Tips for importing CAD into Abaqus or similar FEM software

Frames:
1) Create geometry in AutoCAD or free alternatives (Draftsight, Nanocad,...). Explode entities if necesary to obtain only lines and save as Frames.DXF
2) Use gCAD3D (it is a free and open software http://www.gcad3d.org/), import Frames.DXF and save as Frames.IGS
3) Import parts as wires with Abaqus/CAE

Planar shells:
1) Create geometry in AutoCAD or similar. Explode entities if necesary to obtain only lines. Separate and save as Contour.DXF and Partitions.DXF
2) Import Contour.DXF as sketch in Abaqus/CAE
3) Create part form sketch called Contour
4) Tools> Partition>Face>Sketch and use the sketch called Partitions

3D Shells and solids:
1) Create regions (command REGION of AutoCAD) and solids in AutoCAD and export as SAT (ACIS) file
2) Import parts as shells and solids with Abaqus/CAE

The latest procedure also works for planar shells but it is less precise.