Lost-Foam Casting Process – How Does It Work?

Since its invention in the early 1950s, lost-foam casting has been a go-to technique for producing detail-oriented and highly dimensionally accurate metal products in several industries. In addition, this casting technique significantly minimizes fabrication costs in foundries due to the minimized need for extra machining. This article explores lost-foam casting, highlighting its benefits and the process steps.

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What Is Lost Foam Casting?

Lost-foam casting is a type of casting that leverages polystyrene pallets or molds to create high-detail metal pieces and parts. The process is ideal for casting complex small to medium metal products that maintain excellent surface finishes and high precision. Unlike other types of casting, the molten metal evaporates the polystyrene foam mold in lost-foam casting, leaving metal products that require little to zero shaking.

Advantages of Lost Foam Casting

The minimal steps required in lost-foam casting result in a corresponding high lead time. While other casting processes leverage several complicated steps to achieve final metal products, lost-foam casting requires minimal steps to achieve complex castings, making it more economical than investment casting. Another advantage of this casting process includes its likelihood of creating high-accuracy metal products with little to no casting defects, eliminating the need for extra machining. Moreover, lost-foam casting saves significant labor and production costs in foundries.

When to Use Lost Foam Casting

Lost-foam casting is ideal for creating metal products in several industries, including automotive, arts, defense, agriculture, and computer technology. The process is suitable for a wide material range, such as cast iron, alloy steel, ferrous alloy, carbon steel, and alloy aluminum, enabling the production of different metal parts. Manufacturers leverage lost-foam casting to fabricate products, such as cylinder blocks, valves, automotive engines, gearbox details, fire hydrants, cylinder heads, and 3D models, since the technique creates castings with high dimensional accuracy. This technique is also well-suited for creating highly detailed and complex products, such as lamp posts, pump housing, pan support, gas burners, and fences. If the designs of your metal products are complicated and you prioritize excellent finishing and dimensionally accurate products, lost-foam casting is the most viable option.

Lost Foam Casting Process Steps

Five steps in lost-foam casting include:

• Making design pattern
• Applying insulation paint
• Inserting the mold into a sand flask
• Pouring the molten metal
• Retrieving the final product

Manufacturers leverage polystyrene foams to design patterns due to their exceptional thermal and chemical properties. These manufacturers can achieve several design patterns by hand-cutting from a solid block foam or machining with computer-aided design (CAD) software. Design complexity is a factor manufacturers consider: more complex designs require manufacturers to make and glue the foam molds. Alternatively, manufacturers can use a process similar to injection molding to design polystyrene beads into the desired mold. This alternative technique is ideal for mass production.

Secondly, the manufacturer coats each resulting mold with insulation paint and air dries them. This coating is essential for ensuring the consistency and durability of the mold surface, protecting it against erosion. After placing these molds in a flask, the manufacturer fills and compacts the flask with un-bonded sand, incorporating a sprue and vents for receiving molten metal and expelling gas, respectively. The next step involves pouring the molten metal, which burns out the foam mold and forms the casting. Lastly, the manufacturer retrieves the finished product from the sand flask.

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The Lost Foam Casting Process: Part One

Abstract:

Lost foam casting is a small, but important part in the recent acceleration to drive technological improvement in industry.
In the automotive industry consumer demand is at its highest which mean materials technology needs to keep pace and with LFC it allows solid aluminum parts to be created to help drive weight and cost savings.

Vehicle manufacturing has become extremely complex, costly, and competitive during the past 30 years. Global competition, vehicle technology, and consumer demands have brought us owner satisfaction surveys, innovations as complex as electronic stability control and the most efficient, yet most intricate engines ever produced. With advances in product technology come demands for advances in product manufacturing.

A significant portion of most brands’ fleets sold in the U.S. have all-aluminum engines. The use of this lightweight metal reduces vehicle weight, increases fuel efficiency and reduces ownership costs. A popular manufacturing process for these all-aluminum engines is called Evaporative Pattern Casting, more popularly referred to as Lost Foam Casting (LFC). The materials most commonly used in LFC are aluminum and iron. As the process name implies, the castings are made from polystyrene foam patterns that evaporate once the molten metal is introduced into the sand casing.

Lost-foam casting (LFC) is a casting method used to create solid metal parts from molten metal. The cost of production of these castings by the LFC process is much less relative to the conventional processes, such as sand casting. Over the past 20 — 25 years, almost 30% of the die cast components have come to be produced by the LFC process. Major strides in the LFC of cast irons and aluminum alloys are attributed to significant research and development endeavors of the automotive industry. Much of these are in the development of new polymers, bead expansion techniques, selection of favorable alloys and parameters. Thus, scientific data related to superheats, heat transfer, flow length, etc. are available to a reasonable extent for LFC of cast irons and aluminum alloys.

The first step of lost-foam casting is the creation of the foam mold. A block of polystyrene foam is cut into the exact shape of the finished product using hand or power tools. For applications where the dimensions of the finished piece must be exact, power tooling is preferred for a more consistent shaping of the foam. The mold is then dipped in sheetrock mud or plaster and coated thoroughly.

After the foam mold is finished, it is buried in a container; for example, a metal drum; filled with compacted sand. The very ends of the foam shape are left exposed to facilitate the entry of the molten metal into the mold. A homemade tool can be used during this step to help the process along further. This tool, which consists of a hinged cylinder that can be opened and closed along the side by long handles, is placed on the sand so that it surrounds the foam piece. When the metal is poured, the cylinder walls contain it and allow it to build up over the piece, creating more pressure and, therefore, a more thorough casting.

Figure 1: Lost Foam Casting

Lost foam casting LFC is used to make outboard engine components (engine block, cylinder head, etc.).

Figure 2: Lost foam casting LFC products

There are various benefits that must be considered in using this process:

• Additives not required
• Binders not required
• Flexibility in design
• Cores not required
• Minimum scrap
• Less machining
• Reduced finishing
• Environmentally friendly
• Reduced energy required
• Reduced insurance premiums
• Smaller footprint
• Reduced manpower

References

1. Lost Foam Casting, NYSERDA, Accessed 03-2016;

2. Lost Foam Casting, LFC, casting process, Accessed 03-2016;

3. L.Bichler: The effect of LFC process variables on solidification and thermal response of AZ91E magnesium alloy castings, Ryerson University, MSc thesis, UMI Number: EC 53425, Toronto, Ontario, Canada 2005;

4. D.E.Palmer: Stress Ratio Effects in Fatigue of Lost Foam Aluminum Alloy 356, Accessed 03-2016;

5. Lost Foam-Background and basics of the Lost Foam Casting Process, FTJ January/February 2010, p.12- xx, Accessed 03-2016

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Date Published: Jul-2016

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