Die Casting – Types , Steps in Pressure die Casting Process
What is Die casting ?
Die casting is a moulding process in which the molten metal is injected under high pressure and velocity into a split mould die. It is also called pressure die casting. The split mould used under this type of casting is reusable.
Types Of Die Casting :
Die casting is categorized two types namely-
- Hot chamber Die Casting Process and Cold chamber Die Casting Process
Metals like Zinc, tin and lead alloys are casted in hot chamber die casting having melting point below 3900C whereas aluminum alloys are casted in cold chamber
die casting machine. Aluminum dissolves ferrous parts in the die chamber and hence preferred to be used in cold chamber die casting. Continuous contact of molten metal is avoided by using a ladle for introducing molten metal directly to the machine.
The Hot-Chamber Die Casting Process
Hot-chamber die casting, sometimes called gooseneck casting, is the more popular of the two die casting processes. In this process, the cylinder chamber of the injection mechanism is completely immersed in the molten metal bath. A gooseneck metal feed system draws the molten metal into the die cavity.
While direct immersion in the molten bath allows for quick and convenient mold injection, it also results in increased corrosion susceptibility. Due to this fact, the hot-chamber die casting process is best suited for applications that utilize metals with low melting points and high fluidity. Good metals for the hot-chamber die casting process include lead, magnesium, zinc and copper.
The Cold-Chamber Die Casting Process
The cold-chamber die casting process is very similar to hot-chamber die casting. With a design that focuses on minimizing machine corrosion rather than production efficiency, the melted metal is automatically- or hand-ladled into the injection system. This eliminates the necessity for the injection mechanism to be immersed in the molten metal bath.
For applications that are too corrosive for the immersion design of hot-chamber die casting, the cold-chamber process can be an excellent alternative. These applications include the casting of metals with high melting temperatures, such as aluminum and aluminum alloys.
Steps in Hot chamber Die Casting Process / Steps In Cold Chamber Die Casting Process
Apart from these two, there are also several other variations of die casting process, such as:
Low Pressure Die Casting – Vehicle wheels and other Aluminum components are fabricated using this process. The removal of the feeders from the process ensures high casting yields.
Vacuum Die Casting – Applications that have post casting heat treatment uses are made through this process. The advantages of this process include reduced turbulence and limited gas inclusions. Vacuum die casting also ensures enhanced strength and low porosity to the material.
Squeeze Die Casting – This process is mostly used for the strengthening of fiber, and it is mostly related to molten Aluminum. It allows for casting metals and allows much lower fluidity.
Semi-Solid Die Casting – It provides minimum porosity and maximum density into the casted material. Also called Thixo-forming, this process gives an added advantage of better precision; it is most commonly used for non-ferrous metals such as Magnesium and Aluminum alloys.
Advantages of the die casting process
1. High production rate.
2. High accuracy in part dimensions.
3. Smooth surface finish for minimum mechanical finishing.
4. Ability to make many intricate parts such as hole opening slot trademark number etc.
5. Much thinner wall sections can be produced which can’t be produced by other casting
6. Varieties of alloys can be used as per design requirements. For example zinc can be used for intricate forms and plasticity, aluminum for higher structural strength, rigidity and light weight.
7. Ability to cast inserts such as pins studs shafts, fasteners etc.
Disadvantages of the die casting process
1. Microporosityinthe die casting products is a common problem because of faster solidification, trapped air and vaporized die lubricants.
2. Undercuts cannot be found in simple two piece dies.
3. Hollow shapes are not readily casted because of the high metal pressure.
4. Limited sizes of the products can be produced based on the availability of the equipment
5. High melting temperature alloys are practically not die casted
6. Flash is present except for very small zinc die casting.
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