What is die casting ?
A precision casting technique, die casting uses a permanent die or mould, into which molten metal is directly discharged. Along with gravity feed system, metal is consistently forced into the mould under high pressure(we called high pressure die casting process. As per the cost incurred in the designing of dies, tooling and other capital costs are relatively high as compared to other operational costs. The operative costs are low due to the high level of industrialization and the small number of fabrication steps which includes the process of direct pouring of metal into a permanent mould. The major die casting alloys are zinc die casting, aluminium die casting, magnesium die casting, copper, lead and tin.
Perfect for bulk and mass production, die casting technology is most appropriate for non-ferrous metals with relatively low melting point of approx 870oC such as lead, zinc, aluminum, magnesium and some copper alloys. The casting metals having high melting point like steel, iron and other ferrous metals lowers die life. Dies are fabricated from two blocks of steel, each including part of cavity, locked and attached together during the casting process. The removable and suspendable cores are used to configure internal surfaces.
In the entire procedure, firstly the molten metal is inserted into the die and held under pressure until it cools and dries. Than, the die halves are opened and casting is detached with the help of an automatic ejection system. To assist ejection and improve surface quality, the die is cleaned between each casting cycle, preheated and lubricated. The molded coating material is also applied to preserve the molten metal from conductive and cool veneer of the mould. Often, cooling systems are used to sustain the desired operating temperature.
In general, there are two basic forms of die casting machines, they are :
- Hot chamber machines – Also regarded as gooseneck machines, they are usually used with zinc, tin and lead based alloys. These machines depend on a pool of molten metal to feed the die.
- Cold chamber machines – They are mostly used with aluminum, magnesium, copper and zinc die casting alloys. Also, these are mostly used when the casting alloys cannot be used in hot-chamber machines.
Finishing, cleaning, machining and fabrication costs are very less.
After the set up of estate, operating costs are also very low compared to most other casting processes.
At high level of production, the total cost of castings is also relatively low as die can maintain very high production rates of approx over 400 shots per hour.
This technique renders high accuracy, consistency and good surface finish with qualitative metal yields.
Provides cleaner work environment and low amount of wastes due to removal of refractory material.
The dimensional accuracy is really outstanding.
Start up costing is very high, in addition dies are also very expensive. The dies used in die casting are usually made out of hardened tool steels because cast iron cannot withstand the high pressures die casting involved.
The technique is limited to high-fluidity metals.
Large production volume and area is needed by die casting manufacturer
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