Low-pressure casting and high-pressure casting are two common casting processes, and they differ in several aspects. Here is a detailed introduction:

Process Principle

• Low-pressure casting: The mold is placed in a sealed container. Compressed air or inert gas is introduced into the container, causing the molten metal to rise steadily along the riser tube under a relatively low pressure (usually 0.02–0.06 MPa) to fill the mold cavity and solidify into a casting.
• High-pressure casting: The molten metal is injected into the metal mold cavity at high speed (usually 0.5–7 m/s) under high pressure (typically 10–150 MPa) and solidifies under pressure to form a casting.

Metal Filling Process

• Low-pressure casting: The molten metal rises steadily under pressure, with a relatively slow filling speed and smooth flow. This process is less likely to cause gas or slag entrainment, resulting in castings with good surface quality and fewer internal defects.
• High-pressure casting: The molten metal fills the mold cavity rapidly under high pressure. Although it can quickly fill complex cavities, it is prone to gas and impurity entrainment, leading to internal defects such as porosity and inclusions in the casting.

Casting Quality

• Low-pressure casting: The smooth filling process results in good surface quality, high dimensional accuracy, and fewer internal defects. The mechanical properties are relatively better, making it suitable for producing complex-shaped, thin-walled castings with high requirements, such as aluminum alloy car wheels.
• High-pressure casting: The castings have high dimensional accuracy and surface finish, and they can produce thin-walled, complex-shaped large castings, such as engine blocks and cylinder heads for automobiles. However, due to the fast filling speed, there are more internal defects, and the mechanical properties are relatively lower. Post-processing treatments such as heat treatment are often required to improve the properties.

Production Efficiency

• Low-pressure casting: The slow filling speed results in a longer production cycle and lower production efficiency, making it suitable for small-batch, multi-variety production.
• High-pressure casting: The fast filling speed leads to a short production cycle and high production efficiency, making it suitable for mass production, such as in the automotive industry.

Equipment Investment and Cost

• Low-pressure casting: The equipment is relatively simple, with lower investment costs and mold expenses. However, the low production efficiency results in higher unit casting costs.
• High-pressure casting: Specialized high-pressure casting machines are required, with high equipment investment and complex mold design and manufacturing, leading to high mold costs. However, the high production efficiency results in lower unit casting costs in mass production.

Suitable Materials

• Low-pressure casting: It is mainly used for casting non-ferrous metals such as aluminum and magnesium alloys. It is less commonly used for metals with poor fluidity, such as cast iron.
• High-pressure casting: In addition to non-ferrous metals like aluminum and magnesium alloys, it can also be used for casting ferrous metals with good fluidity, such as gray cast iron and ductile iron.

Mold Life

• Low-pressure casting: The mold is subjected to lower forces, with less thermal and mechanical stress, resulting in a longer mold life.
• High-pressure casting: The mold is subjected to significant thermal and mechanical stress under high pressure and temperature, leading to faster mold damage and a shorter life.