Macro MeshToPart

Description

This macro converts selected meshes to parts. It has a broad tolerance, so use it only with objects that have no curves otherwise you'll get errors or weird results

import FreeCAD,FreeCADGui,Mesh,Part,MeshPart
 
for obj in FreeCADGui.Selection.getSelection():
    if "Mesh" in obj.PropertiesList:
        faces = []      
        mesh = obj.Mesh
        segments = mesh.getPlanarSegments(0.01) # use rather strict tolerance here
 
        for i in segments:
          if len(i) > 0:
             # a segment can have inner holes
             wires = MeshPart.wireFromSegment(mesh, i)
             # we assume that the exterior boundary is that one with the biggest bounding box
             if len(wires) > 0:
                ext = None
                max_length = 0
                for i in wires:     
                   if i.BoundBox.DiagonalLength > max_length:
                      max_length = i.BoundBox.DiagonalLength
                      ext = i
                wires.remove(ext)
                # all interior wires mark a hole and must reverse their orientation, otherwise Part.Face fails
                for i in wires:
                   i.reverse()
                # make sure that the exterior wires comes as first in the lsit
                wires.insert(0, ext)
                faces.append(Part.Face(wires))
 
        shell=Part.Compound(faces)
        solid = Part.Solid(Part.Shell(faces))
        name = obj.Name
        FreeCAD.ActiveDocument.removeObject(name)
        FreeCAD.ActiveDocument.addObject("Part::Feature",name).Shape = solid 

Link

The discussion on the forum Convert mesh to solid?