Investment casting, also known as investment casting or lost wax casting, is a process in which models are made from fusible materials such as wax and plastic. First, these models are coated with multiple layers of refractory paint, which dries and hardens to form a monolithic shell. Then, the model is heated to melt and disappear, and then the shell is baked at a high temperature and poured into liquid metal. After cooling, the casting is finally formed.

2. What is the manufacturing process for investment casting?

Moulding material preparation, wax mould making, mould forming, mould repair, painting, sanding, stripping, baking, pouring, cooling, sanding, cleaning.

3. What are the advantages of choosing investment casting?

The main advantages of investment casting over other casting methods include:

High precision and low roughness: the dimensional accuracy of the castings can reach 5~7 grade, and the surface roughness can reach Ra25-6.3μm, which is capable of casting parts with complex shapes:
Casting of thin-walled and small castings: minimum wall thickness up to 0.5 mm, weight down to a few grams.
Fine details: castings with fine patterns, lettering, fine grooves and curved air holes can be cast.
Shape Freedom: Virtually unlimited shapes and cavities, enabling the production of complex parts that would be difficult to manufacture by other methods.
Wide choice of materials: suitable for a wide range of materials such as cast alloy steel, carbon steel and heat-resistant alloys.
Flexible production batches: suitable for single to mass production.

Of course, this method also has its shortcomings, such as investment casting due to the complexity of the process, so the production cycle is relatively long, and is not suitable for urgent orders for the manufacture of parts.

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II: Types of molding materials and performance requirements

1. Type of material:

Moulding materials used in investment casting are varied with the development of technology, and are mainly divided into high-temperature materials, medium-temperature materials and low-temperature materials.

The melting point of low-temperature materials is lower than 60℃, such as the widely used paraffin-stearic acid materials;
The melting point of high-temperature materials is higher than 120℃, such as the materials composed of rosin, ground wax and polystyrene;
The medium-temperature materials are between the two and are usually categorized into rosin-based and wax-based materials.

2. Performance requirements for investment casting materials:

Thermophysical properties: suitable melting temperature and solidification interval, small thermal expansion and contraction, high heat resistance, no precipitates or phase changes.
Mechanical properties: e.g. strength, hardness, plasticity, flexibility, etc.
Process Properties: Includes viscosity, ash, coating properties and drapability.

III: Molding process

According to the specified composition and proportion of materials, the raw materials are melted and mixed, filtered to remove impurities and poured into the mold for compression.
The main methods of compression molding are injection molding and extrusion molding.
Injection molding is carried out at low pressure, while extrusion molding is carried out at high pressure. The advantages and disadvantages of filling and curing need to be considered for different molding methods.

IV: Shell production process

Shell making includes two processes: painting and sanding.
Before painting, the mold needs to be degreased, and the paint should cover the surface of the mold uniformly to avoid blanks and local accumulation.
After painting, sanding is carried out to enhance the strength and air permeability of the shell.
The size of the grit should be selected according to the level of painting, and the top layer should be sanded with a fine grit to ensure a smooth surface cavity.
After each layer of painting and sanding is completed, it must be fully dried and hardened.

V: Casting defects and prevention methods

Defects in investment castings are categorized as surface defects, internal defects, and size and roughness overruns.
Surface and internal defects such as undercasting, cold segregation, shrinkage holes, air holes, etc., which are related to the pouring temperature of the alloy liquid, the baking temperature of the shell and the process.
Dimensional and roughness overruns are usually related to factors such as mold design, casting wear, and shell strength. For example, when castings are underpoured, it may be due to low pouring temperature, insufficient shell temperature, casting wall thickness is too thin, pouring system design is unreasonable. It is necessary to take corresponding measures to solve the specific problems.

VI: Conclusion

Investment casting is not a simple process. In order to obtain high quality castings, it is crucial to choose a professional investment casting manufacturer, Allied Metal has more than 20 years of experience in casting and has successfully cooperated with many companies to provide you with professional investment casting services. Please feel free to contact us for more information.