Vaccum casting is a technology using ventilation to cast mold,mainly used for prcision castings,and steel casting,especially stainless steel castings and also widely used in auto parts casting.Structural automotive components with thin to medium wall sections are expected to meet high requirements such as:
• good welding characteristics
• high mechanical strength
• low production scatter
To satisfy them, a high structural quality is required.Vacuum casting creates good conditions for decisively reducing gas porosity, since air is evacuated from the die cavity.
Depending on the alloy used, the required values may be achieved in vacuum casting even without additional heat treatment. But if such treatment is necessary, it will produce surface flaws in the presence of even minor gas porosity, which cannot be tolerated on the end product.
Casting process requirements:
Following are the requirements for an optimal vacuum casting process:
• The vacuum equipment must offer high performance, and the die and shot assembly must be tightly sealed to ensure high process reliability.
• It must be possible to control the velocity and pressure profiles with high precision and high reproducibility and in real time – which can be taken for granted with Buhler SC machines.
• Additional influencing factors such as molten metal feed, die temperate control, plunger lubrication, and die spraying are also optimized to an extent crucial to quality.
Optimized vacuum casting process:
The casting process assisted by high vacuum will satisfy the above requirements with a high degree of certainty. Each individual step is optimized,especially in torder to further reduce the gas porosity compared with previous vacuum applications.
The process takes place as follows:
1.Pure and degassed metal is filled with low turbulenc into the shot sleeve.
2.When the puluger has passed over the filling hole,this will trigger avacuation of the shot sleeve and die.
3.Even before the fast shot phase,high negative pressures are generated in the die.
4.Perfilling and die filling are carried out on the basis of an injection profile matched to the specific component.
5.The vacuum shut-off valve integrated in the die closes independently of the metal feed rate,tripped by a metal pulse at the very last moment of filling,allowing total gas removal.The process is completed by the pressure intensification phase,which again is matched to the specific component.
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