Investment casting, also known as lost-wax casting, is a metal forming process that allows for the manufacturing of intricate, detailed and high-quality metal parts. This process has been used for thousands of years and continues to play an important role in manufacturing today.

What is Investment Casting?

Investment casting begins with the creation of a wax pattern, which is a disposable model of the desired final metal part. The wax pattern is formed by injecting melted wax into a metal die. Once cooled, the wax forms an exact replica of the part. Multiple wax patterns are attached to a central wax gating system to form a complete wax assembly, known as a wax tree.

This wax tree is then repeatedly coated in ceramic slurry. The slurry consists of fine refractory particles suspended in liquid, which surrounds the wax pattern to form a ceramic shell. This shell is built up layer-by-layer until it is the desired thickness. The ceramic shell is allowed to harden, and then the wax is melted out in an autoclave. This leaves the hollow ceramic mold ready for metal pouring.

Investment Casting Process Steps

The investment casting process involves several key steps:

1. Wax Pattern Creation: Wax patterns are formed by injecting wax into metal dies. The wax patterns are a disposable model of the final cast part.
2. Assembly: Multiple wax patterns are attached to a central wax gating system, known as a wax tree or cluster.
3. Shell Building: The wax tree is repeatedly dipped in ceramic slurry, allowing a hard ceramic shell to build up around the wax pattern.
4. De-waxing: The ceramic shell is heated in an autoclave oven, melting out the interior wax pattern and leaving a hollow mold.
5. Pouring: Molten metal is poured into the ceramic shell mold to form the casting.
6. Breakout: Once the metal solidifies, the ceramic shell is broken away.
7. Cut-off: The castings are cut from the central gating system that fed metal into the mold.
8. Finishing: Additional cleaning and surface finishing operations are performed as needed.

Benefits of Investment Casting

There are many reasons investment casting has remained such a valued manufacturing process for centuries. Here are some of the key benefits:

• Ability to produce complex, detailed shapes not possible with other methods.
• Excellent surface finishing quality and dimensional accuracy.
• Wide range of metals can be cast, including stainless steel, cobalt, aluminum and more.
• Lower cost per part for small batch production compared to other processes like machining or forging.
• Minimal secondary machining required since parts are near net shape.
• Flexibility in design changes – wax patterns can be easily modified.

Applications of Investment Casting

Some of the most common applications of investment casting include:

• Aerospace: Blades, fittings, turbine components
• Medical: Joint replacements, implants, surgical equipment
• Automotive: Turbochargers, valves, drivetrain components
• Military/Defense: Missile and radar components
• Industrial: Pump housings, valves, tooling
• Jewelry: Rings, pendants, bracelets

Investment Casting Process Improvement

While investment casting has been used for thousands of years, there are still continual improvements being made to the process. Some modern advancements include:

• Using 3D printers to “print” wax patterns rather than injection molding for more flexibility.
• Simulating mold fill and solidification with software to optimize gating designs.
• Utilizing rapid prototyping to quickly iterate pattern designs.
• Automating parts of the wax assembly and shell-building steps for higher output.
• Using x-ray inspection of castings to reduce defects.

Choosing an Investment Casting Service Provider

Many companies do not have the in-house capabilities to perform investment casting, so they rely on investment casting service providers. When selecting a investment casting service provider, some key factors to consider include:

• Range of size capabilities
• Types of metals cast
• Secondary processing offerings such as heat treatment or machining
• Quality certifications
• Years of experience and industry reputation
• Tooling design support
• Rapid prototyping services

Investment casting service providers who offer complete solutions from design through finished parts can provide the best value to customers.

The Future of Investment Casting

Investment casting has come a long way from its early origins thousands of years ago. While the fundamental principles remain the same, new technologies and simulation tools have allowed the process to become more efficient, consistent and cost-effective. 3D printing, advanced materials and automation will likely continue advancing investment casting in the future.

Companies looking for a way to produce complex, high-quality metal components in lower volumes should consider the benefits of investment casting. This versatile process can create an astounding array of part geometries out of various alloys, all while keeping costs under control. With so many advantages, it’s no wonder investment casting has stood the test of time and will continue playing an integral role in manufacturing.