What is Complete equipment for lost foam casting and Why Do We Use Them?

The lost-foam casting process

Lost-foam patternmaking

The lost-foam casting process begins with the creation of the EPS patterns (or pre-forms). Pre-expanded polystyrene is moulded in an aluminium die and heated; this causes the polystyrene beads to expand further and fuse. The die is then cooled to allow the pattern to be ejected, after which the pattern is aged until stable for casting (the pattern will slightly contract as it cools fully). This may take several days at ambient temperature, but can be shortened to hours if patterns are cured in a heated environment.

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As the casting will reproduce every detail of the pattern, patternmaking is the critical step for ensuring the accuracy and finish of the cast piece. It must be dimensionally accurate, taking into account the abovementioned shrinkage. The patterns – which are relatively delicate compared to other casting patterns and moulds – must also be carefully handled so as to avoid distortions or damage.

The density of the EPS is similarly important. The lower the density, the easier it is to ensure complete filling of the mould, but the poorer the surface finish and the greater the risk the pattern will distort during handling and sand compaction. A high density will, however, increase resistance to the flow of molten metal, making it difficult to ensure complete filling of the mould, and particularly of thin sections. EPS density must balance these factors, being the minimum possible to achieve the specified surface density and pattern strength.

A final consideration is the foam itself. High carbon irons, such as ductile irons, are prone to lustrous carbon defects when cast using EPS patterns. This considerably limited the applicability of lost-foam casting in the early years of the technology. However, the development of EPS-PMMA copolymers for lost-foam patternmaking has changed this. These copolymers vaporise completely under heat, eliminating the residues that caused the lustrous carbon defects when using EPS.

Assembling the patterns

After aging, the patterns are assembled for casting. If the pattern comprises multiple pieces, these are now glued together. The use of such multiple-part patterns allows the production of highly-complex geometries; however, care must be taken to avoid excess glue extruding from the join, as this will be reproduced as a surface defect in the casting.

Multiple smaller patterns are usually assembled into a cluster around a central foam piece, called a tree, to allow for concurrent casting of multiple pieces. Larger pieces are cast singly. The patterns are then covered in a ceramic refractory coating – usually by dipping into a ceramic slurry bath.

Coatings and sand investment

Coatings, such as SEMCO perm and STYROMOL water-based coatings from Foseco, play an important role in many casting processes, acting as a protective barrier between the mould and the molten metal. The coatings used for lost-foam castings have some additional roles, however. They must be relatively strong, when dried, so as to stiffen the pattern and reduce the risk that it will distort during sand compaction. They must also be permeable to allow the escape of liquid and gaseous ESP residues during mould filling.

How permeable depends on the application:

• In high-temperature applications, such as iron casting, coating permeability is tailored to the specific demands of the customer and casting application, and controls the filling speed of the of the mould; it therefore represents a critical factor within the overall process. In addition, as large volumes of gas are produced quickly as the pattern vaporises, permeability will be higher when compared to lower-temperature processes, to avoid metal blowback up the sprue.
• In lower-temperature processes, such as aluminium casting, the patterns degrade to form residues of lower molecular weight polymers and monomers. In addition allowing the escape of gases from the melt, the coating must therefore also be capable of absorbing these residues quickly enough to avoid slowing the filling process (and causing misruns), but with sufficient control to prevent turbulence in the pour.2  

After coating, the patterns are ready to be mounted to a pouring funnel (sprue) and placed into the flask. Dry, loose sand is then poured around the pattern.

As the sand is added, the box is vibrated to compact the sand and ensure it flows into any cavities in the pattern. The level of vibration should be sufficient to ensure the patterns are fully encased, but avoid damage to or distortion of the patterns. It should also be remembered that sand cannot be induced to flow against gravity! The patterns must therefore be placed so that any cavities are filled either horizontally or downwards.

The sand itself should be free flowing to facilitate pouring into the flask and full encasement of the pattern. It must also be permeable to allow the release of any gases and liquids residues produced during the pour (see above). Relatively coarse, spherical-grained sands are therefore preferred.

Filling and shake-out

At this point, the moulds are ready to be filled with the molten metal. The method of filling will vary with the application. In low-temperature castings (such as aluminium), selecting a coating with optimum permeability (see above) allows sufficient control of the fill to allow direct pour. In iron casting applications, however, the higher density and heat of the melt means pours are usually bottom-gated in order to achieve adequate control of the filling process. A vacuum may also be employed to maintain accurate casting dimensions and help remove the gases during pouring.

After the metal has solidified, the flask is dumped onto a shakeout conveyor, and proceeds through the shakeout area to remove loose sand and coating. Because no binder is used in the process, the sand is easy to reclaim and recycle. Individual castings are removed from the tree (when used) and the ingates removed. The castings are then ready for final machining, although due to the high-quality of casting provided by the lost-foam process, this step may be eliminated (or, at the very least, reduced to a minimum).

Introduction to Lost Foam Casting

Lost foam casting, also known as evaporative pattern casting, is a casting process that uses a foam pattern to create a mold for casting metal parts. The process involves creating a foam pattern of the desired part, coating it with a refractory material, and then casting molten metal into the pattern. The foam pattern is evaporated by the heat of the molten metal, leaving behind a casting with the desired shape and features.

Overview of the Lost Foam Casting Process

The lost foam casting process involves several key steps, including creating the foam pattern, coating the foam pattern with refractory material, and casting molten metal into the pattern. The process is known for its ability to produce complex castings with high accuracy and surface finish.

History and Development of Lost Foam Casting

Lost foam casting has its roots in the s and s, when it was first developed as a method for producing castings with complex geometries[^1](https://www.asminternational.org/documents///G_Sample.pdf). Over the years, the process has evolved and improved, with advances in foam pattern production, refractory coatings, and casting technology.

Advantages and Limitations of Lost Foam Casting

Lost foam casting offers several advantages over traditional casting processes, including the ability to produce complex castings with high accuracy and surface finish. However, the process also has some limitations, including material limitations and surface finish issues. In this article, we will explore the benefits and limitations of lost foam casting in more detail.

The Lost Foam Casting Process

The lost foam casting process involves several key steps, including creating the foam pattern, coating the foam pattern with refractory material, and casting molten metal into the pattern.

Creating the Foam Pattern

The first step in the lost foam casting process is to create a foam pattern of the desired part. The foam pattern is typically made from a type of plastic foam, such as polystyrene or polyurethane, using a variety of techniques, including:

• CNC machining: The foam pattern is machined from a block of foam using a CNC machine.
• Injection molding: The foam pattern is produced using an injection molding process.
• 3D printing: The foam pattern is produced using a 3D printing process.

The foam pattern is designed to be slightly larger than the desired casting to account for shrinkage during the casting process.

Coating the Foam Pattern with Refractory Material

Once the foam pattern is created, it is coated with a refractory material to provide a heat-resistant surface for the molten metal to contact. The refractory coating is typically applied using a dipping or spraying process.

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The refractory coating serves several purposes, including:

• Protecting the foam pattern from the heat of the molten metal
• Providing a smooth surface for the molten metal to flow over
• Reducing the risk of defects in the casting

Casting Molten Metal into the Pattern

The final step in the lost foam casting process is to cast molten metal into the foam pattern. The molten metal is poured into the foam pattern, where it evaporates the foam and fills the cavity.

The casting process is typically carried out in a sand mold, which is vibrated to ensure that the molten metal fills the cavity completely. The molten metal is then allowed to solidify, and the casting is removed from the mold.

The following diagram illustrates the lost foam casting process:

graph LR;
    A["Create Foam Pattern"] --> B["Coat with Refractory Material"];
    B --> C["Cast Molten Metal"];
    C --> D["Remove Casting from Mold"];

Applications of Lost Foam Casting

Lost foam casting is used in a variety of industries, including the automotive, aerospace, and industrial equipment industries.

Automotive Industry Applications

Lost foam casting is widely used in the automotive industry to produce complex castings, such as engine blocks, cylinder heads, and transmission components. The process is particularly well-suited for producing castings with complex geometries and internal features.

Some examples of automotive castings produced using lost foam casting include:

• Engine blocks
• Cylinder heads
• Transmission components
• Brake components

Aerospace Industry Applications

Lost foam casting is also used in the aerospace industry to produce complex castings, such as turbine blades and other aircraft components. The process is particularly well-suited for producing castings with complex geometries and high-precision tolerances.

Some examples of aerospace castings produced using lost foam casting include:

• Turbine blades
• Aircraft engine components
• Structural components

Other Industrial Applications

Lost foam casting is used in a variety of other industries, including the industrial equipment, agricultural equipment, and construction equipment industries. The process is particularly well-suited for producing complex castings with high-precision tolerances.

Some examples of industrial castings produced using lost foam casting include:

• Pump components
• Gear components
• Valve components

Benefits and Limitations of Lost Foam Casting

Lost foam casting offers several benefits over traditional casting processes, including the ability to produce complex castings with high accuracy and surface finish. However, the process also has some limitations, including material limitations and surface finish issues.

Advantages of Lost Foam Casting

The advantages of lost foam casting include:

• Complex geometries: Lost foam casting is particularly well-suited for producing castings with complex geometries and internal features.
• High accuracy: Lost foam casting can produce castings with high accuracy and precision tolerances.
• Cost-effectiveness: Lost foam casting can be a cost-effective process for producing complex castings, particularly in low-to-medium volume production runs.
• Reduced machining: Lost foam casting can produce castings with complex features and geometries, reducing the need for machining operations.

Limitations of Lost Foam Casting

The limitations of lost foam casting include:

• Material limitations: Lost foam casting is typically limited to producing castings from certain materials, such as aluminum, iron, and steel.
• Surface finish: Lost foam casting can produce castings with a rough surface finish, particularly if the refractory coating is not applied correctly.
• Defects: Lost foam casting can be prone to defects, such as porosity and inclusions, if the process is not controlled correctly.

The following table summarizes the benefits and limitations of lost foam casting:

Benefits Limitations Complex geometries Material limitations High accuracy Surface finish issues Cost-effectiveness Defects Reduced machining

Conclusion

Lost foam casting is a versatile and cost-effective process for producing complex castings with high accuracy and surface finish. While the process has some limitations, it is widely used in a variety of industries, including the automotive, aerospace, and industrial equipment industries. By understanding the benefits and limitations of lost foam casting, manufacturers can make informed decisions about whether the process is suitable for their production needs.

References

FAQ

What is lost foam casting?

Lost foam casting is a casting process that uses a foam pattern to create a mold for casting metal parts.

What are the advantages of lost foam casting?

The advantages of lost foam casting include the ability to produce complex castings with high accuracy and surface finish, cost-effectiveness, and reduced machining operations.

What are the limitations of lost foam casting?

The limitations of lost foam casting include material limitations, surface finish issues, and defects.

What industries use lost foam casting?

Lost foam casting is used in a variety of industries, including the automotive, aerospace, and industrial equipment industries.

What types of castings can be produced using lost foam casting?

Lost foam casting can be used to produce a wide range of castings, including engine blocks, cylinder heads, transmission components, turbine blades, and other complex components.

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