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Expanded polystyrene. Image Credit: Shutterstock.com/Audrius Merfeldas

Lost-Foam Casting: Definition, Importance, How It Works, Applications, and Advantages

Xomety X
By Team Xometry
September 6, 2023
 11 min read
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Lost-foam casting, sometimes known as the expanded polystyrene process, is a unique technique in the field of metal casting. This creative approach produces intricate metal components using a foam design that evaporates as molten metal is put into the mold. The procedure is essential for creating elaborate and sophisticated designs that could be difficult to cast using conventional techniques. Figure 1 is a diagrammatic representation of a lost-foam casting process:

lost-foam casting process diagrammatic

Diagrammatic representation of a lost-foam casting process.

Image Credit: https://www.researchgate.net/figure/Lost-foam-casting-LFC-process_fig2_338222698

This article will examine the fundamental principles of lost-foam casting, as well as its numerous uses in the manufacture of items from cast iron and other metals and their alloys.

What Is Lost-Foam Casting?

Lost-foam casting, also known as evaporative casting or the expanded polystyrene process, is a sophisticated technique for crafting intricate metal components. This procedure makes use of an expanded polystyrene (EPS) foam mold. The foam pattern may be cut from a foam block, carved, or produced using a process akin to injection molding. The foam mold is then given a ceramic refractory covering to isolate it from the sand surrounding it in the mold frame. Sand holds the EPS mold in place as molten metal is poured into it. As the foam evaporates, the required metal shape is left behind.

What Is the Origin of Lost-Foam Casting?

Lost-foam casting has its origins in a patent that H.F. Shroyer filed in April 1956. He proposed the idea of embedding foam patterns within green sand to cast metal. This creative method required cutting a pattern from expanded polystyrene (EPS) and supporting it with bonded sand throughout the casting process. Shroyer's creative strategy, which was formally patented in 1958, served as the basis for lost-foam casting, often known as the whole-mold technique.

What Is the Importance of Lost-Foam Casting in Manufacturing?

Lost-foam casting is important in the industrial industry because it uses less energy than sand casting and has a smaller carbon impact. Additionally, it reduces waste production and metal consumption. This helps to create a cleaner and more productive industrial environment.

How Does Lost-Foam Casting Work?

Lost-foam casting first involves creating a pattern of the desired shape from expanded polystyrene (EPS) foam. The foam pattern is then placed within a mold box and packed on all sides with sand, leaving a passage through which to pour molten metal onto the foam. The polystyrene vaporizes due to the heat from the molten metal, which shapes the casting inside the mold. Intricate and sophisticated metal items can be produced with amazing precision by ejecting the casting from the mold chamber after it has been formed.

What Makes Lost-Foam Casting Stand Out Among Other Types of Casting?

Lost-foam casting has definite advantages over conventional casting techniques like sand casting or investment casting. Complex shapes and elaborate designs are possible that could be difficult with other approaches. Lost-foam casting can also reduce material waste and streamline manufacturing procedures, making it more effective and economical. To learn more, see our guide on the Types of Casting.

What Is the Process of Lost-Foam Casting?

Here is a step-by-step explanation of the procedure:

1. Use Foam Molds for Foam Pattern and Gating System Production

In lost-foam casting, foam patterns mimic the precise geometry of the finished metal object. The gating system has passages that direct molten metal into the mold and may be integrated into the foam pattern or attached (glued on) later. These passages enable precise designs and streamlined metal flow, resulting in castings that are accurate and effective.

2. Bond Patterns and Runners To Create a Mold Bundle Module

Tightly bind the foam patterns and gating mechanisms to form the mold bundle module prior to  casting. This assembly makes the casting process easier by ensuring precise component alignment, reducing mistakes, and facilitating reliable, consistent manufacture of complex metal parts.

3. Apply Dip Paint and Allow the Paint To Dry

An application of refractory dip paint follows the assembly of the mold bundle module. When this paint dries, it creates a protective ceramic coating that improves the mold's surface toughness, heat resistance, and capacity to handle the temperature and pressure of the molten metal.

4. Place the Module in a Sandbox and Fill It With Dry Sand

Coat the mold bundle module, set it within a molding flask, and cover it in dry sand. This phase ensures accurate replication of the desired metal part by supporting the module's shape, keeping it in place during casting, and facilitating uniform sand compaction.

5. Vibrate Molding To Fill the Cavity and Compact the Sand

Sand may now flow into every nook and cranny of the mold bundle module thanks to vibrations imparted to the molding flask. Through careful sand compaction and the elimination of air spaces, this procedure enables the creation of a high-quality casting with exact measurements and fine details.

6. Pour Molten Metal To Vaporize the Foam and Create Desired Castings

Carefully pour the molten metal into the mold, replacing the vaporized foam patterns. The metal solidifies to create the desired casting as it fills the spaces the foam left behind. As a result, the finished product closely resembles the planned form while minimizing flaws and blemishes. This technique supports complicated and complex shapes.

7. Clean the Castings After They Have Cooled

After the castings have cooled and set, clean the casting to get rid of any remaining sand, ceramic shells, and other impurities. To produce high-quality and aesthetically pleasing metal parts, this phase means that the final castings fulfill quality requirements, have smooth surfaces, and are ready for subsequent finishing procedures or assembly.

The lost-foam casting process significantly lowers labor requirements and waste production. It is also possible to recycle used dry sand, which is in line with objectives for lowering emissions and using less energy.

What Is the Type of Sand Used in Lost-Foam Casting?

The use of dry sand is common in lost-foam casting. Some practitioners choose "green sand," fine, soft sand that has been blended with bentonite clay. Due to the combination's improved pliability, it can keep its shape even when somewhat damp. Even though "green sand" isn't usually green, its clay content makes it a good material to use when casting complicated foam shapes.

What Are the Metals Used in Lost-Foam Casting?

Metals used in lost-foam casting are discussed below:

1. Stainless Steel

Stainless steel is a versatile alloy composed mainly of iron and chromium. It is notable for its great corrosion resistance and amazing strength. This metal is preferred for uses that call for both durability and aesthetic appeal. Molten stainless steel is carefully poured into the foam design during the lost-foam casting procedure. The molten metal replaces the foam as it evaporates, forming the required complex shape. Stainless steel might be more expensive to make and more difficult to work with, but it has high strength and corrosion resistance. To learn more, see our guide on Stainless Steels.

2. Aluminum Alloys

Aluminum alloys are characterized by their blend of aluminum with other elements. They offer a remarkable combination of lightweight properties and effective thermal conductivity. In the area of lost-foam casting, these alloys find their application where parts necessitate a particular blend of strength and weight. Their lightweight nature and thermal conductivity stand as advantages, while their suitability for certain strength-demanding applications might be limited. To learn more, see our Aluminum Alloy article.

3. Steels

Steels, encompassing various steel types tailored to specific applications, present a versatile array of properties in lost-foam casting. These options span a spectrum of strength, hardness, and wear resistance, catering to diverse industrial needs. While offering a spectrum of advantageous attributes, it's worth noting that certain nuances might arise, such as the need for precise alloy selection based on application requirements. For more information, see our guide on Steels.

4. Cast Irons

Cast irons, notably encompassing variations like gray iron and ductile iron, play a crucial role in lost-foam casting with their pronounced attributes. Their remarkable compressive strength and resistance to wear make them prime candidates for heavy-duty applications. However, while they excel in specific scenarios, the casting process requires precise controls and considerations to ensure optimal outcomes.

5. Nickel Alloys

In lost-foam casting, nickel alloys take center stage due to their distinctive attributes. These alloys boast remarkable resistance to both high temperatures and corrosion, making them ideal contenders for use in extreme environments and specialized applications. However, their exceptional properties often come with considerations related to cost and specific alloy selection to match the intended application requirements. For more information, see our guide on Nickel Properties.

Can Copper Alloys Be Used as Casting Material for Lost-Foam Casting?

Yes, the lost foam casting process can be employed with copper alloys. However, casting copper alloys successfully requires careful consideration due to the unique challenges they pose. Molten copper alloys have the potential to produce sulfurous gases and are prone to absorbing oxygen, which can result in casting defects. Special precautions are necessary to address these issues. The incorporation of specific openings or risers within the mold becomes imperative. These serve a dual purpose: facilitating the controlled pouring of the molten metal and allowing the escape of impurities and gases that may compromise the casting quality.

What Are the Applications of Lost-Foam Casting?

The primary uses of lost-foam casting are in the creation of parts with internal channels, thin walls, and delicate designs. The method excels in producing components like cylinder heads, engine blocks, and cooling system housings. Its capacity to perfectly reproduce intricate forms and details helps to produce high-quality and precisely engineered parts.

What Industries Use Lost-Foam Casting Products?

A wide range of industries, including: the automotive, marine, military, and agricultural fields, find use for lost-foam casting. It is a useful approach in creating components for these various sectors.

What Is the Quality of Lost-Foam Casting Products?

Lost-foam casting produces high-quality components with intricate details due to its ability to replicate complex shapes accurately. The durability of these products depends on factors such as: the chosen material, design considerations, and proper casting techniques. When executed with precision, lost-foam casting can yield durable and reliable products.

Are Lost-Foam Casting Products Heat Resistant?

Yes, products made with lost-foam casting can be heat resistant. The method is used to make heat-resistant components, especially those with elaborate designs and small sizes. It is often employed to make components that have strong heat-resistance qualities, which helps to make them suitable for a variety of applications.

What Are the Advantages of Lost-Foam Casting?

Listed below are the advantages of lost-foam casting:

  1. Excels in producing castings with high dimensional accuracy. 
  2. Inherently avoids flash, the unwanted material accumulation on castings. The absence of a draft requirement ensures clean castings with impeccable dimensional accuracy.
  3. It's simpler than many other casting methods, involving fewer steps. 

What Are the Disadvantages of Lost-Foam Casting?

Listed below are some disadvantages of lost-foam casting:

  1. When closed-die molding is employed for pattern creation, the cost of the die can become a significant factor.
  2. While patterns are lightweight and easy to handle, they are susceptible to damage and distortion. This requires careful handling throughout the process.
  3. The presence of burnt polystyrene foam can lead to a higher degree of porosity in the castings. This can potentially affect their structural integrity and quality.

Is Lost-Foam Casting Expensive?

Yes, lost-foam casting is more expensive than other techniques. But, it has the advantage of having tighter tolerances, being lighter, and having features that are as-cast, which cut down on machining and cleanup time. It is possible to cast a large number of components that need milling, turning, drilling, and grinding with a small amount of machine stock. 

Is Lost-Foam Casting the Same as Investment Casting?

No, lost-foam casting and investment casting are not the same thing. While lost-foam and investment casting are similar, the latter uses wax patterns while the former uses expanding polystyrene foam. The selection of pattern material distinguishes the two methods even though they are fundamentally similar.

What Is the Difference Between Lost-Foam Casting and Sand Casting?

Lost-foam casting and sand casting are distinct techniques employed in metal casting. Lost-foam casting excels in detailed, high-surface finish parts, while sand casting's versatility lies in larger components. While both yield metal parts, they differ significantly in their processes, complexity, costs, and the part types they cater to. Table 1 below lists their differences in more detail:

Table 1: Difference Between Lost-Foam Casting vs. Sand Casting
Lost-Foam CastingSand Casting
Process
Lost-Foam Casting
Molds are made from foam designs coated with refractory material, which are then vaporized by molten metal to form the component.
Sand Casting
Compacted sand molds capture patterns to define part shape, with sand removed after solidification.
Complexity
Lost-Foam Casting
Facilitates intricate, detailed, and complex parts with ease.
Sand Casting
Better suited for simpler, larger parts due to molding limitations.
Surface Finish and Tolerance
Lost-Foam Casting
Yields smooth surface finish and precise dimensions.
Sand Casting
Typically results in rougher surfaces and looser tolerances.
Cost and Tooling
Lost-Foam Casting
Foam pattern cost offset by avoiding complex molds; higher upfront cost.
Sand Casting
More cost-effective for low to medium volumes; cheaper pattern materials.
Part Size and Weight
Lost-Foam Casting
Adaptable for both small and large parts.
Sand Casting
Suited for larger components, particularly in heavy machinery.

Summary

This article presented lost-foam casting, explained it, and discussed how it works and its various applications. To learn more about lost-foam casting, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including casting and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.

Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.

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