Investment casting is widely used for producing components with excellent surface finish and high dimensional accuracy. The process utilizes a single-piece ceramic shell mold, eliminating parting lines and enabling intricate external geometries.
While cores are extensively used in sand casting, their use in investment casting is less common. This is because the wax pattern and ceramic shell can inherently produce complex shapes. However, when internal cavities, undercuts, or hollow sections are required, ceramic cores become necessary.
Cores in Investment Casting
A core is a precision-shaped insert positioned inside the wax pattern prior to shell building. Its purpose is to create internal features or geometry that cannot be achieved with the wax pattern alone. Investment casting predominantly uses ceramic cores due to their high-temperature resistance and dimensional stability, making them suitable even for superalloy castings.
Types of Cores Used
| Core Type | Material | Used For | Notes |
|---|---|---|---|
| Ceramic core | Zircon, alumina, silica, mullite | Gas passages, turbine blades | Most common for aerospace and precision parts |
| Soluble wax core | Water-soluble or polymer wax | Small internal channels | Removed by hot water before shelling |
| Salt core (rare) | Sodium chloride + binders | Auto turbo parts | Has high strength, dissolves after casting |
| Hybrid core | Soluble wax + ceramic | Very intricate design | Used where one method alone fails |
| Material | Removal Method |
|---|---|
| Ceramic core | Hot caustic autoclave leaching (NaOH), ultrasonic agitation |
| Soluble wax core | water dissolution before shell building |
| Salt core | Water dissolution post-casting |
Soluble Wax Cores
Soluble wax cores are temporary internal wax structures used in investment casting to create cavities, holes, and undercuts that cannot be molded with standard tooling. After being inserted into a wax pattern, the core is dissolved before ceramic shell construction, leaving an accurate hollow wax cavity for the final casting.
Water dissolution before shell building is used where the temporary internal wax structure must be removed early, creating an accurate hollow wax cavity for the final casting.
Process Visuals: Core-to-Wax and Core-to-Metal Transfer
Ceramic Cores
Ceramic-based cores are particularly well suited for producing thin and intricate internal sections due to their excellent compatibility with the shell-building process. They offer stable handling during shelling without distortion or degradation.
From a performance standpoint, ceramic cores provide high-temperature stability, adequate mechanical strength, improved surface finish, and superior dimensional accuracy. As a result, ceramic material–based cores are more suitable than alternative core materials for applications requiring precise internal geometries and tight tolerances.
Capability Examples
Key Points
- Material: Water-soluble wax or PEG-based blend that can be molded and later dissolved.
- Manufacturing: Injected into precision molds using wax injection machines.
- Function: Provides internal geometry where ceramic cores are unnecessary or too difficult.
- Removal: Dissolved using warm water, ultrasonic bath, or controlled chemical leaching.
- Accuracy: High dimensional precision (±0.05–0.10 mm) and smooth internal surface finish.
- Controls: Requires stable handling conditions (low stress, controlled temperature/humidity).
Key Engineering Requirements
| Requirement | Target Value | Why Important |
|---|---|---|
| High temperature stability | > 1500°C (for nickel alloys) | Must not deform during pouring |
| High green/bake strength | > Sufficient to survive wax injection | Wax injection pressure ≈ 3–10 bar |
| Controlled leachability | After casting | Must be removable (chemical leaching or vibration) |
| Dimensional accuracy | ±0.15 mm typical | Ensures internal geometry accuracy |
| Gas permeability | >20% | Prevents trapped gases or core blow defects |
Where Ceramic Cores Are Used Most
- Aerospace turbine and hot-section components: internal cooling passages and thin-walled hollow cavities (blades/vanes and hollow structures).
- Power and energy: complex internal flow geometries in high-temperature, corrosion-resistant castings.
- Critical industrial applications: components where internal geometry accuracy drives performance, weight reduction, and reliability.
By combining core-making, wax injection, and investment casting process control, IPCL helps customers achieve repeatable internal geometries and thin-walled hollow features for critical components. Share your drawing or 3D model and our team can review manufacturability and propose a core + casting route.
Contact IPCL
General Enquiries: direct1@ipcl.in
New RFQs / NPD: npd@ipcl.in