Lost Foam Casting line

Lost foam casting Process:

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; 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.

Next, the foam cluster is coated with ceramic investment, also known as the refractory coating, via dipping, brushing, spraying or flow coating. This coating 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. After the coating dries, the cluster is placed into a flask and backed up with un-bonded sand. The sand is then compacted using a vibration table. Once 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.

Lost foam casting process Advantages:

This casting process is advantageous for very complex castings that would regularly require cores. It is also dimensionally accurate, maintains an excellent surface finish, requires no draft, and has no parting lines so no flash is formed. The un-bonded sand of lost foam casting can be much simpler to maintain than green sand and resin bonded sand systems. Lost foam is generally more economical than investment casting because it involves fewer steps. Risers are not usually required due to the nature of the process; because the molten metal vaporizes the foam the first metal into the mold cools more quickly than the rest, which results in natural directional solidification.[3][5] Foam is easy to manipulate, carve and glue, due to its unique properties. The flexibility of LFC often allows for consolidating the parts into one integral component; other forming processes would require the production of one or more parts to be assembled.

The two main disadvantages are that pattern costs can be high for low volume applications and the patterns are easily damaged or distorted due to their low strength.If a die is used to create the patterns there is a large initial cost.

This process eliminates the need for sand binders and cores. The sand is unbonded and a foam pattern is used to form the shape of the casting. The foam pattern is “invested” into the sand at the Fill & Compact process station allowing the sand into all voids and supporting the foam patterns external form. The sand is introduced into the flask containing the casting cluster and compacted to ensure all voids and shapes are supported.

The flask is transported to the pouring operation. The foam is evaporated as the metal is poured allowing the metal to take the shape of the casting cluster. Separation of sand and metal is accomplished at a Flask Dump Station. With no binders in the sand this process is performed with ease. Systems can be designed to accommodate quenching operations if required. The cluster proceeds to the casting finishing area for sprue, gate and riser removal. The sand is reprocessed by classification and cooling to be re-used. Thermal reclamation of the sand will extend the useful life. Lost Foam offers an environmentally friendly process with the added advantage of more accurate casting.

Foam patterns are created from polystyrene beads. The beads start as hard granules, very similar in size and shape to sand granules. The beads are expanded, allowed to stabilize and then molded into the desired shape. More complex shapes require multiple patterns to be glued together. The assemblies are then attached to a generic, central foam piece called a tree. Multiple patterns can be produced on a single tree. After assembly, the entire tree is dipped into a refractory coating to strengthen the tree. The assembled, strengthened tree is attached to a pouring funnel (called a sprue) and placed into the flask.