Eagle Precision

EAGLE PRECISION SERVICES | LOST WAX CASTING

Lost wax casting is a molding technique that begins with a wax replica of the final part. The wax replica is coated in an investment casting slurry to form a ceramic mold. After the mold sets, the wax is melted and drained away, which gives the process its name: “lost wax” casting. Molten metal is then poured into the hollow shell. Once the metal cools and hardens, the ceramic shell is broken off to reveal the cast part.

Eagle Precision Cast Parts, Inc. specializes in high-quality lost wax casting services. Our management team often engages with customers in the early design stages of each new project. We provide expert advice to assist with producing parts with complex and intricate geometries and superior surface finishes, all while ensuring that each part is designed for manufacturability. Our process is compatible with many alloys, including but not limited to stainless steel, aluminum and bronze. With the precision of lost wax casting, we can hold tolerances as tight as +/- .005” per inch.

At Eagle Precision we maintain strong relationships with both local and national suppliers who are essential in adding specialized services such as heat treatments, coating and plating, machining operations and non-destructive testing to the castings that we manufacture. These trusted suppliers consistently meet the stringent quality and specification requirements of our customers and regulatory bodies. Their expertise allows us to incorporate value-added operations in any project, guaranteeing both top-quality outcomes and operational efficiency.

Click below to download our Investment Casting Quick Reference Guide.

Inside, you’ll find:

• Dimensional Tolerances
• Capabilities
• Design Recommendations
• Materials Poured

What is lost wax casting?

“Lost wax” casting, also often known as investment casting or precision casting, is one of the oldest forms of casting in existence. It’s also one of the most versatile, cost effective and widely used casting methods today. Over thousands of years the technique of lost wax casting has evolved very little, but the science behind the process and modernization of equipment has allowed the industry to continually innovate. Essentially, lost wax casting is a manufacturing process that can use nearly any alloy and allows for complex shapes to be formed with accurate dimensions, tight tolerances and smooth surface finishes. This allows the lost wax casting technique to fabricate parts that cannot be achieved through other casting methods and makes it an excellent choice for a broad range of products.

The history and applications of lost wax casting

The earliest examples of lost wax casting date back to 3,500 BC, making it one of the oldest casting methods known (1). Before its invention, open stone or ceramic molds were used to cast metals. The lost wax casting technique allowed for much greater detail and smoother finish, vastly expanding the possibilities of metal casting.

The malleability of wax makes the lost wax process ideal for creating complex and smooth-surfaced components, which are challenging with other casting methods. Historically, this process was predominantly used for crafting intricate jewelry and artworks. Cultures worldwide, from ancient China and Pre-Columbian societies to African civilizations and Renaissance Italy, employed the lost casting technique for millennia to produce everything from ornamental jewelry to large bronze and gold figures. Its industrial applications, however, only gained popularity in the early 20th century.

The modernization of lost wax casting

Modern lost wax casting gained prominence during the Second World War due to the defense industry’s urgent need for precision parts (2). Traditional casting methods couldn’t meet the high demand for specialized alloys and complex shapes required for new technologies like jet propulsion systems. These systems needed metals with high melting points that were difficult to machine. Lost wax casting proved invaluable because it allowed for the production of near-net-shape parts with minimal finishing, using virtually any alloy, significantly enhancing manufacturing efficiency.

Lost wax casting today

The lost wax casting technique remains one of the most precise metal casting methods, distinguished by its exceptional dimensional accuracy, fine detail and smooth surface finish. It is compatible with a wide range of metals and high-temperature alloys, making it highly versatile. Although the terms “lost wax casting” and “investment casting” refer to the same process, “investment casting” is the term more commonly used in industrial contexts today, while “lost wax casting” is often associated with more artistic applications like sculpture and jewelry.

The “investment” in investment casting refers to the process of coating the wax pattern in ceramic slurry. “Investing” is any process in which an object is dipped into liquid, and a layer of the liquid attaches itself to the object.

What is the lost wax casting process?

The lost wax casting process, at least for industrial applications, is highly standardized while retaining much of the traditional procedure. While each foundry has its own techniques, and there is some variation from part to part, the stages are generally similar, starting with the creation of a master pattern and ending with the finished metal piece.

Overview of the lost wax casting method

The technical process using the lost wax casting method usually comprises the following steps:

1. Produce a master pattern. The master pattern, often made from wax, wood, plastic or metal, is a replica of the final product. It must be carefully calculated to account for factors like expected shrinkage, critical areas and castability.
2. Produce a master die. Since the wax pattern and mold are destroyed during the investment casting process, a new wax pattern is needed for each casting. The master die, which must also be carefully calculated, is used to manufacture these wax patterns.
3. Produce wax patterns. Once the master die is ready, molten wax is poured in to form the wax patterns. The number of wax patterns matches the final number of castings to be produced, as each individual casting requires a new wax pattern.
4. Assemble wax patterns into a tree. The wax patterns are attached to a central wax gating system, forming a tree-like assembly with a pouring cup at the top that will serve to introduce the molten metal into the mold. Combining several wax patterns along a common sprue increases efficiency by allowing multiple patterns to go through the remaining steps simultaneously.
5. Coat the tree with the first layer of investment material. A thin shell is built around the assembled tree pattern cluster by dipping it into the investment material and then drying it. This first layer is specially formulated to create an ideal surface finish, as it will directly contact the final casting.
6. Coat the tree with additional layers of investment material. Once covered with the first layer, the pattern tree is repeatedly dipped into a slurry of fine-grained silica or coarse investment material and dried. This process, known as “investment,” is repeated until the mold walls reach the desired thickness. Then, the pattern tree is left to harden.
7. Melt the assembly to remove wax from the mold. The hardened ceramic pattern trees are placed upside down in an oven and heated until the wax melts and drains out of the mold.
8. Pre-heat the mold. To prepare the mold for pouring, it must first be preheated to 1000-2000 degrees F, depending on the properties of the metal to be poured. This heating removes residual wax, strengthens the mold, helps the molten metal to retain its liquidity, and improves dimensional accuracy by allowing the mold and casting to cool and shrink together.
9. Pour in molten metal. Molten metal is poured into the mold while it’s still hot, allowing it to flow easily through thin and detailed sections. There are various standard pouring methods depending on the material, mold size and available facilities.
10. Remove the casting. Once the metal cools and solidifies, the ceramic mold is broken off. Typically, mechanical equipment facilitates this process, employing vibration or pressurized water. The individual castings at this point are still attached to the sprue and runner in the tree pattern formation, and they must be cut away from the sprue, and each finished to grind away any excess metal.

Minimizing machining needs

The lost wax casting process often requires minimal machining. Finishing operations like grinding or blasting can be used to smooth the part, especially at the gates, and remove imperfections. Eagle Precision’s services include any post processing required to bring the part to spec. We work with our partners to handle heat treatment, coating and hot isostatic pressing (HIP).

To learn more about the investment casting process, download our Investment Casting Process Guide, prepared by Eagle Precision.

What equipment is required for lost wax casting?

The lost wax casting process stands out for its precision in producing intricate metal parts. Achieving such precision requires high-quality equipment capable of tight tolerances with repeatable accuracy. Machinery and manufacturing processes must be able to process both small and large volumes quickly and seamlessly without compromising product quality.

At Eagle Precision, we deploy advanced technology throughout the lost wax casting process. Our skilled team operates state-of-the-art machinery to ensure excellence at every stage. Leveraging expertise in 3D solidification software and advanced metrology, we utilize 3D printing technology to rapidly produce prototype or low-volume metal parts. This approach enables us to meet even the most demanding customer specifications with ease.

Which metals and alloys are used in lost wax casting?

A wide variety of materials can be used within the lost wax casting process. Eagle Precision has extensive knowledge and experience casting a large range of ferrous and non-ferrous grade alloys.

Consult our Eagle Precision Cast Products Alloys Chart for our current list of poured alloys to help you make informed decisions for your projects.

Investment Casting Applications

Below are some examples of Eagle Precision Cast Parts investment casting applications. Visit our Industries Page to see sample photos of Eagle Precision parts.

• Agricultural machinery and tillage tools
• Military and defense equipment
• Fluid handling components
• Mining equipment
• Cast parts for the oil and gas industry
• Railroad components and train accessories
• Transportation and freight industry components
• Utilities and power generation industry parts
• Turbine blades
• Pumps
• Control valves
• Combustor components
• Lifting hooks and swivels
• Triggers
• Hand tools
• Lock parts
• Pipe fittings

Investment casting is also an excellent option for prototyping due to its quick and cost-effective production, allowing for testing and validation before full-scale production. For a real-life example of Eagle Precision’s expertise in prototype casting, read our Hydrant Guard Case Study.

References:
(1) Hunt, L. B. (1980). The long history of lost wax casting: Over five thousand years of art and craftsmanship. Marshalltown, South Africa: International Gold Corporation Limited.
(2) Developments in investment casting process—A review, Science Direct
https://www.sciencedirect.com/science/article/abs/pii/S0924013612001823