How to export geometry as a CAD part (STEP or Parasolid)


Convert a Topology Optimized part into a CAD format and export it to a CAD program.  

Convert an implicit model into a CAD format and export it to a CAD program.  

Applies to:

  • Export to CATIA
  • Export to ANSYS
  • Export to PTC Creo
  • Export to Siemens NX
  • Export to Solidworks


There are two ways to produce a b-rep in nTop. Your model complexity determines which of the procedures below to use. If you have a low-complexity model, such as a part generated from Topology Optimization, unfilled shells, or parts with very coarse patterns or ribs, use Procedure 1. For lattices and other medium-complex parts, use Procedure 2. Note that depending on your use case for exporting your models to your CAD system, other data types, such as a quad or tri mesh or a simplified representation, may be sufficient. If you would like more information on which data type to use for which activity and how part complexity is defined, please read this article.

Procedure 1:

Procedure 1 is targeted at low-complexity models. The result is a b-rep in which the NURBS are nicely aligned with the body's features. This typically produces fewer faces and makes the b-rep model easier to edit in a CAD system. However, this approach only works reliably on fairly simple models, such as those produced by topology optimization. If your model is more complex, see Procedure 2. 


1. Convert to a Mesh: Convert your topology-optimized part to a mesh. 

2. Refine Mesh: Refine your mesh by using Remesh Surface, Simplify by Threshold, Simplify by Amount, or other simplification methods. This step allows for easier conversion to a quad mesh. Make sure your mesh has no meshing errors. Take a look at these articles for tips on refining and creating a mesh: 

3. Quad Mesh: Convert the refined Mesh to a quad mesh using the Quadrangulate Mesh block. The quad mesh allows easier and faster conversion to a CAD Body format. 

  • A quad mesh is a very useful model and a step for converting. The mesh can be exported into other systems using the Export Mesh block. 
  • Check out this article if you encounter errors when converting to a Quad Mesh. 


4. Optional: Use a Refine Mesh block to refine the Quad Mesh, capture further details, and reduce rounding near sharp edges.


5. Convert to CAD: Convert the refined (or un-refined) quad mesh into a CAD Body using the CAD Body from Quad Mesh block.


6. Export: Add an Export Part block and choose your save location and file type, *.STEP or *.x_t (Parasolid). If you are exporting to SolidWorks or Siemens NX, we recommend using the Parasolid format so that no translations are needed. 

Once your part is exported, you can import it into any program that accepts STEP or Parasolid inputs. The part can have further operations applied, added to a larger assembly, and more. 


Procedure 2:

For more complex models that have lattice structures in them, we recommend the approach described below. It produces NURBS surfaces that are not necessarily nicely arranged, but it’s much more likely to work on complex models.


1. CAD Body from Implicit Body (Beta): Use this block to convert simpler structures to CAD format easily. You can then export the generated CAD body to STEP or Parasolid format using the Export Part block. 

Note: The optional Preserved CAD input lets you provide a list of CAD Bodies, and the block will attempt to sew in faces from the CAD Bodies into the final result. If the face extends outside the implicit boundary, or if the algorithm doesn’t succeed in sewing, the face will be ignored.


And that’s it! You’ve successfully exported your part in a CAD format

Do you still need help? Contact the support team, and we’ll be happy to help!

Download the Example file:

More on this topic:


 cad lattice part export body parasolid step geometry preserved 
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