Imported geometry from other CAD packages, especially ones built on a different kernel than Onshape, sometimes imports with errors denoted by both the Import feature and the part in the Parts list showing in red.
This is a common occurrence in any type of CAD import scenario and is not unique to Onshape. This Tech Tip focuses on how to repair these models.
Import File Type
First, you should always try to get a Parasolid model for import if at all possible. Parasolid is built on the same kernel as Onshape, so you are least likely to have errors when importing models in this format.
Next, you should check the model for anything that would be considered invalid in Onshape. One of the most obvious things would be non-manifold edges or vertices. In imported CAD, this frequently manifests itself as two parts of a solid only intersecting at a vertex or an entire edge as shown here:
Be sure to check for surfaces that are passing through each other. When surfaces do not share an edge, the intersection between them will not have a black edge line.
Additionally, check for any open surfaces. Under the View cube, there is an option to highlight boundary edges. With it on, any open surface edges will highlight in red.
Additional Analysis with IGES Import
Sometimes, the source of the issue is not obvious. To help troubleshoot further, export to IGES and then import again. The IGES type imports as a series of surfaces when it cannot import as a valid body.
Use Boolean to start combining surfaces. You can select them either from the Surfaces list or graphically. When the surfaces selected are connected, they automatically combine, reducing the number of surfaces in the list.
Once you select a surface that causes invalid geometry, some or all of the combined surfaces will reappear in the Surfaces list and invalid edges will highlight in red in the graphics view.
Correcting Invalid Geometry
To correct the issues in all of these scenarios, you will likely need to delete the faces causing the invalid geometry. Select the Delete Face command and delete all the invalid faces. Choose the Leave Open option as shown below.
Use Surfacing tools to close the gaps and create valid geometry. For invalid imports, the Import feature will always show red, but your model is repaired when the part no longer shows red in the Parts list.
For surface imports (such as IGES), the model is repaired when the surfaces have been combined into a part.
All import repairs will involve some surfacing. Check out our Tech Briefing on Surfacing Tips and Best Practices for an in-depth look at all of Onshape’s surfacing tools.
Interested in learning more Onshape Tech Tips? You can review the most recent technical blogs here.