Metal die castings are machines that are designed for forcing molten metal under high pressure into the molds to create a unique profile of metal parts. The molds used in metal die castings consist of two hardened steel dies, which have been customized. For different materials that are intended to cast, there are two types of metal die casting machine to choose, which are the hot-chamber and cold-chamber type.
The steel mold’s function is similar to mold in injection molding machines in the plastic industry. Injection molding is the method to create products by injecting molten plastic into the molds and then cooling the products down. Using the molds, both injecting molding for plastic materials and metal die casting for metal parts are methods that are suitable for mass production of complicated shaped products.
Typically, metal die castings are made from non-ferrous metals. The main differences between ferrous and non-ferrous metals lie in the iron content and the malleability. Ferrous metals such as carbon steel and alloy steel contain iron while non-ferrous metals don’t. This makes metal die castings that made from non-ferrous metal have greater resistance to rust, corrosion and better malleability. Some common materials that die castings are made of include zinc, tin-based alloy steel, copper, lead, aluminum, magnesium and so on.
Since the casting equipment and the reusable hardened steel dies which act as the molds are relatively expensive to manufacture, metal die castings are suitable for a high volume of casting small or medium sized products. Metal die casting can produce sharply defined products with greatly smooth surface finishes and accurate dimensions. Also, it eliminates secondary machining operations and provides a faster machining rate, which saves time in high-volume production. Moreover, the inserts such as threads, heating units, high strength bearings can be cast-in depending on the applications.
Metal die casting machines can be basically divided into two types, which are hot-chamber machine and cold-chamber machine. When selecting the proper machine, the cast material is the key factor.
This type of die casting machine is also known as gooseneck machines. In hot-chamber die casting, the injection unit is immersed in the molten material, the molten metals enter into the cylinder/gooseneck when the port opens. Subsequently, the hydraulic-powered piston will force the material out through the nozzles into the die. As the parts are solidified, the plunger withdraws, and the mold/die opens. The casting will be ejected, and the casting cycle completes.
The advantages of hot-chamber die casting machines are the fast cycle times and the ability to melt the metal materials directly in the machines. Cycle times can be less than one second when casting tiny products weighing less than 30 grams; for products weighing several pounds, the casting time is still shorter than one minute. However, this type of metal die casting can only perform casting with metal materials that have lower melting point, such as zinc-based, tin-based and lead-based alloys. Aluminum cannot be casted in the machines.
When the cast materials are not available in hot-chamber die casting, for example, aluminum, magnesium, copper and alloys that have large content of metals mentioned above, you can use the cold-chamber type. The casting process in the machine begins with the metal melting which takes place in a separate furnace. A precise amount of molten material will be poured into a cool shot chamber through automatic ladle or by hand. At high pressure, the hydraulic or mechanical piston will force the metal into the die. More molten metals are poured and fed than needed in the cold-chamber, this helps maintain sufficient pressures to fill the cavity solidly. The cold-chamber die casting machines are suitable for casting alloys with high melting points due to the position of the plunger and cylinder are not immersed in molten metal. However, the processing time in these types of machines is slower than hot-chamber types.
Some common die casting alloys include zinc, copper, lead, aluminum, tin and magnesium. Ferrous metals are also available in die casting machines.
Zinc and Magnesium are the most suitable and easiest materials for casting. The feature ensures longer tool life. They have high ductility and also high impact strength. It is cost-effective for small-sized products.
Copper is relatively harder and has the highest mechanical properties of die casting. It also has impressive wear and corrosion resistance and strength that is similar to steel materials.
The material is light in weight and has great stability for complex shapes or thin wall casting. It also has excellent heat and electrical conductivity, which allows operation at high temperatures.
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