.

The “Make Multibody Part” command is available from the Tools pull-down menu or command search:

Figure 7. Make multibody part feature in Command Search.

In addition to bringing over solids (which it does by default) the user can opt to bring over additional items such as reference geometry and surface bodies. So long as you don’t click “Break link to original assembly,” it will maintain an associative connection.

Figure 8. Make multibody part property pane.

That’s really all there is to it — now we have a part file with 288 bodies (exactly like the “Save as Part” method) except we still have an external reference linking us to the source model.

Figure 9. Result of “Make Multibody Part” feature.

From here we could perform the same types of simplification using tools like Delete/Keep Body to simplify down to only the components we need, except any geometry preparation or further modifications we perform will update if the referenced assembly ever updates.

The multibody environment has many other benefits for geometry simplification as well, such as easy access to direct editing tools like the Delete Face and Move Face features. I’d highly recommend checking out the article Direct Editing in SOLIDWORKS to learn more about those powerful tools.

Correcting interferences can also be important for preparing a model for simulation, and another great benefit here is that since Interference Detection is available in Multibody parts as well (as of 2019 and newer versions of SOLIDWORKS), you aren’t really losing out on much functionality that would be relevant for model preparation.

Note also that there is no reason that the “Make Multibody Part” command has to be used from the top level assembly, either — it could conceivably be applied to subassemblies to make more lightweight representations of them to improve assembly performance, for instance.

Conclusion

Simplifying SOLIDWORKS assemblies down to multibody parts has always been an extremely powerful workflow, but due to its tendency to completely break associativity with the model it was a workflow I rarely recommended to users and only reserved for the most extreme cases myself.

Now that the “Make Multibody Part” feature allows reducing an assembly to a multibody part with an associative link, this has jumped up my tier list to become my go-to simplification tool for complex models!

From my testing so far, this feature is quite robust, and I haven’t run into any issues or unexpected behavior. I’m sure there are many more scenarios where it could prove useful beyond simplification for simulations or protection of intellectual property. I’d encourage you to give it a try!