Meshing a fused geometry in FreeCAD for complex models.

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Fused Mesh in FreeCAD FEM Workbench
Fused Mesh in FreeCAD FEM Workbench

Some times we need to create two objects separately but in the end fuse them together to make the final FEM mesh, or imagine that you need to place boundaries on very specific places on your solid that require some kind of section. Here I got into some problems with FreeCAD to understand how to make it work. In this article I will share the configuration that worked for me to be able to split the geometry in multiple bodies that can have different materials and boundaries but have all a common single grid. What I will not be approaching in this article is contacts between multiple seperate bodies.

  1. TOOLS USED
  2. PROCEDURE
  3. FINAL COMMENTS

1. TOOLS USED

For this article I used FreeCAD with the FEM workbench (Calculix and Gmsh). The solver was Calculix and meshing with Gmsh. 

2. PROCEDURE

To start I created as a geometry two cubes staked on top of each other. The top cube was bigger than the bottom cube. For this I created two sketches. There are many ways to create the two volumes from here. I used the Part workbench and the sketch workbench to create the geometries. Each sketch was extruded by the Extrude button in the Part Workbench. The key to bind different bodies is to use in the part workbench “Make a compound of several shapes” button. If you create a mesh at this stage the grid between the two bodies won’t be connected. To have then connected additional in the Part workbench you will need to select the “Fuse Objects” button. After this you will have a connected grid and can check by seeing if the mesh of the two bodies are coincident on the touching zones.

For a short movie please refer here:

I tested the generated and specifically placed a boundary connection displacement between the two bodies. As demonstrated bellow it is possible to have multiple bodies split as if only one part exists. 

3. FINAL COMMENTS

The ability to split complex bodies can help create boundaries, define materials or mesh in more detail as commercial software like Ansys with Spaceclaim or Designmodeler allow. Calculix and the FreeCAD FEM workbench integration worked great.