How Investment Casting Is Used, and What is the Investment Casting Process

When it comes to metals, Investment Casting is one of the most widely used rapid prototyping techniques, as well as the one that is moving the fastest towards manufacturing application. Instead of using molded wax to create patterns, rapid prototyping processes are used to create them. Models are typically created through the stereolithography process, which is the most widely used method. Honeycomb build patterns are commonly used because they allow the plastic pattern to expand when it is burned out without causing the mold to be cracked. Because of the ash that may remain after pattern burnout, selective laser sintering and laminated object manufacturing are being used less frequently for this purpose in recent years. The Sanders model maker, which uses inkjet technology to produce wax parts with extremely high resolution and accuracy, is also frequently employed. A wide range of castable engineering materials are used in the production of the castings, and the process is being used to produce very low volume production components when the cost savings on pattern tooling are significant.

How Investment Casting Is Used, and What is the Investment Casting Process

When making complex-shaped components, investment casting is typically used because it allows for tighter tolerances, thinner walls, and a better surface finish than can be achieved with sand casting. The method by which the mold is created distinguishes investment casting from other types of casting. A wax pattern is created for the part, which is then dipped into a fine ceramic slurry that contains colloidal silica and alumina to create the final product. It is necessary to dry the mold and heat it in an oven in order to melt out the wax, leaving a ceramic shell mold that can be used for casting. Precision casting of aerospace components, such as gas turbine blades, is accomplished through the investment casting method, also known as the lost wax process. Investment casting of aluminum alloys results in a lower strength than sand castings, but it allows for tighter tolerances, a better surface finish, and the ability to produce thin-walled sections, all of which are advantageous.

Neither Investment Casting Services nor die casting are incapable of producing parts with similar geometric shapes and sizes. The disposable pattern is created by injecting wax into a mold, as you will learn below. As a result, features that are difficult or expensive to injection mold or die cast (for example, undercuts) are also difficult or expensive to investment cast. In most cases, investment casting is used when low production volumes (e. g., less than 10,000 pieces) are anticipated, whereas die casting is typically used when high production volumes are anticipated.

A wide variety of metal alloys can be used to create investment cast parts. These include aluminum and copper alloys, carbon and low alloy steels, stainless steels, tool steels, as well as nickel and cobalt alloyed alloys. You will learn in the following section that die castings must be limited to metals with low melting temperatures, primarily zinc and aluminum, due to the nature of the process.

Investment casting is the process of creating a metal die or mold, which can be accomplished through either machining or casting. The more complicated the shape (as a result of undercuts, for example), the more expensive the metal dies are to produce. Following the formation of the mold, wax is injected into the mold to create a pattern. The external shape of the wax pattern is a close match to the internal shape of the silicone mold. Removed from the mold and attached to a wax base that contains a gate, the wax pattern is now ready to be used. The wax patterns are attached to a tree that contains the runners, gates, and other features that will feed and distribute the molten metal if the production volume is large enough to support them. In this step, the wax patterns are covered with a metal hollow tube, into which a slurry (such as plaster of Paris) is poured to completely cover the patterns. The finished mold is placed in an oven, where the wax is removed through a process of melting and evaporation. Following this, the mold is usually placed in a second oven for 12 to 24 hours to allow the mold to cure completely.

To create parts, molten metal is poured into the mold cavity and allowed to solidify before the parts are removed. The melt is poured into the mold while it is still hot in order to make filling the mold easier. When the part has cooled to the touch, the mold is destroyed and the part is carefully removed. Investment casting is capable of producing tolerances and surface finishes that are so good that machining is rarely necessary.

The investment casting process itself is relatively straightforward and well established; however, the production of premium, high integrity, and high-quality components suitable for increasingly demanding aerospace applications is not without its challenges. Production of fully dense castings with low porosity, inclusions, oxides, and impurities and a very fine microstructure, as well as a modified eutectic structure is now possible, and as a result, fully dense castings are now manufactured on an industrial scale.

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