Gravity die casting is one of the standard processes for the manufacture of high-integrity automotive castings. It represents proven and absolute precision technology for the production of large batch quantities. This process is used in carousel casting units or in shuttle technique particularly for the manufacture of engine castings. Optimum heat dissipation from the solidifying casting through the die leads to short solidification times. This results in castings which have good mechanical properties, especially after an additional heat treatment.
In addition to producing ever more complicated cylinder heads for petrol and diesel engines, gravity die casting is also used for the manufacture of diesel engine blocks with cast-in grey iron liners.
In gravity die casting processes, the melt is metallurgical treated in the holding furnace, which is positioned near the dies?
The quantity of melt for one casting is transported in a ladle and poured into the riser system of the mould by tilting the ladle. The melt fills the mould cavity smoothly from the bottom up until it appears in the risers positioned above the casting.
In the example shown, i.e. the casting of a cylinder head, the mould filling and solidification Conditions can be influenced by the design of the gating system and the risers in the top core. Directional solidification can be forced by using water cooling in the bottom of the die.
Low pressures die casting:
Low pressure die casting is a well-known casting process, especially for aluminium wheels in passenger cars. The process is also used in the production of big V-engine blocks in hypereutectic aluminium alloys and in the casting of air-cooled cylinder heads for motor cycles. Mould filling is controlled by regulating the pressure in the casting furnace. The melt flows through the riser tube which is positioned under the melt surface of the furnace and fills the mould very smoothly with clean melt from the bottom up. After mould filling, solidification starts from the opposite end of the mould in the direction of the tube. By increasing the pressure in the casting furnace, good feeding is guaranteed. Cycle times are long due to the fact that the casting is connected to the big melt volume by the riser tube during solidification.
High pressures die castings:
• Filling speed and intensification pressure differentiates high-pressure die casting from most other casting processes.
• After liquid metal is transferred to the shot sleeve (s. fig. below), the plunger slowly closes to shut-off the filling port.
• The plunger is then moved towards the die at a controlled but high speed in order to fill the die cavity.
• With the potential for highly automated operation, the high-pressure die casting (HPDC) process is capable of extremely high levels of productivity. HPDC machines are size rated by the closing force...
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