What is the difference between gravity casting and low-pressure casting?

Gravity casting and low-pressure casting are two common metal casting processes, with the main difference being the filling method and pressure source. Gravity casting relies on the gravity of the molten metal to fill the mold, while low-pressure casting pushes the molten metal up and into the mold through external air pressure (usually 0.01-0.05MPa).

Comparison of Technical Principles

Gravity casting: Metal liquid naturally flows into the mold without external force, suitable for thick walled components with simple structures, such as wheels, brackets, etc. The pouring temperature is usually 100-150 ℃ higher than the melting point of the material.

Low pressure casting: Compressed air is introduced into the sealed furnace, and the metal liquid rises steadily along the riser. The filling speed is controllable (generally 0.5-2m/s), making it more suitable for thin-walled complex parts such as car cylinder heads.

Process characteristics

Surface quality: Low pressure casting can achieve a surface roughness of Ra6.3-12.5 μ m due to smooth filling, which is better than the Ra12.5-25 μ m of gravity casting.

Porosity: The porosity of low-pressure castings can be controlled below 1%, while gravity castings typically have a porosity of 3-5%.

Mold lifespan: Low pressure casting molds can withstand less pressure and have a lifespan of over 100000 cycles, while gravity casting molds have a lifespan of approximately 50000 to 80000 cycles.

Application scenarios

Gravity casting is suitable for scenarios with small batch sizes and low precision requirements, with low single piece costs (about 60% of low-pressure casting).

Low pressure casting is suitable for large quantities of high-precision parts. Although the equipment investment is high (about 2-3 times that of gravity casting equipment), the material utilization rate can reach over 95% (gravity casting is about 70%).

Industry standards

Low pressure castings are commonly used in automotive industry standards such as ISO/TS16949, while gravity casting follows the general casting standard ASTM A703.

Choose Suggestions

When the product wall thickness is greater than 6mm and the annual output is less than 10000 pieces, gravity casting is preferred;

For parts with thin walls (<3mm) and high air tightness requirements, low-pressure casting is preferred.