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What is die casting and its development since the 19th century? The following article will explain this and many other basics, such as the use of different processes and materials.
Die casting is one of the most economical and fastest forming processes. The advantage of this production process is that hundreds of castings can be produced relatively quickly using only one mold. All the components produced are of uniform quality, and the unit cost is relatively low. But what exactly is the manufacturing process? What materials can be used and in which areas can castings be used?
Die casting is an automated casting process in which liquid melt is pressed into the mold under high pressure (150 to 1200 bar) and high filling speed (up to 540 km/h). Usually low melting point alloys are used. This casting process is particularly suitable for mass and mass production of parts, because it is different from sand casting, such as the use of permanent metal molds, which do not need to be destroyed after casting. Large and complex parts with low wall thickness can be produced.
Prototypes made from sand molds for thin-walled and fine die-cast parts
The die-casting mold is made of high-quality heat-resistant steel and consists of two halves, which form a cavity into which the liquid melt is pressed during the casting process. The two halves are located on a fixed and a movable machine board. During the casting process, high pressure is applied to the mold half, which is why the mold is equipped with a latch. In addition, certain parts of the mold are cooled and/or heated so that the casting solidifies as needed. The production of molds is very expensive and time-consuming, but only one of them can produce tens of thousands to millions of castings. Another advantage of reusable molds is that the melt cools quickly.
In die casting, there are two different parts manufacturing methods: hot chamber die casting and cold chamber die casting. In these two manufacturing processes, the mold is sprayed with release agent before the casting process to ensure that subsequent cast parts can be easily removed from the mold. However, the melt is not poured directly into the mold cavity, but first filled into the casting chamber of the die casting machine. From there, the alloy is pressed into the mold by the piston (the so-called casting device) through one or more channels. The difference between the two processes lies in the structure of the casting chamber as described below.
Hot-chamber die-casting method One of the characteristics of hot-chamber die-casting machines is that the casting chamber is always in contact with the liquid alloy. The melt enters the casting chamber through the valve, where it is pressed into the closed die-casting mold at high speed by the piston. This process is used for low melting point alloys such as zinc, lead or tin.
Cold Chamber Die Casting Method The cold chamber die casting machine is designed in such a way that the casting device is located outside the melt. To produce the part, the alloy is filled into the casting chamber and pressed into the die casting mold through the channel. This process is suitable for materials with higher melting points. For example, these include aluminum and copper.
After the alloy is pressed into the mold in both processes, the part solidifies under strong pressure, so that the latch of the mold can be opened. The gated parts are taken out of the mold through an automatically operated thimble and can be further processed if necessary. In short, the casting process can be divided into the following steps, which actually happen in hundredths of a second-or even only one thousandth of a second:
Cold chamber die casting for improving quality and reducing costs
Cold chamber die casting is the most popular process in the mass production of light metal castings. Now read about the key factors in achieving low-cost lightweight design concepts.
In die casting, non-ferrous metals are used to make parts, and the choice of alloy for a particular application depends on budget, weight, and material characteristics.
Aluminum is one of the most important materials, with a share of over 80%, followed by zinc and magnesium. However, copper, lead and tin can also be used. Alloys have different characteristics. For example, aluminum (600°C) and magnesium (520°C) have high melting points, and zinc (380°C) and lead (320°C) have low melting points.
Die casting alloys have many advantages:
Magnesium application areas
Innovative uses of magnesium die castings
Various processes are used in casting practice. Castings can also be produced without high pressure. For example, in the sand casting process, the alloy is poured into a mold made of sand, which must be broken to expose the manufactured part (disappearing foam). In investment casting, which is used to make very small castings, molds and models (usually made of wax or plastic) are also destroyed after the casting process. Another example is gravity die casting, which uses permanent metal molds but does not use high pressure to press the melt into the mold. Instead, castings are made by gravity or filled with molds.
The die casting process is also different. For example, there are processes that use high pressure or low pressure to produce components. Although high pressure die casting accounts for about 50% of light metal casting output, low pressure die casting only accounts for less than 20% of total output.
Low-pressure die-casting mainly uses low-melting-point alloys. Parts from 2 to 150 kg can be cast. The advantage is that it can achieve very high strength values and complex geometric shapes, as well as improved material utilization and dimensional accuracy. This process is not suitable for thin-walled parts, because only a minimum wall thickness of 3 mm can be obtained. It should also be mentioned that the casting cycle using low pressure die casting is slower than the casting cycle under high pressure.
In high pressure die casting, the melt is pressed into the mold under high pressure and high speed, thus speeding up the casting cycle. In addition, it is possible to produce thin-walled castings with a smoother surface (minimum wall thickness 1 mm). However, the disadvantages of this manufacturing process are high operating and investment costs, low strength values, and limited die casting weight because it depends on the closing force of the machine.
Die casting is mainly used for mass production, that is, to cast many parts of the same type. Although high pressure is used in the manufacturing process, high casting quality can still be achieved. The die casting process is particularly suitable for the production of very thin (up to 1 mm) (lightweight) parts.
Most commonly, die-cast parts are manufactured for the automotive industry, such as wheels, cylinder blocks, cylinder heads, valve bodies, and manifolds. This sector accounts for approximately 84% of castings produced by German foundries. 3 The use of aluminum components can reduce the weight of the vehicle, thereby reducing fuel consumption. In addition, there are other industries that use die castings:
In the future, other industries (such as electric vehicles) will attract the interest of foundries. This provides great potential for light metal castings. 4
Die casting was born in the middle of the 19th century, when the publishing industry was booming. The goal is to be able to print newspapers and books quickly, flexibly, and cost-effectively. These included hand-operated equipment (1838) that could cast tin-lead alloys into letters, a rotary printing press (1846), and finally a Linotype typesetting machine (1886). One of the main elements of this machine is an integrated die-casting machine, which pours liquid lead into a wire mold made of brass letter molds. After casting, the matrix returns to the matrix magazine, and the cast lead wire is ejected. The leads are then assembled into a page, which is used as a printing plate for sheet-fed printing or a template for a circular printing plate required by the rotary printing process.
Use structural components for success
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In the first 30 years, die casting was actually only used in the printing industry. The turning point came when Herman H. Doehler founded Doehler Die Casting Company in 1908. The company was considered the world's largest manufacturer of die castings in the early 1940s and existed until 1998. Contains all the basic components of a modern die casting machine, developed in 1925 by Joseph Soss and Louis H. Morin in the United States.
At the end of the 19th century and the beginning of the 20th century, new products were launched and industrial production increased rapidly. Manufacturers recognize the advantages of die casting, which can be used to economically produce parts for typewriters, cash registers, watches, and electrical appliances. Toy manufacturers also use die casting to produce toys and model cars that are as realistic as possible. Last but not least, the emerging automotive industry and its suppliers have become important buyers of die casting products.
Since the beginning of the 20th century, the speed of die-casting technology has become faster and faster. Initially, lead and tin, two metals with relatively low melting temperature and good ductility, were mainly used for die casting. Around 1914, research on zinc and aluminum alloys with higher strength began. Copper and magnesium alloys were added in the 1930s. Magnesium has a specific gravity of 1.74 g/cm3, which is one-third lighter than light metal aluminum (2.75 g/cm3). It is now mainly used in the automotive industry and experienced its first boom as a die-casting material between 1946 and 1978: Volkswagen The Beetle’s engine and gearbox are made of this material. However, die casting technology has not stopped at this level of development. These machines are equipped with sophisticated control technology and are becoming more and more powerful. Tool steels with improved properties enter the market for mold manufacturing, and the physical properties of die-casting alloys have been optimized. Therefore, castings with very thin wall thickness and high mechanical properties can be produced today. Current topics include automation, energy and raw material efficiency, complex shapes, hybrid parts, process automation and digitalization (Industry 4.0).
1) Dynacast, die-cast metal, available from https://www.dynacast.de/druckgussmetalle-al-mg-zn
2) Metal casting, available at http://www.themetalcasting.com/pressure-die-casting.html
4) Nuremberg Messe, 2018, available at https://www.euroguss.de/de/news/presseinformationen/zukunft-von-druckguss-7sxvrxjjb7_pireport
5) Nuremberg Messe, 2018, available at https://www.euroguss.de/de/news/fachartikel/fachartikel-druckgiessen-nl2jm1fcex_pireport
KUG BD Guss, 2009, Die Casting-Mass production of highly complex thin-walled light metal castings, available at https://www.kug.bdguss.de/giessverfahren-inhalte/druckguss/
Powerguss-Haus der Gießerei-Industrie, die casting-how does it work? , Available at https://www.powerguss.de/was-ist-giessen/druckguss/
Lechuga, G., 2016, die-casting facts infographic, available at https://www.slideshare.net/GermnLechuga/die-casting-facts-infographic
Dynacast, die-cast, available from https://www.dynacast.de/druckguss
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