The Lost Foam Casting Process | How Lost Foam Casting Works

At ChinaSavvy, our specialized team offers unsurpassed lost foam metal casting services, working with various metals and supplying in all your finishing needs. Able to deliver tight tolerances , the lost foam casting video below gives a basic description, with the basic steps of the lost foam casting process detailed below;

1. First, a foam pattern and gating system is made, in most cases using the foam molding press. The process of pattern making can vary depending on the number of items that will be replicated. In most cases the pattern is molded in polystyrene (2.5% polystyrene and 97.5% air) in a closed mold.
   The pattern can be molded with either the risers and gates already in place, or it can be assembled (usually glued) from various molded parts. In the pattern making process, very detailed attention is needed as it will determine the quality and reliability of the final product.
   Techniques for making patterns include: Closed die molding, assembly of the pattern from various parts and machining the pattern from a solid piece of polystyrene.
2. The gating systems and pattern (either one molded piece or assembled from various parts) are glued together to make what is called the cluster. This cluster is now coated with a permeable refractory coating and left to dry under very controlled conditions. A hard shell and supportive outer mass is formed around the pattern.
   This ‘coating’ is very much like the one seen in lost wax casting and manufacturers will make use of various ‘coating’ materials, depending on the requirements of the final product and, more particularly, the desired finish.
3. This dried and coated cluster is now invested in a foundry flask with loose, unbounded sand which is vibrated in order to provide a tight compaction, leaving behind the pattern/shape in the sand.
4. Now the molten metal is poured on to the top of the gating system, which is responsible for directing the molten metal through the cluster. The molten metal being poured causes the the pattern made in the first step to immediately vaporize.
   Pouring will continue until the mold is filled and, in cases where the use of risers are not applied, extreme care is taken to ensure that the correct amount of molten material is poured.
5. Once the mold has been filled, it is left in order for the molten material to solidify. Once solidification has taken place, the sand and shell mold is broken, and risers and gates are removed, leaving behind the final casting/product.
6. The final product can then also be heat treated or undergo other finishing operations much like what is seen in other casting processes.

The first step involves the cutting or machining of blocks of EPS (expanded polystyrene) into the shape of the final product/metal casting. This process is generally used for large, low quantity parts.

For smaller, high quantity parts, EPS steam injection is used to create a foam pattern.

The surfaces of the EPS parts are now sprayed or painted with a hard coat, where after it is placed in a mold and feeds and risers are added.

Casting sand is now added to the mold and compressed, followed by the pouring of the molten metal through the feed. Because of the high temperature of the molten metal, the EPS foam evaporates, leaving the pattern in the metal.

After the molten metal has solidified, the casting is removed from the sand and shake-out continuous. This step in the lost foam metal casting process involves the removal of the remaining sand and surface paint on the casting.

The feeds and risers are then removed, leaving behind the cast and completing the lost foam casting process. These lost foamed parts can undergo further finishing processes such as heat treatment f required.

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Further Suggested Reading:

• Lost Foam Casting Tolerances
• Metals that can be Lost Foamed
• Problems of Surface Carbon in Lost Foam Cast Parts
• Surface Finish for Lost Foam Cast Parts