First, a pattern is made from polystyrene foam, which can be done by many different ways.
For small volume runs the pattern can be hand cut or machined from a solid block of foam,or a sheet of foam core board if the geometry is simple enough it can even be cut using a hot-wire foam cutter.
If the volume is large, then the pattern can be mass-produced by a process similar to injection molding.
Pre-expanded beads of polystyrene are injected into a preheated aluminum mold at low pressure.
Steam is then applied to the polystyrene which causes it to expand more to fill the die.
The final pattern is approximately 97.5% air and 2.5% polystyrene.
Pre-made pouring basins, runners, and risers can be hot glued to the pattern to finish it.
The foam pattern does not need to be coated with investment if high detail is not needed, simply putting the foam pattern in a box,
filling with sand and vibrating will do. However, when detail is needed, the foam cluster is coated with ceramic investment,
also known as the refractory coating, via dipping, brushing, spraying or flow coating.
After the coating dries, the cluster is placed into a flask and backed up with un-bonded sand which is compacted using a vibration table.
The refractory coating captures all of the detail in the foam model and creates a barrier between the smooth foam surface and the coarse sand surface.
Secondly it controls permeability, which allows the gas created by the vaporized foam pattern to escape through the coating and into the sand.
Controlling permeability is a crucial step to avoid sand erosion.
Finally, it forms a barrier so that molten metal does not penetrate or cause sand erosion during pouring.
Once the sand is compacted, the mold is ready to be poured. Automatic pouring is commonly used in LFC,
as the pouring process is significantly more critical than in conventional foundry practice.
There is no bake-out phase, as for lost-wax.
The melt is poured directly into the foam-filled mold, burning out the foam as it pours.
As the foam is of low density, the waste gas produced by this is relatively small and can escape through mold permeability, as for the usual outgassing control.