What Are the Differences Between Low-Pressure and High-Pressure Die Casting?

Die casting technology is widely used today, especially for light alloy parts. However, many buyers and engineers still find the differences between low-pressure die casting (LPDC) and high-pressure die casting (HPDC) unclear. This is especially true when choosing between low volume die casting production and high-volume manufacturing. To better understand the difference, it helps to first look at how each process works.

Low-Pressure Die Casting (LPDC)

In low-pressure die casting, the mold is placed above a sealed crucible filled with molten metal. Compressed gas creates a low pressure of 0.06–0.15 MPa on the molten metal surface, pushing the metal upward through a rising tube into the mold cavity. The casting then solidifies under controlled conditions.

LPDC offers several clear advantages. Because pressure continuously feeds molten metal into the cavity, the casting has high dimensional accuracy and a dense internal structure. Since the metal is drawn from below the melt surface, where slag is less likely to enter, the final part is also cleaner. Low gas porosity improves mechanical strength and makes LPDC parts suitable for heat treatment. This process is often used for complex medium-thickness parts, with minimum wall thickness typically around 3 mm.

LPDC is also a practical choice in some low volume die casting production projects, especially when the part requires better internal quality, heat treatment capability, or more stable mechanical properties than HPDC can provide. Although the production speed is lower, LPDC can be a better fit when part performance matters more than cycle time.

High-Pressure Die Casting (HPDC)

In high-pressure die casting, molten metal is injected into the die cavity under 15–100 MPa pressure and at a filling speed of about 10–80 m/s. The cavity fills quickly, and the metal solidifies rapidly.

The main advantage of HPDC is very high efficiency. Its short cycle time makes it ideal for high-volume production. It also provides excellent surface finish, typically around Ra 6.3 µm, and in some cases even Ra 1.6 µm. Another major benefit is its ability to produce thin-walled parts, with wall thickness as low as 0.3–0.5 mm.

However, HPDC parts usually have higher porosity and lower density than LPDC parts. This reduces mechanical strength and generally makes them unsuitable for heat treatment, because trapped gas may expand during heating and cause blistering or cracking. HPDC parts are also not recommended for large machining allowances, since removing the dense surface layer can reduce part strength. In most cases, the recommended machining allowance is less than 0.25 mm.

For this reason, HPDC is usually the better choice for large-scale production, while it may be less suitable for low volume die casting production when the project places more importance on internal quality, post-processing, or heat treatment.

Summary

Conclusion

In simple terms, low-pressure die casting offers better internal quality, lower porosity, and heat treatment capability, making it suitable for parts that require higher strength and post-processing. It can also be a reasonable option for low volume die casting production when casting quality is more important than speed. High-pressure die casting, by contrast, is better suited to large-volume manufacturing of thin-walled parts where fast cycle time and surface finish are the main priorities.