What are the stages of diecast casting?

Casting by die-casting is done through five main stages of mold preparation, molten material injection, cooling, mold opening and cutting.

The first step in the production of parts by pressure casting is the preparation of die cast parts. This template consists of two fixed and movable parts. The fixed part of the mold is placed on the fixed plate of the diecast machine and its moving part is placed on the moving plate of the machine. The main activities in the preparation of a die casting mold include the following:

Cleaning: removing the remaining material on each part of the mold and cleaning the surface of the parts after each cycle. Casting in order to prevent the reduction of the surface quality of the part
lubrication: applying lubricants such as grease or oil to the parts after every two or three casting cycles (according to the material of the mold) in order to facilitate Opening and closing the mold
Closing the mold: Connecting the fixed and moving parts, tightening them and applying the appropriate force to the mold to keep it stable during the injection of molten materials

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In the next step, the molten metal is transferred from the furnace to the machine chamber. The way to transfer molten materials depends on the type of diecast machine (cold chamber or hot chamber). After the transfer process, molten metal is injected into the mold under high pressure. The injection pressure in the diecast method is usually between 70 and 1400 bar. This pressure provides the force required to keep the molten material stable during the solidification process (liquid to solid phase change).

The amount of molten material injected into the mold is called shot. The time required to fill all the cavities and ducts of the mold is also known as injection time. This time is very limited and is usually less than 0.1 seconds. Limited injection time prevents non-uniform freezing of different parts. The injection time is one of the parameters that is considered in the design of the pressure casting process.

The design of the injection time in diecast is based on the thermodynamic properties of the material and the wall thickness. The thicker the wall, the longer the injection time. In case of using a cold chamber device, the time of manually pouring the molten material from the bottle into the shot chamber should be considered as one of the design parameters of the injection time.

As the molten material enters the cavity of the mold, these materials begin to cool and change phase from liquid to solid. Reducing the temperature of the mold and the materials inside it is done by the cooling system. After all the cavities are filled and the molten material solidifies, a piece with the desired shape is formed. It is not possible to open the mold before the end of the cooling time and complete freezing of the part. This time is determined according to thermodynamic properties, maximum wall thickness and mold complexity. The greater the thickness of the part wall and its geometric complexity, the longer the time required for complete cooling.

After the cooling time of the piece, it is possible to open the movable part of the mold and remove the piece with the help of the exit mechanism or so-called spring system. The time to open the mold is a function of the technical capabilities of the device and the time of complete exit is a function of the dimensions of the part containing the part and its falling time. Due to the contraction caused by the shrinkage of the part in the process of freezing and sticking of the material to the wall of the mold, the exit process is done by applying force by special pins. After the piece is removed, it is possible to close the mold again and repeat the injection process.

The injection of molten material into the cavities is done through the ducts of the mold. Due to the remaining molten materials in these ducts during the cooling process, appendages are created on the part. The last stage of making the part by die casting method, the surface appendages must be removed by manual or mechanical methods. The time required to remove excess material depends on the dimensions of the part. The materials separated in this process are transferred to the waste or recycling section (for reuse).