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Low Pressure Die Casting (LPDC)

Low pressure die casting uses small pressure, typically around 20-100 kPa (2.9-14.5 psi), instead of gravity to fill a die. Unlike the traditional die casting process, it has a unique setup and uses several pieces of equipment. Below is an illustration of the setup and pieces of equipment that are needed.

The process begins with a melting furnace which melts the metal alloys and brings them to the casting temperature. For example, aluminum has a casting temperature of 710-7200C.

The molten metal will then go to a holding furnace below the mold, which functions as a container while maintaining the liquid at the casting temperature.

Low pressure forces the molten metal through a riser tube into the mold. The liquid metal moves under constant pressure until the molten metal solidifies in the die cavity.

On solidification, the pressure is released, and the remaining molten metal goes back through the riser tube to the holding furnace for recycling. Finally, the casting will be easily removed once the mold is cooled.

 

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Aluminum Low Pressure Die Casting (LPDC) Examples

Aluminum Die Casting (Aluminum Housings) Application

Advantages of Low Pressure Die Casting

LPDC has many advantages making it an applicable die casting method in several industries. Below are a few advantages of the process.

High Accuracy

Parts made using the process are highly accurate. This is due to the maintained low pressure during the solidification. Therefore, there is a continual filling of the die cavity, compensating for the shrink in volume as the molten metal solidifies. Due to the high accuracy, it is the best method for making axially symmetrical parts such as wheels.

It Forms Highly Pure Castings

The castings are highly pure due to the little to no slag responsible for the impurity. The low level of slag is due to the setup of the casting machine. Generally, slags are on the surface of molten metals. However, since the riser tubes go down the holding furnace, the liquid metal forced into the cavity does not contain slags. Hence the highly pure casting. Also, since this is a low pressure process, the chance of slag entering the mold is low.

Moreover, the process does not lead to oxidation of the molten metal due to the stable filling process. Stability reduces or eliminates tumbling, impacting, and splashing of the molten metal during the process. Hence, there is no formation of oxidation slags that can affect the purity of the castings.

It has a Good Formability

The low-pressure filling leads to good formability because of the improvement in the fluidity of liquid metal. Therefore, castings made using the process have a clear outline and smooth surface. Generally, the process is ideal for making cast parts with complex geometries because of its high formability.

Crystallization

Since the casting solidifies under pressure, it can crystallize and form a compact structure. Therefore, castings made via the process are solid and are suitable for making parts that require good strength values.

 

Low Pressure Die Casting vs. High Pressure Die Casting

Low pressure and high pressure die casting are applicable in different scenarios depending on the component complexity, the number of parts, and the manufacturing budget. Below is a clarification on the differences between the two and the advantages of low pressure die casting over high pressure die casting.

Cycle time

The low pressure die casting pressure range is around 0.7bar to 1 bar. On the other hand, high pressure die-casting involves high pressure (often over 1000bars).

As a result, low pressure die casting has a lower cycle time than high pressure die casting. This is visible in the latter being responsible for about 50% of light metal castings ahead of low pressure’s 20%.

Strength of Part

Parts made from low-pressure casting have high strength values since solidification occurs under constant pressure for a long time to form a compact and dense structure. Parts made using high pressure also have good strength value. However, you cannot compare their strength to parts made using low pressure since the pressure is high and the time is fast.

Quality of Casting

Castings made using low pressure have higher quality than high-pressure casting. This is due to the reduction in volume due to shrinkage being complemented by constant molten metal injection into the die cavity until solidification.

Also, these castings are purer due to the lesser amount of slag present, and they have no pores. This is unlike high-pressure castings, which can have pores due to the high pressure, and slags are injectable into the die cavity.

Cost

High-pressure die casting incurs a higher operating and investment cost than low-pressure die casting due to the required machines. However, it has a lower part cost due to its fast cycle time. Learn how to calculate die casting costs.

Thickness

Low-pressure casting is the ideal method for making thick parts. However, it is unsuitable for thin-wall parts (not suitable for thickness under 3mm). On the other hand, high-pressure casting can make thin wall parts (under 0.40mm).

 

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