Die casting uses high pressure to inject molten metal into a mold to form a part or design. An extinct printing method called linotype used the die casting method to produce plates for large printing presses. Its development replaced or augmented the previous gravure printing process. With the development of computers, typesetting machines disappeared, replaced by efficient technical methods.
There are two types of die casting - cold chamber and piston or gooseneck. These methods vary depending on how the molten metal is injected into the mold. Understanding the differences between these two processes can help determine the production method for part designs.
Cold chamber die casting is used for metals with high melting points. Common materials used in this process are metal alloys such as aluminum, brass, and copper. The cold chamber process requires the use of a furnace and ladle to pour molten metal. In the cold chamber process, there are two methods of introducing molten metal into the mold—with a ladle or through a high-pressure plunger. Cold chamber die casting requires higher pressures than other die casting methods, but it takes several minutes for the molten metal to solidify. Additionally, molds can have multiple cavities, allowing multiple parts to be produced simultaneously.
In the piston or gooseneck process, the piston is removed and the mold is submerged in molten metal. When the die is fully immersed and the gooseneck is full, the piston extrudes the molten metal from the gooseneck into the die. The piston process has a fast cycle time of approximately 15 minutes to produce parts quickly and efficiently. This method is limited to low melting point metals and cannot be used for aluminum that sticks to the sides of the mold.
The first step in the die casting process is to create two parts of a reusable steel mold. To ensure easy removal of the casting from the mold, a lubricant is used to help regulate the temperature and to aid removal when the mold separates. The two parts are then firmly clamped together and injected with molten metal. Die casting has the flexibility to produce highly complex and complex parts or very simple parts, but is limited to non-ferrous metals.
There are four basic categories of molds: single-cavity, multi-cavity, combination, and unit. As the name suggests, single-cavity molds have a single cavity, while multi-cavity molds can have similar or different cavities, depending on the process. A multi-cavity mold with different cavities is called a combination. Unit molds have multiple cavities connected by runners and can produce multiple parts in one casting.
Despite the limitations of using only non-ferrous metals, die casting has the advantage of producing parts that are dimensionally correct and have excellent shape tolerances. The ability to have dimensional consistency and a uniform design are two qualities that have made it popular over the years. Like some other casting techniques, die casting requires little machining after casting.
The biggest disadvantage of die casting is the process cost, which is mainly related to the production and processing of the mold. Although they can be designed using computer software, they are produced using molten steel, which limits the ability to experiment and make prototypes. Since molds can be stored and reused, this is an excellent way to produce large numbers of parts, reducing initial investment costs. It should not be considered for single parts, prototypes or small batches.
The mechanical properties of die castings are limited. They are rarely considered as assemblies and not as structural parts. Die castings are designed for immediate use, such as engine blocks.