Steps in the Investment Casting Process

Investment casting, also known as lost wax casting, is a widely used casting process that can be used to produce a variety of complex and delicate metal parts. The process involves more than 30 steps, each of which plays a vital role in ensuring the quality and accuracy of the final product. In this article, we will take a deep dive into the various steps of the investment casting process and explain each step in detail.

The first step in investment casting is to make a model (before this, a mold for the production model must be made according to the drawings provided by the customer). The model made is usually made of wax or similar materials to replicate the desired shape of the final product. After the wax model is trimmed and inspected, the model is connected to the wax pouring system (sprue rod), which is customarily called a group number, and the wax scraps on the wax tree are blown clean.

Once the model group number is completed, the residual release agent and other oil stains that affect the sticking of the wax tree are cleaned with a cleaning agent, and then coated with fine ceramic slurry powder. The outer shell mold is made by repeatedly dipping the model into the backing ceramic slurry several times (usually about four to five times) and finally coated with fine ceramic slurry to ensure that the shell is thick and durable.

After the ceramic shell is dried, it is heated (about 170 degrees) and pressurized (about 7-8 atmospheres) in a dewaxing kettle to remove the wax in the shell mold, leaving a cavity in the shape of the desired product. This step is called dewaxing and is critical to ensure that the molten metal can fill the cavity during the casting process.

The next step is to preheat and heat the shell mold to the required temperature. At high temperatures (below 1200 degrees), the silica sol shell mold will increase in strength, and most of the water will evaporate completely, ensuring that the shell mold can withstand the extreme temperatures of the molten metal without cracking or breaking. When the shell mold is poured with molten steel at high temperature (red shell), the molten steel is more likely to fill the shell mold cavity and is less likely to have defects such as cold shut.

After the shell mold is preheated, the casting process can be carried out. Pour the molten metal (usually steel or aluminum) into the shell mold. The molten metal fills the cavity and solidifies to take the shape of the desired product.

After the molten metal is completely solidified, the shell mold is peeled off to reveal the newly cast metal part. This step is called shelling and is usually done using mechanical methods such as vibration or sandblasting.

The final step in the investment casting process is grinding the feed port and finishing the casting. This includes removing any excess material, such as the gating system or rough edges, and finishing the surface of the casting, welding defective castings, and shaping deformed castings. Depending on the specifications required for the final product, finishing may include processes such as grinding, polishing, or heat treatment.

In summary, the investment casting process involves several basic steps, each of which helps to produce high-quality metal parts. From pressing the wax pattern to the final finishing, each step requires precision and attention to detail to ensure that the final product meets the required requirements. By understanding and following these steps, investment casting companies can easily produce complex and fine-surfaced metal parts.