Lost foam casting is a type of evaporative-pattern casting processes are similar to investment casting but foam is used for the center wax pattern. This process takes advantage of the low boiling point of foam to the investment casting process be simplified by eliminating the need to melt the wax out of the mold.
First, a pattern is made of polystyrene foam, which can be done through many different channels. For small volume runs the pattern can be cut manually or machined from a solid block of foam; if the geometry is simple enough that it can even cut using hot-wire foam cutter. If the number is large, then the pattern can be mass-produced by a process such as injection molding. Pre-expanded beads of polystyrene 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% and 2.5% polystyrene air. Can be pre-formed pouring basins, runners, and hot glued risers to complete the pattern.
Next, the cluster is investing ceramic coated foam, also known as the refractory coating, by dipping, brushing, spraying or flow coating. This coating creates a barrier between the surface and the surface smooth foam coarse sand. Secondly it controls permeability, allowing the gas created by the vaporized foam pattern to escape through the coating and into the sand. Control is a crucial step to avoid permeability sand erosion. Finally, it forms a barrier to prevent molten metal to penetrate or cause sand erosion during pouring. After the coating dries, the cluster is put into a flask and backed up with un-bonded sand. The sand is then compacted using vibration table. Once compacted, the mold is ready to be poured. Automatic pouring commonly used in SMD, as the process of pouring far more important than in conventional foundry practice.
There is no phase bake-off, as lost-wax for. The melt is poured directly into the mold foam-filled, burning off the foam as it pours. As the low density foam, the waste gas produced by the relatively small and can escape through permeability mold, as your usual outgassing control.