Lost Foam Castings

Evaporative pattern casting uses molds which will melt or evaporate upon contact with hot molten metal to generate intricate, complex metal parts. Polystyrene foam frequently serves as a mold material in a “lost foam” casting process. 

Today, the majority of evaporative pattern casting conducted within manufacturing environments involves foam casting. Automation and mass-production help make this type of casting a very efficient choice in some metal parts fabrication settings.

A Brief History of Lost Foam Casting

Evaporative pattern casting has contributed to manufacturing for centuries. However, during most of this period, artisans relied upon wax (not polystyrene foam) to form a mold.

Lost foam casting represents a fairly recent innovation. The work of H. F. Shroyer contributed to the development of this technology. He received a patent in 1958 for devising a way to perform casting using polystyrene foam embedded within casting sand. 

Manufacturing firms around the world quickly appreciated the commercial benefits of this newly invented casting process. Today, lost foam casting has become an important way to form many types of metal objects and parts.

Foam Casting Process

The process of lost foam casting strongly resembles lost wax investment casting methods. However, foam (typically polystyrene foam) substitutes for wax during casting. 

Today manufacturers utilize this process widely to create metal parts comprised of aluminum alloys, cast irons, nickel alloys or steels. Infrequently, they also cast work pieces in copper alloys or stainless steels this way.

The process of lost foam casting in a mass production environment typically involves creating a detailed polystyrene mold inside an aluminum die. A manufacturer applies steam to heat polystyrene beads placed within the metal mold. The polystyrene will assume the contours and dimensions of the interior of the aluminum die as it expands under the influence of the moisture and heat. Mold makers remove the completed polystyrene mold to finish it, typically by attaching any additional desired features, such as gates.

Manufacturers can also prepare lost foam molds by carving polystyrene foam directly into desired shapes. They may create prototype molds using this technique, for instance.

The manufacturer then paints or sprays the finished polystyrene mold completely to encase it within a “refractory coating” of ceramic material without obscuring any of the mold details. The coated mold sits with an enclosing shell. This finished mold will fit inside a vented flask or other vented container. The manufacturer packs the mold securely inside the container using heavily compacted sand to hold it in position before adding molten metal.

The hot metal causes the polystyrene mold to evaporate on contact. Evaporating gases escape through the vents. When the metal cools, the manufacturer removes it from the sand and brushes away any clinging debris to reveal the work piece. Manufacturers remove excess metal from gates during the machining process. They frequently rely on foam casting to create ornate, decorative and complex metal work pieces using this technology.

Applications

Lost foam casting enjoys many industrial applications. Its comparative simplicity and low cost make this technology a popular addition to hobby foundries, also. Artists sometimes rely on this form of casting to create statues, for example.

Since manufacturers employ foam casting to create ornate, complex and detailed parts comparatively inexpensively, this process frequently assists prototype manufacturers. It has found wide application within many fields, including the automotive industry. 

Manufacturers sometimes use lost foam casting to create cast cylinder heads or other complex shapes, for instance. Since they can produce metal parts in many different kinds of metals and metal alloys using this process, this casting method holds wide appeal for companies seeking efficient, cost-effective and versatile manufacturing services.

Key Advantages of Lost Foam Casting

Currently, lost foam casting offers a number of important advantages during metal parts manufacturing. Although not always a preferred method for casting certain types of metals or precision parts, it does offer some key advantages.

1. This process of casting can permit the generation of complex, ornate shapes. Polystyrene foam will assume the shape of an aluminum die reliably with the addition of steam.
2. This form of casting often proves highly cost-effective. Particularly when a manufacturer requires the production of a complex or unusual shape, lost foam casting may supply the most affordable production method.
3. Depending upon the size and dimensions of the part, some other casting techniques may not achieve comparable results. Lost foam casting can reproduce parts of many different sizes.
4. This process usually does not require extensive machining. Manufacturers frequently need to extract excess metal from some areas of the part, including any gates. However, the ability to cast complex shapes may enable companies to avoid some other frequent tooling expenses.
5. Depending upon the selection of the metal alloys, this form of casting often permits a manufacturer to generate large runs of cast parts with excellent surface finish properties. 
6. Lost foam casting finds widespread utility in “low tech” environments also, making the process easily adaptable for use in the construction of artistic works and prototype models. Lost foam casting may permit a manufacturer to create several initial prototype models of a proposed product affordably, for instance.
7. In industrial settings, it frequently becomes possible to use a single mold to generate multiple lost foam castings. This ability to combine castings helps maintain the cost-efficiency of production. Additionally, industrial manufacturers typically re-use and recycle the majority of the sand used to support the mold, a money saving practice.
8. Skilled lost foam casting will permit the effective casting of narrow or thin dimensional shapes under some circumstances. This aspect contributes to the utility of this manufacturing process.

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