Lost Foam Casting

Lost foam casting is a modern metal casting technique where patterns made of expanded polystyrene (EPS) foam are used. The foam pattern is coated with a refractory material and surrounded by unbonded sand, which allows for the gas resulting from the molten metal evaporating the foam to escape.

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Advantages and Disadvantages

Rapid prototype casting offers numerous advantages. It reduces the cost and lead time for part creation, involves minimal to no machining, and allows high design flexibility. Engineers can create incredibly complex shapes, such as thin-walled parts, which are otherwise difficult to produce. Finished metal parts also benefit from a superior surface finish. However, this method does require considerable time to craft a CAD design and necessitates a high level of expertise. In addition, part size is limited by the printing area of the machine, and the metals suitable for this process are those with lower melting points.

In this article, we will delve into lost foam casting, a versatile metal casting method widely used in modern casting processes.

What is lost foam casting?

Lost foam casting utilizes expanded polystyrene (EPS), commonly known as styrofoam, as the pattern material. This pattern is placed in silica sand, which is compacted using a vibration system. When molten metal is poured into the mold, the EPS melts and evaporates, allowing the metal to fill the created space. This method is referred to as evaporative casting, which is a type of casting without binders.

Lost foam casting stages

Creating patterns with EPS materials

Patterns can be formed out of EPS material to match the desired object shape. This is done by molding polystyrene foam granules within metal molds, which are then heated with moisture to bind the grains together forming the pattern.

Creating a gating system (casting channel)

The gating system, which includes the runner, sprue, and pattern, is constructed from polystyrene foam. Once created, it's assembled with the pattern to form a cluster.

Pattern coating with ceramic material

The pattern is coated with ceramic powder or a similar material dissolved in colloidal silica. This coating serves to hold the sand mold together and ensures a smooth cast surface. The thickness of the coating can vary based on requirements, with thicker coatings potentially trapping gases and causing defects in the cast object.

Inserting the coated pattern into the molding frame

The coated pattern is placed within a molding frame and surrounded by sand, which is compacted using vibration. This ensures the pattern stays securely in place within the mold.

Pouring Liquid into Molds

Molten metal is poured into the mold created by the foam pattern, causing the foam to evaporate or become gas, allowing the metal to flow into and fill the space.

Mold Disassembly

Once the casting is cooled, the mold is disassembled. As the cast objects do not contain a binder, they easily separate from the molded sand.

The Advantages and Disadvantages of Lost Foam Casting

Lost foam casting, commonly used for aluminum alloy castings, stands out for its cost-effectiveness and environmental benefits. Some of the advantages include:

• Flexible design options for casting patterns.
• Ability to create intricate shapes and complex objects.
• Absence of mold partitions.
• No core wear.
• Reduction in labor costs in the foundry.
• Polystyrene foam patterns are economical and easy to produce.
• Reduction of environmental pollution due to binder-less sand that can be reused directly.
• Higher dimensional accuracy and casting quality.

However, the method does have some drawbacks, such as an increased degree of porosity due to the burnt polystyrene foam.

Conclusion

To sum up, Lost Foam Casting is a versatile and cost-efficient casting method with distinct advantages and some limitations. For any further questions or details, feel free to leave a comment or contact our team directly.

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