For a 2.5D injection molding simulation a surface mesh is needed.
All surfaces of the chosen CAD model will be covered with triangle elements to build a closed mesh.
A surface mesh can be generated automatically with a CAD-System by exporting it as stl-file. This format is often used in rapid prototyping processes.
But the quality of such a mesh is not accurate enough for an injection molding simulation.
The mesh carries the geometry information and need to be optimized.
It is important to have a high amount of elements as well as to make sure that each element has a good aspect ratio.