Permanent Mold Castings

Permanent Mold Casting:

A type of casting in which mold can be used multiple times and it is open to get the final product.

Types of Permanent Mold Castings:

There are three types of Permanent mold castings:

1. Basic Permanent Mold Casting (or Gravity Die Casting)
2. Die Casting 
3. Centrifugal Casting

1. Gravity Die Casting:

A type of casting process in which molten metal flow under action of gravity.

Steps involved are:

• Mold cavities are machined and hinged to permit accurate opening and closing.
• Two cavities are forced by hydraulic cylinder to close it.
• Molten metal is then poured.
• Cavities are open by hydraulic cylinder.
• If you want complex structure then add core.
• The die life depends on the melting temperature, the higher the melting point, the shorter the mold life.
• If sand cores are used instead of metal cores then called Semi-permanent mold casting.

Variation of Basic Permanent Mold Casting:

Variation of gravity die casting are as follows:

A. Slush Casting:

A type of casting process which is used to produce hollow casting.

Steps are as follows:

• Cavities are closed by means of hydraulics.
• Pouring metal is then poured and allowed to cool.
• Mold is inverted and remaining liquid is poured out.

B. Low Pressure Casting:

A type of gravity die casting in which molten metal flow into mold due to pressure difference.

Steps are described as follows:

• Mold is placed in an airtight chamber that contains a crucible of molten metal.
• Pressure is applied in airtight chamber of about 3-15psi.
• This pressure forces the molten metal to flow from ladle to mold.

C. Vaccum Permanent Mold Casting:

A type of basic permanent mold casting in which molten metal flow into mold due to pressure difference.

Steps are as follows:

• Vaccum is generated into mold cavity by drawing air out from it.
• Molten metal flow from high pressure to low pressure.
• Benefits rerained like bottom feed, minimal metal disturbance during pouring, self rising and downward directional solidification.

2. Die Casting  (or Pressure Die Casting):

A type of Permanent mold casting in which molten metal is injected into mold cavity under high pressure and is maintained during solidification.

There are two types of die casting which are discuss ahead:

A. Hot Chamber Die Casting:

A type of die casting in which metal is melted in a container attached to machine and plunger is used to inject the liquid metal under high pressure into the cavity.

Steps of Hot Chamber Die Casting are as follows:

• Die is closed and plunger is used to inject molten metal into the cavity.
• Plunger forces the molten metal to flow through gooseneck, runner and gates into the die maintaining pressure of about 7-35MPa during cooling and solidification.
• Puller is withdrawn, die is opened and we get solidified part.

B. Cold Chamber Die Casting:

A type of doe casting in which metal is melted into a separate furnace and is transported through ladle into the die casting machine.

Steps involved are as follows:

• Due is closed and ram is used to inject molten metal into the cavity.
• Ram forces the metal to flow into cavity maintaining pressure of about 14-140MPa durine solidification.
• Ram is withdrawn, die is opened and we get the final product.

3. Centrifugal Casting: 

A type of casting processes in which mold is rotated at high speed so Centrifugal force distributes molten metal to outer region of die cavity.

There are 3 types of centrifugal casting which are discuss below:

A. True Centrifugal Casting:

A type of centrifugal casting in which mold is rotated to produce tubular parts.

• Mold is rotated at high speed about 300-3000rpm.
• Only simple and hollow parts are produced.
• Core, Riser and gating system are not required.

B. Semi Centrifugal Casting:

A type of centrifugal casting in which Centrifugal force is used to produce solid parts rather than tubular parts.

• Density of metal in final casting is greater at outer regions than center of rotation.
• Rorational speed is lower than that of TCC.
• Complex shape can be produce.

C. Centrifuge Centrifugal Casting:

Mold is designed with part cavities that are located away from axis of roration so that molten metal is poured into mold is distributed to these cavities.

• Low rorational speed is required.
• Only for small parts.

Reference:

• University Notes 
• Book Fundamental of Modern Manufacturing 6th Edition by Mikell P. Groover
• Videos from youtube and Google 
• Images from google images