Investment casting, also known as lost wax casting or precision casting, is a precision casting method with less and no cutting. Investment molding materials (usually low melting point materials such as wax) are used to make investment molding samples and form a module. Then paint (refractory material) is applied to the surface of the module. After drying and solidification, the module is heated to melt out the molding material. A hollow shell is formed, and the metal liquid is poured into it after high-temperature sintering, and the casting is obtained after cleaning.

• Characteristics of investment casting

Castings have high dimensional accuracy (CT4-CT7); low surface roughness (Ra1.6-6.3um). The cutting allowance of castings is reduced, and near-net-shape casting can even be achieved.

Capable of producing thin-walled castings with complex shapes. Such as the front receiver (composed of inner and outer rings and 14 blades). For example, engine blades have a minimum wall thickness of 0.7mm.

Alloy materials are not restricted. Steel, copper, aluminum, titanium, magnesium, etc. Nickel-based high-temperature alloys with high melting points, low melting point metals such as zinc and tin.

Investment casting has certain limitations. The process is cumbersome, the production cycle is long, and the size of the castings should not be too large.

• Investment Casting Process Flow

1. Design and manufacture the molding.

The mold used to make the wax pattern is called a stamper. It is required to have high dimensional accuracy and surface finish. It is made of aluminum alloy, steel, fusible alloy, plaster or plastic material according to the production batch.

2. Make wax patterns.

The material of the wax mold is usually made of 50% paraffin and 50% stearic acid. After melting, use a wax press to press the paste wax material into the mold. After solidification, take it out and put it into cold water to cool down to prevent deformation. The sprue mold is usually made of a wooden rod or aluminum rod dipped in a 2-3mm wax shell, and then the wax patterns are welded to the sprue mold with an electric heating knife to form a module.

3. Shell making.

Dip the module into a coating made of quartz powder and water glass (or silica sol), take it out, sprinkle it with quartz sand, and then put it into a hardener (commonly used ammonium chloride or aluminum chloride) solution to harden it into a Layer the shells and repeat the above operations until a shell thickness of 5-10mm is formed.

4. Dewaxing and roasting.

Put the molded shell into a hot water tank at 95-100℃ to melt the wax mold and float it out. Then bake the mold shell at 800-900℃ (water glass mold shell) to increase the strength and remove the mold shell. Moisture, residual wax, saponification, etc.

5. Pouring and cleaning.

The fired mold shell is often poured while it is hot after being released from the furnace in order to produce thin-walled castings. After the casting is cooled, destroy the mold shell, take out the casting and cut off the pouring and riser system, and then carry out the casting post-processing process, that is, use sandblasting, shot blasting, alkali boiling and electrochemical cleaning methods to remove the residual shell and adhesive on the surface and inner cavity of the casting. Sand, chloride, etc. are removed to obtain castings with smooth surfaces.