What is Die Casting?
Die Casting is a metal casting process characterized by the injection of molten metal under high pressure into a steel mold cavity, known as a die. Following the metal injection, the die casting machine clamps onto the mold, forming a die casting part which quickly solidifies. Dies, are very durable and can be formed to produce any number of complicated shapes with an impressive degree of accuracy and repeatability.
Die casting parts are typified by their sharply defined, smooth or textured surfaces and dimensional consistency. The rating of a die casting machine is given in Clamping Tons Universally. This rating represents the amount of pressure exerted on the die. Die casting machines can range in size from a few hundred to several thousand tons.
Producing parts via the die casting process is considered to be the most efficient way of converting raw material into a finished product. Die castings are best suited for mass production of small to medium sized products, and are used to produce many commercial, industrial, and consumer products.
The majority of die castings are made from non-ferrous metals, such as aluminum, copper, lead, magnesium, pewter, tin, and zinc based alloys. Once cast, little or no machining is required. A complete die casting cycle can vary from less than a second for small components up to 2-3 minutes for larger components.
Cold Chamber and Hot Chamber Die Casting
Cold Chamber Die Casting
In a cold chamber process, molten metal is ladled into a cold chamber for each shot. There is less time exposure of the melt to the plunger walls or the plunger. This casting process is particularly useful for metals such as aluminum and copper that alloy easily with Iron at higher temperatures.
Hot Chamber Die Casting
In a hot chamber process, the pressure chamber is connected to a die cavity and immersed permanently into the molten metal. The inlet port of the pressurizing cylinder is uncovered as the plunger moves to the open position. This allows a new charge of molten metal to fill the cavity. Thus, the hot chamber casting process can fill a mold cavity much faster than can the cold chamber process. The hot chamber process is used for metals with a low melting point and high fluidity, such as tin, zinc, and lead, which tend not to alloy easily with steel at their melting temperature. Aluminum, zinc and copper alloys are the materials frequently used in die-casting. Pure aluminum, however, is rarely cast due to its high shrinkage and susceptibility to hot cracking.
Die Casting is vastly superior to other manufacturing techniques. Chief among its advantages is its ability to produce complex shapes with high levels of tolerance. Die casting also offers other production advantages:
• Produces parts with thinner walls and closer limits of dimension.
• Can produce complex shapes – such as those which cannot be achieved by using bar or tubular stock.
• Die cast parts are heat resistant and maintain good tolerance levels.
• Produces stronger, lighter parts than other casting methods.
• Die cast parts are more efficient to produce – fewer operation processes and less waste of materials.
• Process can be automated for greater efficiency.
• Lowest labor and finishing costs.
• Identical castings can be mass produced in the thousands before new tools are required.
• Part surfaces can be smooth or textured, providing ease of application and use.
History & Process of Die Casting
The process of die casting using pressure injection can be traced back to the mid 1800’s. The components used in the early days were tin and lead, but their use tapered off with the introduction of zinc alloys and aluminum alloys. Die casting has greatly evolved over the years, from low pressure injection techniques to the use of casting dies utilizing pressures as high as 4500 psi. Today, the die casting process is unmatched for its ability to produce high quality products with excellent surface finishing characteristics.
Aluminum & Zinc Alloy Parts
- Aluminum Alloy Parts have good corrosion resistance and mechanical properties, high thermal and electrical conductivity, as well as strength at high temperatures. Aluminum is often cast at a temperature of 650 C. It can be alloyed with silicon and copper. Silicon increases the melt fluidity, whereas copper increases hardness and reduces ductility.
- Zinc Alloy Parts are the easiest alloy to die cast. Zinc is economical for small die cast parts and has a low melting point. The casting is done at a fairly low temperature of 425 C so the part does not have to cool much before it can be ejected from the die. This, in combination with the fact that Zinc can be run using a hot chamber process allows for a fast fill, fast cooling.