The Investment Casting Process
Investment casting is a manufacturing process in which a wax pattern is coated with a refractory ceramic material. Once the ceramic coating material is dry and hardened, the wax is melted out and leaves an internal cavity the shape of the final product’s geometry. Molten metal is poured into the cavity where the wax pattern was. The metal solidifies within the ceramic cavity, cools, and the ceramic is removed from the metal casting. The result of this process is a net to near-net precision metal component which can be used for a broad range of applications in various industries.
The Ancient Art of Investment Casting
The ancient art and science of investment casting is also known as the lost wax process. Investment casting was developed over 5500 years ago and can trace its roots back to both ancient Egypt and China. Parts manufactured in industry by this process include dental fixtures, gears, cams, ratchets, jewelry, turbine blades, machinery components and other parts of complex geometry.
The Investment Casting Process
Investment casting is a manufacturing process in which a liquid material is poured into a ceramic mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is the casting, which is broken away from the ceramic mold to complete the process. The steps within the investment casting process are as follows:
- Pattern Creation - The process begins with a precision-engineered wax replica of the desired end product—the key to achieving such a detailed casting. The wax replica is produced from a wax injection mold that is built here at Aero Metals and can reproduce millions of wax parts over its lifetime.
- Mold Creation – The wax “pattern” is then dipped into a ceramic slurry several times, drying between each dip, building a strong ceramic shell around the wax pattern(s). Within a high pressure and heat vessel, the wax is then melted out and creates the ceramic mold hence the name “lost wax” casting. The ceramic shell mold is then placed into a high temperature oven to cure (polymorph) the ceramic mold and prepare it for accepting molten metal.
- Pouring - The mold is preheated in a furnace to approximately 1000°C (1832°F) and the molten metal is poured from a ladle into the gating system of the mold, filling the mold cavity. Pouring is typically achieved manually under the force of gravity, but other methods such as vacuum or pressure are sometimes used.
- Cooling - After the mold has been filled, the molten metal cools and solidifies into the shape of the final casting. Cooling time depends on the thickness of the part, thickness of the mold, and the alloy used.
- Casting Removal - After the metal has cooled to the touch, the ceramic mold can be broken away from the part(s), and the casting removed. The ceramic mold is typically broken using water jets, vibration, or other methods. Once removed, the parts are separated from the gating system by either sawing off or cold breaking (using liquid nitrogen).
- Finishing - Often, post-cast finishing operations such as grinding, sandblasting, or shot-blasting are used to remove the gate(s). Heat treatment is also sometimes used to anneal or harden the final part before sending to the customer.
In addition, within the post-casting stage Aero Metals is fully equipped to handle any finishing, if necessary.
Investment Casting Materials
Aero Metals can create precision metal components through investment casting using nearly any metal. However, the advanced quality materials we most commonly use, include:
The investment casting process is most beneficial for casting metals with high melting temperatures that cannot be forged, pressure casted, or molded in plaster or sand. Typical investment castings include parts with complex geometries, such as turbine blades, firearm components, marine parts, and other industrial components.
Investment Casting Benefits
There are many benefits associated with investment casting in the manufacturing of precision metal components, some of which include:
- Mold design versatility
- Increased complex design capabilities
- Provides for a smoother surface (125 RMS)
- Highly accurate, repeatable-designs
- Time & cost savings versus fabrication and machining
- Produces numerous types of products
- Numerous types of metal alloys can be used