What are the cons of lost foam casting?

In lost foam casting, the foam pattern used to create the desired shape of the final metal part is vaporized or burned away during the casting process. Here's what happens to the foam:

1. Placement: The foam pattern, which is made of expandable polystyrene (EPS) or similar materials, is placed into a molding flask, which is then filled with unbonded sand or another refractory material. The foam pattern is typically coated with a refractory material to enhance its heat resistance and prevent it from sticking to the molten metal.

2. Metal Pouring: Once the mold is prepared, molten metal is poured directly into the mold cavity. The high temperature of the metal causes the foam pattern to rapidly decompose.

3. Foam Vaporization: As the molten metal comes into contact with the foam pattern, the foam begins to vaporize due to the intense heat. The heat from the metal causes the foam to break down and release gases, which escape through the sand mold.

4. Metal Solidification: After the foam pattern has been completely vaporized, the molten metal fills the void left by the foam, taking on the shape of the desired part. The metal then solidifies within the sand mold.

5. Cooling and Solidification: Once the metal has solidified, the casting is allowed to cool within the mold until it reaches a temperature at which it can be safely handled.

6. Shakeout and Cleaning: After cooling, the sand mold is typically broken apart to reveal the solid metal casting inside. Any residual sand and debris are removed from the casting through processes such as shakeout, shot blasting, or tumbling.

7. Finishing Operations: Depending on the desired surface finish and dimensional accuracy, the casting may undergo additional finishing operations such as machining, grinding, or polishing to meet the required specifications.

Overall, the foam pattern in lost foam casting serves as a sacrificial material that is consumed during the casting process, allowing for the creation of intricate and complex metal parts with minimal machining requirements and material waste.