Die Casting

Description
Die casting is a manufacturing process that can produce metal parts with complex geometrical shapes through the use of reusable molds. The casting process involves the use of a furnace, metal, die-casting machine and dies. The metal, typically non-ferrous alloys such as aluminum or zinc, is melted in the furnace and then injected into the dies.
Die casting process can be used for the production of engine components, pump components and appliance housing. It includes green sand molding, precision casting, lost foam casting, V-process casting and lost wax casting. The dies can be divided into alloy mold, sheet metal mold, plastic mould, stamping dies, casting mould, extrusion dies, die casting mold and other molds.

Advantages of Die Casting
1. This casting process can produce large parts or form complex shapes.
2. Using die casting process, the products will have good surface finish and high accuracy.
3. Other characteristics are high production rate, stable and reliable performance as well as low labor cost.
4. Die casting can create high strength parts, and its scrap materials can be recycled.

Process Cycle of Die Casting
It consists of five main stages, the details are as follows:
1. Clamping
The first step is the preparation and clamping of the two halves of the die. Each die half is first cleaned from the previous injection and then lubricated to facilitate the ejection of the next part. The lubrication time increases with part size, the number of cavities and side-cores. There is no necessary for lubrication after each cycle, but after 2 or 3 cycles, depending upon the material. After lubrication, the two die halves, which are attached inside the die casting machine, are closed and securely clamped together. Sufficient force must be applied to the die to keep it securely closed while the metal is injected. The time required to close and clamp the die is dependent upon the casting machine, and larger machines with greater clamping forces will need more time. This time can be estimated from the dry cycle time of the machine.
2. Injection for die casting process
The molten metal, which is kept at a set temperature in the furnace, is next transferred into a chamber where it can be poured into the die. The method of transferring the molten metal depends on the type of die casting machine, whether a hot chamber or cold chamber machine is being used. Once transferred, the molten metal is injected at high pressures into the die. Typical injection pressure ranges from 1,000 to 20,000 psi. This pressure holds the molten metal in the mould during solidification. The injection time is very short, typically less than 0.1 seconds, in order to prevent early solidification of any one part of the metal. The proper injection time can be determined by the thermodynamic properties of the material and the wall thickness of the casting. A greater wall thickness will require a longer injection time. If a cold chamber die casting machine is used, the injection time must also include the time to manually ladle the molten metal into the shot chamber.
3. Cooling for die casting process
After the molten metal enters the die cavity, it will begin to cool and solidify. When the entire cavity is filled and the molten metal solidifies, the final shape of the casting is formed. The die can not be opened until the cooling time has elapsed and the casting is solidified. The cooling time will be influenced by the thermodynamic properties of the metal, the maximum wall thickness of the casting and the complexity of the die. A greater wall thickness will need a longer cooling time. The geometric complexity of the die also requires a longer cooling time because the additional resistance to the flow of heat.
4. Ejection of die casting process
After the predetermined cooling time has passed, the die halves can be opened and an ejection mechanism can push the casting out of the die cavity. The time to open the die can be estimated from the dry cycle time. The ejection time should include the time for the die casting to fall free of the mould. The ejection mechanism must apply some force to eject the part because during cooling the part shrinks and adheres to the die. Once the casting is ejected, the die can be clamped shut for the next injection.
5. Trimming
During cooling process, the material in the channels of the die will solidify attached to the casting. This excess material must be trimmed from the die casting either manually via cutting or sawing, or using a trimming press. The scrap material can be discarded or be reused in the casting process. Recycled material should be reconditioned to the proper chemical composition before it is combined with non-recycled metals and reused in the die casting process.

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