Investment casting, also known as precision casting, produces precise and reliable parts that exactly match design tolerances. The process of investment casting is built on the concept of a wax pattern that is enveloped in a ceramic slurry.
What is Investment Casting?
Investment casting begins with the creation of a wax pattern in a metal die. The two halves of the die, that contain the shape of the final part, are sealed together, and injected with wax that fills the die to create the investment castings.
The wax pattern is removed from the die and placed on an assembly pattern that includes a wax sprue and gate. Multiple wax patterns of the same or diverse shapes are placed on the wax sprue. The assembly pattern, or tree, is dipped in a ceramic slurry to coat the wax patterns.
The ceramic coated tree is dipped several times in stucco to thoroughly coat it. The stucco coating is allowed to harden and form a firm covering over the ceramic coated wax patterns.
The hardened stucco coated assembly tree is heated, which melts the wax, which runs out the bottom of the assembly tree. The empty mold is subjected to 870° C or 1598° F to 1095° C or 2003° F, a process called burnout, to remove remaining moisture or wax residue as well as sinter and solidify the mold.
With the wax removed, and after the burnout process, the assembly tree, which is now a mold tree, is filled using gravity pouring, pressure forced air, or other pressure forced methods. If the molded part has intricate minute details, extra force may be necessary to ensure the pattern is completely filled.
Divesting, or shaking out, is the process of removing the stucco shell. This can be completed by hand using a hammer or by a media blaster, vibrator, waterjet, or chemical solvent such as liquid nitrogen. The completed investment castings are removed from the sprue and gate for final finishing, which may involve grinding.
There are several possible final steps in the process that include the removal of impurities, welding, and straightening. These finishing operations are designed to improve the tolerances of the investment castings.
Benefits of Investment Casting
Investment casting is a faster production method that produces flawless parts with a smooth finish and tolerances of ± 0.005 per inch. It is a process that requires significantly less tooling and lower equipment costs.
One of the normal problems with the casting method is shrinkage, which is accounted for in the computer design phase. This is not necessary in investment casting. The computer rendering is exactly duplicated in the casting process without shrinkage or adhesion, which increases a parts ability to endure stressful conditions.
Many modern parts have precisely designed intricately detailed components that require dies and molds with minute shapes. Investment casting is an ideal solution because of the accuracy of its tolerances and ability to adhere exactly to the computer design parameters.
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