Die casting, or pressure casting, is a relatively recent technology: the first machines were built in the twentieth century, but it has evolved very rapidly in recent decades. The die casting process is particularly suited to producing large volumes of small and medium-sized components that require a good level of accuracy, surface quality and dimensional consistency.
Its evolution has been driven by the growing demand for consumer goods (household appliances, cars, motorcycles, mechanics, etc.) and it is now used in every field. The equipment needed to produce die castings consists of specific die casting machines and dies.
Satisfactory results can only be achieved with in-depth technical and scientific knowledge. Today castings can be obtained with very complex geometries, minimal thicknesses, tight tolerances and high mechanical properties. Good results are obtained only if all the factors affecting the process are constantly controlled and monitored, which is why the experience, sensitivity, intuition and creativity of all the company staff are decisive.
The die casting process uses at least three essential components:
- The machine
- The die
- The alloy
The die casting machine
Die casting machines are driven by hydraulic power, supplied to the fluid by electrically driven pumps. The most common machines are horizontal ones, which in turn are divided into "cold chamber machines" and "hot chamber machines".
In hot chamber machines the melting furnace is part of the machine and the injection unit sits in the crucible. The crucible, heated by a burner furnace, contains the molten metal, which is drawn through a hole by the plunger into the injection chamber and from there forced into the die through a nozzle. The die consists of a fixed half and a moving half, which slides on guide pins and can therefore be moved by hydraulic systems to eject the solidified casting.
The die must be designed so that, after opening, the casting is held by the moving half and can only be removed by the ejectors: pins housed in holes in the die and driven by springs which, when the die opens, eject the casting.
In cold chamber machines the metal is melted in a separate crucible. The injection chamber is connected directly to the fixed half of the die; the molten metal is poured each time by the operator into the injection chamber through a dedicated hole.
The plunger, driven by an oil-hydraulic or hydraulic system, forces the molten metal into the die cavity. Here too the die can be opened to remove the casting by means of ejectors.
The die
The die gives the part its shape. A good casting depends largely on the quality of the die design and manufacture, as well as on how it is used once mounted on the machine.
It consists of several elements, made of different types of steel and heat treated in the area that determines the shape of the casting.
Die casting alloys
The materials used for castings belong to the family of non-ferrous metals and alloys:
- Aluminium and its alloys,
- Zinc and its alloys (Zamak),
- Copper and its alloys (brass, bronze),
- Magnesium and its alloys,
- Tin and its alloys.