Objective:
Learn how to export nTop models to CAx systems.
Applies to:
- nTop 3.28
Solution:
There are different pathways for you to export your geometry out of nTop, you can choose the pathway based on your activity and part complexity from the table below:
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Activity |
Part Complexity |
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Top Opt parts, Unfilled Shells |
Graph Lattices with < 10k beams TPMS Lattices with < 1k cells |
Graph Lattices with > 10k beams TPMS Lattices with > 1k cells |
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N/A (in lattice region) |
N/A (in lattice region) |
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N/A (in lattice region) |
N/A (in lattice region) |
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CAD (native CAD format) |
CAD (native CAD format) |
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CAD (native CAD format) |
CAD (native CAD format) |
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Part Complexity:
In this context, complexity refers to the number of faces in the CAD Body. This determines the usability of the model within traditional CAD systems.
Low
- Parts that are generated from Topology Optimization, unfilled shells, and parts with very coarse patterns or ribs. These usually have a few hundred to a few thousand faces.
Medium
- These are parts with medium-coarse textured models or lattices containing beams, faces, or TPMS cells:
- Beam or face-based lattices: up to 10k beams or faces
- TPMS: up to 1k unit cells
- Implicit models at this level of complexity can be converted into CAD Bodies with 50k or fewer faces, so their detailed geometry can be consumed by traditional CAD systems.
High
- These are parts with fine-grain textures, beam or face-based lattices with over 10k beams or faces, or TPMS lattices with over 1k unit cells. Typically these have many thousands or even millions of faces, so their detailed geometry can not be consumed by traditional CAD systems.
Activities:
Visualization
- The 3D Model is visualized, usually in the context of the product(s) in which it is used, to judge aesthetics, fit, and accessibility. The target system might be a rendering app like Keyshot, rather than a CAD system. nTop has Precision Render that can be used to save High Resolution renders as images.
Clearances
- Checking that required clearances are present between parts. In particular, checking that parts do not interfere. Rough clearance checks can be performed with mesh models, but accurate interference checking requires CAD models.
Weight studies
- The most common study is a “weight roll-up”, which just involves adding up the weights of the individual parts in an assembly. To perform balance studies of parts we would need the center of mass of each part. In the case of rotating parts, moments of inertia are also important.
Assemblies
- Incorporating the part into an assembly, and defining mating relationships and joints. This requires analytic curves and surfaces, mostly circles, planes, and cylinders.
Part additions
- Adding further geometry to the nTop part, such as bosses, holes, and fillets.
Part mods
- Editing operations that modify the shape of the nTop part.
Drawings
- Producing engineering drawings and other types of illustrations. Generating dimensions on engineering drawings requires analytic geometry.
FE modeling
- Generating finite element models (i.e. meshes with special properties)
Complex CAM
- Surface milling using 3-axis or 5-axis motions.
Archiving
- Saving models for future re-use or for legislative/compliance reasons. Usually, the file formats are either STEP or native CAD formats. At many companies, CAD files in the corporate PDM system are the official repository of all product data.
Delivery
- Delivery of models to satisfy some contractual commitment. Usually, the file formats are either STEP or native CAD formats.
Data Transfer Paths
As outlined below, nTop can transfer geometry to CAx systems in many ways.
Tri Meshes
Meshes of triangles, such as STL or 3MF files. The STL format is helpful because a wide variety of systems support it. However, its design leaves much to be desired, and 3MF meshes are preferable in situations where they are supported. Triangle meshes are the natural format for visualization and many digital mockup studies, such as clearance analysis, weight roll-ups, etc. Very fine triangle meshes can also be used for NC milling, though this is not ideal. These articles have detailed instructions on generating meshes.
Quad Meshes
Meshes of quadrilaterals (4-sided shapes). These are usually in the OBJ format. These are useful because some CAD systems interpret them as the "cages" of subdivision surfaces upon import. The CAD system can then edit the subdivision surfaces to refine their shape. Examples of this capability are the NX "Realize Shape" module, Catia Imagine & Shape, and Creo Freestyle. This article has detailed instructions on generating a quad mesh.
CAD (B-rep)
Triangle and quad meshes are just special kinds of boundary representations. Still, we're talking about the boundary representation here, the classical ones with curved surfaces, as typically used in CAD systems. It is worth noting that some CAD systems (especially NX, SolidWorks, and others based on Parasolid) treat triangle meshes more-or-less the same as classical curvy b-reps. So, when communicating with these systems, the extra step of producing a classical b-rep may not be necessary.
There are two ways to produce a b-rep in nTop, and your model complexity will determine which approach you should take:
Low
For low complexity models, use the approach described here. 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 pretty simple models, such as those produced by topology optimization.
Medium
For more complex models, we recommend the method described here. It makes NURBS surfaces that are not necessarily nicely arranged, but the output is G1, tangent continuous.
Simplified Bodies
Lattice or texture designs with millions of faces are too complex to be consumed by traditional CAx systems. In case of any downstream CAx functions requiring the mass properties of implicit designs, nTop has a block for exporting the simplified body of implicits. This simplification includes an envelope shape that can be used in clearance analyses. We also export a collection of smaller bodies whose densities are chosen to produce the correct weight, the center of gravity, and the moment of inertia results in CAD system calculations. For information about creating simplified bodies in nTop, please see here.