Die casting is a metal casting process characterized by the use of a mold cavity to apply high pressure to the molten metal. Molds are usually machined from high strength alloys, some of which are similar to injection molding.
Most die castings are made from non-ferrous metals, such as zinc, copper, aluminum, magnesium, lead, tin, and lead-tin alloys, as well as alloys thereof. Depending on the type of die casting, a cold chamber die casting machine or a hot chamber die casting machine is required.
In this post, the main topic is the manufacturing process of die casting. In order to give you comprehensive understanding of the die casting process, we will introduce you the basic 2 types of die casting machines and the detailed manufacturing procedures. After reading the post, you will greatly optimize the production process.
1. Two types of die casting machines
Die casting machines can be divided into two types, hot chamber die casting machines and cold chamber die casting machines. The difference lies in how much force they can withstand. Typical pressure ranges from 400 to 4,000 tons.
1.1 Hot chamber die casting machines
Hot chamber die casting, sometimes referred to as gooseneck die casting, relies on a pool of molten metal to fill the die under pressure. At the beginning of the cycle, the piston of the machine is in a retracted state, at which point the molten metal can fill the “gooseneck”.
The pneumatic or hydraulic-powered piston squeezes the metal and fills it into the mold. The advantages of this system include a fast cycle times (approximately 15 cycles per minute), easy automation, and the ability to melt metal.
However, the disadvantages include the inability to die-cast a metal with a high melting point, as well as the die-casting of aluminum, since aluminum will carry the iron out of the molten pool.
Thus, hot chamber die casting machines are commonly used for alloys of zinc, tin and lead. Moreover, hot chamber die casting is more applied for die casting small castings, rather than large castings.
1.2 Cold chamber die casting machines
Cold die casting can be used for die casting metals that cannot be used in hot chamber die casting processes, including aluminum, magnesium, copper, and zinc alloys with higher aluminum content.
In this process, the metal needs to be melted first in a separate crucible. A certain amount of molten metal is then transferred to an unheated injection chamber or nozzle. These metals are injected into the mold by hydraulic or mechanical pressure.
Due to the need to transfer molten metal into the cold chamber, the biggest disadvantage of this process is the long cycle of time.
Cold chamber die casting machines are also available in vertical and horizontal types. Vertical die casting machines are usually small machines, while horizontal die casting machines are available in various models.
2. Detailed manufacturing steps in die casting
The high pressure die casting process consists of four steps, including mold preparation, filling, injection, and shake out, which are also the basis for various improved die casting processes.
In the preparation process, it is necessary to spray a lubricant into the cavity. In addition to helping to control the temperature of the mold, the lubricant can also help removing the casting, and then the mold can be closed.
The molten metal is filled into the mold with a high pressure, which is in the range of about 10 to 175 MPa. When the molten metal is filled, the pressure is maintained until the casting solidifies.
The dies are then opened and the shot (shots are different from castings because there can be multiple cavities in a die, yielding multiple castings per shot) is ejected by the ejector pins.
High-pressure injection results in a very fast filling of the mold so that the molten metal can fill the entire mold before any part solidifies. In this way, surface discontinuities can be avoided even in thin-walled sections that are difficult to fill.
Most die castings can be used to perform structures that cannot be completed by casting, such as drilling and polishing.
2.4 Shake out
The process of shake out requires separating the scrap, including gates, runners, spures, and flash. This process is usually done by extruding the casting through a special dressing die. Other sand falling methods include sawing and grinding.
2.5 Defect inspection
Defects can be checked after the shake out process is completed. The most common defects include stagnation and cold heading.
That’s all you need to know when you need to manufacture quality products through the die casting technology. Leave a comment below if you have any questions.
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