The mold used to obtain the shape of the casting is called pattern, and the mold used to obtain the inner cavity of the casting is called core box. Sometimes the core made of the core box can also be used to obtain the shape of the casting. According to the different materials used to make pattern and core box, it can be divided into three categories: wood mold, metal mold and plastic mold.
1. wood mold. Pattern and core box made of wood. The wood is light, easy to be processed and shaped, short production cycle and low cost. But it is not durable and easy to deform. It is the most widely used pattern material in single piece or small batch production.
2. metal mold. Pattern and core box made of metal material. Commonly used metal materials are aluminum alloy, copper alloy and gray cast iron. Aluminum alloy is the most commonly used metal material because of its light weight, easy processing and forming, and not easy to rust.
3. plastic mold. The performance of plastic mold is between wood mold and metal mold.
In practical production, wood mold is widely used. Because the wood mold forms the cavity of the mold, the structure of the wood mold must consider the characteristics of the casting. If it is convenient to take the mold, the slope (called draft slope) shall be made on the wood mold wall perpendicular to the parting surface; the connection between the upper wall and the wall of the wood mold shall adopt the fillet transition; on the processing part of the part, the redundant metal layer (called machining allowance) cut during the cutting process shall be reserved, considering that the size of the wood mold is larger than the size of the part (called shrinkage allowance) after the metal is cooled; and The part with hole on the part, the wood mold is solid without hole, and bulges a piece (called core head). It can be seen that there is a difference between wood mold and parts. Therefore, wood mold is generally not manufactured directly according to the part drawing, but based on the part drawing, the parts must be designed for casting process, and the casting process drawing must be drawn before the wood mold and core box are manufactured.
The above tooling (pattern and core box, etc.) shall be used with care to maintain its accuracy, such as avoiding pounding their surfaces during the process of sanding; after the mold or core box is lifted, it shall be cleaned with a brush immediately, and wiped with cotton yarn, otherwise the mold (core) sand is not easy to clean after air drying, and the working surface shall be scratched when it is removed with hard objects; after use, it shall be cleaned and placed on the rack to prevent moisture.
Large complex parts usually depend on several sand cores and sand mold parts to form their geometry. When running the core, a sample plate is needed to check whether the position and size of each other are correct. Complex sand cores are often manufactured in blocks. Sometimes it is necessary to use the lower core fixture to assemble them and then put them into the cavity together.