A Quick Guide to Investment Casting

A 5,000-year-old process, investment casting has evolved to become one of the most essential casting methods used by manufacturers today.

During the investment casting process, hot wax is first injected into a metal mold in order to create a detailed model of the part. This wax model is then repeatedly coated with a refractory ceramic material, forming multiple hardened layers. The wax is removed via high-temperature melting, leaving only a hollow, molded shell representation of the original part. Next, hot metal is poured and solidified into the mold.

In order to remove the metal casting from the original shell, various techniques can be employed, from hammering to water jetting. The final part may be customized and finished with heat treating or other machining processes.

The Advantages of Investment Casting

Also known as “lost-wax casting,” investment casting allows for unique benefits across a range of different industries. First off, the process allows for the production of extremely complex parts with thin, intricate features and excellent overall dimensional accuracy, achieving tolerances as tight as +0.003 in. (0.076 mm).

Finished investment casting parts also offer smoother surface finishes without any visible parting lines that may require removal. With investment casting, whole parts can be manufactured without the use of machining, welding, or assembly. Complex, multipart assemblies can also be cast in a single run.

And for investment casting manufacturers, the technique can be utilized for a variety of components across countless industries, allowing for expanded production capacity. Thanks to the wide range of metals available for use with investment casting, manufacturers are afforded greater design flexibility.

The Disadvantages of Investment Casting

In rare cases, parts such as turbine blades, aircraft door frames, and other heavy components may be made using investment casting techniques. However, the process is usually ideal for smaller castings or complex parts weighing less than 250 lb. It’s important to remember that there are hole-size limitations for the mold; no less than 1/16” diameter is achievable before problems begin to occur.

While this casting technique is both flexible and reliable, it’s not ideal for high-volume runs due to the labor, setup, and cycle times required for initial wax patterns and shell molds. Investment casting manufacturers must also think carefully about the economics of part production, as overall quality may be affected. And finally, investment casting does entail fairly expensive startup costs.

Industries Served by Investment Casting

From dental fixtures to heavy gears, investment casting is the go-to technique for multiple applications. Jewelers use investment casting for rings, pendants, and other small or intricate pieces. In the aerospace sector, numerous alloys are cast for interior components, landing and braking parts, bearing cages, and more.

For firearms manufacturers, investment cast parts offer greater precision and smoother surfaces than traditional machining offers, as well as near-net shape results that eliminate waste. In commercial and private hydraulic applications, common investment casting products include gate, rotary, and plug valve configurations made from stainless steel, iron, and brass. Other industries making use of investment casting include military, home hardware, automotive, medical, food and beverage, oil and gas, and railroad.

Materials and Products Produced Using Investment Casting

Virtually any metal can be investment cast — from durable brass plumbing components to lightweight magnesium-alloy aircraft canopies to stainless steel flywheels in automobiles. Whether users require a simple hammer from the hardware store or a customized, complex vacuum relief valve for railroad cars, investment casting provides the versatility needed to create a range of small- to medium-sized metal products.

Commonly used materials include steel, bronze, aluminum, cobalt, stainless steel, Monel, and both ferrous and non-ferrous metals. New automation technology has also improved some areas of the investment casting process, allowing for the creation of products that were previously unobtainable with this technique.

Investment Casting Through the Ages

Investment casting is based on an ancient manufacturing process that was used by Egyptian and Chinese civilizations. The materials, methods, and processes involved have evolved over the course of thousands of years, and manufacturers can now achieve low- or medium-volume production for complex metal components without the need for extensive post-processing.

And with new advancements in metal alloy compositions introduced to the market every year, the product and material options for investment casting continues to broaden, helping today’s manufacturers to compete on a global scale.