Issues with CAD File Import using Interchange in Unreal Engine 5.5

Development Pipeline & Plugins
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1

Hello,

I am setting up a pipeline to process CAD files using Interchange in Unreal Engine 5.5. However, I am encountering several issues with different file types:

  1. Wire Files
    When importing .wire files via Interchange (either “Import into Level” or into the Content Browser), DataPrepAsset, or Datasmith Import into the Scene (with CADKernel enabled or disabled), I get the following error:

Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x0000000000000098

libalias_api
libalias_api
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UnrealEditor_WireInterface2025_0
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This issue does not occur in 5.4 when using Datasmith Import, but Interchange doesn’t seem to support .wire files in 5.4 either. Additionally, the CAD Cache is not used with Interchange in 5.4.

  1. STEP and 3DXML Files
    When using Interchange Import into Level, these files result in Static Mesh Actors being created but no Static Mesh Assets in the Content Browser.
    Direct import into the Content Browser works, but no import dialog appears, and the CAD Cache is not linked to these assets.

  2. CATProduct/CATPart Files
    Importing these files via Interchange Import into Level works well, but there is no reimport dialog to modify the import parameters afterward even though right click, reimport, works well.
    When attempting to import a large CATProduct file (~866,000 Actors) via Interchange Import into Level, the editor becomes unresponsive even after waiting a long time.
    Using DataPrepAsset with this file also crashes after some time. The only method that works is importing directly via Datasmith Import into the Level, but this does not allow for automating data processing beforehand.

  3. IGS Files
    Although I do not work with .igs files often, I tested them via Interchange and encountered errors when importing into the Content Browser.

Are these known issues with Interchange in Unreal Engine 5.5? Are there workarounds or fixes available to address these problems?

Thank you for your support!

1 Like
2

Hello @PiouPiouValum

  1. The wire crash is worrisome, by any change can you share it with me in DM or I can send you a box link. Is it a file from Alias 2025?

At the moment Interchange CAD is still experimental, more work is necessary to stabilize it.
For the moment if you are in production or if Interchange CAD fails you should use the Datasmith import.

Thank you for reporting the different issues, I will make sure we have corresponding tickets in our tracking system for those.
What were the errors around IGS imports?

3

Hello @UE_FlavienP

Unfortunately, I am under NDA, so I cannot share any files with you.

Wire File Issues

I have Alias 2025 installed, but if I am correct, the original .wire file is from Alias 2023.
I have always experienced some issues with .wire files, even in previous versions of Unreal. Specifically:

  • Some parts had tessellation issues, leading to visible holes in the mesh.
  • Enabling or disabling the CAD Kernel made no difference.

This morning, I attempted to import a .wire file using Dataprep (or Datasmith Import from Level) and encountered the following error:

Assertion failed: IsValid() [File:D:\build++UE5\Sync\Engine\Source\Runtime\Core\Public\Templates\SharedPointer.h] [Line: 1113]

UnrealEditor_CADKernel
UnrealEditor_CADKernel
UnrealEditor_DatasmithWireTranslator2023_1
UnrealEditor_DatasmithWireTranslator2023_1
UnrealEditor_DatasmithWireTranslator2023_1
UnrealEditor_DatasmithWireTranslator2023_1
UnrealEditor_DatasmithWireTranslator2023_1
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kernel32
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IGS File Crash

I am also retrying the .igs import process to reproduce the crash that occurred earlier with Unreal.

CATProduct Large File Handling

Do you have any recommendations for importing a CATProduct file containing over 866,000 actors using DataPrep without splitting the file into multiple parts? So far, the only successful method is importing directly into the level via Datasmith, but this doesn’t allow for any pre-import processing.

This is the error I encounter when importing this file using DataPrep:

Fatal error: [File:D:\build++UE5\Sync\Engine\Source\Runtime\Core\Private\Containers\ContainerHelpers.cpp] [Line: 8]
Trying to resize TArray to an invalid size of 2147483665

UnrealEditor_Core
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Thank you for your assistance!

4

Hello,
UE uses a dll file in your Alias application to read the wire file.
The crash you see, in your second message, is that your 5.4 install is trying to use Alias 2025 and fails because of compatibility issue. The crash itself should be handled better but, anyway, in that situation your wire import would fail.

Now, what I see in your first message is that you also have a crash with UE 5.5. This is a bug we would like to fix but will be tricky as we did not reproduce it with our test files yet.

Regarding your 800K actors import, once interchange CAD is production ready you will have more options to simplify product tree on import. But even that might not be the solution if you still end with hundreds of thousands of actors. The solution of importing and processing several sub assemblies individually will always remain less taxing on the engine and computer ressources than your full catproduct.

5

Regarding 3DXML and Step import without assets, it would be useful if you have the log that goes with those imports if you could share them with us.

For the Dialog window on reimport, it is an option to toggle ion the editor preferences

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6

Hello @UE_FlavienP

Sorry for the late reply, I’ve had a busy few days.

Thank you for pointing out the Reimport setting—I had been looking only in the project settings for Interchange.

Regarding my crash with .wire files in 5.5, unfortunately, I am unable to share my .wire file due to confidentiality. However, if you could guide me on how to help you investigate this bug, I’d be happy to assist.

I will install the 2023 version of Alias to see if the import issues persist in Unreal 5.4.

I will also share the logs related to 3DXML and STEP files soon.

Thank you!