Investment Casting Process
Wax Injection to Surface Finishing
With over 5000 years of research and development, PCT has had amply time to optimize the ancient lost wax investment casting technique. Our investment casting process incorporates the latest in metal forming technology to produce high precision, near-net-shape parts. The investment casting process is a highly repeatable, allowing for complex internal and external geometry without the need for secondary operations.
Tool & Mold Design
Tooling and wax pattern design is arguably the most critical step of the investment casting process. Rapid prototype patterns can be generated from CAD models using various resins and polymers.
Several factors are taken into consideration during the design process, including parting plane location, gate location, injection location, wax and metal shrinkage, slide location, and intended function of the cast part.
Wax Pattern Injection
Pattern injection begins by melting virgin wax devoid of any contamination, filler separation, and air entrapment. Wax is then poured into an aluminum wax injection mold until the desired thickness has been reached.
We constantly monitor wax temperature to ensure a consistent layer of wax is formed within the mold, which is later left to cool and solidify. Water cooled platens are used to accelerate solidification and therefore reduce production time.
Wax Pattern Assembly (Gating Process)
Following cooling, wax patterns are removed from their molds and attached to runner systems, also known as "sprues". The complete assembly of patterns and runners is affectionately known as the "tree."
Ceramic Shell Building
The actual "investment" part of investment casting process, ceramic shell building is a three step process. Step one involves dipping the wax pattern assembly (tree) in slurry and draining it evenly. Step two is to cover the tree in ceramic grain. Step three is to allow the slurry-ceramic material to thoroughly dry.
The process is repeated several times to form a layered ceramic shell around the wax tree.
The ceramic shell-wax tree is placed in a high temperature, high pressure vessel for wax removal. While wax is being melted inside the ceramic shell, pressure forces the wax to run out through the runner system.
This process leaves the ceramic shell devoid of wax. The resulting cavity is comprised of the previously existing wax pattern shape and runner system.
Casting of Parts
Molten metal alloys are poured into the preheated ceramic shell. As the metal cools, it solidifies into the shape of the cavities left behind in the ceramic shell by the wax patterns.
Ceramic Shell Removal (Dewax)
After the molten metal has cooled, the ceramic shell material is removed from the castings and runner system. This is accomplished by mechanically vibrating the tree.
Each individual casting is then removed from the runner system. The runner system is melted again and poured into other ceramic shells.
The castings are now ready for any secondary operation: grinding, heat treating, straightening, machining, plating, non-destructive testing, and finally shipment to the customer.
We perform a variety of inspections to ensure the quality of our investment casting process, including:
- Fluorescent Penetrant Inspection
- Radiographic (X-ray) Inspection
- Chemical Analysis Determination
- Mechanical Property Testing
- Internal Borescope Inspection
- Hardness Testing
- Dimensional Inspection
- Magnetic Particle Inspection
Our engineers are happy to answer any additional questions you may have on the investment casting process by email, or call us at 888-775-3590.