Mould Components
Die casting is a manufacturing process in which molten metal is poured into moulds or dies in a foundry. Die casting is often used to make components for the automotive industry and many other small components. In fact, die-cast parts can be found in many things as they are durable, dimensionally stable, and can provide complex shapes within closer tolerances compared to other foundry cast production methods.
The most common types of die casting are hot and cold. The difference between them is that hot chamber die casting heats metals in the casting machine while cold chamber heats metal in a furnace and transfers the molten metal to the casting machine. The process produces complex shapes with close tolerances, heat resistance, and high tensile strength with little need for additional tooling and shaping.
Read more on Die Casting
The die casting unit comprises of a clamping unit, die assembly, and the injection unit. There are various die casting processes - the two popular being hot chamber die casting and cold chamber die casting.
The casting die has four major functions:
- Hold the molten metal in the shape of the desired casting
- Provide means for molten metal to get into the space where it is to be held in the desired shape
- Remove heat from the molten metal to solidify the metal
- Provide for removal of the solidified metal
There are 5 basic types of dies and moulds - pressing dies, casting dies, forging dies, injection moulds and compression moulds. Of course, there can be a different way of classifying dies and moulds too. However most of them have common components that include:
The mould base: The mould base is the outer steel (or other suitable material) shell that holds all the other die parts together. It consists of two halves which form a cavity into which the liquid melt is pressed during the casting process. It is split or parted into two halves, one of which is stationary and the other is moving. Each die half is first cleaned from the previous injection and then lubricated to facilitate the ejection of the next part. The stationary half mold base has a number of components and features that are important to the die’s function that include clamp slots, guide pins, pryslots and mounting / clamp plate. The moving half couples the ejection system to the cavities, and provides a means for aligning the two die halves.
Guide bushings: guide bushings are round holes located at the four corners of the die, designed to accept the guide pins. With the guide pins, their purpose is to align the two die halves. If the die uses guide blocks, the bushings are replaced with wear plates for two sides of the guide blocks.
Ejector box and ejector system: The ejector box refers to the area that encloses the ejector system of the casting die. The ejector system resides in the box, and facilitates removal of the solidified metal once the die casting process is completed.
Ejector plate: the heads of the entire ejector pins rest on the ejector plate. As the ejector plate moves forward, it pushes on the pins and ejects the casting.
Core pins: these are usually used to cast round holes in the part.
Cam pin: is a pin mounted into the stationary mold base at an angle. It fits through a hole in the slide carrier and causes it to slide in and out with the closing and opening motion of the machine.
Cavity blocks: the term ‘cavity blocks’ includes all the specialized tool steel that is used to form the actual casting. This could include core pins, interchangeable inserts within the cavity blocks and various slide cavity components.
Cooling lines: most cavity blocks will have cooling lines in them. These are necessary to perform one of the basic die functions: Remove heat from the molten metal to solidify the metal.
Heaters: some dies may use electric cartridge heaters to control temperature instead of cooling lines or in addition to cooling lines. These heaters will have wiring associated with them to power them.
Runner: the runner is the die cast alloy distribution system within the casting die. It takes the alloy from the biscuit or sprue and directs it to the die cavities, where the casting is actually made. The runner terminates at the gate. The wiring can pose a shock hazard if not properly maintained.
Gate: is the smallest restriction in the alloy flow path, located at the edge of the casting. The gate is used to control the flow of the alloy into the die cavity.
Vents: a vent is a path from the die cavity to outside the die. Vents usually start at an overflow, but they can start at the edge of the cavity if necessary.
Sprue post: the sprue post is the beginning of the metal distribution system. Proper cooling in the post is very important to consistent operation of the die.
Overflows and lifters: the overflows are small pockets of alloy located around the edge of the casting. They can be used to perform several jobs.
Of course, there are other parts in a mould as well; we have tried to cover the major ones.
In order to achieve perfect casting, or castings with minimal post-processing, it is necessary to get everything right. This includes good designing, choice of right casting process and choice of the correct metal / alloy. Thanks to advances in technology, CAD drawings and simulation / modelling techniques have helped foundries in India and other parts of the world deliver quality castings.