Low-pressure die casting (LPDC) is an aluminum casting process that uses gas pressure to slowly fill molten aluminum from the bottom of the mold. This method can produce die casting parts with high strength, high precision, and extremely low porosity. It is particularly suitable for parts with complex structures and high performance requirements, and is widely used in demanding industries such as automotive and aerospace.
This guide will explain the low-pressure die casting process flow, the materials used, the advantages and disadvantages, design points, comparison with other casting processes, and its typical applications. Keep reading to see if LPDC is right for your next project.
Low-Pressure Die Casting Process Flow
Aluminum Alloy Melting
Aluminum alloys are melted in a sealed crucible furnace to prevent oxidation and impurity contamination and ensure a stable melt temperature.
At CEX Casting, we use a centralized melting system that can effectively remove excess gas and impurities from the raw materials and purify the aluminum liquid, thereby suppressing casting defects at the source.
Pressurization Process
In LPDC, the aluminum liquid is steadily pushed into the mold by applying a low-pressure inert gas of 0.7–1.5 bar.
This method controls the flow rate, avoids turbulence and splashing, and effectively reduces the risk of filling defects such as pores and cold shuts.
Bottom Filling
The molten aluminum enters the bottom of the mold through the ceramic riser and slowly fills the mold cavity from bottom to top.
This path allows the air to be discharged naturally, reduces the probability of oxidation, and significantly improves the density and internal cleanliness of castings.
Controlled Solidification
The mold is cooled while maintaining the air pressure to achieve a uniform and directional solidification process.
This can effectively avoid shrinkage and internal stress, and obtain castings with excellent mechanical properties.
Demolding and Cleaning
After the casting solidifies, the air pressure is released, and it is ejected. The flash and gate are then removed and cleaned or post-processed.
Due to the excellent surface quality, casting parts made by LPDC usually require very little post-processing.
Common Materials for LPDC
A356
A356 has excellent fluidity and low shrinkage characteristics, which are very suitable for the low-pressure filling method of LPDC.
The alloy can maintain uniform structure, low porosity, and strong processing stability during slow solidification.
AlSi10Mg
AlSi10Mg has a dense structure and good feeding performance, which can adapt to the bottom-up filling mold structure of LPDC.
Its good heat treatment response and solidification controllability make it very suitable for precision aluminium components.
A319
A319 is suitable for the low-pressure slow solidification process of LPDC, and its slow solidification characteristics help to improve dimensional stability.
At the same time, the alloy has good fluidity and structural density, which can stably adapt to the mold filling process.
AlSi7Mg
AlSi7Mg has excellent air tightness and shrinkage resistance, which is highly matched with the bottom injection process of LPDC.
Its low deformation tendency and good surface performance can achieve high stability under low-pressure casting.
AlSi9Cu3
AlSi9Cu3 can effectively suppress internal stress in the controlled cooling environment of LPDC.
Its good fluidity and solidification characteristics support the high density and high repeatability requirements in the LPDC process.
Advantages of LPDC
High Mechanical Properties
LPDC can form a fine, uniform metal structure through slow filling and directional solidification.
This dense structure significantly improves tensile strength and overall mechanical stability, reducing microcracks and stress concentration in die casting parts.
Low Porosity
The aluminum liquid is filled from bottom to top, the process is stable, and the metal flow is smoother.
The process can effectively exhaust gas, significantly reduce the incidence of pores and inclusions, and improve the overall density of aluminium alloy die casting.
Excellent Surface Quality
Due to the low metal flow rate and less turbulence in the LPDC process, the surface of the casting is smoother.
The stable mold temperature control further improves the appearance quality and surface treatment compatibility of the finished products.
High Dimensional Accuracy
Thanks to its low-pressure and well-controlled filling process, LPDC ensures smooth and uniform mold filling with minimal turbulence.
When combined with directional solidification, this enables the production of castings with high dimensional accuracy.
High Material Utilization Rate
The closed and precisely controlled metal delivery in LPDC minimizes flash, overflow, and excess runners.
This significantly reduces material waste and improves yield, making it a cost-efficient choice for large-scale production.
High Design Freedom
LPDC supports castings with complex structures, including details such as cavities, thin walls, and reinforcing ribs.
The process is stable, and it can achieve multi-structure integration, reduce parts assembly, and simplify the overall design.
High Product Consistency
LPDC is suitable for automated operation, and the process parameters are easy to set and can remain stable for a long time.
This ensures that each casting maintains the same quality and performance in mass production.
Disadvantages of LPDC
Large Equipment Investment
Requires a pressurized furnace, ceramic riser, complex molds, etc. The initial equipment investment is high, suitable for medium or large batch production at a professional die casting company.
Slow Production Cycle
Compared with high-pressure die casting (HPDC), LPDC has slow cooling and filling speeds and low production capacity.
However, the quality of the finished product makes up for the lack of production speed.
High Cost for Small Batches
The mold and equipment costs are high, which is not suitable for small batch orders or rapid prototyping. Gravity casting or sand casting is recommended for small batches.
LPDC Design Points
Maintain Uniform Wall Thickness
LPDC has a slow filling process, and uniform wall thickness helps the metal flow smoothly and solidify evenly, which can avoid shrinkage and excessive heat concentration in aluminium alloy die casting.
Set a Reasonable Draft Angle
LPDC uses rigid metal molds. If there is not enough draft, the casting is easy to stick to the mold or be damaged.
It is usually recommended to set 0.5° to 3° to ensure smooth demolding and extend the life of the mold.
Design a Cooling System
The directional solidification of LPDC depends on effective cooling channel design.
A reasonable temperature control layout can reduce the risk of thermal cracks, optimize the internal structure, and ensure that the casting is stably formed during the pressure holding process.
Optimize Runners
LPDC has a slow filling process and is more sensitive to runner design.
The runner should be as short and straight as possible, avoiding sharp bends or contractions to reduce turbulence and oxidation inclusions.
Reasonable Setting of Gate and Exhaust System
LPDC relies on low-pressure precision feeding, and the gate and exhaust system must be carefully designed.
Balanced pouring and smooth exhaust can effectively reduce porosity, inclusions, and insufficient pouring.
Comparison of LPDC with Other Casting Methods
Comparison with High-Pressure Die Casting (HPDC)
LPDC uses low pressure, slow filling, and stable metal flow, which can significantly reduce porosity and obtain higher mechanical strength and density.
High-pressure die casting injects aluminum liquid at high speed and high pressure, with fast molding speed and low unit cost, but it is easy to form internal porosity, which is not suitable for parts that require heat treatment or high-strength requirements.
Comparison with Gravity Casting (GDC)
GDC relies entirely on gravity filling, with limited fluidity and filling capacity, and it is difficult to achieve thin-walled or complex structure molding.
In contrast, LPDC uses air pressure to push the metal to fill the mold from bottom to top, which can better control the filling process and adapt to more complex geometric designs and higher dimensional accuracy requirements.
|
Characteristics |
LPDC | HPDC | GDC |
|
Pressure |
Low pressure | High pressure | None (gravity) |
| Porosity | Low | High |
Medium |
|
Temperature |
Slow | Fast | Medium |
| Strength | High | Medium |
Medium |
|
Complexity |
High | Medium | Low |
| Surface Quality | Very good | Excellent |
Good |
| Investment Cost | High | High |
Low |
Typical Applications of LPDC
Automotive Industry
LPDC is often used to produce structural parts such as aluminum alloy wheels, suspension arms, and gearbox housings.
These aluminium die casting components require high strength, long fatigue life, and strict dimensional tolerances.
Aerospace
LPDC is used to manufacture sealed structural parts such as brackets, housings, and lightweight covers.
Its high mechanical properties and low porosity meet the strict safety requirements of aircraft.
Industrial Equipment
LPDC is suitable for complex die casting products such as pump bodies, motor housings, and valve housings.
It has good density and pressure resistance and can withstand long-term mechanical loads.
Consumer Electronics
LPDC can be used for precision casting of heat sinks, equipment housings, and structural parts, with excellent surface quality and dimensional accuracy, while combining aesthetics and strength.
Conclusion
LPDC is a highly stable and controllable die casting process.
With its process characteristics such as slow filling, directional solidification, and low-pressure feeding, LPDC has significant advantages in dimensional consistency, mechanical properties, and overall quality.
As a professional aluminum casting manufacturer in China, CEX Casting provides a full-process solution from mold design, casting, surface finish, to bulk delivery.
Contact us now to get a tailored solution for your next aluminium casting project.