INVESTMENT CASTING PROCESS

Investment casting, also known as lost-wax casting, is one of the oldest and most precise metal-forming techniques. It is favored for its ability to produce complex geometries with exceptional surface finishes and tight tolerances.

Here is a step-by-step breakdown of the industrial investment casting process.

The process begins with the creation of a wax pattern. This is typically done by injecting wax into a metal die (mold) that has been precision-machined to the dimensions of the final part. Because wax shrinks as it cools, the die is designed to be slightly larger than the final product.

To maximize efficiency, multiple wax patterns are attached to a central wax "sprue" or runner. This creates a pattern tree, allowing many parts to be cast simultaneously in a single mold.

The wax assembly is dipped into a high-grade ceramic slurry and then immediately coated with fine sand (stucco). This process is repeated several times—allowing the layers to dry between dips—until a thick, high-strength ceramic shell is formed around the wax.

Once the ceramic shell is dry, it is placed in an autoclave or flash-fire furnace. The heat melts the wax, which drains out of the bottom of the shell, leaving a hollow cavity that perfectly matches the shape of the original patterns.

The empty ceramic shell is heated to high temperatures (often between 500°C and 1000°C). This strengthens the ceramic and prevents the molten metal from cooling too quickly. Molten metal is then poured into the preheated shell.

After the metal has solidified and cooled, the ceramic shell is broken away through mechanical vibration, water blasting, or chemical leaching. This process is known as knockout.

The individual metal parts are cut away from the central sprue. Any remaining gates or imperfections are ground down. Depending on the requirements, the parts may undergo:

• Shot blasting for surface texture.

• Heat treatment to improve mechanical properties.

• Precision machining for ultra-tight tolerances.

Once the metal parts are separated from the "tree," they undergo a series of finishing and corrective steps to ensure they match the client's specifications.

• Heat Treatment: Castings are often subjected to processes like annealing, quenching, or tempering. This alters the molecular structure of the metal to achieve specific hardness, ductility, or tensile strength.
• Surface Finishing: To achieve the final desired look and feel, parts may undergo shot blasting (to remove scale), vibratory finishing (to smooth edges), or passivation (to improve corrosion resistance).
• Secondary Machining: While investment casting produces "near-net-shape" parts, high-precision features like threaded holes or extremely flat mating surfaces are finished using CNC machining.

Before dispatch, parts undergo rigorous testing to ensure both surface integrity and internal soundness.

Visual & Dimensional Inspection

• Visual Check: 100% of parts are inspected for surface defects like cracks, inclusions, or "misruns" (where metal didn't fill the mold completely).
• CMM Measuring: A Coordinate Measuring Machine (CMM) uses a high-precision probe to verify that the part’s dimensions fall within the required tolerances (often as tight as $\pm 0.127\text{ mm}$).

Non-Destructive Testing (NDT)

• Dye Penetrant Inspection (DPI): A fluorescent dye is applied to the surface. Under UV light, this dye reveals microscopic surface cracks invisible to the naked eye.
• Magnetic Particle Inspection (MPI): Used for ferromagnetic metals to detect surface and near-surface discontinuities.
• X-Ray/Radiographic Testing: To ensure there is no internal porosity or gas bubbles, X-rays are used to see "inside" the metal, ensuring a solid, dense structure.

The final stage ensures that the precision-crafted parts arrive at their destination in perfect condition.

Anti-Corrosion Treatment:

• Many parts (especially steel) are dipped in anti-rust oil or VCI (Vapor Corrosion Inhibitor) solutions to prevent oxidation during transit.

Custom Packaging

• Parts are often placed in individual cells within foam inserts or plastic trays to prevent "metal-on-metal" contact, which could cause scratching or denting.

Documentation

• Every shipment is accompanied by a Material Test Report (MTR) and a Certificate of Conformance (CoC), proving the chemical composition and quality standards have been met.

Logistics

• For international orders, parts are typically packed in export-grade wooden crates that are heat-treated (ISPM 15) for global shipping compliance