Casting is a major component of modern manufacturing, allowing for complex components to be cast to exacting dimensions with consistent mechanical properties. Many methods of casting are in widespread use, with two of the more notable methods being investment casting and lost foam casting. Both of these manufacturing methods utilize a temporary pattern to create the end product, which is made of cast metal.

Investment casting and การหล่อโฟมที่หายไป are two different casting processes. In investment casting patterns of wax are used in combination with a ceramic shell. Lost foam casting uses patterns of foam that are completely dissolved in the molten metal. This difference in process route results in big differences for the required equipment, for the mold preparation, for the surface finish, for the costs and for the areas of application.

What Is Lost Wax Casting?

Basic Definition of Lost Wax Casting

Lost wax casting is a very precise method of casting. To make a Lost wax casting, first a wax pattern is made. Then the wax pattern is covered with layers of ceramic slurry and refractory material. There are several layers of each that are allowed to dry. After the layers have been applied and dried the heat is raised to burn out the wax, leaving an empty shell of ceramic. Molten metal is then poured down a pouring cup to fill the shell. The metal then solidifies and the shell is broken away to reveal the cast part.

How the Lost Wax Process Works

There is a step by step guide on how to make a lost wax cast: Making a wax pattern, assembling the wax patterns, building a ceramic shell around the wax, dewaxing, firing the ceramic shell, pouring the molten metal, allowing the metal to cool, removing the ceramic shell from around the cast part, cutting and grinding to size and inspecting the part for any defects. Lost wax castings can produce parts with very fine surface details, thus it is well suited for making complex castings that require a high surface finish.

Common Advantages of Lost Wax Casting

The lost wax casting process is able to produce thin walls, exacting shapes, smooth finishes and precise dimensions. It is typically used for creating small to medium sized parts made from metal, because of the process’ high degree of precision. There are a lot of steps involved with the process which can result in longer production time and higher labor costs than other types of castings.

What Is Investment Casting?

Investment Casting as a Precision Process

Investment casting is closely related to the lost wax casting process. In many industries the term investment casting and lost wax casting is used to describe the same process. The term “investment” is used to describe the ceramic shell material that surrounds the wax pattern and becomes the mold shell.

Materials Used in Investment Casting

Investment casting is suited for a wide range of metals such as stainless steel, carbon steel, alloy steel, aluminum alloys, bronze and other castable metals. This process is commonly used in many industries such as production of machinery and parts, energy sector, fluid control equipment, vehicles and other engineering components.

Main Strengths of Investment Casting

The main strength of investment casting is its high precision. Because of the process, it is possible to cast complex parts and they can have fine details. Therefore the need for heavy machining is reduced. Investment casting is especially used for parts that require smooth surfaces, tight tolerances and stable repeatability.

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Basic Definition of Lost Foam Casting

Lost foam casting is a type of evaporative pattern casting. It uses an expanded foam pattern instead of a wax pattern. The foam pattern is of the exact same shape as the finished casting. After coating and drying the foam pattern is placed in a flask and covered with dry sand.

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When the metal is poured into the mold, the metal vaporizes the foam pattern. The molten metal then fills the space where the foam had previously been. Once the metal has cooled, the finished casting is removed from the mold. In contrast to investment casting, the pattern is not removed from the mold prior to pouring the molten metal. It vaporizes in the molten metal as it fills the mold.

Why Lost Foam Casting Is Used

Lost foam casting is particularly suitable for very complex components that would contain a large number of cores or require many parting lines. It allows integrated casting structures to be produced, saves assembly work and thus increases efficiency when all process stages are effectively controlled. Lost foam casting is primarily used to manufacture components for machinery, for example pump bodies, valve bodies, and other cast components such as housings and engine parts as well as general industrial castings.

Similarities Between Investment Casting and Lost Foam Casting

Both Use Disposable Patterns

Both processes use patterns that are not part of the finished cast. For investment casting this would be to use wax patterns. For lost foam casting this would be to use foam patterns. Both methods are formed by the pattern.

Both Can Produce Complex Parts

Both methods have the ability to generate very complex shapes. All internal features, curved surfaces, detailed edges and near net shapes can be designed and generated with both methods by the proper design of the process.

Both Reduce Machining Requirements

Both rapid prototyping techniques are able to make very detailed parts in close to the actual part geometry, thus they can save a lot of secondary machining time and material and increase manufacturing efficiency.

Both Require Strong Process Control

Two casting processes that demand process control are investment casting and lost foam casting. All aspects of the casting process can affect the finished casting; including pattern, coating, mold preparation, temperature, metal, and cooling.

Differences Between Investment Casting and Lost Foam Casting

Pattern Material Difference

In investment casting we use wax patterns for creating the cavity of the cast part. In Lost foam casting we use expanded foam patterns. In both casting methods there is something that is removed or destroyed before the cast part is cast. In investment casting the wax is melted out of the cast part cavity before the molten metal is poured into the mold cavity. In Lost foam casting the solid foam is vaporized in the molten metal stream pouring into the mold cavity.

Mold Structure Difference

In investment casting a ceramic shell is used to make the mold. This has to be strong enough to hold the molten metal after the wax has been removed from the cavity. In lost foam casting a coated foam pattern is submerged in dry sand. The pattern is compacted in the sand and forms the casting.

Pattern Removal Difference

Investment casting has wax in the mold before it is cast. Lost foam casting has the pattern made of foam in the mold until the molten metal is poured into the mold. The pattern then disappears into the molten metal as it fills the cavity.

Surface Finish Difference

Investment castings have a smooth surface finish and superior dimensional control. Also, good castings can be produced with Lost Foam Casting. However, surface finish of castings produced with Lost Foam Casting greatly depends on number of factors, i.e. on foam density, on coating thickness, on drying of coating, on how sand is compacted, and on pouring process.

Cost and Production Difference

While Investment Casting can offer cost effective production of high precision parts, the use of the ceramic shell in the Investment Casting process creates time penalties. However, Lost Foam Casting can be very efficient at production of complex components as well as high volume production. The process of foam molding, coating, drying as well as sand handling must however be supported by good and stable equipment.

Industrial Equipment Support for Lost Foam Casting Production

Foundries setting up new production lines for Lost Foam Casting or upgrading existing ones must pay special attention to the reliability of the equipment. This affects the quality of the patterns, the stability of the coating, the drying process, the vacuum system and finally the quality of the castings.

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