Pressure casting an automated casting process in which the liquid melt is pressed into a mold under high pressure (150 to 1200 bar) and at a high filling speed (up to 540 km/h). Usually alloys with a low melting point are used. This pressure casting process is particularly suitable for series and mass production of components because, unlike sand casting, for example, permanent metal molds are used which do not have to be destroyed after casting. It is possible to produce large and complex components with low wall thicknesses.
Molds
The die casting molds, made of high quality, heat resistant steel grades, consist of two halves which form a cavity into which the liquid melt is pressed during the casting process. The halves are located on a fixed and a movable machine plate. During the high integrity die casting processes a high pressure casting process is applied to the mold halves, which is why the mold is equipped with latches. In addition, certain parts of the mold are cooled and/ or heated so that the casting solidifies as desired. The production of the molds is very expensive and time-consuming, but several tens of thousands to over a million castings can be produced with just one of them. A further advantage of the reusable casting molds is that the melt cools down quickly.
Functionality and Procedures
In die casting, there are two different process of manufacturing components: hot chamber and cold chamber die casting process. In both manufacturing processes, the mold is sprayed with a release agent prior to the casting process in order to ensure that the subsequently cast part can be easily remover from the mold. However, the melt is not poured directly into the mold cavity, but is first filled into the casting chamber of the die casting machine. From there, the alloy is pressed into the mold by a piston (the so-called casting set) through one or more channels. The difference between the two processes lies in the structure of the casting chamber as described below.
A characteristic feature of hot chamber die casting machines is that the casting chamber is constantly in contact with the liquid alloy. The melt passes through a valve into the casting chamber, where it is pressed at high speed into the closed die casting mold by the piston. This process is used for alloys with a low melting point, such as zinc, lead or tin.
Cold chamber die casting machines are designed in such a way that the casting set is located outside the melt. To produce a component, the alloy is filled into the casting chamber and pressed into the die casting mold through channels. This process is suitable for materials with a higher melting point. These include, for example, aluminum and copper.
After the alloy has been pressed into the mold in both processes, the component solidifies under the strong pressure, whereupon the latches of the mold can be opened. The part with gate is removed from the mold by automatically operated ejection pins and can be further processed if necessary. In simple words, the casting process can be divided into the following steps and in practice takes place in hundredths of a second - or even only thousandths of a second:
Cold chamber die casting is the most popular process in the mass production of light metal castings.