Overview#
Shape Optimization takes a solid build-volume or approximation of a part and removes material where it contributes least to stiffness. Autodesk describes the result as a 3D mesh that guides your design refinement. You do not choose a stress or displacement limit: the default global objectives maximize stiffness while reducing mass as much as possible, with a Target Mass (default Auto) and optional global constraints (Preserve Regions, Symmetry Planes and Min Member Size). Autodesk stresses that the results do not reflect the stress created by the loads, so you must validate the new design with a Static Stress or other stress study.
How it differs from Generative Design: shape optimization works inside a simulation study on a target body, supports load cases, and returns one mesh per solve. Generative Design has its own workspace with design spaces, obstacle geometry, manufacturing methods and many outcomes (see the generative pages). Shape optimization is the simpler study.
Licensing: Shape Optimization is a basic study that costs 3 tokens per solve, or is covered by the Fusion Simulation Extension (only Linear Static Stress cloud solves are covered by the subscription). The Solve dialog shows the live cost. Personal-use availability is not stated in the Simulation help.
Where to find it#
- Simulation workspace > Setup tab > Study panel > New Simulation Study, then select Shape Optimization.
- A Shape Optimization panel on the Setup tab holds Preserve Region, Symmetry Plane and Shape Optimization Criteria. Defined items appear in the browser under the Shape Optimization Settings node.
- Settings (Manage > Settings): Name, Remove Rigid Body Modes and Shape Optimization iteration tolerance (default 0.005).
- Results: the optimized shape plus the Load Path Criticality result; Autodesk offers Promote Mesh to bring the shape into the Design workspace as a mesh body.
Step by step#
- Prepare the build volume. Create a body larger than the final part that includes the required constraint and load contact points. Select the target body for the study.
- Create a Shape Optimization study. You may adjust study and mesh settings in the New Study dialog.
- Assign materials, apply constraints and structural loads as for a static stress study. Shape optimization supports multiple load cases.
- Create Preserve Regions where material must remain intact (bolt holes, connection locations). The region types are Box, Cylinder and Sphere. Every entity that has a load or constraint is preserved by default (the Preserve Entities with Loads and Constraints check box).
- Open Shape Optimization Criteria. Leave Target Mass at Auto (Autodesk says Auto reduces the chance of slender members, disconnected geometry or a solve failure) or enter a specific value; the Stiffness objective is fixed and not editable. Add a Min Member Size if manufacturing needs a minimum thickness, and optionally a Symmetry Plane.
- Check the mesh. Autodesk says shape optimization results are highly mesh dependent and encourages a mesh sensitivity study.
- Run Pre-check and Solve (cloud solve, 3 tokens without the extension).
- Review the optimized shape and the Load Path Criticality result.
- Export the optimized mesh or use Promote Mesh to place it in the Design workspace as a reference mesh body overlaid on the original design.
- Modify the CAD model by hand using the mesh as a template, remove unnecessary material, then clone the shape optimization study and change the study type to Static Stress, Nonlinear Static Stress or another structural study. Cloning brings the loads and constraints with it.
- Review stress, displacement and safety factor on the modified design. Never skip this step.
Options reference#
| Option | What it does | Notes/default |
|---|---|---|
| Target Mass | Upper limit on the mass of the non-preserved part of the target body (expression is less than or equal) | Default Auto; too low a manual value can make the optimization fail; Autodesk says a fine mesh should reach the target within about 3 to 5 % |
| Stiffness objective | Maximizes stiffness for the given loads and constraints | Not editable |
| Preserve Region | Keeps material intact inside a Box, Cylinder or Sphere | Can be shown, isolated, suppressed, deleted, copied to another study |
| Preserve Entities with Loads and Constraints | Preserves loaded and constrained entities | On by default |
| Symmetry Plane | Forces symmetry about a plane | Up to three mutually perpendicular planes based on one model face, through the body centroid |
| Min Member Size | Lower limit on member thickness | Cannot be less than the minimum mesh element size; Autodesk recommends at least 2 to 3 times the mesh size |
| Iteration tolerance | Allowed shape change between iterations | Default 0.005; smaller is more accurate and slower |
| Load Path Criticality | Result showing how critical regions are to the load path | Contour on the legend bar |
Tips and pitfalls#
Warning: Autodesk states the result does not reflect the stress created by the loads. Always revalidate with a stress study.
Tip: Include every realistic load case. General guidance: an optimizer removes material that no load case needs, leaving the part weak against an unmodelled load.
Tip: General guidance: leave extra stock around preserve regions so the optimizer can build smooth load paths into them.
Warning: The result is a mesh body that Autodesk says serves as a guide or template. Plan for a remodel step in the Design workspace.
Tip: If the shape barely changes or the solve fails, check the Target Mass and Min Member Size against the mesh size, and keep the target at Auto unless you have a reason.
Warning: Each solve costs 3 tokens without the extension. Check the Solve dialog first; failed jobs are refunded.
Practice exercise#
Create a 120 x 60 x 20 mm block (illustrative size) with two 10 mm holes at one end and a 10 mm hole at the other. Create cylinder Preserve Regions around the holes. Fix the two-hole end, apply 500 N down on the single-hole end. Run Shape Optimization with Target Mass at Auto. Expected result: a shape with material concentrated along the load paths. Remodel it, and run a static stress study on the final geometry to verify the safety factor.
Worked example: lightening a bracket#
All numbers are illustrative assumptions, not Fusion output. A steel bracket envelope of 120 x 60 x 20 mm has a volume of 144 cm^3; at a typical steel density of 7.85 g/cm^3 it weighs about 1.13 kg before holes. The load is 500 N at the free end, which has a single 10 mm hole, with two 10 mm holes on the fixed end.
- Baseline: run a static stress study on the full block. Displacement is tiny and stress is far below yield, showing how overbuilt a solid block is.
- Shape optimization: preserve the hole regions, leave Target Mass at Auto, set a Min Member Size of 3 mm with a 1 mm absolute mesh (Autodesk's own example pairing).
- Result: expect material concentrated along the load paths. If you instead type a Target Mass that is too low, the optimization may fail.
- Remodel: use the promoted mesh body as a template, build a simplified tapered web with fillets, clone the study to Static Stress and check safety factor against your own target (the default thresholds are 2.0 and 4.0).
Choosing criteria#
| Need | Setting |
|---|---|
| Let Fusion pick a sensible mass reduction | Target Mass Auto |
| Hit a specific mass | Specific Target Mass; keep it above what the preserved entities require |
| Avoid thin members for manufacturing | Min Member Size of at least 2 to 3 times the mesh size |
| Symmetric result from a symmetric problem | One to three Symmetry Planes |
| Keep bolt holes and interfaces | Preserve Regions (Box, Cylinder, Sphere) and the default Preserve Entities option |
Because the study maximizes stiffness for a mass, there is no stress constraint to set. Check stress afterwards in the cloned static stress study.
Mass target sweep#
If you want to explore trade-offs, run the same study at several specific Target Mass values and compare displacement in follow-up static stress studies. Autodesk gives no sample numbers; expect diminishing returns as the target falls (general behavior), and note each run costs 3 tokens without the extension. Stop where the displacement or stress in the validation study starts to rise sharply.
Manufacturing intent#
Pure topology results are organic and expensive to machine. The Min Member Size constraint is Autodesk's built-in way to account for a minimum thickness; Autodesk's example is a 3 mm minimum member with a 1 mm mesh. For CNC machining or printing, remodel the mesh into a manufacturable shape. Specific web thicknesses, corner radii or overhang angles depend on your process and are not given in Autodesk's shape optimization help; for manufacturing-constrained outcomes use the Generative Design workspace, which has manufacturing methods.
Converting and remodeling the result#
- Export the optimized mesh, or use Promote Mesh to put it in the Design workspace as a reference mesh body.
- Use it as a template: overlay it on the original design and remove material from the indicated areas.
- Rebuild the preserved features (holes, bosses) as exact geometry.
- General practice: add fillets where webs meet bosses to reduce peak stress.
- Clone the study to a Static Stress (or other) study and re-run, adding any load cases not modelled earlier.
Failure modes and fixes#
| Symptom | Cause | Fix |
|---|---|---|
| Result is almost the original block | Preserve regions or loaded entities cover most of the body | Shrink preserve regions; check Preserve Entities |
| Result disconnected from a load | Preserve Entities option turned off | Keep loaded and constrained entities preserved |
| Very thin members | Target mass too low or no Min Member Size | Use Auto, raise the target or add Min Member Size |
| Asymmetric result for symmetric problem | No symmetry plane set | Add a Symmetry Plane |
| Solve fails | Min Member Size below the element size, or target mass unreachable | Check Min Member Size against the mesh size; raise the target |
| Revalidation shows low safety factor | Smoothing hid stress peaks; load cases missing | Add fillets and load cases |
Practice exercise#
Run a mass-target sweep and revalidate.
- Build the 120 x 60 x 20 mm block with three 10 mm holes and a 500 N load.
- Run static stress on the solid and record mass, displacement and peak stress.
- Run shape optimization with Auto and with two specific Target Mass values (for example 60 and 40 percent of the original mass) and the same preserved regions; record the resulting mass of each.
- Choose a result, remodel by hand with a tapered web, clone the study to static stress and record the safety factor.
- Compute the mass saved and the stiffness-to-mass ratio (force per displacement per kg) for the solid and the final design.
Related#
- Static Stress Study
- Loads and Constraints
- Generative Design Workspace
- Cloud Solve and Credits