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. For more information on which data type to use for which activity, and details on how part complexity is defined, 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 features of the body. 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 in it. 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 by using the Quadrangulate Mesh block. The quad mesh allows for easier and faster conversion to a CAD Body format. 

  • A quad mesh is not just a step for converting, but also a very useful model itself. The mesh can be exported into other systems by using the Export Mesh block. 
  • If you encounter errors when converting to a Quad Mesh, check out this article. 


4. Optional: Use a Refine Mesh block to refine the Quad Mesh and capture further details and reduce the amount of 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 Mesh block (This block has been renamed to CAD Body from Quad Mesh in 3.17).



6. Export: Add an Export Part block and choose your save location and file type, either STEP or 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 have the freedom to import it into any program that accepts STEP or Parasolid inputs. The part can have further operations applied to it, be added back to a larger assembly, and more. 


Procedure 2:

For more complex models, 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 easily convert simpler structures to CAD format. Pair this block with the Export Part block to export the new CAD body to STEP or Parasolid format. 



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

Are you still having issues? Contact the support team, and we’ll be happy to help!

Download the Example file:

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  • Procedure 2 does not work.
    Example file fail.
    And CAD from implicit body bloc are not available anymore.
    this article should be updraded

  • True, that block is not available for usage

  • @Didier Guillon-Cottard
    I just tested the example file for procedure 2 and it opens just fine with no errors. The CAD Body from Implicit Body (Beta) block is still available. You may not be able to see it if you don't have beta blocks enabled in the settings.

    @Akshat Chaudhari
    As I told Didier, this block is still available. Please make sure to have beta blocks enabled.

  • The block is visisble thank you for letting me know about this, however it is not working for my boolean union body, it is leaving some parts out.

  • Thanks for this tutorial. Is it possible to preserve the implicit body face when converting to a cad body? I need the single face for the fluid input and output regions in ansys.


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