High Pressure Die Casting
Here, the liquid metal is injected with high speed and high pressure into the metal mould. The basic equipment consists of two vertical platens. The bolsters are placed on these platens and this holds the die halves. Out of the two platens, one is fixed and the other movable.
This helps the die to open and close. A specific amount of metal is poured into the shot sleeve and afterwards introduced into the mould cavity. This is done using a hydraulically-driven piston. After the metal has solidified, the die is opened and the casting eventually removed.
Types of High Pressure Die Casting:
Both the processes are described below. The only difference between the two processes is the method being used to inject molten metal into the die.
Hot Chamber Process
The hot-chamber process is applicable only for zinc and other low melting point alloys that does not affect and erode metal pots cylinders and plungers.
The basic components of a hot-chamber die-casting machine and die are illustrated below:
The workings of a hot chamber process goes like this. The molten metal for casting is placed in the holding furnace at the required temperature adjacent to(sometimes as part of the machine itself) the machine. The injection mechanism is placed within the holding furnace and most of its part is in constant touch with the molten metal. When pressure is transmitted by the injection piston, the metal is forced through the gooseneck into the die. On the return stroke, the metal is drawn towards the gooseneck for the next shot.
This process ensures minimum contact between air and the metal to be injected. The tendency for entrainment of air in the metal during injection is also minimised.
Cold Chamber Process
The difference of this process with the hot-chamber process is that the injection system is not submerged in molten metal. On the contrary, metal gets transferred by ladle, manually or automatically, to the shot sleeve. The metal is pushed into the die by a hydraulically operated plunger. This process minimises the contact time between the injector components and the molten metal, which extends the life of the components. However the entrainment of air into the metal generally associated with high-speed injection can cause gas porosity in the castings. In the cold chamber machine, injection pressures over 10,000 psi or 70,000 KPa is obtainable. Generally steel castings along with aluminium and copper based alloys are produced by this method.
High pressure gallery
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