Conjugate heat transfer in a 3d printer

Hello there, i am trying to use the conjugate heat transfer simulation on an 3D printer.

I created a “flow region” inside and outside thanks to Simscale’s CAD mode”.

The build plate is at 200°C, the air inside is at 150°C and the air outside is at 20°C

I am trying to see the temperature on the edge of the 3D printer, the steel’s faces.

I don’t understand what is wrong or how to solve the error that I am witnessing.

Can somebody help me ?

Here is a link to my project :

Hi there :slight_smile: This is probably because some faces belong to more than one region (as they are in contact).
Maybe you can create your external flow volume in a way that it is not touching the edge of the 3D printer?

If anyone else has a suggestion, feel free to contribute :slight_smile:

Best regards,


I noticed that you already have some successful simulations in the project, so I believe you were able to spot the problem in the meantime.

In any case, the issue here is with the wall 2 & wall 3 boundary conditions, which have been defined to interfaces:

This is not allowed, since it overconstrains the system. For more notes, please check the first “Important” box in this documentation page: Contacts & Interfaces in Solid Mechanics and CHT | SimScale



Thank you for your help, i was able to run the simulation but, i have another problem.

I think that i didn’t choose the right boundaries, you see i calculated that I should have a temperature of at least 149°C (422°K) at the edge of the steel’s faces, but when I look at the results it shows 85°C (358°K) for the hottest part.

I try to turn of the boundaries of 20°C on the outside flow region that is surrounding the printer and adding a natural convection of 150°C to the flow region inside but when I try to launch the simulation I have this error.

I tried to do it with only one face but the end is the same.

What kind of boundaries should I use?


I noticed that you are currently running the case as a transient simulation. Is this a requirement for your analysis? Or would you be interested in the equilibrium state of the system?

Furthermore, as the documentation page that I linked states, defining a boundary condition to an interface (i.e. the interface between two volumes) overconstrains the system and causes the error that you are facing.

In short, the only faces that can receive a boundary condition are the boundaries of your geometry (i.e. the 6 external bounding box faces of your flow region). The other faces cannot receive a boundary condition.

I’d suggest that you go through the LED natural convection cooling tutorial, which should provide you good insights with respect to the set up.



Thank you for such a great article, it really helped me to fix my printer.

Thank you!